Doctoral Degrees (Food Science)

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Antibiotic 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.
The 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.
The 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.
Factors influencing colour variation and oxidative stability of South African game meat species
(Stellenbosch : Stellenbosch University, 2016-03) Neethling, Nikki Elrita; Hoffman, Louwrens C.; Suman, S. P.; Sigge, G. O.; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.
ENGLISH ABSTRACT: It is believed by many that the future of South African game farming depends on the development of a sustainable game meat industry. To develop such an industry, game meat products of consistently high quality must be supplied to consumers. To ensure the quality and consistency of these meat products, standard processing guidelines are required. No such guidelines are currently available and research on meat quality of South African game meat is thus required to establish these guidelines. There is currently only limited research available on the meat quality of game meat. Meat colour is important as it is the sole quality factor which consumers can use at the time of purchasing to select meat. Consumers prefer meat which is bright red in colour as they perceive it to be fresher, more wholesome and of higher quality than discoloured meat. Discoloured meat is often discounted, resulting in a loss of profits. Thus, maintaining the bright red colour of meat is essential in ensuring maximum profits. Colour stability is thus an important meat quality attribute which must be examined. Currently no research exists regarding the colour stability of South African game species. The colour stability of three major South African game species, blesbok (Damaliscus pygargus phillipsi), springbok (Antidorcas marsupialis) and fallow deer (Dama dama) were evaluated by measuring surface colour attributes (L*, a*, b*, hue, chroma and R (630/580)), surface myoglobin redox forms (percentage deoxymyoglobin, percentage oxymyoglobin and percentage metmyoglobin) and various biochemical attributes (pH, metmyoglobin reducing activity, oxygen consumption, thiobarbituric acid reactive substances, total, heme and non heme iron and total myoglobin) of three muscles, the infraspinatus (IS), longissimus thoracis et lumborum (LTL) and biceps femoris (BF) over an eight day colour stability trial at 2°C. The data indicated that the IS was the most colour stable of the three muscles for all the game species. For both the blesbok and fallow deer, the LTL was observed to be marginally more colour stable than the BF, whereas the LTL and BF for the springbok were observed to have similar colour stabilities. Overall the colour stability of the IS was determined to be eight days or more and that of the LTL and BF only one day for all three game species. Although significant gender differences were observed for the colour stability data, these were disregarded as no gender differences were visually perceived. Despite the similarities in colour stabilities noted for the muscles of the three game species, species differences were observed for various of the surface and biochemical attributes highlighting the need for both muscle and species specific processing strategies to improve colour stability of game meat. This study provided baseline data for the colour stability of game meat, specifically springbok, blesbok and fallow deer. It also highlighted the vast amount of research that is still required to ensure that the colour stability of game meat is optimised to ensure maximum colour stability.
Factors influencing the flavour of the meat derived from South African game species
(Stellenbosch : Stellenbosch University, 2016-03) Neethling, Jeannine; Hoffman, Louwrens C.; Muller, M.; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.
ENGLISH ABSTRACT: In South Africa, wild and free-living animal species that are dependent on the natural vegetation present in their habitat as food source, are referred to as ‘game species’. Game species are utilised for live animal sales, trophy hunting, non-trophy recreational hunting and game meat production. The latter is of economic importance, as the export of game meat is a very lucrative industry for South Africa. However, only small quantities of fresh game meat is sold locally in South Africa, which is attributable to a lack of scientific information on the chemical composition and sensory quality of game meat that is required to enable proper marketing of game meat products. Game meat is derived from female and male animals of various species, located throughout southern Africa. However, differences in the dietary regimes of game species between farm locations, in addition to species and gender differences could influence the composition and sensory quality of game meat. Differences in the fatty acid content and volatile compound profile could influence the aroma and flavour of meat, yet no research exists that has established the volatile compound profile of South African game meat. The volatile compound profile of the longissimus thoracis et lumborum muscle of commonly consumed game species (springbok, Antidorcas marsupialis; blesbok, Damaliscus pygargus phillipsi; gemsbok, Oryx gazella; impala, Aepyceros melampus; red hartebeest, Alcelaphus caama; and kudu, Tragelaphus strepsiceros) from various farm locations was mainly lipid-derived, containing compounds such as aldehydes, alcohols and 2-pentylfuran. Farm location and gender had a significant influence on the fatty acid content and volatile compound profile of springbok and blesbok meat. Furthermore, the fatty acid content and volatile compound profile of game meat differed significantly between the six species, while gender differences were more species-specific. Descriptive sensory analysis was used to establish the sensory profile of game meat in this study. The latter, in addition to physical measurements (thaw and cooking loss percentage, ultimate pH and Warner-Bratzler shear force) and the proximate composition (moisture, protein, intramuscular lipid and ash) were used to establish the sensory quality of game meat derived from different farm locations, species and genders. Farm location had a significant influence on the sensory quality of springbok meat, while this was not evident for blesbok meat. Selected physical, proximate and sensory attributes differed significantly between the six game species, however, when conducting multivariate analyses using all of the sensory attributes as variables it is clear that springbok meat illustrated a prominent gamey sensory profile and thus associated with a different set of sensory attributes than the other five game species. This study also indicated that gender differences in the sensory quality of game meat are more species-specific. It is therefore recommended that the meat industry should take farm location (for springbok and not blesbok) and species into account during the marketing of game meat. As the influence of gender on the sensory profile of the game meat from the selected species in this study was of minor importance, it is recommended that this factor not be considered during the marketing of game meat derived from these six game species. However, the magnitude of the influence of species and gender on the sensory quality of game meat could change when other factors such as season and farm location come into play
Polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticide residues in selected marine fish species along the coast of South Africa
(Stellenbosch : Stellenbosch University, 2016-03) Rufina-Mary Chinelo, Chukwumalume; Hoffman, Louwrens C.; Opara, Linus U.; Stander, Marietjie; O’Neill, Bernadette; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.
ENGLISH ABSTRACT: Fish consumption is being threatened by the accumulation of hazardous substances within the flesh due to natural occurrences and anthropogenic activities. This tends to undermine the health benefits derived from fish consumption. Human exposure to hazardous compounds has been predominantly through dietary intake and fish in particular. In this study, global priority contaminants, polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) were assessed in some marine fish species of commercial and local consumption importance. The study aims were to assess the occurrences, levels and profiles of selected organic contaminants in marine species covering low trophic (resident) fish species (blacktail and hottentot); middle trophic species (yellowtail and snoek) and the high trophic (predatory) species (tuna and sharks). Also by using diagnostic ratios, the pollution input sources/history was determined and the locations and species with increased burdens, identified. Screened fish were considered safe for consumption based on comparison with regulatory critical values. Extraction of target compounds (analytes) were efficiently carried out following the quick, easy, cheap, efficient, rugged and safe (QuEChERS) method and analysed simultaneously with gas chromatography coupled to mass spectrometry triple quadrupole (GC-MS/MS). Quality control measures were in place and reference material analysed for method validation. Limit of detection, quantitation and percentage recoveries of analytes were within acceptable values. All the analysed species showed evidence of contamination but with variations in profiles and levels. The profile trend was predominantly low molecular weight (LMW) (i.e. non-carcinogenic) PAHs, however, from Port Elizabeth and Dassen Island high molecular weight (HMW) PAHs predominated. PAHs contamination levels in this study ranged from low contamination (<100 μg/kg) in samples from Hout Bay (87.29 ± 1.96 μg/kg wet weight (ww) in hottentot) to a moderate contamination (<1000 μg/kg ww) in tuna dark muscle from False Bay (636.31± 36.03 μg/kg ww). The PAHs acceptable/presence indicator, benzo(a)pyrene was found in excess of the European Union (EU) maximum limit (2 μg/kg ww) in fish from 8 locations with highest (29.79 ± 0.81 μg/kg ww) in Blue Shark (False Bay). Intra and inter species variations were observed and considered to be due to fish size, lipid content, feeding habit, trophic level and locational input sources. The hottentot and soupfin shark species were not found with measurable levels of benzo(a)pyrene and could be considered acceptable species for human consumption so as to minimize exposure to carcinogenic PAHs. However, the highest DDT level (760.50 ± 484.53 μg/kg ww) was recorded in hottentot (Dassen Island) but was below the Food and Drug Administration (FDA) action level (5000 μg/kg ww). A holistic risk assessment study that will evaluate fish health benefits (nutrients) against the risks (contaminants), plus the effect of heat (cooking methods) on measured contaminants in studied species is recommended for future study.
The prevalence of Campylobacter and Arcobacter species in ostriches from South Africa
(Stellenbosch : Stellenbosch University, 2020-04) Shange, Nompumelelo; Gouws, Pieter Andries; Hoffman, Louwrens C.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
ENGLISH ABSTRACT: The overall aim of this thesis was to determine the prevalence of Campylobacter and Arcobacter species in ostriches from South Africa. In humans Campylobacter and Arcobacter species can cause of gastroenteritis, Guillian Barré syndrome, septicaemia and bacteraemia. Previous research has indicated that the consumption of contaminated poultry meat is the main route of infection for humans and by extension poultry species are deemed primary reservoirs of Campylobacter and Arcobacter species. Currently, there is a lack of information regarding Campylobacter and Arcobacter species in relation to ostriches from South Africa. Artificially and naturally reared ostrich chicks at the age of 2, 4, 6 and 12 weeks were sacrificed, and caeca samples were excised. Campylobacter spp. (C. jejuni) was detected in artificially reared chicks, on the 12th week. A persistent presence of Arcobacter (A. skirrowii) was detected from the 2nd until 12th week of life for both artificially and naturally reared ostrich chicks. Additionally, cohorts that belonged to the same batch as the sacrificed ostrich chicks, regardless of the rearing process were sampled at the slaughter age of 10 and 12 months. Arcobacter spp. (A. skirrowii) and Campylobacter spp. (C. jejuni) were isolated from 56-70% of slaughter age birds. Cloacal swabs were also obtained from live ostriches reared on 30 different farms situated in South Africa (Oudtshoorn). Cloacal swabs were processed with family specific PCR (n = 168 pooled cloacal swabs), the Cape Town protocol (n = 836 cloacal swabs), ISO 10272-1:2006 (n = 836 cloacal swabs) and a selective Arcobacter spp. method (n = 415 cloacal swabs). Family specific PCR determined an average prevalence of 24.63%. The ISO 10272-1:2006 method and Cape Town Protocol determined a prevalence of 16.83% and 0% for Campylobacterspp., respectively. For Arcobacter spp. a prevalence of 18.80% and 39.14% was determined with the Cape Town protocol and selective Arcobacter spp. method, respectively. Higher prevalence levels were determined when ostriches were sampled during spring and autumn, respectively. Higher prevalence levels were also detected in ostriches reared on farms that made use of borehole water. Higher prevalence levels were seen for ostriches reared on farms with wild water birds. During slaughter, Arcobacter spp. were detected at a prevalence level of 73% at post-skinning. At post-evisceration, 73% and 83% of samples were contaminated with Campylobacter spp. and Arcobacter spp., respectively. At post-chilling, 66% and 67% were contaminated with Campylobacter spp. and Arcobacter spp., respectively. Additionally, a second study to evaluate the occurrence of Campylobacter spp. and Arcobacter spp. was conducted to see whether routine testing was required for abattoirs. E. coli and coliforms were also enumerated to determine the occurrence of faecal contamination during slaughter. Overall, a low occurrence of Campylobacter spp. (0.98% and 0%), Arcobacter spp. (1.31% and 1.64%), E. coli (0.13 log cfu/g) and coliforms (0.53 log cfu/g) was determined for all three abattoirs. Antibiotic resistance in Campylobacter spp. and Arcobacter spp. isolated from ostriches and ostrich meat was determined. Campylobacter spp. and Arcobacter spp. isolates were generally resistant to antibiotics in the following order cephalothin, vancomycin and erythromycin and tetracycline. The majority of Campylobacter spp. (92.86%) and Arcobacter spp. (80.95%) isolates exhibited multi-drug resistance. Overall, this research shows that ostriches from South Africa can be considered as potential carriers of species belonging to the Campylobacteraceae family and infection can occur at young age. Carcasses can be contaminated during slaughter and species carried by ostriches can be resistant to essential antibiotics; ultimately highlighting the need for routine testing of Campylobacter and Arcobacter species.
Profiling of traditional South African biltong in terms of processing, physicochemical properties and microbial stability during storage
(Stellenbosch : Stellenbosch University, 2017-03) Jones, Maxine Sylvia; Hoffman, Louwrens C.; Gouws, Pieter Andries; Arnaud, E.; Stellenbosch University. Faculty of AgriScience. Dept. of Food Science.
ENGLISH SUMMARY: In South Africa, there are no processing guidelines for biltong production and therefore the industry uses different processing parameters which results in variation in the product. The same process was used throughout this study and drying was done using constant parameters – temperature 25 ± 2°C, relative humidity 30 ± 5%, air velocity 2 ± 0.2 m/s. An initial study investigating the influence of vinegar addition during the production of beef biltong showed that vinegar addition does not influence its drying kinetics. The biltong reached a 50% weight loss after 66 hours and a 65% weight loss after 96 hours. The use of different meat muscles (topside, semimembranosus and silverside, biceps femoris), beef with subcutaneous fat and gemsbok (Oryx gazelle) showed differences (p ≤ 0.05) in drying rates when dried to a targeted weight loss of 65%. The two lean beef muscles both dried in 96 hours. The gemsbok topside took only 78 hours with a drying pattern similar to the lean beef topside. The fatty beef topside took 118 hours to dry. The microbiological profile of beef biltong over a three month shelf-life storage were studied. Final weight loss during drying and packaging method (modified atmospheric packaging and vacuum packaging) did not have an effect (p > 0.05) on the microbiological profile. Total viable counts and coliforms were only reduced in biltong with vinegar added. After drying, yeasts and moulds were already present at high levels (~ 2.5 log cfu.g-1) but not visible. After six weeks, yeasts and moulds became visible. Staphylococcus aureus was present at less than 20 log cfu.g-1 while Listeria monocytogenes, Salmonella spp. and Escherichia coli were not present during the three month storage period. Yeast and mould growth on biltong is a problem and therefore a challenge study was included. Beef biltong produced without and with vinegar and dried to a 50% or 65% weight loss were inoculated with yeasts and moulds. No yeast and mould growth was seen on biltong with vinegar but 1.8 – 2.5 log cfu.g-1 was detected after 34 days. Biltong without vinegar showed yeast and mould growth after 10 days with levels of 2.8 – 3.1 log cfu.g-1. Saccharomyces spp. (yeast) and Aspergillus spp., Fusarium spp. and Penicillium spp. (moulds) were the most common yeast and moulds. A small-scale study using ultrasound in the salting step of beef biltong processing showed that ultrasonic-brining did not have an effect on either the salting or drying kinetics contrary to what was expected. Throughout the study the physicochemical properties of the beef biltong gave consistent results. An approximate 50% and 65% weight loss produced biltong with a moisture content of 50% and 30%, respectively and water activity of 0.74 – 0.78 and 0.81 and 0.86, respectively. Weight loss or the addition of vinegar did not play a role in the salt content (dry basis). Beef biltong without vinegar had a pH 5.56 – 5.75 while the addition of vinegar to biltong lowered the pH of biltong to 4.89 – 4.93. It is recommended that the biltong industry should standardise their drying parameters to avoid variation in quality and for a more microbial stable product. Vinegar could be added as it has an effect on the yeast and mould growth. Biltong with water activity ranging from 0.74 to 0.83 does not have a shelf-life of more than three months when using modified atmosphere packaging or vacuum packaging. The data generated in this study serves as a base-line for future studies focused on optimising and standardising the drying procedures applicable to biltong.
Status of mercury and other heavy metals in South African marine fish species
(Stellenbosch : Stellenbosch University, 2015-12) Bosch, Adina Cornelia; Hoffman, Louwrens C.; Sigge, G. O.; Kerwath, Sven E.; O’Neill, Bernadette; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.
ENGLISH ABSTRACT: Fish is an important food source in South Africa as it is globally, thus the importance of determining and monitoring its safety in terms of metal contaminants and consumer safety. Effective methodology for analysing total metal concentrations and toxic metal components together with representative sampling protocol for sampling individual fish and larger catches are therefore required for accurate assessment of meat safety. Both inductively coupled plasma mass spectrometry (ICP-MS) and high pressure liquid chromatography coupled to ICP-MS was validated as effective methods for accurately determining concentrations of total metals and individual Hg species, respectively. Consequently, it was found that total mercury loads in fish meat consisted mainly of toxic methylmercury (MeHg) components with a minor addition of an inorganic Hg (iHg) component and ethylmercury concentrations being negligible. This proportion of MeHg to iHg varied between muscle types in yellowfin tuna (Thunnus albacares), with higher iHg concentrations in dark muscle than in white muscle, whereas the toxic MeHg concentrations did not vary across the carcass. The MeHg to tHg relationship was caused to vary with variation in fish weight, being described by the following prediction model: 𝑐𝑀𝑒𝐻𝑔=0.073+1.365∙𝑐𝑡𝐻𝑔−0.008∙𝑤; taking into account fish weight as covariate. For the eight other fish species studied [blacktail (Diplodus sargus capensis), hottentot (Pachymetopon blochii), yellowtail (Seriola lalandi), snoek (Thyrsites atun), blue shark (Prionace glauca), shortfin mako (Isurus oxyrinchus), soupfin (Galeorhinus galeus) and smoothhound (Mustelus mustelus)], the relationships between MeHg and tHg were constant even with varying fish sizes as iHg components were considered an insignificant portion of tHg (ctHg = cMeHg). The tHg measurements could therefore be used as accurate indicators of MeHg concentrations without requiring addition speciation analyses. Sampling from the cephalic region of the dorsal white muscle tissue proves representative of the entire edible portions (white muscle) of larger fish (tuna and sharks spp.) for determining both total metal concentrations and toxic Hg components. Where Hg concentrations are positively correlated to fish size (yellowfin tuna, yellowtail and soupfin), subsamples should include individuals representing the entire size range present per catch. A summary of metal concentrations in all eight species studied indicate that Hg is the main metal of concern where a single portion of certain fish (yellowfin tuna, shortfin mako, soupfin and smoothhound shark) consumed per week could exceed regulatory limits for safe Hg intake, whereas other fish species (hottentot) could be consumed daily without concern of Hg toxicity. Information provided by this study will prove useful to both the fishing and processing industry as well as to health authorities providing information for dietary exposure assessments.

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Browsing Doctoral Degrees (Food Science) by browse.metadata.advisor "Hoffman, Louwrens C."

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