Doctoral Degrees (Food Science)
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- ItemPhysicochemical, functional and structural properties of flour and starch from dry heat-treated wheat(Stellenbosch : Stellenbosch University, 2024-03) Van Rooyen, Jana; Manley, Marena; Oyeyinka, Samson; Simsek, Senay; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.ENGLISH ABSTRACT: Dry thermal treatment techniques as a pre-processing method for whole wheat or flour are gaining popularity for enhancing wheat properties. The effect of heat treatment on flour functionality is of critical importance for achieving the desired outcome. This study aimed to investigate the effect of forced convection roasting on the physicochemical, functional and structural properties of whole wheat kernels, flour and starch. Firstly, chemical-structural changes in whole wheat and flour, due to roasting, were investigated by determining the effect of roasting conditions and wheat types on shortwave infrared (SWIR) spectral data using ANOVA simultaneous component analysis (ASCA). Secondly, optimum roasting conditions were determined to (1) enhance flour viscosifying properties and (2) maintain protein integrity of the produced flour. Finally, ¹H time domain (TD) nuclear magnetic resonance (NMR) was used to investigate the molecular dynamics of the starch-water systems during heating and to differentiate between starch isolated from roasted and unroasted wheat as well as maize starch. Changes in whole wheat and flour due to roasting were characterised by determining the effect of roasting temperature, roasting frequency and wheat types on SWIR spectral data by applying ASCA. Roasting at different conditions significantly affected the chemical-structural properties of moisture, protein, starch, lipids and enzymes in wheat and/or flour as observed by the main variations in the loading line plots. Wheat roasting at 115 ºC and 140 ºC significantly affected protein stability in the white flour as well as in the whole wheat flour and kernel, respectively. Milling as well as roasting at 115 ºC and 140 ºC were responsible for starch damage observed in the white and whole wheat flour, respectively. Significant differences between hard and soft wheats were also indicated. Wheat roasting at 115 ºC and 65 Hz was predicted, by response surface methodology (RSM), to be the optimum conditions that would improve flour viscosifying properties. Optimally roasted wheat showed grain puffing, slight damage to the starch granule surface and destruction of the protein matrix. Compared to an unroasted sample, lowered relative crystallinity along with formation of amylose-lipid complexes were observed. Increased viscosities, compared to the control, were attributed to the combined effect of starch and protein properties affected by heat treatment. RSM predicted 108 ºC and 80 Hz as the optimum wheat roasting conditions that would maintain protein integrity. Increased viscosities, compared to the control, were ascribed to conformational changes in protein structures. Proteins were observed to be more heat sensitive than starch. At these optimum conditions, the starch granule structure and relative crystallinity remained relatively unaffected. TD-NMR experiments accurately demonstrated the interaction between starch and water, and the distribution of hydrogen atoms in the starch-water systems. The change in relaxation times enabled differentiation between unroasted, optimally roasted wheat starches and maize starch. Results obtained by TD-NMR, thermal and rheological analysis methods were comparable. The pulse sequences and signal processing methods used identified key characteristics associated with the structural (crystallinity), thermal (onset of gelatinisation) and rheological (maximum stiffness) properties of different starches. TD-NMR was shown in this study to be an effective and simple method to perform crystallinity measurements and study starch gelatinisation.
- 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.
- ItemMulti-stakeholder perspectives on food labels and the future of healthy eating(Stellenbosch : Stellenbosch University, 2022-12) Todd, Melvi; Joubert, Elizabeth; Guetterman, Timothy; Sigge, Gunnar; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: South Africa, like many other countries throughout the world, is grappling with the increasing burden of non-communicable diseases, caused in part by an unhealthy diet. This study investigated how changes to the presentation of nutritional information on food labels can potentially help South Africans judge the healthiness of food, thereby potentially guiding them towards healthier choices and beneficial health outcomes. As a point of departure for the study, the value-adding potential of legislating health claims on food labels was considered. Draft legislation to allow health claims have been pending since 2014, and the legislation also does not address any claims pertaining to the health potential of our indigenous food plants, despite notable research spending in this area. Interviews (n = 49) with stakeholders with varied expertise revealed strong evidence for economic value creation potential from health claims, however, this was skewed towards businesses. The findings were less clear about other forms of value and the potential beneficiaries. Developing metrics that people understand and that relate to all forms of value will be required to ensure that health claims on food labels, should they be permitted, do not only benefit a select group of stakeholders. Delving deeper into the question of whether legislating health claims on food labels would be useful for consumers revealed more challenges than opportunities. Persistent impediments to use of the information and unresolved questions about the substantiation and enforcement of health claims were of particular concern. At the same time, no solution appeared apparent for reaching consumers in the informal market with nutritional information. While legislating health claims is not recommended at present, numerous front-of-pack (FOP) label proposals were made by the interview participants. In the final stage of the study, consumers (n = 1 261) were asked to compare FOP labels and a health claim relative to a no-label control, applied to a fictitious cereal product, a commonly consumed processed food in South Africa. Both health warnings and health star rating showed promise in terms of assisting consumers in identifying less healthful products, but effect sizes were largest for the warning label. This outcome requires validation with more product categories, as well as testing in real-world settings. The study culminated with the presentation of a three-phased nutritional labelling strategy for South Africa: ‘Make it clearer’, ‘make it simpler’, ‘make it smarter’ - intended to illustrate the need to take action now whilst simultaneously planning for the future. At a policy level, while South Africa plans for the implementation of FOP labels, we should be actively planning for the labelling of the future – one which will be more technologically enabled. The findings of this study may provide policy-makers and decision-makers, such as the Department of Health, with valuable information about the presentation of nutritional information on food labelling (i.e. selecting FOP labels for further real- world testing), as well as setting the course for the future.
- 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.
- ItemValue addition of pomegranate seed oil: Effect of seed pretreatment methods on yield, quality attributes and functional properties(Stellenbosch : Stellenbosch University, 2021-04) Kaseke, Tafadzwa; Opara, Umezuruike Linus; Fawole, Olaniyi Amos; Sigge, G. O.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: Efficient and cost-effective processing protocols which enhance oil recovery and quality are required by processors in the seed oil industries. Currently, there is no established pomegranate seed oil processing procedure in South Africa, which could be one of the reasons hindering the development of pomegranate seed oil industry, despite the readily available fruit raw material. Furthermore, cold pressing, which is the current and most preferred pomegranate seed oil extraction technique by oil processors and consumers is associated with low recovery of oil. Physical or chemical pretreatment of seeds has been demonstrated to improve oil recovery and quality in other fruit seeds and field crops; however, the application of these pretreatments to enhance pomegranate seed oil extraction efficiency and quality is limited. Therefore, the overall aim of this study was to establish a suitable pomegranate seed pretreatment method for high oil yield, quality, and functional properties. In Theme B, the effect of seed pretreatment on three common pomegranate cultivars in South Africa was examined. To evaluate if blanching as a pretreatment technique for oil extraction adds value to pomegranate seed oil (PSO), seeds of ‘Wonderful’ pomegranate fruit were blanched at 80, 90, and 100 °C for 3 and 5 min. Blanching pomegranate seeds at 90± 2 °C for 3 to 5 min significantly improved oil yield, stigmasterol, punicic acid, total phenolic content (TPC) and 2.2-diphenyl-1-picryl hydrazyl (DPPH) radical scavenging capacity. Given the significance of cultivar on seed pretreatment efficacy and oil quality, blanching (95± 2 °C for 3), microwave heating (261 W for 102 s) and enzyme pretreatment (1.7 %, 40 °C, pH=4.5 and 5 h) were investigated on the seeds of three different pomegranate cultivars (‘Wonderful’, ‘Herskawitz’, and ‘Acco’). Blanching and microwave heating of ‘Wonderful’ and ‘Acco’ seeds improved the oil yield and colour, whilst they enhanced the antioxidant capacity of oil extracted from ‘Herskawitz’ seeds. However, oil extracted from ‘Acco’ after seed enzyme pretreatment exhibited higher oil yield, total carotenoids content (TCC) and, DPPH radical scavenging capacity relative to ‘Wonderful’ and ‘Herskawitz’. The results showed that the quality of PSO from pretreated seeds is cultivar dependent. The study reported in Theme C investigated the influence of blanching (95± 2 °C/3 min) and microwave heating (261 W for 102 s) pomegranate seeds on the quality of oil extracted by cold pressing, the most preferred seed oil extraction technique by oil processors and consumers but with low oil yield. Both blanching and microwave pretreatment of seeds prior to pressing enhanced oil yield, TCC, TPC, DPPH and 2.2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging capacity. Although the levels of oil oxidation indices were significantly higher in microwaved than blanched seeds, they remained within the limits of Codex Alimentarius Commission (CODEX STAN 19-1981) standard on cold pressed vegetable oils. The oil palmitic acid, oleic acid, and linoleic acid significantly increased after microwave heating of seeds, whilst punicic acid decreased, which could be attributed to increased heat penetration and oxidation of the fatty acid. Conversely, the fatty acid composition of PSO was not significantly altered by seed blanching, indicating that the nutritional quality of the oil was not affected. Blanching of seeds is, therefore, a valuable step that could be incorporated into the PSO production process. The studies in Theme D, focused on blanched seed storability, oxidative stability, shelf-life and functionality of PSO from blanched seed and blended oils. Blanching pomegranate seed did not cause significant deterioration of the oil quality after seed storage. More so, storing pomegranate seed at 25 and 35 °C for 6 months did not result in a considerable reduction in oil quality, with respect to peroxide value, anisidine value and total oxidation value. In paper 9, the lipid oxidation kinetics, thermodynamics parameters, and shelf-life were estimated, given the improved extractability of bioactive compounds and enhanced antioxidant capacity of PSO from pretreated seeds. The Arrhenius model and activated complex theory were applied to calculate the activation energy (Ea), enthalpy (ΔH‡), entropy (ΔS‡) and Gibbs free energy (ΔG‡), which ranged from 6.2 to 8.59 kJ mol⁻¹, 3.69 to 6.38 kJ mol⁻¹, -146.62 to -155.06 J K⁻¹ mol⁻¹ and 48.13 to 64.74 kJ mol⁻¹, respectively. These thermodynamic parameters showed that the lipid oxidation reactions in all PSO extracts were non-spontaneous, endothermic, and endergonic. Moreover, the developed Arrhenius models established that blanching seeds may increase the PSO shelf-life at 25 °C from 21 to 24 days. In contrast, microwave heating may not change the shelf-life. The higher initial level of peroxide value and increased polyunsaturated fatty acids could explain the insignificant effect of seed microwaving heating on the oil shelf-life. The study provided valuable insights useful in the design of PSO packaging, the establishment of storage conditions and application of novel technologies to preserve the storage life. In paper 10 (Theme D) the functionality and oxidative stability of PSO from unblanched and blanched seeds (95± 2 °C/ 3 min) were investigated by blending with semi-refined sunflower oil (SO) considering the detrimental health effects of synthetic antioxidants. The study showed that blended oils (85: 15 w/w) had better oxidative stability, a lower rate of antiradical activity depletion and concentration of volatile oxidation compounds than SO, although this did not significantly (p > 0.05) vary between the blended oils. Despite this, the formulation of PSO blends is a novel and desirable development for the food industry, which is currently interested in specialty oils and functional foods formulations to improve human nutrition and health. Overall, this study has established that the improvement of PSO quality through seed pretreatment is a function of cultivar. This could be ascribed to the genetic variation of the pomegranate cultivars investigated. The study has also demonstrated that seed pretreatment is essential to improve the performance of safe and green but low oil yielding technologies such as cold pressing. Blanching of pomegranate seed may enhance the oxidative stability and shelf- life of PSO. Furthermore, the study provides scientifically based information that can be used to develop strategies to improve the storability of PSO from pretreated seeds and retain the health promoting properties.