Doctoral Degrees (Food Science)
Permanent URI for this collection
Browse
Browsing Doctoral Degrees (Food Science) by Title
Now showing 1 - 20 of 56
Results Per Page
Sort Options
- ItemAntibiotic resistant bacteria prevalent in livestock and wildlife species in South Africa(Stellenbosch : Stellenbosch University, 2019-04) Van den Honert, Michaela Sannettha; Gouws, Pieter Andries; Hoffman, Louwrens C.; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.ENGLISH ABSTRACT: Much research has focussed on the fate of antibiotics in clinical settings whereas research of antibiotics in natural environments has been comparatively limited. It has been hypothesised that wildlife could play a significant role in the development of antibiotic resistant bacteria in nature as a variety of wildlife species carry antibiotic resistant bacteria and cover a large territory throughout their lifespan The aim of this study was to determine whether wild ungulates, namely, African buffalo (Syncerus caffer), black wildebeest (Connochaetes gnou), blue wildebeest (Connochaetes taurinus), bontebok (Damaliscus pygargus), eland (Taurotragus oryx), fallow deer (Dama dama), impala (Aepyceros melampus) and springbok (Antidorcas marsupialis), host antibiotic resistant bacteria, specifically, Escherichia coli, Enterococcus faecalis and Staphylococcus aureus, from various South African farms. The Kirby-Bauer disk diffusion method was used according to the Clinical and Laboratory Standards Institute 2018 guidelines. Overall, antibiotic resistance among the wild ungulate species was low towards the selected antibiotics. On average, the antibiotic resistance levels were 8% E. coli (N= 353), 4% E. faecalis (N= 194) and 22% S. aureus (N= 106). The highest antibiotic resistance was towards antibiotics which are of natural origin, namely the β-lactams and streptomycin. These antibiotics are found in the soil microbiome, produced by Actinobacteria. In addition, certain resistant genes were detected using the polymerase chain reaction in isolates which showed phenotypic resistance. The resistant genes sul1 (40%), sul2 (80%), sul3 (0%), blaCMY (98%), tetA (63%), tetB (75%), tetC (0%) and aadA (98%) were detected in resistant E. coli isolates (N= 44); tetK (7%), tetL (100%), tetM (100%), blaZ (100%), vanA (95%) and vanB (10%) in resistant S. aureus (N= 5) and E. faecalis (N= 22) isolates. The results of this study indicate that wildlife can be considered a natural reservoir of antibiotic resistant genes. The wildlife were also found to be more multi-drug resistant than the livestock. Thus it is speculated that these resistant genes are picked up from the soil and the surrounding environment and are spread by the animals as well as by other natural vectors like the wind and flies. Various factors and agricultural practices were found to influence the antibiotic resistance of the bacteria harboured by the wildlife species, namely, co-grazing with livestock, the practice of wildlife supplementary feeding and farm history of antibiotic use. Bacteria isolated from game meat was frequently more antibiotic resistant than bacteria from the faeces, indicating human cross-contamination during slaughter. The level of antibiotic resistance determined in this study from the bacteria of the wildlife from pristine areas, could serve as a baseline for monitoring the influence of human activities on the development of antibiotic resistance in various environments, which this study contributed towards.
- ItemAntimicrobial effects of chitosan and essential oils on postharvest diseases of pomegranate fruit(Stellenbosch : Stellenbosch University, 2017-12) Munhuweyi, Karen; Opara, Umezuruike Linus; Caleb, Oluwafemi James; Lennox, Cheryl L.; Sigge, G. O.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: Pomegranate (Punica granatum L.) fruit diseases often caused by a range of fungi and bacteria, pose significant financial, nutritional and postharvest losses along the value chain. This study aimed at identifying pomegranate postharvest diseases in South Africa and improving the shelf life of whole and minimally processed pomegranates using chitosan and essential oils (EOs). To identify pomegranate postharvest pathogens and their origin in the value chain, samples of leaves and fruit at different development stages were collected from commercial orchards of cultivars ‘Herskawitz’ (mid harvest) and ‘Wonderful’ (late harvest) located in the Western Cape region of South Africa. Fungi were isolated from healthy and intact pomegranate flowers (open, closed, diheased), immature fruitlets buds, immature green fruit and ripe pomegranate fruit as well as leaves. Isolated fungal pathogens were identified using phylogenetic analysis of the internal transcribed spacer (ITS: ITS1 and ITS2) of the nuclear ribosomal DNA and the 5.8S ribosomal RNA genes. Aspergillus niger Tiegh., Cytospora spp., Clonostachys spp., Embellisia eureka E.G. Simmons, Pestalotiopsis spp., Nigrospora oryzae and Rhizopus stolonifer Ehrenb., were associated with non-disinfected plant materials. The major pomegranate spoilage pathogens were isolated from surface sterilised samples and comprised of Alternaria spp., Aureobasidium pullulans, Botrytis spp., Penicillium spp., and Pilidiella granati Sacc. (syn. Coniella granati [Sacc.] Petr. & Syd.). The open flower stage had the highest incidence of spoilage pathogens and the same pathogens were isolated from fruit at postharvest. Pathogenicity tests were carried out on the major postharvest spoilage pathogens isolated namely Botrytis sp., Penicillium sp. and P. granati. This is the first report of P. granati on pomegranate fruit in South Africa. A restriction fragment length polymorphism (RFLP) tool was developed for the detection of pomegranate postharvest pathogens. This tool will be important in the monitoring of pomegranate pathogens in orchards and packhouses. The antifungal activity of crab shell chitosan (0-10 g/L) and fludioxonil (0-1.0 g/L) was tested against Botrytis sp., Penicillium sp. and P. granati previously isolated from pomegranate. Pathogen sensitivity to crab shell chitosan based on the EC50 values (concentration causing a 50% reduction in mycelial growth) showed that P. granati (EC50-0.47 g/L) was the most sensitive followed by Botrytis sp. (EC50-1.19 g/L) and Penicillium sp. (EC50 2.21 g/L). For fludioxonil Penicillium sp. (EC50 0.02 mg/L) was the most sensitive followed by P. granati (EC50 0.48 mg/L) and Botrytis sp. (EC50 0.09 mg/L). Pre-treating wounded fruit (preventive treatment) with chitosan prior to pathogen inoculation gave better disease control (30-66% decay reduction) compared to introducing the chitosan after pathogen inoculation as a curative strategy (18-38%). Applying chitosan (0, 2.5, 7.5 and 15 g/L) as an edible coating on minimally processed pomegranate arils prior to cold storage significantly (P<0.05) lowered counts for mesophilic aerobic bacteria, yeast and moulds. In addition, the chitosan treatment also maintained the physico-chemical attributes of the arils (total soluble solids (TSS), titratable acidity (TA), moisture, colour, firmness, total phenolics, anthocyanins and ascorbic acid). The findings demonstrate that crab shell chitosan can be considered as a potential green fungicide for postharvest disease management of both whole and minimally processed pomegranate fruit. A follow up study to enhance the antimicrobial properties of chitosan was conducted using chitosan as a polymeric carrier of volatile EOs (cinnamon, lemongrass and oregano). The EOs were assayed for antifungal activity against Botrytis sp., Penicillium sp., and P. granati. Lemon grass was the least effective EO as it failed to provide complete inhibition of any of the fungal pathogens while oregano EO was the most potent as it gave complete inhibition of P. granati by both vapour and direct contact methods. In vivo application of chitosan-oregano as an edible coating effectively controlled fungal growth by 59-100% but induced negative effects on the fruit skin. When applied as active film, the chitosan-oregano film still significantly (P < 0.05) reduced fruit decay by 34-100% without elucidating cosmetic damage to the fruit rind. The findings revealed the potential application of chitosan-EO based films in developing antimicrobial based active food packaging systems. To further improve use of EOs in antimicrobial packaging, cinnamon and oregano EOs were encapsulated in β-cyclodextrin (β-CD) and a nanofibrous matrix based on chitosan and polyvinyl alcohol (PVA) to reduce the thermal instability of the EOs and achieve prolonged release. A GC-MS analysis revealed that the β-CD was significantly (P < 0.05) more efficient in encapsulation of cinnamon EO (4.86%), compared to oregano EO (1.75%). However, similar EO concentrations were obtained when the essential oils were incorporated into electrospun chitosan based nanofibres. The EO based β-CD microcapsules and nanofibres both had antimicrobial effect on Botrytis sp. and thus could be used in antimicrobial packaging. This study identified the major postharvest spoilage pathogens of pomegranates in the Western Cape Region of South Africa and further determined that the orchard was the major source of these pathogens. Crab shell chitosan independently and in combination with EOs was shown to effectively control pomegranate postharvest pathogens on whole and minimally processed fruit. While exposing the pomegranate fruit to direct contact with EO emulsions reduced postharvest spoilage it also resulted in a negative cosmetic appearance of the fruit rind. However, exposing fruit to in-direct contact with encapsulated EOs controlled postharvest spoilage without affecting the fruit cosmetic appearance.
- ItemAntioxidant capacity of Pinotage wine as affected by viticultural and enological practices(Stellenbosch: University of Stellenbosch, 2006-12) De Beer, Dalene; Joubert, E.; Marais, Jeannine; Manley, M.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Food Science.The aim of the study was to provide the South African wine industry with guidelines for the production of Pinotage wines with optimal total antioxidant capacity (TAC), while retaining sensory quality. The contribution of individual phenolic compounds to the wine TAC is important in this regard. The wine TAC was measured with the 2,2 -azino-di(3-ethylbenzo-thiazoline-sulphonic acid radical cation) (ABTS +) scavenging assay. The contributions of individual phenolic compounds to the wine TAC were calculated from their content in the wines and the Trolox equivalent antioxidant capacity (TEAC) of pure phenolic standards. The effects of climate region, vine structure, enological techniques (pre-fermentation maceration, juice/skin mixing, addition of commercial tannins, extended maceration) and maturation (oak barrels, alternative oak products, oxygenation) on the phenolic composition, TAC and sensory quality of Pinotage wines were also investigated. The TEAC values of quercetin-3-galactoside, isorhamnetin and peonidin-3-glucoside were reported for the first time. TEAC values observed for most compounds were much lower than those reported previously, although TEAC values for gallic acid, caftaric acid, caffeic acid and kaempferol were consistent with some previous reports. Caftaric acid and malvidin-3-glucoside were the largest contributors to the wine TAC. The contents of monomeric phenolic compounds and procyanidin B1, however, only explained a small amount (between 11 and 24%) of the wine TAC, with the remaining TAC attributed to oligomeric and polymeric phenolic compounds and other unknown compounds. Some synergy between different monomeric phenolic compounds was also demonstrated. All the viticultural and enological factors investigated affected the phenolic composition of Pinotage wines, while the wine TAC was only affected by some treatments. Changes in wine TAC could not always be explained by changes in phenolic composition as the contribution of oligomeric, polymeric and unknown compounds could not be assessed, but could play a large role. Differences in wine colour were also difficult to explain due to the large number of factors involved and the dark wine colour, which made objective measurements difficult. The concentration of vitisin A, an orange-red pyranoanthocyanin, was increased consistently as a result of prefermentation maceration treatments and affected the wine colour of oxygenated wines. Increased wine TAC was observed when cultivating Pinotage grapes on bush vines and in cooler climatic regions, compared to cultivation on trellised vines in warmer climatic regions. All the climatic regions and vine structure treatments, however, resulted in wines with good sensory quality. In terms of enological techniques, pumping-over, as opposed to punching-down and rotor treatments, is not recommended as a juice/skin mixing technique, due to reduced wine TAC, colour and sensory quality. Pre-fermentation maceration, addition of commercial tannin preparations, and oak maturation using traditional and alternative treatments, resulted in improved sensory quality, but with no change in wine TAC. However, optimisation of the tannin addition protocol may result in increased wine TAC if additions are made after fermentation or higher dosages are used. Oxygenation of Pinotage wine needs further investigation to optimise the protocol, as improvements to the wine colour and fullness were observed for some treatments, but loss of sensory quality and TAC were observed in most cases.
- ItemThe authentication of regionally unique South African lamb(Stellenbosch : Stellenbosch University, 2017-03) Erasmus, Sara Wilhelmina; Hoffman, Louwrens C.; Muller, M.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: Noted for its unique herbaceous flavour which is imbued from a diet of indigenous fragrant plants, Karoo lamb is marketed as one of South Africa’s finest meat products. It is also the first fresh meat product to receive Protected Geographical Indication (PGI) status in South Africa. Its distinct quality is imparted through natural grazing of the sheep on the Karoo veld of the Northern parts of the country. Although it is considered common knowledge to South Africans that Karoo lamb is different to that of lamb meat from other regions, there is a lack of scientific evidence to verify these claims. In order for Karoo lamb to receive official recognition and protection as an authentic product, it is vital to confirm such claims. The aim of the study was to validate the authentic nature of regionally unique South African lamb using analytical techniques. Emphasis was placed on Karoo lamb, while the characteristics of other region of origin lamb, such as the Rûens and Free State lamb, were also determined. A key aspect of the study was to link the characteristic diet, related to its origin, to the sensory and chemical profiles of the meat and fat. The findings show that diet plays an integral part in the sensory characteristics of Karoo lamb meat and hence, have a significant influence on the sensory and chemical profile of South African lamb. Descriptive sensory analysis (DSA), fatty acid analysis, solid-phase microextraction (SPME), isotope ratio mass spectrometry (IRMS), near-infrared reflectance spectroscopy (NIRS) (using a portable MicroNIR spectrometer) and proton transfer reaction-mass spectrometry (PTR-MS) proved to be very successful analytical tools for the authentication of lamb, distinguishing Karoo from Non-Karoo lamb. A key finding was the detection of volatiles, specifically terpenes, present in both the Karoo bushes and the Karoo lamb meat and fat. Terpenes were prominent in the fat tissue and detected at mass ratios m/z 81 and m/z 137 using PTR-MS. The dominant terpenes were tentatively identified as α-pinene, β-pinene, limonene and trans-caryophyllene using SPME. The highest concentrations of terpenes were detected in Karoo lamb, while the Non-Karoo lamb did not or hardly contained any. Within the Karoo, regional differences were apparent as Hantam Karoo lamb had the highest ratings for herbaceous aroma and flavour and contained the greatest concentration of terpenes. Therefore, it is proposed that Karoo lamb is marketed according to its region of origin. Herbaceous aroma and flavour attributes associate with a diet rich in fragrant Karoo plants which were verified with stable isotope ratio analysis. The stable isotopic ratios were indicative of the extensive grazing diet of the animals where discrimination between diets composed of grass, Karoo bushes, lucerne/alfalfa (Medicago sativa) and a combination of grass and Karoo bushes were achieved. The results confirm that Karoo bushes are responsible for the distinct aroma and flavour of Karoo lamb. Hence, the results serve as evidence for its certification and justify the protection of its indicator status. It is recommended that the meat industry utilise the value linked to origin and invest in the marketing of regionally unique lamb. In order to prevent fraudulence and the misuse of protected names, the meat industry should also implement NIRS and PTR-MS as a rapid and effective origin based testing method. The combination of these two techniques improves the discriminative power and allows reliable origin classification.
- ItemBioprospecting South African indigenous fruits byproducts as natural antioxidants in processed meat products(Stellenbosch : Stellenbosch University, 2022-12) Pfukwa, Trust Mukudzei; Mapiye, Cletos; Manley, Marena; Fawole, Olaniyi A; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.ENGLISH ABSTRACT: As the global convenience food retail market grows, food losses due to oxidative degradation are on the rise, increasing the demand for preservatives. Additionally, consumers are demanding safe natural antioxidants as synthetic antioxidant consumption has been linked to adverse health effects. The current study aimed to determine the potential of indigenous fruit byproduct extracts as natural antioxidants in processed meat products. South African indigenous fruits including Carissa macrocarpa A.DC., Diospyros whyteana (Hiern) F.White, Dovyalis caffra Warb., Harpephyllum caffrum Bernh., Olea europaea L. var. africana (Mill.) P.S.Green, Colpoon compressum P.J.Bergius, and Syzygium guineense DC. were collected from Kirstenbosch National Botanical Garden in Cape Town, South Africa. Firstly, the phenolic content of crude extracts from lyophilised seed and peels/pulp of each fruit were evaluated using UPLC-ESI-Q-TOF/MS and their in vitro chemical antioxidant activity determined using four antioxidant assays namely; DPPH, FRAP, ORAC and lipoxygenase inhibition. Secondly, the effect of purification, using XAD7HP macroporous resin, and fruit type (H. caffrum peel, HCP vs. S. guineense, SGS) on the phenolic composition and in vitro chemical antioxidant activity of the extracts was evaluated and followed up with a Caco-2 cell-based method. The potential of HCP-purified extracts (HCP-PE, 250 ppm, 450 ppm and 650 ppm), to protect Saccharomyces cerevisiae against H2O2-induced stress using RNA sequencing (RNA-seq) was then investigated. Lastly, the in producto antioxidant efficacy of HCP-PE at 0, 250, 450 and 650 ppm to enhance shelf stability (colour stability, myoglobin oxidation, TBARS, carbonyl formation and thiol loss) and sensory quality of beef patties was evaluated in comparison with sodium metabisulfite (SMB). The findings showed that hydroxycinnamic acids and total phenolic concentration (TPC) were highest in D. caffra seed, while flavonoids, anthocyanins, hydrolysable tannins, and proanthocyanidins were highest in the crude extracts (CE) from C. compressum seed, Olea Africana pulp, SGS and HCP, respectively (P ≤ 0.05). The HCP-CE had the highest FRAP and lipoxygenase activity, while SGS-CE had the highest DPPH activity (P ≤ 0.05), showing potential for further antioxidants evaluation. Purification increased HCP TPC by 200 %, while a 20 % decrease was observed for SGS (P ≤ 0.05). The HCP-PE had the highest chemical antioxidant activity across the purification × fruit type interactions. Regardless of concentration, HCP-PE cellular antioxidant activity was comparable to that of SMB (P > 0.05). The HCP-PE cytotoxic effects increased (P ≤ 0.05) in a dose-dependent manner but were lower (P ≤ 0.05) than that of SGS and SMB. The HCP- PE influenced ribosome biogenesis and spliceosome, enabling the priming of S. cerevisiae for efficient oxidative stress response and recovery. The tendency towards cytotoxicity increased at high HCP-PE concentration (650 ppm) leading to proteasomal and pro-apoptotic activity (P ≤ 0.05). The HCP-PE improved colour, TBARS, carbonyl formation and thiol loss compared to the control (P ≤ 0.05), with no significant difference in the performance of HCP-PE treatments (P > 0.05). Regarding sensory quality, HCP-PE reduced (P ≤ 0.05) tenderness and juiciness, while undesirable flavours increased (P ≤ 0.05) in beef patties compared to control and SMB. Taken together, the evidence showed that South African indigenous fruits extracts, particularly HCP-PE at 450 ppm, are a source of safe antioxidants for food applications. This work has laid a foundation for valorisation of indigenous fruit byproducts as natural antioxidants for wider food applications.
- ItemBruise damage susceptibility of pomegranates and impacts on fruit quality(Stellenbosch : Stellenbosch University, 2019-03) Hussein, Zaharan; Opara, Umezuruike Linus; Fawole, Olaniyi Amos; Sigge, G. O.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: The consumption of pomegranate (Punica granatum, L) fruit is attributed to its health and nutritional benefits, which are linked with reported high antioxidant capacity, antimutagenic, anti-inflammatory, anti-atherosclerotic and anti-hypertension activities. Postharvest handling of pomegranate fruit takes a couple of weeks (5 – 8) and includes a series of operations from harvest to export (i.e. harvesting, sorting, packing/repacking and transportation). In the course of these operations, there are various situations where pomegranate fruit are subjected to multiple modest drop impacts that predispose the fruit to varying levels of excessive external forces resulting in bruise damage. Impacts may occur as the result of sudden fall of fruit onto other fruit, parts of the tree, harvesting bucket and bin, or any other uncushioned surfaces in the course of loading and offloading. The presence of a bruise on pomegranate fruit causes produce quality deterioration that contributes to downgrading, rejection of produce and ultimately, to postharvest losses. It is therefore important to understand the mechanism of bruising and how to minimise it. The overall aim of this research was to investigate the bruise damage susceptibility of selected pomegranate fruit cultivars, to ascertain the effects of bruising and storage duration on fruit quality attributes and finally, to explore the feasibility of non-destructive measurements to detect and characterise bruise damage. The studies reported in Chapter 4 investigated the susceptibility of three pomegranate fruit cultivars (‘Acco’, ‘Herskawitz’ and ‘Wonderful’) to impact bruising. The impact threshold required to bruise pomegranate fruit was investigated for each cultivar with a view to identify the cultivar that is most susceptible to bruising. The probability of bruise occurrence (PBO) was determined from the population of selected fruit impacted at minimal drop heights (0.10, 0.15, 0.20 m). At the drop impact of 0.10 m, results showed that ‘Wonderful’ had the lowest impact threshold, with a PBO value of 0.44 and an impact energy of 371.87 mJ, whereas neither ‘Acco’ nor ‘Herskawitz’ showed any signs of bruising. At the drop impact height of 0.15 m the highest bruise occurrence was seen in ‘Wonderful’ (PBO = 1; 692.98 mJ), followed by ‘Acco’ (PBO = 0.75; 406.26 mJ) and ‘Herskawitz’ (PBO = 0.5; 511.57 mJ). These results showed that ‘Wonderful’ fruit had a higher susceptibility to bruising compared to the other investigated cultivars, and therefore needs to be handled with extra care during harvest and postharvest handling. Furthermore, the study investigated the effect of cold (5 ºC) and ambient (20 ºC) storage temperatures on bruise damage susceptibility. Fruit were dropped at higher drop impact levels (0.2, 0.4 and 0.6 m), stored for a period of 10 d at either 5 ºC or 20 ºC, during which the physiological responses including weight loss and respiration rate were evaluated. Bruise size were determined in terms of bruise volume (BV) and bruise area (BA), while bruise susceptibility was calculated as the BV per unit of impact energy. The results revealed that bruise size and bruise susceptibility at higher drop heights (0.2, 0.4 and 0.6 m) were cultivar dependent and in the order of ‘Wonderful’ > ‘Herskawitz’ > ‘Acco’. The bruise size of cold (5 ºC) conditioned pomegranate fruit was significantly higher than that of fruit conditioned at an ambient (20 ºC) temperature. Further results showed that drop impact bruising had a larger effect on the fruit physiological response (respiration rate and weight loss) for bruised fruit in comparison to non-bruised fruit. Fruit impacted at higher drop impact levels (0.4 or 0.6 m) exhibited two to three-fold higher respiration rate than fruit bruised at a lower impact level (0.2 m) or nonbruised fruit. Respiration rate and weight loss increased with prolonged storage duration and at an ambient temperature, both in bruised and non-bruised fruit. Further study to evaluate the feasibility of X-ray micro-computed tomography (X-ray µCT) in detection and characterization of bruise damage on pomegranate fruit is reported in Chapter 5. Pomegranate fruit bruised by dropping at 0.6 m was scanned with X-ray µCT. The results showed that two-dimensional CT images of fruit scanned at 0 h (immediately after drop impact), 48 h, 3 d and 5 d after impact bruising showed no evidence of bruise damage. Changes in bruise-damaged tissue as characterised by a darker appearance were observed in pomegranate fruit scanned after 7 d of impact bruising. Furthermore, visual assessment of two-dimensional X-ray µCT images were buttressed by the results of quantitative µCT data analysis. The latter demonstrated that bruised pomegranate fruit can be visualised and differentiated from 7 d after impact bruising with lower grey values (18000 - 30000) compared with non-bruised fruit (26000 - 34000). The image analysis and quantitative µCT data obtained in this study confirmed that X-ray µCT is not a suitable non-destructive method to detect and characterise fresh bruises (immediately bruised) on pomegranate fruit. Studies to explore alternative non-invasive techniques, such as a hyperspectral imaging system for early detection of fresh bruises on pomegranate fruit, are warranted. Chapter 6 focused on evaluating the physical, biochemical and microstructural changes of impact-bruise damaged pomegranate fruit. The results showed that there were significant changes in colour (browning), peel electrolyte leakage (PEL), polyphenol oxidase (PPO) enzyme activity and accumulation of reaction oxygen species (ROS) measured in pomegranate fruit peel with increasing drop impact bruising. The combination of time and temperature (in which fruit was incubated) significantly (p < 0.05) contributed to changes in PEL, PPO enzyme activity and fruit browning. Cellular microstructural differences between control and bruised fruit tissues were visible in scanning electron microscope images after 4 and 48 h of drop impact. These findings provided evidence that the loss of membrane integrity of pomegranate fruit skin cells are caused by impact bruising. Chapter 7 covered the study on bruise damage of pomegranate during long-term cold storage, focusing on susceptibility to bruising and changes in textural properties of fruit. Fruit from cold (5 ºC) storage were impact bruised from different drop heights (0.2, 0.4 and 0.6 m). The bruise volume and bruise area of pomegranate fruit increased with increasing drop impact heights and storage duration for the first two months of storage, and then decreased in the last month of storage. Similarly, the results of textural properties showed that increase both in puncture resistance, cutting and compression strength were dependent on impact bruising and storage duration. These results have demonstrated that bruise damage would result in significant changes in fruit textural attributes with concomitant low consumer appeal. Studies in Chapter 8 investigated the effects of bruising and long-term cold (5 ºC) storage on the physiological response, physico-chemical quality attributes, textural properties and antioxidant content of pomegranate fruit. Respiration rate and weight loss of whole fruit were both influenced by increasing drop impact bruising and storage duration. Furthermore, there were increases in chemical quality attributes (total soluble solids, titratable acidity, Brix-to-acid ratio and BrimA), and antioxidant content of bruised pomegranate fruit during long-term storage. This was partly attributed to the concentration effect due to an increased moisture loss from bruise damaged fruit. Results on changes in aril colour and texture were dependent on both bruising and storage duration (p < 0.05). Overall, this research represents a pilot study aimed at providing scientific insights to broaden the understanding of pomegranate fruit susceptibility to bruising during postharvest handling and its impacts on fruit quality. The findings in this dissertation have established that bruise susceptibility of pomegranate fruit is dependent on the level of drop impact, cultivar, storage temperature and duration. Furthermore, this study showed that bruising, storage conditions and duration play a crucial role on physiological responses (i.e. respiration rate and weight loss), textural properties and chemical quality attributes of the fruit. From a practical point of view, the study has revealed that, bruise damage affects the sensory appeal of pomegranate fruit during storage, which could result in downgrading of fruit market value or complete fruit loss.
- ItemCharacterisation and quantification of microstructure, physicochemical and functional properties of oven and forced convection continuous tumble roasted cereal grains(Stellenbosch : Stellenbosch University, 2017-03) Schoeman, Letitia; Manley, Marena; Du Plessis, Anton; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: The use of roasted cereal grains in foods can improve organoleptic properties, enhance shelf life, ease incorporation into ready-to-eat products and increase antioxidant activity. Structural, physicochemical and functional changes will inevitably occur during roasting and this study aimed to investigate these properties. X-ray micro-computed tomography (μCT) was used as a non-destructive technique for characterising and quantifying microstructural changes in individual cereal grains induced by conventional oven and forced convection continuous tumble (FCCT) roasting at 180°C for 140 s. X-ray μCT uses differences in X-ray attenuation arising from differences in density within a sample. X-ray tomograms of the raw and roasted wheat and maize kernels were obtained, using a General Electric Phoenix model V|Tome|X L240 X-ray μCT system with a source voltage of 60 kV and an electron current set at 240 μA. Analysis of the whole kernel and regions-of-interest (ROIs) was performed with VGStudio Max 2.2 three-dimensional (3D) software. Qualitative results were depicted as two-dimensional (2D) transmission images and 3D volumes. Internal structural changes were observed as a loss of endosperm integrity, detected as a decrease in attenuation. For both cereal grains oven roasting was associated with a larger increase in kernel volume (wheat=4.47%; maize=10.76%) than FCCT roasting (wheat=1.57%; maize=3.41%), as well as larger relative density decreases (wheat=2.76%; maize=6.33%) in comparison to FCCT roasting (wheat=0.55%; maize=1.92%). During FCCT roasting the material density (excluding air) remained unaffected. Structural changes can strongly influence physicochemical and functional properties. Kernel hardness and hectolitre mass (HLM) can be helpful to assess the milling yield, which was not affected (P>0.05) by either roasting methods. Scanning electron microscopy (SEM) illustrated the starch-protein morphology, where both roasting methods resulted in a partially disintegrated protein network and swollen and/or ruptured starch granules in the oven-roasted samples. Quantification of these structural differences included crystallinity determinations using X-ray diffraction (XRD), thermal properties using differential scanning calorimetry (DSC) and pasting properties employing a Rapid Visco Analyser (RVA). The reduction in crystallinity for both FCCT (wheat=0.12%; maize=0.45%) and oven (wheat=0.16%; maize=1.83%) roasting was consistent with the decrease in gelatinisation enthalpy (ΔH). Only partial gelatinisation occurred in both the oven (wheat=17.16%; maize=25.27%) and FCCT-roasted (wheat=10.14%; maize=16.23%) samples. Oven roasting caused more adverse changes in most of the measured properties, being a more destructive process. With FCCT roasting the samples are continuously moving, resulting in an even heat transfer in comparison to oven roasting where the samples are stationary. FCCT roasting maintained more of the favourable characteristics, i.e. microstructure, hardness and milling yield and will thus result in a more acceptable final product. This study demonstrated the capability of X-ray μCT in combination with image analysis as a non-invasive technique to study microstructural changes in cereal grains, induced by roasting, both in a qualitative and quantitative manner and at a relatively high spatial resolution of 12 micron. The results integrate qualitative and quantitative information that could be useful for understanding structure-property relationships in terms of further processing and utilisation, e.g. the development of value-added products with improved digestibility and viscosity or delayed staling phenomenon.
- ItemCharacterising the flavonoid profile of various citrus varieties and investigating the effect of processing on the flavonoid content(Stellenbosch : Stellenbosch University, 2016-03) Hunlun, Cindy; Sigge, G. O.; De Beer, D.; Van Wyk, J.; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.ENGLISH ABSTRACT: Phenolic compounds in citrus fruit are specific for each species and variety and may be influenced by environmental conditions during the growing season and post-harvest practices. The exact chemical composition of citrus produced in South Africa is currently not known even though 2 million tonnes were produced in 2012. Various citrus varieties are produced for export, local fresh markets as well as processed into value-added products sold on the local market. In the current study South African citrus fruit (satsuma, clementine, navel and valencia) as well as products such as frozen concentrated orange juice (FCOJ), made-from-concentrate and not-from-concentrate orange juices produced from these varieties were characterised in terms of chemical and phenolic composition as well as total antioxidant capacity (TAC). Samples from two regions and three seasons were evaluated to determine the effect of variety as well as seasonal and regional differences. Citrus juice characteristics evaluated, included: °Brix, titratable acidity (TA), °Brix:acid ratio, pH as well as ascorbic acid (AA). Furthermore, the phenolic composition of the citrus fruit was quantified using high-performance liquid chromatography coupled with diode-array detection (HPLC-DAD). The TAC was determined using 2,2’-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay, Oxygen Radical Absorbance Capacity (ORAC) assay and Ferric Reducing Antioxidant and Ascorbic Acid (FRASC) assay. Eight phenolic compounds were quantified and included four flavanone-O-glycosides, two flavonols, a flavone and phenolic acid. The phenolic composition of different citrus varieties showed great variation between different seasons. Varietal difference was evident although there was some overlap between citrus varieties within the same season. Hesperidin and narirutin were the predominant flavanone-O-glycosides in sweet oranges, which included navel and valencia varieties, with vicenin-2 and ferulic acid-O-hexoside also present in high quantities. Regarding the FCOJ samples the results of the juice characteristics indicated that those from the WC sampling site were more mature compared to those of EC. Varietal differences were evident and variety proved to be the most significant factor that accounted for the variances in juice characteristics and phenolic composition. Seasonal differences were less evident. Variation that could be ascribed to regional differences was found for the individual phenolic composition. FCOJ from EC were characterised as having higher levels of the individual phenolics, total phenolic composition (TP) and TACDPPH and TACORAC. Of all the FCOJ varieties, navel was found to be the most mature, irrespective of season and region and was the variety with the highest TP. The predominant flavanone found in the MFC and NFC orange juices were hesperidin (HD) and narirutin (NART) followed by the flavone-C-glucoside vicenin-2 (VIC2) and a hydroxycinnamic acid namely ferulic acid-O-hexoside. Three other minor phenolic compounds where also quantified. The results indicated that NFC juices had higher levels of the individual phenolics as well as higher TACORAC. The results further showed that the phenolic composition of the MFC juices where dependent on the juice formulation, i.e. the quantity of orange juice added and not the treatment type (pasteurisation versus ultra-high temperature pasteurisation). Lastly, the results highlighted the lack of information pertaining to the processing, storage and shelf-life stability of the identified and evaluated phenolic compounds.
- ItemComprehensive characterisation of the phenolic composition of Cyclopia pubescens (honeybush)(Stellenbosch : Stellenbosch University, 2019-12) Walters, Nico Albertus; De Beer, Dalene; Joubert, Elizabeth; Williams, Paul James; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.ENGLISH ABSTRACT: Cyclopia pubescens Eckl. & Zeyh, endemic to South Africa, is under threat of extinction. This threat can be negated through commercial cultivation if utilised as honeybush tea. Lack of knowledge of the phenolic composition of this Cyclopia species is a hurdle in the development of value-added products such as nutraceuticals, providing the incentive for a comprehensive investigation of the phenolic profile of C. pubescens. A reversed-phase (RP) high-performance liquid chromatography-diode-array detection (HPLC-DAD) method using a biphenyl column was developed and validated. Eight phenolic compounds, representing major compounds (3-β-D-glucopyranosyl-4-O-β-D-glucopyranosyliriflophenone, 3-β-D- glucopyranosylmaclurin, 3-β-D-glucopyranosyliriflophenone, mangiferin, isomangiferin, vicenin-2, narirutin and hesperidin), were identified and a further six compounds tentatively identified by comparison of their retention times, UV–Vis spectra and high-resolution mass spectrometric (HR-MS) characteristics with those of authentic reference standards and literature, respectively. The predominant accumulation of the compounds in the leaves or stems of C. pubescens was determined for a small number of available genotypes (n = 17), affording some indication of variation between plants in the field genebank of the Agricultural Research Council. For further elucidation of the phenolic profile, the focus fell on minor phenolic compounds. Increased separation power was required and therefore an analytical comprehensive two-dimensional (2D) separation method utilising normal-phase (NP) high- performance countercurrent chromatography-DAD (HPCCC) as the first dimension and RP ultra(U)HPLC-DAD as the second dimension. High loading capacity and selectivity of HPCCC and high selectivity and resolving power of UHPLC resulted in ca 81% orthogonality. A total of 32 compounds were (tentatively) identified by comparing their UV– Vis and HR-MS characteristics to those of reference standards and literature. The HPCCC method was subsequently upscaled to semi-preparative mode and eight phenolic compounds were isolated in adequate quantities for unambiguous structural elucidation using 2D nuclear magnetic resonance, gas chromatography-MS analysis after acid- catalysed hydrolysis of the glycoside, derivatisation and determination of optical activity. (2R)-5-O-[α-L-rhamnopyranosyl-(1→2)-β-D-glucopyranosyl]eriodictyol, (2S)-5-O-[α-L- rhamnopyranosyl-(1→2)-β-D-glucopyranosyl]eriodictyol and (2S)-5-O-[α-L-rhamnopyranosyl- (1→2)-β-D-glucopyranosyl]-5,7,3ʹ,4ʹ-tetrahydroxyflavan have not been previously reported in literature. The five other compounds include the two flavanones, (2S)-5-O-[α-L- rhamnopyranosyl-(1→2)-β-D-glucopyranosyl]naringenin and R-neo-eriocitrin, the two phenolic acids, 3-O-α-L-arabinopyranosyl-3,4-dihydroxybenzoic acid and 4-O-β-D-glucopyranosyl-cis-4-hydroxycinnamic acid, and an anisole, 4-(4ʹ-O-β-D-glucopyranosyl-3ʹ- methoxyphenyl)-2-butanone. Natural deep eutectic solvents (NADES) (n = 7) were evaluated to improve extraction efficiency and obtain a more representative phenolic profile of C. pubescens. Hot water and 40% EtOH, commonly used for extraction of Cyclopia plant material, represented the benchmark solvents. Stereoisomers were selectively extracted by the different NADES solvents. Application of an on-line HPLC-ABTS assay showed that these stereoisomers also differed in Trolox equivalent antioxidant capacity. Glutamic acid based NADES (n = 2) provided superior extraction efficiency, but low eutectic stability made these solvents unsuitable for high-throughput extraction; therefore, the most suitable NADES for extracting the phenolic compounds of C. pubescens was choline chloride:proline (CcP) (1:3, molar ratio). The optimal extraction temperature for NADES, tested over the range 40 to 90 °C, was 70 °C instead of 93 °C for water when using a 20 min extraction time. The best extraction solvent for phenolic compounds remains 40% EtOH, but NADES can be used to selectively extract phenolic compounds.
- ItemThe contribution of phenolics to the bitter taste of honeybush (Cyclopia genistoides) herbal tea(Stellenbosch : Stellenbosch University, 2018-12) Alexander, Lara; Joubert, Elizabeth; De Beer, Dalene; Muller, Magdalena; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.ENGLISH ABSTRACT: The occurrence of bitter taste in some production batches of Cyclopia genistoides herbal tea not only challenges efforts of the honeybush industry to achieve consistent product quality, but also adversely affects consumer purchase intent. Previous studies have attempted to understand this phenomenon by determining associations between the bitter intensity of honeybush infusions and their individual phenolic concentrations. Despite some significant correlations between specific compounds and bitter intensity, the data did not give conclusive evidence of the cause of bitterness. The current investigation thus aimed to provide decisive proof of the role of phenolic compounds in the bitterness of C. genistoides herbal tea. To achieve this, the first phase of the study utilised a hot water extract of unfermented C. genistoides plant material (yielding an infusion with a bitter intensity of ~45 on a 100-point scale), separated by column chromatography into three fractions rich in benzophenones, xanthones and flavanones, respectively. The bitter taste of the fractions was determined by descriptive sensory analysis (DSA) and discrimination tests, and their individual phenolic content was quantified by high-performance liquid chromatography. The benzophenone-rich fraction was not bitter (< 5), the flavanone-rich fraction was somewhat bitter (~13) and the xanthone-rich fraction was considered distinctly bitter (~31). Further investigation of the bitter xanthone-rich fraction included a focussed DSA comparison of the major xanthones and regio-isomers, mangiferin and isomangiferin. This comparison revealed that isomangiferin was only somewhat bitter (~15) and modulated the distinct bitter taste of mangiferin (~30) by suppressing it (~22). The second phase of the study focussed on possible bitter taste modulation by the benzophenone- and flavanone-rich fractions, as well as their major individual phenolic compounds using DSA. The results indicated that modulation is dose-dependent, and identified 3-β-D-glucopyranosyl-4-β-Dglucopyranosyloxyiriflophenone (IDG) and naringenin-O-hexose-O-deoxyhexoside B (NHDB) as novel bitter modulators for their respective bitter suppressing and enhancing activities. In addition, a mixture of NHDB and its isomer, NHDA, formed upon heating of NHDB (to simulate the effect of fermentation), did not have any modulatory effect on bitter intensity and should be investigated further. For the third and final phase of the study, a large data set was utilised to produce a robust statistical model for the prediction of bitter intensity of infusions from their individual phenolic concentrations. Fermented and unfermented samples of several genotypes of C. genistoides and C. longifolia in the Agricultural Research Council’s honeybush plant breeding programme were analysed. Both species contain high xanthone and benzophenone levels and have been found to produce bitter infusions. The data also allowed the investigation of the effects of fermentation on bitter intensity and individual phenolic concentrations of the infusions. The final independent validated stepwise linear regression model was able to predict bitter taste of the infusion (R2 = 0.859) using the concentration of only five phenolic compounds (IDG, hesperidin, 3-β-D-glucopyranosylmaclurin, mangiferin and isomangiferin) and soluble solids content, common to both C. genistoides and C. longifolia.
- ItemCritical evaluation of the accuracy of the enumeration methodology of Coliforms and E. Coli in water from rivers used for the irrigation of fresh produce(Stellenbosch : Stellenbosch University, 2012-12) Brand, Amanda Salome; Britz, T. R.; Sigge, G. O.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: The accuracy of methods for the enumeration of coliforms and Escherichia coli present in river water intended for the irrigation of fresh produce has been critically evaluated to determine whether the results of the traditional method were reliable in indicating faecal pollution. The potential of rapid alternative methods were also explored. Baseline monitoring of the Berg River showed the presence of potential pathogens such as Salmonella, and also that E. coli levels exceeded international guidelines for the safe irrigation of minimally processed foods (MPFs) in 20.5% of cases, which indicated faecal intrusion. An exploratory study into the use of microbiological and physico-chemical parameters in predicting E. coli numbers, as a rapid alternative to direct enumeration, was conducted. These measurements, neither individually nor in combination, could accurately predict the E. coli numbers. The rapid method Colilert-18 was compared against multiple tube fermentation (MTF) for the enumeration of coliforms and E. coli. Spearman rank correlation coefficients showed that Colilert-18 had acceptable (r2=0.69) and fair (r2=0.74) correlations with MTF for coliform and E. coli enumeration, respectively. Bland and Altman statistics were used to determine pollution influence, and Colilert-18 showed increasing disagreement with MTF at very high concentrations of coliforms and E. coli. Bacterial isolates obtained from MTF reactions were identified using biochemical and mass spectrometry methods. These identifications revealed that the greatest contributors to inaccurate coliform enumeration by MTF were false negative coliforms which fail to produce gas from lactose. Numerical biochemical data suggested that these isolates may be able to use other carbohydrates preferentially over lactose. Inaccurate E. coli enumeration was caused by E. coli strains which could not utilise lactose or 4-methylumbelliferyl- -D-glucuronide (MUG), as well as non-E. coli isolates which were able to hydrolyse MUG. The method of transfer of bacteria between MTF media was also identified as problematic for accuracy. Monoplex polymerase chain reaction (PCR) differentiation of MTF isolates showed that detection of the uidA gene showed the greatest accuracy in the detection of E. coli, while the multiplex PCR protocol for detecting diarrheagenic E. coli pathotypes identified one strain of enteroaggregative E. coli (EAEC). A qualitative methodological risk classification was used, in combination with the individual reactions of MTF isolates, to elucidate their contribution to enumeration inaccuracy and to evaluate the effect of MUG and Levine-eosin methylene blue (L-EMB) agar. The classification indicated that inaccurate enumeration of E. coli was more problematic than that of coliforms, but revealed that the exclusion of MUG from MTF may increase the accuracy of E. coli enumeration. The omission of L-EMB would have very little effect on E. coli enumeration accuracy. This work confirmed that MTF is fairly reliable in the enumeration of coliforms and E. coli. Inaccuracies are primarily attributable to atypical organisms which are considered to make up a small proportion of the total bacterial population. Colilert-18 was shown to be an acceptably accurate alternative, and its rapid production of results can be highly advantageous in the monitoring of irrigation water used for MPFs.
- ItemDevelopment and effect of an N-3 fatty acid-rich spread on the nutritional and cognitive status of school children(Stellenbosch: University of Stellenbosch, 2006-03) Dalton, Annalien; Smuts, C. M.; Witthuhn, R. C.; Wolmarans, P.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Food Science.Long-chain polyunsaturated fatty acids (LCPUFA), especially the n-3 LCPUFA metabolic products eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) play an important role as regulators in many biological processes. To date hake (Merluccius capensis) heads, a rich source of EPA and DHA, have been discarded at sea. The South African Fisheries Policy Development Committee concerned with the environmental impact of this practice has rendered it undesirable. The high prevalence of under-nutrition amongst children in South Africa can be addressed by the supplementation of their diet with this unexploited fish source. The aim of the current study was to develop a microbiologically safe and sensory acceptable sandwich spread using fish flour prepared from fish heads, as a prime ingredient. The intervention trial aimed to compare the effects of an increased dietary intake of n-3 LCPUFA, specifically DHA, on the blood fatty acid levels and absenteeism (as indicator of immune function), as well as the cognitive status, of the subjects. The microbiological content of the sandwich spread was determined after storage for 20 d at 5°C and 15 d at 25°C. Sensory evaluation was performed by consumers (n = 95; M:F = 44:51; 6 – 9 yr) to determine acceptance of the five different flavours individually incorporated into the sandwich spread to mask the fishy note and to provide different flavour options. For the intervention trial subjects (n = 351) were stratified within class group (A - E) and gender and randomly assigned to two treatment categories, an experimental group (EG; n = 174) receiving 25 g sandwich spread.d-1 (191.66 mg DHA. d-1) and a control group (CG; n = 177) receiving an analogous placebo. On school days (104 d), each subject received two sandwiches consisting of two slices of bread (ca. 60 g), spread with 25 g of either the placebo or the experimental spread. Blood samples were drawn at baseline and post intervention. Plasma fatty acid and red blood cell (RBC) membrane status, C-reactive protein levels, as well as vitamin and micronutrient status, were determined. Trained test administrators conducted a battery of cognitive tests. According to South African Government health standards, the sandwich spread remained microbiologically safe after storage. Male and female consumer respondents revealed a significant difference between gender preferences of the five different spread flavours (p <0.05). Significant treatment effects (p <0.05) were observed in n-3 LCPUFA status of the EG, as well as for their absenteeism from school. The two subtests of the Hopkins Verbal Learning test, Recognition and Discrimination Index, showed significant differences between the EG and CG (p <0.05) post intervention in the Grade 2 subjects. The Spelling tests also showed a significant difference between the two groups (p <0.05). In the current study a microbiologically safe and sensory acceptable sandwich spread was developed and tested during an intervention trial, and could possibly in future, provide a healthier option in the School Nutritional Programme. This study proved that supplementation of children (6 - 9 yr) with n-3 LCPUFA, with specific reference to EPA and DHA from a marine source, could have a beneficial effect on their fatty acid status and absenteeism from school. Based on the outcomes of the Hopkins Verbal Learning test and Spelling test, the current study proved that an n-3 fatty acid-rich spread improved the learning ability and memory of children.
- ItemDevelopment and validation of prediction models and rapid sensory methodologies to understand intrinsic bitterness of Cyclopia genistoides(Stellenbosch : Stellenbosch University, 2018-03) Moelich, Erika Ilette; Joubert, E.; Muller, M.; Næs, T.; Stellenbosch University. Faculty of AgriScience. Dept. of Food Science.ENGLISH ABSTRACT: Cyclopia species, endemic to South Africa, is used for the production of honeybush tea. This herbal tea has grown from a product consumed only locally to one currently marketed worldwide. Cyclopia species is high in polyphenols, well-known for its health related properties, but these compounds could contribute to bitterness, which may elicit negative consumer response. One of the species, C. genistoides, is high in polyphenols but also associated with bitterness, contrary to the characteristic sweet taste and honey-like flavour associated with honeybush. The polyphenolic content of four Cyclopia species were quantified with high-performance liquid chromatography diode-array detection while descriptive sensory analysis (DSA) was used to determine the taste intensities of these samples. The link between phenolic content and bitterness was investigated. Based in the phenolic content of C. genistoides and C. longifolia, partial least squares (PLS) regression analysis identified four compounds, mangiferin, isomangiferin, iriflophenone-3-C-glucoside-4-O-glucoside and iriflophenone-3-C-glucoside, as candidate predictors of bitterness. This model will find application as screening tool in cultivar development research programs. Production of honeybush lags behind demand, forcing the industry to use blends of Cyclopia species, including C. genistoides, to supply in the increased demand. The distinct differences in the sensory profiles associated with different Cyclopia species require that special care is given to blending to ensure a consistent, high quality product. DSA was used to evaluate the effect of blending of C. genistoides with other Cyclopia species on bitterness. Blending of C. genistoides with C. subternata, C. intermedia or C. maculata in a ratio of 2:3 were effective in reducing bitterness to below perceptible levels. The sensory profile of C. genistoides- C. subternata blends were further quantified using DSA and was described as “fynbos floral”, “apricot”, “woody”, “fruity sweet” and “fynbos sweet” aroma and a sweet taste. Based on these results, inclusion of C. genistoides at 40% when blending different Cyclopia species, is recommended. Blending at this standardised ratio will result in a well-rounded product with bitterness below perceptible levels. The herbal tea industry expressed the need for time- and cost-effective methods for sensory screening of infusions to improve quality and product consistency. The validity of three rapid profiling methods {sorting, projective mapping and polarised sensory positioning (PSP)} for the sensory characterisation of honeybush infusions were investigated using a trained panel. The efficacy of partial (aroma or palate attributes) or global (all attributes) evaluation was compared within each rapid method. Product configurations similar to that of DSA demonstrated the validity of all three methods for broad sensory profiling of Cyclopia species. Sorting on palate attributes resulted in additional differentiation between samples with only subtle differences. Sorting demonstrated to be the most effective method for the broad sensory profiling of honeybush infusions and could find application in the honeybush industry as screening tool. PSP on the other hand could find application in quality control programs where poles that represent specific quality attributes, should be included. Implementation of valid, scientific methods, such as sorting and PSP, will aid the honeybush industry in their effort to supply a product with consistent quality and high consumer appeal.
- ItemDevelopment of a gastroretentive anti-diabetic nutraceutical incorporating polyphenol-enriched fractions of Cyclopia genistoides(Stellenbosch : Stellenbosch University, 2020-04) Miller, Neil; Joubert, Elizabeth; Manley, Marena; Malherbe, Christiaan Johannes; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: Extracts of honeybush (Cyclopia genistoides) containing glycosylated xanthones, mangiferin (1) and isomangiferin (2), and benzophenones, 3-β-D-glucopyranosyliriflophenone (3) and 3-β-D-glucopyranosyl-4- O-β-D-glucopyranosyliriflophenone (4) inhibit α-glucosidase (AG), a key digestive enzyme and treatment target for postprandial hyperglycaemia associated with type 2 diabetes. Ultrafiltered green C. genistoides extract served as the starting material for the development of an optimised production protocol for xanthone- and benzophenone-enriched fractions (XEFs and BEFs) by macroporous adsorbent resin chromatography. Inter-batch variation in the phenolic content of the raw material manifested as variation in the composition and degree of enrichment of target compounds in XEFs and BEFs. The in vitro AG inhibitory effects of C. genistoides phenolics, extract, XEF and BEF, combined with the commercial AG inhibitor (AGI), acarbose, were investigated using the combination index. The single-compound AGIs demonstrated potency in the descending order: acarbose (IC50 = 44.3 µM) > 1 (102.2 µM) > 2 (119.8 µM) > 3 (237.5 µM) > 4 (299.4 µM). Potency of the extract and fractions was strongly linked to their xanthone content. XEFs (xanthone content = 22.3–48.1 g/100 g) were produced using ten different batches of plant material and tested at a fixed concentration (160 µg/mL), achieving 63 to 72% enzyme inhibition. BEFs (benzophenone content = 11.4– 21.7 g/100 g) achieved enzyme inhibition of 26 to 34%. There was a weak linear correlation (R² < 0.43) between the target compound content of the fractions and their AG inhibition potency. Synergistic AG inhibition at > 50% effect levels was observed for all combinations of acarbose with fractions (XEFs, BEFs) or target compounds (1–4). Combinations of acarbose with 1 and 2 gave the highest theoretical in vitro acarbose dose reduction (> six-fold) across all effect levels. XEFs showed greater theoretical acarbose dose reduction (≈ four-fold at 50% inhibition) than BEFs, demonstrating the potential of XEFs as a supplement to acarbose. In a subsequent in vivo oral sucrose tolerance test in normal and diabetic Wistar rats, XEF (single orally administered dose of 300 mg/kg body weight) did not result in significantly lowered postprandial blood glucose or in an improved effect in combination with acarbose (5 mg/kg body weight). The suitability of C. genistoides phenolics as non-toxic active pharmaceutical ingredients (APIs) was confirmed in a liver cell model, which indicated no cytotoxicity following acute or chronic exposure. Ex vivo intestinal transport studies using porcine jejenum showed that the target compounds (1–4) are poorly absorbed, confirming their suitability as APIs aimed at an intestinal target, and re-emphasising the low risk of systemic toxicity. XEF and BEF were subsequently incorporated (alone and combined) in a non-effervescent gastroretentive tablet formulation containing low-density styrene-divinylbenzene co-polymer as floating agent. The tablets floated in an in vitro medium (0.1 N HCl) for at least 8 h and released APIs through a diffusion-based process, described by the Weibull model (R² > 0.99). API degradation during storage under adverse conditions (12 weeks at 40 °C) followed first order reaction kinetics with the order of compound stability: 4 > 1 > 2 > 3.
- ItemDevelopment of a quality grading system for the honeybush (Cyclopia spp.) tea industry(Stellenbosch : Stellenbosch University, 2020-12) Du Preez, Brigitte Von Pressentin; Joubert, Elizabeth; Muller, Magdalena; Moelich, Erika Ilette; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: Honeybush tea, produced from Cyclopia species endemic to South Africa, has attained an international footprint within the global herbal tea sector. As demand is exceeding supply to a primarily export market, all production batches should meet optimum quality standards. The lack of standardised sensory quality criteria and assessment methods within the commercial sector has resulted in tea of variable sensory quality reaching the market. The trade of inconsistent and inferior quality products will be detrimental to the reputation of honeybush tea and consumer acceptance, and ultimately the honeybush industry. The need for a scientifically founded quality grading system to evaluate, differentiate and communicate the sensory quality of honeybush tea was addressed through four quality control elements, i.e. a sensory lexicon and wheel, sensory quality standard, quality scoring method, and rapid quality classification methods. The previously developed honeybush aroma lexicon and wheel were revised, based on a newly established comprehensive sensory and physicochemical dataset. Data of samples of the main commercial Cyclopia species (C. intermedia, C. subternata and C. genistoides), processed on laboratory- and commercial-scale, were incorporated to represent the sensory space in terms of different qualities. Universal chemical-based reference standards were developed and validated to replace food-based reference standards in the aroma lexicon to facilitate standardised assessment of honeybush sensory quality. The established sensory quality standard was founded on the comprehensive dataset and input from industry. Sensory quality parameters for the tea infusions and dried plant material were identified, and parameter specifications for ‘high’, ‘moderate’, ‘low’ and ‘poor’ quality classes were defined through expert focus groups. A user-friendly quality scoring method that incorporates a scorecard and colour reference card, was developed and validated for the assessment and classification of production batches based on obtained parameter and total score values and citation frequencies of specific attributes. The validity of reference-based rapid methods, polarised sensory positioning (PSP) and polarised projective mapping (PPM), were investigated for their discrimination ability as time-efficient classification tools to distinguish between infusions of large samples sets of variable sensory quality within commercial and research context. The efficacy of the use of physical (p) poles (tea infusions) and novel theoretical (t) poles (descriptions), representative of the four sensory quality classes, as references, were compared within each method, using a trained panel. Product configurations similar to that of a classical sensory profiling method, descriptive sensory analysis, demonstrated the validity of the method variations for broad quality classification based on key sensory quality parameters. PPM-p indicated the highest discrimination ability between the quality classes. Recommended amendments to theoretical pole descriptions would improve feasibility for commercial application. The quality scoring method and PPM-t were tested by a panel of industry representatives, and the need for industry assessor training in sensory quality parameters was emphasised. Implementation of the proposed integrated quality grading system will equip honeybush industry role-players in delivering a final product of consistent sensory quality within the honeybush value chain.
- ItemThe development, implementation and evaluation of a housing education literacy programme for semi-literate recipients of government subsidised housing(Stellenbosch : University of Stellenbosch, 2006-03) Venter, Maria Dorothea; Van Wyk, A.S.; Strydom, H.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Food Science.In the ten years since the inclusive elections of 1994, the South African government has created an international precedent in the housing field. It is widely acknowledged that in this period it has delivered more subsidised houses than any other country in the world. The housing backlog is still between 2 to 3 million and growing every year, so housing policies for the future must continue to , not only provide subsidised housing for a large part of the population but also seeking to establish a viable market for low-cost housing units and to create sustainable human settlements for low-income groups. There are a therefore large numbers of new consumers that enter the housing market for the first time.
- ItemEffect of forced convection roasting on physicochemical and antioxidant properties of whole grain maize (Zea mays L.) and optimisation of roasting conditions(Stellenbosch : Stellenbosch University, 2016-03) Bala, Shuaibu Mallam; Manley, Marena; Opara, Umezuruike Linus; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: Maize (Zea mays L.) is the most cultivated cereal and grain crop in the world and it is used as a staple food in developing countries such as Nigeria, South Africa, Mexico and economically less privileged countries. The grains of maize are processed into intermediate products (flour and meal) which are utilised for the production of different types of ready to eat foods. In most cases, the flour or meal used is refined (bran and germ removed) and not pregelatinised. Heat-processing methods of maize that uses dry heat reduced the nutritional quality of intermediate and end products. Forced convection roasting (FCR), a novel heat-processing technique, that has an additional advantage of using superheated steam was used to study the changes in physicochemical, proximate composition and antioxidant properties of Nigerian (S28, S33) and South African (H2G1, H7D1) maize varieties. Roasting temperature and rotating speed (determining roasting time) limits (150 to 220 °C) and (30 to 90 Hz), respectively were used for the roasting in a forced convection continuous tumble roaster (FCCTR). Roasting conditions (temperature/rotating speed) of the maize varieties were optimised for the production of whole grain flour or meal. Comparison of the proximate composition, antioxidant and pasting properties of the optimally processed whole grain flour or meal with raw whole grain flour or meal and an unroasted refined commercial maize meal (CMM) was made. The nutritional quality and antioxidant properties (content and activity) of the Nigerian maize S28 (yellow kernel) and S33 (white kernel) were not negatively affected by FCR. For the South African maize varieties, FCR did not show a negative effect on the proximate composition and antioxidant properties except the increase in total phenolics content of H2G1. Variations in the physicochemical properties such as bulk density, kernel hardness, colour and pH of the roasted maize varieties did not compromise the quality of the optimally processed whole grain flours. The prediction models of moisture content, whiteness index (WI), yellowness index (YI), total essential amino acids (TEAA) and total amino acids (TAA) had good fit (R2 >0.8) with the experimental data and non-significant (p ≤0.05) lack-of-fits. The desirability profiling of moisture content, WI and YI indicated 189.9 °C/90 Hz and 140.9 °C/49.8 Hz as the mean optimum roasting conditions of S28 and S33 maize varieties, respectively for the production of high quality whole grain flour or meal. Similarly, the desirability profiling of moisture content, WI, YI, TEAA and TAA showed the mean optimum roasting conditions of H2G1 and H7D1 white maize varieties to be 185.0 °C/65.5 Hz and 182.6 °C/55.0 Hz, respectively. The carbohydrate, crude protein, fat and fiber, ash, total phenolics and flavonoids as well as free radical scavenging capacity of the optimally processed whole grain flours did not significantly differ from those of the raw whole grain flours of each of the maize varieties. Both whole grain flours of the raw and roasted maize grains had higher proximate composition, total phenolics, total flavonoids and antioxidant activity than CMM, except the carbohydrate content which was found to significantly higher in the later. The optimally processed whole grain flour of each maize variety had a non-significantly lower pasting temperatures and significantly higher pasting viscosities compared to the raw whole grain flour. This indicated better pasting characteristics of the optimally processed whole grain flours with reference to the raw whole grain flours of the maize varieties. However, CMM had significantly lower pasting temperatures and higher pasting viscosities than the whole grain flours which indicated better pasting properties of the former. Considering the non-negative effect on proximate composition and antioxidant properties, and better pasting characteristics of whole grain flours of the roasted maize varieties, it could be concluded that FCR is a good alternative for roasting maize grains in the process of producing whole grain flours with the best quality for human consumption. It was also observed that the whole grain flours had better nutritional and antioxidant properties, but poorer pasting properties compared to CMM.
- ItemThe effect of muscle type and ageing on Near Infrared (NIR) Spectroscopy classification of game meat species using a portable instrument(Stellenbosch : Stellenbosch University, 2021-04) Dumalisile, Pholisa; Williams, Paul James; Manley, Marena; Hoffman, Louwrens C.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: Meat and meat products represent a large proportion of the human diet as it is known to provide valuable proteins, and is a good source of minerals, particularly iron, and zinc. Because of its nutritional characteristics it tends to be a commodity of demand to consumers. Game meat offers even higher nutritional attributes than any other red meat category because of its low fat and high protein levels making game meat a highly priced product thereby causing it to be an appealing target for species substitution. Also, fraudsters prefer to use products that are easy to adulterate and difficult to detect. To mitigate the fraudulent substitution of meat products, food authentication and labelling is promoted. The conventional methods of authentication such as DNA based techniques are expensive and slow for the rapidly expanding meat trade. Near infrared (NIR) spectroscopy, a rapid non-destructive, environmentally friendly instrument is thought to be an alternative and cheap solution for on-site meat authentication purposes, although this technology has not yet been evaluated for its suitability to distinguish different South African game species and/or muscles. To evaluate the ability of NIR spectroscopy to distinguish between selected game species’ (impala (Aepyceros melampus), blesbok (Damaliscus pygargus phillipsi), springbok (Antidorcas marsupialis), eland (Taurotragus oryx), black wildebeest (Connochaetes gnou) and zebra (Equus quagga)) Longissimus thoracis et lumborum (LTL) muscle steaks, a handheld MicroNIR™ OnSite spectrophotometer was used in a spectral range of 908–1700 nm. After the spectral data was pre-treated with smoothing, SNV-Detrend, the PCA scores plot revealed two clear clusters separating the medium-sized antelopes and large-sized species. The waveband responsible for the separation as indicated by the loadings line plot situated at 1372 nm, was associated with fat. The developed classification models revealed that the steaks could be distinguished with linear discriminant analysis (LDA), soft independent modelling by class analogy (SIMCA) and partial least squares discriminant analysis (PLS-DA) at classification accuracies ranging from 68 - 100%, 67 - 100% and 70 - 96%, respectively. Also, NIR spectroscopy in combination with multivariate data analysis techniques was used to discriminate between different muscle steaks from longissimus thoracis et lumborum (LTL), infraspinatus (IS) and supraspinatus (SS), biceps femoris (BF), semitendinosus (ST) and semimembranosus (SM) of impala and eland species; and samples from fan fillet (FF), big drum (BD), triangle steak (TS), moon steak (MS) and rump steak (RS) of ostriches. Classification accuracies developed with PLS-DA models ranged from 85 to 100% throughout. It is interesting that good classifications accuracies were achieved when the muscles were grouped according to their anatomical locations, irrespective of the muscle used, PLS-DA models yielded accuracies of 97%, 81% and 92% for eland, impala and ostrich, respectively. Even though NIR spectroscopy in combination with multivariate data analysis techniques could successfully distinguish the different muscle types within animals, and muscles across different species, the instrument did fall short in discriminating the ageing periods of blesbok, eland, and ostrich muscles. However, it is postulated that there is still room for improvement when the device is coupled with machine learning. In summary, the handheld MicroNIR™ OnSite spectrophotometer demonstrated its capability in discriminating between different species of game meat indicating that the instrument could potentially be used in the authentication of game meat.
- ItemThe efficacy of bacteriophages FO1a and S16 in the reduction of Salmonella on chicken carcasses in a South African poultry processing environment(Stellenbosch : Stellenbosch University, 2022-12) Wessels, Kirsten; Gouws, Pieter Andries; Rip, Diane; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: Much of the research surrounding bacteriophages (phages) as a processing aid for the control of Salmonella on chicken meat has been conducted in vitro in the laboratory. Information about the efficacy and application of bacteriophages as part of a hurdle concept in the chicken processing environment is limited. In South Africa, the use of certain antibiotics in live broilers and the use of chlorine-containing antimicrobials in the processing environment, are still permitted as Salmonella control methods. The incidence of Salmonella in chicken meat in South Africa is unclear, but previous research has repeatedly shown that the use of antibiotics and/or chlorine selects for resistance in Salmonella. The aim of this study was to determine the efficacy of a commercial phage cocktail PhageGuard S™ (PGS) (FO1a and S16 phages) in the reduction of Salmonella on chicken carcasses through a validated spraying system in a South African chicken processing plant. This study also investigated the incidence and antibiotic susceptibility profiles of Salmonella isolated from chicken carcasses in the plant. The PGS was applied at a 1% (v/v) concentration onto chicken carcasses via a spraying system (validated specifications: 530 µm nozzle diameter, 200 mesh strainer and 3 Bar pump pressure) after the chlorine spin chilling step. Neck skins samples were collected before the inside- outside wash step (N= 80) and after the PGS application step (N= 160). The neck skin samples were tested for Salmonella presence/absence (EN ISO 6579/A1 (02/2006)) and confirmed using Vitek®. Confirmed Salmonella isolates were screened for antibiotic susceptibility using the Kirby-Bauer disk diffusion method according to M100 from the Clinical and Laboratory Standards Institute (CLSI, 2020). Confirmed Salmonella isolates from neck skin samples collected after PGS application were re-exposed to PGS in the laboratory via a killing assay (Micreos Food Fafety, NL) to determine if the isolates were resistant to the PGS. Before the inside-outside step the Salmonella incidence was 60% with a large portion of these isolates showing resistance to tetracycline (56.3%) and sulfonamide (43.8%). After the combination of the inside-outside wash step, chlorine spin chilling and PGS application, the Salmonella incidence decreased to 23.75%, where more than half of these isolates showed resistance to tetracycline (63.2%) and sulfonamide (55.3%). For the killing assay, all isolates which survived PGS in the processing environment were reduced by 100% in the laboratory, highlighting that the phages were unable to reach the Salmonella via the spray application, and not that the Salmonella was resistant to the phages. The results in this study showed that the multi-drug resistant Salmonella in the chicken neck skins survived a complete immersion in chlorine but were successfully reduced by PGS, making phages a potential solution to many persistent microbial problems. This study also provides valuable insight into implementing phages into the large-scale hurdle concept of a processing environment and highlights the importance of the application method to ensure safe delivery of the phages to the target bacteria for a high efficacy.
- ItemEstablishment of a genetic database and molecular methods for the identification of fish species available on the South African market(Stellenbosch : Stellenbosch University, 2011-12) Cawthorn, Donna-Maree; Witthuhn, R. C.; Steinman, H. A.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: Consumers have the right to accurate information on the fish products they purchase to enable them to make educated seafood selections that will not endanger their own wellbeing or the wellbeing of the environment. Unfortunately, marine resource scarcity, financial incentives and inadequate or poorly enforced regulations have all promoted the mislabelling of fish species on global markets, the results of which may hold economic, conservation and health consequences. The primary aims of this study were to determine the most commonly available fish species on the South African market, to establish and compare DNA-based methods for the unambiguous identification of these species and to utilise the most applicable methods to evaluate the extent of mislabelling on the local fisheries market. The results from surveys of n = 215 restaurants and n = 200 retail outlets in four South African provinces (Western Cape, Kwa-Zulu Natal, Eastern Cape and Gauteng) indicated that 34 and 70 nominal fish types were available in restaurants and retail outlets, respectively, the most common of which were kingklip, salmon and hake. Over 30% of the fish species being sold were of conservation concern, while several outlets marketed specially-protected, illegal-to-sell species in South Africa. Fish purveyors were poorly equipped to provide information on the identity, origin, production method (farmed/wild) and sustainability of the fish they were selling and the labelling of many packaged fish products was in contravention with South African regulations. Data were published for the first time comparing the efficiency of five methods (urea-SDS-proteinase K, phenol-chloroform, salt extraction, SureFood PREP kit and Wizard Genomic DNA Purification kit) for the extraction of DNA from the muscle tissue of fish species available in South Africa. The SureFood kit was identified as the most suitable method for DNA extraction from fish muscle, extracting significantly (P < 0.05) higher DNA yields than all other methods evaluated and being simple and safe to use. A comprehensive reference library of genetic information was compiled for the first time that contains sufficient DNA sequence data from different mitochondrial DNA loci (16S ribosomal RNA (rRNA), 12S rRNA and cytochrome c oxidase I (COI) genes, as well as the control region) to allow the explicit identification of 53 fish species in South Africa. Although 16S and 12S rRNA gene sequencing allowed the identification of most fish to the genus level, the discrimination of closely-related, congeneric species was problematic when based on these gene regions. Conversely, the vast majority (98%) of fish examined could be readily differentiated by their COI sequences, with only members of the genus Thunnus requiring supplementary control region sequencing for species confirmation. Lastly, sequencing of the COI region was used to show that 9% of fish samples collected from local seafood wholesalers and 31% of samples from retail outlets were mislabelled. This study has established that fish mislabelling is a reality on the South African market and that DNA-based methods should be applied by both industry and regulatory bodies to deter illegal activities and to promote transparency on the domestic fisheries market.
- «
- 1 (current)
- 2
- 3
- »