Masters Degrees (Food Science)
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Browsing Masters Degrees (Food Science) by browse.metadata.advisor "Britz, T. J."
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- ItemAnaerobic bioconversion of liquid and solid wastes from the winemaking process(Stellenbosch : Stellenbosch University, 2015-02) De Kock, Michelle; Sigge, G. O.; Britz, T. J.; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.ENGLISH ABSTRACT: South Africa is a developing country that relies on its agricultural sector as a main source of overall economic welfare. Development does not only give rise to new technology and new products but also results in increased amounts of liquid and solid waste. Generally, the production of wine is considered an environmentally friendly process, but significant amounts of natural resources and organic amendments are necessary, while generating large amounts of liquid and solid wastes. Anaerobic digestion (AD) is an attractive and proven treatment option for both liquid and solid wastes as valuable products and depollution can be obtained. AD of liquid waste results in an effluent and biogas, while anaerobic composting of solid waste results in an organic amendment, leachate and biogas. The overall objective of this study was to investigate the operational feasibility of the cotreatment of leachate produced during the anaerobic composting (AnC) of grape skins in an upflow anaerobic sludge blanket (UASB) reactor while treating winery wastewater. This first aim of this study was to investigate the efficiency of the anaerobic composting of grape skins. Laboratoryscaled digesters (1L) were utilised as anaerobic composting units. The most important operational parameters were identified (pH, moisture content and inoculum (size, ratio, composition)) in order to produce a pH stable, odour free compost in 21 days. Experimental studies highlighted the importance of shredding waste as well as the addition of calcium oxide and green waste to increase the initial pH of the composting mixture. After optimising a 50% (m.m-1) cow manure inoculum, lower inoculum concentrations (10, 15 and 25% (m.m-1)) were investigated to make the process more economically viable. A 10% (m.m-1) anaerobic compost (AC) inoculum was found to produce the most favourable results in terms of pH stabilisation and leachate generation. A 50% (m.m-1) moisture level performed the best by attaining a pH > 6.5 on day 6 and having the highest end pH (7.65) on day 21, while white and red grape skins in an equal ratio were found to generate a higher end pH. With all these optimum parameters in place (shredded waste, green waste, CaO, inoculum, moisture, grape skins), a compost with a final pH (7.09), moisture (58%), nitrogen (2.25%), phosphorous (0.22%) and potassium content (1.7%) was obtained. The optimised parameters were scaled-up (1:10) by using polyvinyl chloride anaerobic digesters (20 L) to suit the operational requirements of the AnC process and also produced a stable compost within 21 days. The second aim of this study was to investigate the combined anaerobic digestion of winery wastewater (WWW) and leachate obtained from the anaerobic composting of grape skins in an upflow anaerobic sludge blanket (UASB). This involved the operation of a 2.3 L laboratory-scale UASB reactor for 205 days. The reactor successfully co-treated WWW and leachate at ca. 8.5 kgCOD.m-3d-1 with a final chemical oxygen demand (COD) reduction of over 90%, a stable reactor effluent pH (7.61) and alkalinity (3 281 CaCO3 mg.L-1). This study showed the feasibility for the combined treatment of liquid and solid waste from the winemaking process. Although the legal limits for reactor effluent disposal onto land was not met, significant reduction in COD concentrations were achieved, whilst producing a soil amendment that could potentially result in cost savings for chemical fertilisers. The benefits related to using anaerobic bioconversion as a treatment option for liquid and solid waste could possibly be advantageous to the wine industry as an environmental control technology, by converting liquid and solid waste into valuable resources.
- ItemAnaerobic bioconversion of the organic fraction from the fruit processing industry(Stellenbosch : Stellenbosch University, 2002-12) Griessel, Wilmare; Britz, T. J.; Fourie, P. C.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: South Africa is a developing country that relies heavily on its agricultural sector for economical welfare especially in the Western Cape Province. However, development gives rise to new technologies, new products, economical stability and unfortunately also to the production of larger volumes of liquid and solid waste. Anaerobic composting is becoming a very attractive treatment option for solid waste disposal because of its unique operational advantages and two valueadded by-products, compost and biogas. Over the last decade progress has been made in anaerobic digestion of solid wastes, but no literature could be found on the anaerobic composting of apple and peach pomace. The main objective of this study was to develop a method to anaerobically compost apple and peach pomace. In the first phase important operational parameters were identified and a method was developed to optimise the parameters. In the second phase of the study, the scaling-up and optimisation of the process were the major objectives. During the first phase of this research 2 L modified glass containers were used as composting units. The most important operational parameters (leachate pH, inoculum source and size, and initial moisture levels) were identified. Anaerobic compost from previous tests, brewery granules and anaerobic sludge were also used as inocula and evaluated for the best source of microbes. After optimising all the identified parameters, good results were obtained, which included higher biogas production, good volume reductions, less bad aromas and a compost product with a neutral pH. After developing the 2 L laboratory-scale method to compost the apple pomace anaerobically, the next step was to ascertain if the method would work if larger volumes of solid fruit waste were composted. A special 20 L composting unit made of PVC was designed to suit the operational requirements of the anaerobic composting process. It was also decided to mix apple pomace and peach pulp together and to use this solid waste source as part of the composting substrate. Different inocula, including cattle manure, anaerobic sludge, brewery granules and anaerobic compost produced in the previous tests, were used. Although good results were obtained with the anaerobic compost and cattle manure as inoculum, the aim was also to decrease the composting period by shortening the pH stabilisation period. To achieve this, it was decided to add NaHC03 to the substrate to be composted to facilitate a faster pH stabilisation. The composting period was subsequently shortened to 25 days with satisfactory results, which included a volume reduction, biogas production and faster pH stabilisation. An upflow anaerobic sludge blanket (UASB) bioreactor was also used to assist the composting process by facilitating the removal of the VFA's present in the composting leachate. This proved to be a valuable addition to the composting process as the UASB bioreactor also provided the composting units with a 'moisturising liquid', which was 'enriched' with a consortium of active anaerobic bacteria when the effluent from the bioreactor was re-added to the composting units. With all the operational parameters in place, good results were obtained and these included a volume reduction of 60% (m/m), a good biogas production, a composting period of only 25 days, a compost that was free of bad aromas, a final compost pH of > 6.5, final leachate COD values of less than 3 000 rnq.l", and a final leachate VFA's concentration of between 0 and 250 rnq.l". If in future research further scaling-up is to be considered, it is recommended that the composting unit be coupled directly to the UASB bioreactor, thus making the process continuous and more practical to operate. If the operational period of the anaerobic composting set-up could be further shortened and the inoculum adapted so that the process could be used for the treatment of other difficult types of solid wastes, it would probably be advantageous for the fruit processing industry to use this method as an environmental control technology.
- ItemAnti-microbial activity of rooibos tea (Aspalathus linearis) on food spoilage organisms and potenial pathogens(Stellenbosch : Stellenbosch University, 2001-12) Schepers, Sonette; Britz, T. J.; Witthuhn, R. C.; Joubert, E.; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.ENGLISH ABSTRACT:Aspalafhus linearis is an indigenous fynbos plant cultivated in the Clanwilliam area of the Western Cape, South Africa. The rooibos tea that is prepared from this plant, has become popular worldwide mainly due to the alleged health properties. Studies on the anti-microbial properties of green, black and oolong teas have shown that these teas have strong anti-microbial activity against a wide range of microbes. No studies have been done on the anti-microbial activity of rooibos tea and the aim of this study was to determine what impact rooibos tea extracts would have on the growth of different food spoilage and potential pathogenic microbes. Water and ethyl acetate extracts of fermented and unfermented rooibos tea were used to determine the inhibitory effect on the growth of an Escherichia coli strain. The E. coli culture was grown in tea-MRS with either added fermented or unfermented rooibos tea extracts. Both the water and ethyl acetate extracts showed a strong inhibitory effect against the E. coli strain in that there was a decrease in the final bacterial cell density (Nmax)(from 0.59 00 to 0.25 00) and the maximum specific growth rate (~max)(from 1.12 h-1 to 0.20 h-1) and an increase in the doubling time (~) (from 0.59 h to 1.80 h) and lag time (tlag)(from 4.81 h to 6.60 h) as the concentration of the soluble solids of the tea extracts was increased from 0.5 to 5.0 g.r1 . Furthermore, it was found that the fermented rooibos tea had a much stronger inhibitory effect (69% decrease in growth at 5.0 g.r1 soluble solids) compared to the unfermented rooibos tea extracts (35.1% decrease in growth at 5.0 g.r1 soluble solids). The resulting data indicated that rooibos tea had a very strong inhibitory effect on the growth of the E. coli strain. It was also found that the water extracts of rooibos tea showed a stronger inhibitory effect on the growth of the E. coli than the ethyl acetate extracts, indicating that the antimicrobial activity of rooibos tea is not exclusively due to the polyphenolic content - individual compounds. It was also determined that the rooibos tea water extracts showed a bacteriostatic action against the E. coli strain in that as soon as the tea is no longer part of the growth medium, the E. coli resumed a normal growth pattern. The data obtained showed that the inhibitory effect of rooibos tea water extracts (69% decrease in growth) against the growth of E. coli was more pronounced than that found when black tea water extracts (25.7% decrease in growth) at the same concentrations were used.Rooibos tea water extracts (0.5 - 5.0 g.r1) of fermented and unfermented tea were also used to determine the inhibitory effect on other food spoilage microbes and potential pathogens. Strains of Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes, Streptococcus mutans, Saccharomyces cerevisiae and Zygosaccharomyces rouxii were grown in the presence of fermented and unfermented rooibos tea water extracts. The effect that fermented rooibos tea had on the growth of all the microbes tested was in the following order: Staph. aureus (90.8% decrease in growth) > L. monocytogenes (89.2% decrease in growth) > Strep. mutans (84.1% decrease in growth) > B. cereus (80.3% decrease in growth) > Sacch. cerevisiae (77.7% decrease in growth) > E. coli (69.0% decrease in growth). The rooibos tea clearly had an inhibitory effect on the growth of all the microbes, with the exception of the Z. rouxii strain where the presence of the tea water extracts was found to enhance the growth. The inhibitory effect of rooibos tea on the growth of these microbes was shown by changes in the growth parameters with Nmax and IJmaxshowing decreases, while the ld and tlagincreased as the concentration of the tea soluble solids was increased. As with E. coli, the fermented rooibos tea water extracts showed the stronger inhibitory effect on the growth of the various microbes. The data obtained in this study suggests that rooibos tea is not effective as an anti-microbial agent against all yeast species, but will strongly retard the growth of specific Gram-positive and Gram-negative bacteria. As long as rooibos tea is present, strong anti-microbial activity will be observed at a cup of tea concentration of 2.5 g.r1 soluble solids. These results may be of value to support the health claims associated with rooibos tea and may in the future lead to the use of rooibos tea as a "natural" food preservative.
- ItemApplication of biogranules in the anaerobic treatment of distillery effluents(Stellenbosch : Stellenbosch University, 2000-12) O'Kennedy, Onicha Deborah; Britz, T. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: The distillery industry produces large volumes of waste water with a high organic content throughout the year. These effluents must be treated in some manner before being discharged or recycled in the factory. Several treatment options are in use presently, but they all have disadvantages of some nature, such as long retention times, bad odours or the need for large areas of land. Considerable interest has been shown in the application of anaerobic digestion, especially the UASB design (upflow anaerobic sludge blanket), to treat this high strength waste water. Thus, the aim of this study was to investigate the efficiency of an upflow anaerobic sludge blanket (UASB) bioreactor using full-strength distillery effluent. The activity of the bacteria in the biogranules was also evaluated by developing an easy and reliable activity method to estimate the general biogas and methanogenic activity and to calibrate this method using different anaerobic granules from different sources. The influence of high strength distillery effluent on the anaerobic digestion process was investigated using a mesophilic lab-scale UASB bioreactor. During the experimental study, the organic loading rate (OLR) was gradually increased from 2.01 to 30.00 kgCOD.m-3.d-1, and simultaneously, the substrate pH was gradually lowered from 7.0 to 4.7. It was found that at an OLR of 30.00 kgCOD. m-3.d-1,the pH, alkalinity and biogas production stabilised to average values of 7.8, 6 000 mg.l-1 and 18.5 I.d-1 respectively. An average COD removal> 90% was found indicating excellent bioreactor stability. The low substrate pH holds considerable implications in terms of operational costs, as neutralisation of the biorector substrate is no longer necessary. The accumulation of fine solids present in the distillery substrate was found at the higher OLR's and resulted in the granular bed increasing with subsequent biomass washout and a lowering in efficiency parameters. However, a possible pre-treatment filtration of these fine solids would eliminate this problem. The success of the upflow anaerobic sludge bed (UASB) process is mainly due to the capability of retaining the active biomass in the reactor. Over the years, several methods have been developed to characterise and quantify sludge activity but each has advantages and disadvantages. There is thus an increasing need for a rapid method to evaluate the activity of the granular biomass. The activity method of Owen et al. (1979) as adapted by Lamb (1995), was thus evaluated in terms of efficiency and applicability in determining the activity of granular samples. The method was found to be inaccurate as well as time consuming and it was thus modified. Results obtained with the modified assay method were found to be more accurate and the impact of the different test substrates (glucose, lactate, acetate and formate) on activity, was more evident. The activity of seven different anaerobic granules, was subsequently evaluated. Biogas (Ss) and methanogenic (SM) activity was not measured in volume of gas produced per unit COD converted or volatile suspended solids (VSS), but as tempo of gas production (ml.h-1) in a standardised basic growth medium. The activity data obtained were also displayed as bar charts and "calibration scales". This illustrative depiction of activity data gave valuable information about population dynamics as well as possible substrate inhibition. The "calibration scales" can also be used to group the general biogas (Ss) and methanogenic activities (SM) of any new biogranule relative to active (O-type) and inactive (W-type) anaerobic granules, providing that the same method of activity testing is used. The "calibration scales" can thus be used to give a fast indication of how the activity value of one sample relates to the activity values of other granules, even when using different test substrates.
- ItemAssessment of microbial levels in the Plankenburg and Eerste Rivers and subsequent carry-over to fresh produce using source tracking as indicator(Stellenbosch : Stellenbosch University, 2012-03) Huisamen, Nicola; Sigge, G. O.; Britz, T. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: The agricultural sector of South Africa is currently facing a serious water crisis. The decreased availability of water as a result of climate change and the constantly growing population has left many farmers increasingly dependant on surface water as primary source of irrigation. Urbanisation along with out-dated and insufficient wastewater treatment works have all contributed to polluting large volumes of these resources. Consequently, many farmers have been forced to use irrigation water, not only of poor quality, but often water which has been polluted with untreated sewage. As a result, this project aimed at investigating the link between the quality of irrigation water and the impact on the safety of fresh produce. A base-line of the microbial load at three sites along the Plankenburg and Eerste Rivers was established using standard microbial methods for the detection of indicator organisms such as total and faecal coliforms, Escherichia coli and Enterococci as well as potential pathogens that included Salmonella, Listeria, Staphylococcus, endosporeformers and aerobic colony counts. Chemical parameters such as pH, alkalinity, conductivity and chemical oxygen demand (COD) were also monitored, but were not correlated to microbial pollution levels in the rivers. High faecal coliform and E. coli concentrations, ranging from 310 to 7 x 106 cfu.100 mL-1 and 230 to 7 x 106 cfu.100 mL-1, respectively, were detected. The recommended irrigation water guidelines of ≤1 000 (WHO, 1989) and ≤4 000 cfu.100 mL-1 (DWAF, 2008) for faecal coliforms and E. coli were exceeded, indicating faecal pollution and thus a high health risk. This health risk was confirmed when potential pathogens such as Aerococcus viridans, Klebsiella, Listeria monocytogenes and Salmonella typhimurium were detected at all three sites. The carryover of organisms from rivers to produce (green beans and grapes) was investigated by comparing the microbial population of the Plankenburg and Eerste Rivers to the population recovered from irrigation water and the surface of fresh produce. Faecal coliforms, E. coli, Aerococcus viridans, Enterobacter aerogenes, Klebsiella, L. innocua, L. grayi, L. monocytogenes and Staphylococcus aureus were detected in all three sample types, indicating a similarity between the microbial populations found in the river, the irrigation water and produce. Thus, the transfer of potential pathogens from the rivers to produce is a strong possibility. The build-up of organisms on the surface of green beans as a result of multiple irrigations was also confirmed by an increase in faecal coliform concentrations from initial concentrations of none detected to 44 000 cfu.100 mL-1 over a 10 day irrigation period. Finally, microbial source-tracking techniques including multi-antibiotic resistance (MAR) profiling, and the API 20E classification system were used to determine genotypic and phenotypic characteristics of 92 faecal isolates (from irrigation water and produce) and 13 reference strains. Numerical classification systems was used to classify the 105 faecal isolates according to the degree of similarity between the genotypic and phenotypic characteristics of the 105 isolates. A high degree of similarity indicates a high probability that isolates originate from the same strain and therefore from the same source, thereby confirming the transfer of organisms Faecal isolates (93 and 98%, respectively) were found to be resistant to Vancomycin at both the 5 and 30 μg concentrations. The majority of isolates presented some resistance to Erythromycin (15 μg) and Ampicillin (25 μg), with 82% of isolates presenting an inhibition zone ≤4 mm. Isolates were sensitive towards Ciprofloxacin (1 and 5 μg), Ofloxacin (15 μg), Ceftriaxone (30 μg) and Cefotaxime (5 μg), which were able to inhibit the growth of 79.8, 93.3, 79.8, 88.5 and 71.2% of the isolates, respectively. The 13 medical reference strains all presented different genotypic and phenotypic characteristics and thereby indicated a high degree of variability between isolates from the same species. Finally, 35% of the isolates could be grouped together based on similar genotypic and phenotypic characteristics, therefore, more than a third of the faecal isolates obtained from the surface of the fresh produce was as a result of faecal contaminants in the irrigation water. It could therefore be concluded that a health risk is associated with the water from the Plankenburg and to a lesser extent, Eerste River when used as source of irrigation, thereby risking the transfer of potentially harmful organisms, present in the rivers as result of faecal pollution, to the surface of fresh produce.
- ItemAssessment of microbial loads of the Plankenburg and Berg Rivers and the survival of escherichia coli on raw vegetables under laboratory conditions(Stellenbosch : University of Stellenbosch, 2010-12) Barr, Alison; Ackermann, Alison; Britz, T. J.; Sigge, G. O.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Food Science.ENGLISH ABSTRACT: Over the last decade, studies on the quality of the water in many of South Africa.s rivers revealed an increase in pollution levels (DWAF, 1996; DWAF, 2000). In agricultural areas of the Western Cape many farmers draw water for irrigation from nearby rivers without knowing what the microbial pollution level is. In order to investigate the current quality of river water in some of the Western Cape.s major rivers and to explore the possibility of pathogen carryover from water onto produce, this research project was initiated. In an exploratory study over a five month period, the microbiological and water chemistry of three selected sites from the upper Berg and two from the Plankenbrug Rivers were assessed. Studied organisms included Salmonella, Staphylococcus, Listeria, endosporeformers, coliforms, Escherichia coli and intestinal Enterococci, while the chemical analysis consisted of pH, alkalinity, conductivity and chemical oxygen demand (COD). Faecal coliform counts ranging from 540 to 1 700 000 cfu.100ml-1 and 490 to 160 000 cfu.100ml-1 were found for the Berg and Plankenbrug Rivers, respectively. The water temperature ranged from 12º to 21ºC with COD values always below 100 mg.L-1. Potential human pathogens such as Salmonella, Staphylococcus, Listeria, endosporeformers, E. coli and intestinal Enterococci were frequently isolated from all five sites that were sampled. These results are of great concern to farmers, fresh produce retailers and consumers alike as the river water is regularly drawn for irrigation of produce that is later consumed raw or after a minimal processing step. From the exploratory study it was concluded that the water from all the sites were not suitable for use in irrigation practices as they regularly exceeded the guidelines for faecal coliforms and E.coli as set out by South African authorities. Irrigation with faecally polluted river water is one way that fruit and vegetables can become contaminated with foodborne pathogens. The risk of disease transmission from potential pathogens present in the irrigation water is influenced by the microbial load present and the numbers carried over to the produce. In this study the carry-over and survival of Escherichia coli on green beans, sugar-snap peas and cocktail tomatoes was assessed under controlled laboratory conditions. The produce was exposed to E.coli under different combinations of exposure times (5, 15 or 30 min), drying times (30 or 120 min) and different inoculum concentration ranges (107, 105, 104, 10³ and 10ª). In all cases a reduction of at least one log value in original inoculum number was found with the 10ª inoculums showing no survivors. Follow-up studies with an exposure time of 60 min and increased drying times of 6 or 12 h. Neither of these parameter changes affected the variation in numbers for the same inoculum or the E.coli survivors. Similar E.coli loads to those detected on the green beans were detected on the sugar-snap peas. The number of survivors on the cocktail tomatoes was much lower than found for the beans and peas. The number of survivors on the cocktail tomatoes was much lower than found for the beans and peas. This was attributed the 'smooth'surface of the tomato skin probably making attachment of the E.coli bacteria difficult. With the exception of the 10ª inoculum range, all E.coli survivors detected on the three types of produce studied exceeded the guideline numbers set for fresh produce. If similar survival patterns are to be found in the environment then results from this study should serve as a warning that the Plankenburg river water is unsafe for use in the irrigation of fresh produce. Some farmers are already treating river water with chlorine prior to irrigation to eliminate the chance of pathogen transfer onto produce. However, this is not a feasible solution for most farmers due to the high cost of implementing a system such as this.
- ItemAssessment of microbial loads present in two Western Cape rivers used for irrigation of vegetables(Stellenbosch : University of Stellenbosch, 2010-03) Lotter, Marijke; Sigge, G. O.; Britz, T. J.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Food Science.ENGLISH ABSTRACT: Agriculture in the Western Cape is not only one of the most important economic sectors but also provides many job opportunities. Over the last few years the sustainability of this successful industry has become threatened by the faecal pollution of rivers used to irrigate produce that will be consumed raw or after minimal processing. This situation not only poses an enormous risk to the health of the consumer but also to farmers who stand to lose their export licenses. The purpose of this study was to determine the microbial types and loads in river water, irrigation water and on irrigated produce. A baseline study was done on four sites in two Western Cape rivers. These sites were chosen to allow for the sampling of river water, irrigation water and irrigated produce so as to determine whether a link between the use of contaminated irrigation water and the microbial population found on irrigated produce exists. The physico-chemical analyses used in the study consisted of: pH, alkalinity, water temperature, conductivity and chemical oxygen demand. The microbial monitoring included the aerobic colony counts (ACC) and the enumeration of the total coliforms, faecal coliforms, staphylococci, enterococci, and aerobic and anaerobic sporeformers present in the water samples. The presence or absence of the potential pathogens like E. coli, Listeria and Salmonella, was also determined. During the baseline study faecal coliform counts as high as 160 000 organisms.100 mL-1 were noted in the Plankenburg River, while counts as high as 460 000 organisms.100 mL-1 were found in the Mosselbank River. Apart from this, high numbers of staphylococci and intestinal enterococci were often found, while E. coli, Listeria and Salmonella were present in samples from both of these rivers. Based on the results of the baseline study on the two rivers it was decided to do a more intensive study on the microbial load of the river and irrigation water as well as irrigated produce from the Mosselbank site. Lettuce and cabbages from a commercial farmer’s fields were chosen as the irrigated produce. During the warmer summer months, ACC counts in the river samples peaked at 12 8000 000 cfu.mL-1, while faecal coliform counts of 1 600 000 organisms.100 mL-1 were found. The three potential pathogens (E. coli, Listeria and Salmonella) were present in all the river samples taken during this period. While the counts of indicator bacteria in the irrigation water was often lower, faecal coliform counts as high as 1 600 000 organisms.100 mL-1 and several other potential pathogens were found on the irrigated lettuce and cabbage. This could indicate a possible “build-up” of contamination on the produce with the repeated application of the tainted irrigation water. According to guidelines published by DWAF in 2008, water to be used for irrigation should not contain more than 4 000 organisms.100 mL-1 faecal coliforms if it is used for the irrigation of crops that are to be consumed raw or after a minimal processing step, as this would increase the health risk to the consumer. Guidelines published by the South African Department of Health are even stricter and state that raw vegetables and fruit should not contain more than 200 coliform organisms per gram, while E. coli and L. monocytogenes should be absent in one gram, and Salmonella spp. in 25 grams of the produce, respectively. From the data obtained during this study it was evident that the two rivers monitored regularly contained faecal indicators at levels much higher than those proposed in national and international guidelines for safe irrigation, making them unfit for the irrigation of MPF’s. It could be concluded that the rivers investigated during this study contained high levels of faecal contamination. Since some of the pathogens isolated from the river and irrigation water and the irrigated produce, it suggests a carry-over of microbial contamination from the river water to the irrigated produce. This was, however, only done using the traditional international methods and the presence of specific pathogens should in future be confirmed by means of molecular techniques.
- ItemThe benefits of the hazard analysis critical control point (HACCP) system in the fishing industry(Stellenbosch : Stellenbosch University, 2000-12) Uys, Rolf (Roelof Christiaan Bosenberg); Basson, D. S.; Britz, T. J.; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.ENGLISH ABSTRACT: International food trade is steadily increasing, as is the global incidence of foodborne diseases. For this reason, governments require that food safety is managed formally and pro-actively within and across the borders of countries. The HACCP system has been proven over the years to be a system, which successfully manages food safety and is fast becoming mandatory in most developed countries. Procedures are also in place to enforce HACCP implementation in South Africa in the near future. The system is preventative in nature and focuses resources on areas, which are critical to food safety, thereby being practical and effective. HACCP has always been and is currently very prominent in the international and local seafood industry. Moreover, South African fish processing companies cannot export their products to most international markets without implementing HACCP. The fish species which are most caught and economically the most valuable in South Africa are the Cape hake (Merluccius capensis and Merluccius paradoxus) and the South African pilchard (Sardinops sagax). This study focussed on applying HACCP principles to these species. HACCP models were developed for a South African pilchard canning operation and a fresh Cape hake processing operation according to the seven principles recommended by the Codex Alimentarius commission. The study showed how the storage of the catch in boat holds was proven to be a critical control point. The hazard was proven to be histamine poisoning due to the fact that boat holds were not cleaned adequately. Histamine-producing bacteria could grow on dirty surfaces and contaminate the catch with the toxin histamine, which could not be destroyed by subsequent canning processes. Viable contact plate counts and histamine-producing bacteria counts were performed. Results showed high counts in both instances, which validates that the point of hold cleaning is a CCP (Critical Control Point). Control measures were implemented in the form of a master cleaning schedule. Viable contact plate counts and histamine producing bacteria counts were repeated after the master cleaning schedule had been implemented. Counts decreased significantly in both instances, which validates the efficacy of the control measures. Ecologically justified, achievable target levels were calculated for viable contact plate counts and histamine-producing bacteria counts, which in future could be used in the HACCP plan of the case study company. The study also showed how a HACCP verification study was conducted on a fresh Cape hake processing operation, in order to illustrate the concept of verification. Microbial growth due to poor temperature control was selected as the hazard. The verification performed was to log times and temperatures during processing, and to ascertain whether temperature control was adequate to prevent the hazard. Logging took place during all stages of processing from catching and holding in the on-board stacker pond, through to selling on a fish market in Vitoria, Spain. Results of the study showed that the fish was reduced to below the critical limit of 3°C within 6 h and that it was kept under the critical limit during all stages of the process. This verifies that the hazard of microbial growth is controlled adequately. This study may be used as a guideline to implement HACCP in a fish processing operation. The hard work, however, lies in customising and streamlining the system for each individual company. In order to achieve this, commitment should be available from top management and the system should be accepted and understood by all employees of the company. HACCP is also dependant on pre-requisite systems such as GMP, which should be in place before the system can work adequately. It is, furthermore, important that HACCP is practiced by all sectors of food processing from farm to fork. The South African fishing industry carries the responsibility of leading the way and showing the rest of the food processing industry how HACCP should be implemented. Being South Africa’s ambassadors in the international food safety arena, it is crucial for the sake of future exports and economic growth that HACCP is implemented and functioning in this area.
- ItemCharacterisation and identification of the active microbial consortium present in Kepi grains(Stellenbosch : Stellenbosch University, 2001-12) Schoeman, Tersia; Witthuhn, R. C.; Britz, T. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: Kepi is an acidic, self-carbonated milk beverage that is produced by fermenting milk with grain-like structures that contain naturally occurring microbes, including lactic acid bacteria (LAB) and yeasts. The specific microbes present in the Kepi grains are responsible for an acidic-alcoholic fermentation of the milk and also contributes to the various health properties exhibited by Kepi. The combination of microbes in the Kepi grains can vary considerably depending on which type of milk is fermented, the method by which Kepi is produced, the origin of the grains and how the grains are stored. In this study, the impact of various environmental conditions including the different stages during Kepi production, grain origin, Iyophilisation and packaging in three different packaging materials, on the microbial community of Kepi grains were studied using selective growth media, morphology and biochemical characteristics. It was found that there was a general decrease in the microbial counts from laboratory produced Kepi grains, the longer Kepi was produced on a continuous basis. This decrease in microbial counts was also observed during the different stages of Kepi production. The average LAB counts obtained from laboratory produced grains decreased from 1.1 x 108 cfu.q" after 3 d of activation to 6.3 x 107 cfu.q' after 10 d of mass production to 9.7 x 106 cfu.q' after a further 30 d of normal Kepi production. The average yeast counts increased from no detectable yeasts after 3 d of activation to 5.7 x 107 cfu.q' after 10 d of mass production and then decreased again to 7.2 x 106 cfu.q' after 30 d of normal Kepi production. The combination of the isolates varied according to the method by which the Kepi grains were produced and the stress conditions that were applied. Laboratory produced Kepi grains contained the following LAB: Lactobacillus fermentum, Lb. brevis 3, Lb. p/antarum, Lb. de/brueckii subsp. de/brueckii, Lactococcus /actis subsp. /actis and Leuconostoc mesenteroides subsp. cremoris. The identified yeasts and mycelial fungi were a Zygosaccharomyces strain, Cryptococcus humico/us, Candida /ambica, C. krusei, C. kefyr and Geotrichum candidum. The influence of grain origin on the microbial content of Kepi grains was also investigated using samples of Kepi grains from eight different Southern African sources. The microbial counts of the various Kepi grain samples were found to vary from 6.0 x 105 cfu.q" to 1.7 x 108 cfu.q". Five Lactobacillus, two Leuconostoc, four Candida, one Saccharomyces and a Zygosaccharomyces strain were isolated from these grains, with each grain type having its own unique microbial combination. The microbial content of the Kepi grains that were Iyophilised, packaged in three different packaging materials and stored at room temperature for two months, was very similar. Lactobacillus delbrueckii subsp. delbrueckii was isolated from the Kepi grains packaged in "low density polyethylene film" (LOPE). The grains packaged in "oriented polyester film" (OPET) contained Lb. delbrueckii subsp. delbrueckii and Lb. brevis, while Lb. delbrueckii subsp. delbrueckii and Lb. curvatus was present in the grains packaged in "methallised oriented polyester film" (MOPET). The average microbial counts obtained from the Kepi grains packaged in OPET (2.7 x 106 cfu.q') were only slightly higher than that of the grains packaged in LOPE (1.2 x 106 cfu.q') and OPET (1.4 x 106 cfu.q'). It was concluded that packaging materials for Kepi grains should rather be evaluated on the quality of Kepi produced with the packaged grains than by the specific characteristics of the packaging materials. The enrichment of Kepi grains with propionibacteria was also evaluated. A polymerase chain reaction (PCR) based method, specifically designed for the rapid identification of propionibacteria, was developed and tested successfully. Using this technique it was concluded that propionibacteria were not a natural part of the Kepi beverage and grains as used in this study. However, during the enrichment of the grains with propionibacteria it was determined that a propionibacteria concentration of 1 x 108 cfu.rnt' was needed for successful PCR amplification results. The data obtained in this study clearly showed that the method by which Kepi is produced, the origin of Kepi grains and the method of Kepi grain preservation changes the relationship between the microbes constituting the grains to such an extent that a different microbial community is assembled. It was also concluded that traditional methods should be used together with newer methods in determining this microbial community.
- ItemCharacterisation and utilisation of microbes in the production of fish sauce and paste(Stellenbosch : Stellenbosch University, 2000-12) Lubbe, Beatrix; Britz, T. J.; Basson, D. S.; Stellenbosch University. Faculty of AgriSciences . Dept. of Food Science.ENGLISH ABSTRACT: Fermented fish products are popular food products mainly consumed and produced in Southeast Asia. These products are not produced in South Africa, and those available to the public are imported. The main action during the production and fermentation of this sort of product, is that of proteolysis, either by the bacteria or enzymes naturally present in the fish. The prevalent microbes present in six fermented fish samples from Bangkok (Thailand) and seven from Khon Kaen (Thailand), were determined, and using numerical methods, clustered into similarity groups using the calculated dendrogram .distance (Do) technique to determine their relation to reference strains. Forty-seven different bacterial strains were isolated, but no yeasts, moulds or lactic acid bacteria were found. Five Gram-negative, oxidase-positive species, five different Staphylococcus species and nine different endospore-forming species of the genus Bacillus, were isolated and identified using the API systems. The data indicated that members of the genus Bacillus were the prevalent organisms in all the products examined. The isolates were also scanned for general enzyme activity using the API Zym technology, and the production of proteases was investigated using the Standard Methods Caseinate and the Universal Protease Substrate methods. It was found that most of the isolated organisms produced protease, which is of major importance in the production of fermented fish products. Proteolytic cultures from the fermented fish products, as well as lactic acid starters, were used in the production of a fermented fresh water fish product. Production parameters including: glucose, inoculum, moisture content and incubation time, were evaluated in order to select optimum fermentation conditions. Fermentation efficiency was determined by measuring the final pH, titratable acid and the free amino nitrogen content. Optimum efficiency was obtained with 5% (w/w) added glucose at a moisture level of 150 ml water per 100 g fish. A factorial design (3 x 3 x 3) was used to indicate viable trends to facilitate optimisation of the fermentation process. The main effects, two-factor and three-factor interactions were calculated. Optimum trends obtained were a glucose concentration of 5% (wlw) , inoculum concentration of 1x10⁸ kve.ml ̄ ¹, an incubation period of 15 days and temperature of 30°C. Three lactic acid starters (226 - Lactobacillus plantarum, 140 - Lactococcus diacetylactis and 407 - Pediococcus cerevisiae) were selected as they produced some of the best fermentation results and are safe to use in food. It was found that a combination of all three strains (226, 140 and 407) yielded the best results. By using the above parameters, an acceptable product was produced in terms of consistency, colour and aroma. Further studies need to be conducted to optimise the safety of the product as well as the flavour, both chemically and sensorically optimisation of the product.
- ItemThe combination of UASB and ozone technology in the treatment of a pectin containing wastewater from the apple juice processing industry(Stellenbosch : Stellenbosch University, 2004-12) Van Schalkwyk, Nico; Sigge, G. O.; Britz, T. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: The South African apple juice processing industry is growing rapidly and during the harvesting season the wastewater volumes and organic loads increase significantly with a considerable environmental impact. These larger apple juice processing wastewater (AJPWW) volumes and chemical oxygen demand (COD) loads subsequently lead to faster increases in the organic loading rate (OLR) of an upflow anaerobic sludge bed (UASB) wastewater treatment system and it is necessary to know if the treatment system can handle such drastic increases over short periods. The objective of the study were to evaluate the efficiency of the UASB process in the treatment of an AJPWW; to determine what effect a substrate viscosity increase, based on a pectin calcium gel has on the performance of an UASB system, and to determine what impact ozonation has on the pectin content, gelformation ability and biodegradability of the AJPWW. The ability of the UASB to maintain stability during the apple-processing season was investigated by increasing the OLR from 2.9 to over 14.0 kg COD.m-3.d-1 in 131 days. During this time the COD removal remained constant at 85%, while the pH and alkalinity remained at levels indicative of good reactor stability. It was thus concluded that the UASB reactor could operate successfully during the apple-harvesting season when wastewater volumes and organic loads increase significantly. In the study it was found that the viscosity of the AJPWW, containing 750 mq.L-1 pectin, increased from 8.5 to 47.0 cps after a 312 rnq.L-1 Ca2 + addition. This increased viscosity substrate was then fed to an UASB reactor at an OLR of 15.0 kg COD.m-3.d-1. During a 12 day increased viscosity (47 cps) feeding stage the COD removal decreased from 94 to 11%, while the reactor pH decreased from 7.5 to 4.9. During this period, pectin accumulated in the UASB and led to biomass washout and rapid UASB failure. The possible elimination of pectin by ozonation was thus investigated, and a 77% decrease in pectin content and 76% decrease in gel formation ability occurred after ozonation. The effect of pre- and post-ozonation on the efficiency of the UASB system was subsequently investigated. It was found that a 10 min pre-ozonation decreased the AJPWW COD by 19% and the total suspended content by 36%, while the soluble portion of the total COD was increased from 81.7 to 92.4%. This increase in soluble COD content should lead to increased wastewater biodegradability. The ozonated AJPWW was then used to replaced the raw non-ozonated AJPWW as reactor feed. Results showed that the COD removal increased from 78 to 90% within 24 h of starting with the ozonated feed. It was also found that the reactor stability improved after AJPWW pre-ozonation as an OLR increase from 10.0 to 16.6 kg COD.m-3.d-1 in 23 days did not detrimentally influence the stability of the reactor. This reactor effluent (COD = 465 rnq.L-1) was then post-ozonated which resulted in 64.8% COD and 79.0% colour reductions. The final effluent had a COD of 180 rnq.L-1 (98% reduction). The ability of the ozonation/digestion system as described in this study to degrade AJPWW at a higher OLR is of value to the apple industry, as it may lead to larger organic pollutant removals and thus a more effiecient treatment system. Increased reactor performance will directly improve the quality of the final wastewater produced, which in turn will have a significant impact on the treatment ability of the South African apple processing industry currently limited by the production of large wastewater volumes.
- ItemCompositional analysis of locally cultivated carob (Ceratonia siliqua) cultivars and development of nutritional food products for a range of market sectors(Stellenbosch : Stellenbosch University, 2008-12) Iipumbu, Lukas; Sigge, G. O.; Britz, T. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.Carob (Ceratonia silliqua) is an evergreen, drought resistant tree of Mediterranean origin. Popularly known as St John’s bread, the carob pod has a long history of use in food (over 4 000 years). Carob has a good nutritional value, a long shelf-life (2-3 years) and it is relatively cheap. Due to its high sugar content, carob is naturally sweet. It also has a nutty chocolate-like flavour, but unlike chocolate or cocoa, carob does not contain any caffeine, thiobromine or oxalic acid. In addition, carob is normally regarded as a healthy food because of its low fat content (0.2 – 2.3%). Carob trees are also found in South Africa, especially in the Western Cape Province. Locally, carob trees have been used mainly ornamentally or as a source of animal fodder, with minimal use of the pods as a nutritious food source. Knowledge of the nutritional composition and the overall nutritional potential of locally (South African) grown carob cultivars is also limited. Carob could potentially be used as an alternative food source in South Africa as currently, most of this nutritious product goes to waste each year. In this study, the feasibility of using carob pods as an alternative source of food in South Africa was investigated. This was done by firstly, analysing the cultivars for proximate composition (moisture, carbohydrates, sugars, dietary fibre, protein, polyphenols, fat and ash) as well as for amino acids, fatty acids and minerals, in order to determine and compare their nutritional contents. Five cultivars (Tylliria, SFax, Aaronsohn, Santa Fe and an “Unknown” cultivar) were examined. The average proximate composition of raw carob pods was 8.17 – 9.56% moisture, 89.57 – 91.12% carbohydrates, 40.69 – 54.74% total sugars (33.70 – 45.09% sucrose, 1.79 – 4.95% glucose and 1.80 – 5.19% fructose), 29.88 – 36.07% dietary fibre, 3.07 – 4.42% protein, 2.58 – 3.08% polyphenols, 0.45 – 0.86% fat and 2.13 – 2.69% ash. Seven essential amino acids were present in all the cultivars, except for methionine which was not detected in the Single unknown cultivar. This study has shown that all the cultivars had good long-chain fatty acid (LCFA) proportions in terms of the saturated to polyunsaturated fatty acid (SFA: PUFA) and n-6 to n-3 ratios. The short-chain fatty acid content of the cultivars was low. All nine minerals (calcium, phosphorus, potassium, magnesium, sodium, manganese, iron, copper and zinc) analysed for in this study were detected in all five carob cultivars and all cultivars were very low in sodium. The impact of various roasting times (45, 60 and 75 min) at 150ºC, on the temperature sensitive components such as sugars, protein and fat, was also examined. Roasting had no significant (P>0.05) effect on the fat content. Although roasting significantly (P<0.05) reduced the sugar and protein content from 54.74 to 32.53% and 3.59 to 3.18%, respectively, levels in both raw and roasted carob still represented a potentially nutritious food source and alternative to cocoa. A variety of food products targeted at the various food market sectors were developed with carob as an ingredient. The formulations for five new food products (bread, porridge, breakfast cereal, mousse and milk-based drink) were developed where carob had successfully been incorporated as an ingredient. Microbiological and consumer sensory analyses carried out showed that all products developed were safe and acceptable. The findings of this study provide useful scientific evidence towards the fact that carob could potentially be used as an alternative food source in South Africa.
- ItemDetection of Enterobacter sakazakii in South African food products(Stellenbosch : University of Stellenbosch, 2005-12) Kemp, Francisca; Witthuhn, R. C.; Britz, T. J.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Food Science.It is estimated by the World Health Organisation (WHO) that thousands of millions of cases of foodborne diseases occur world–wide every year. Enterobacter sakazakii is a member of the family Enterobacteriaceae and has been identified as an occasional contaminant of powdered infant formula milk (IFM). Enterobacter sakazakii is an opportunistic emerging pathogen and has the ability to cause a severe form of neonatal meningitis. This organism was referred to as “yellow pigmented Enterobacter cloacae” until 1980 after which it was renamed as E. sakazakii. The current method for the detection of E. sakazakii is very time consuming and includes pre–enrichment, enrichment in Enterobacteriaceae enrichment broth, subsequent plating on violet red bile glucose agar and subculturing on tryptone soy agar. In this study a polymerase chain reaction (PCR) method was developed for the identification of the presence of E. sakazakii in infant food products. A part of the 16S ribosomal RNA (rRNA) gene from E. sakazakii was amplified using the primer pair Esak2 and Esak3. An internal amplification control (IAC) was constructed as part of the PCR detection method. The 850 base pair (bp) E. sakazakii PCR product was digested with AluI and the two fragments containing the primer binding sites were ligated, resulting in a 240 bp IAC. During this study a positive band for both the target DNA (850 bp) and the IAC (240 bp) was simultaneously observed when the IAC was added to the PCR mixture at a concentration of 0.72 pg.ml-1. Four of 22 South African food products tested positive for the presence of E. sakazakii, using both the PCR and recommended culturing methods. The PCR method was used successfully for the detection of E. sakazakii within three days and thus provides a possible alternative and improvement on the recommended current culturing methods. Other microorganisms present in the products tested included Escherichia coli, Klebsiella pneumoniae, Raoultella terrigena (“Klebsiella terrigena”) and Chryseomonas luteola. Since E. sakazakii is usually present in low numbers in food products, it is possible that these few cells are unevenly distributed in the products, making it important to take multiple samples when evaluating IFM and thereby ensuring that even low numbers of this pathogen are detected.
- ItemDetermination of the methanogenic potential of an apple processing wastewater treatment system(Stellenbosch : University of Stellenbosch, 2006-12) Paulsen, Cindy; Sigge, G. O.; Britz, T. J.; Muller, E.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Food Science.The food and beverage industry generates large volumes of wastewater annually. The disposal of factory effluent from the fruit processing industry has always been a cause of concern to both the fruit processors and controlling bodies responsible for effluent management. Traditional disposal of wastewater into sewerage works has become undesirable due to its economical and environmental impacts. Therefore, on-site anaerobic treatment of wastewater has received considerable interest due to lower capital outlays and energy recovery possibilities. Thus, the aim of this study was to establish an operational treatment profile for an anaerobic pond system treating fruit-processing wastewater. The specific activity of the microbial populations was also monitored to determine the effect of the fruit processing seasons (peak and off-peak season). The biogas production potential at various temperatures was also assessed to determine the viability of methane recovery. The influence of the processing and environmental conditions on the ponds’ performance was established by monitoring various process parameters. The results showed that the chemical oxygen demand (COD) levels decreased during the off-peak season but the pond pH remained relatively stable between 6.0 and 6.4 during the entire year. Pond alkalinity was found to be dependent on the regular lime dosing to maintain the necessary alkalinity. The volatile fatty acid (VFA) concentrations indicated that the microbial populations of the pond were functioning well. However, a decrease in microbial activity and VFA concentrations were observed at the lower temperatures during the winter months. The temperature profile of the pond showed that the pond temperature was impacted by the fluctuations in the ambient air temperature. The general trend established by the operational treatment profile clearly showed the impact of the peak and off-peak season. The sludge activity of the anaerobic pond was evaluated to determine the effect of the apple-processing peak and off-peak season on the specific activity of the acidogenic and methanogenic populations within the sludge. An activity test using four different test media was used during the activity assays. Sludge samples were taken at four different sampling positions across the pond’s sludge bed. The sludge was also subjected to a biogas formation study, which was designed to simulate pond conditions on laboratory scale in order to evaluate the biogas production potential of the anaerobic pond. The cumulative biogas volume and total CH4 composition showed little or no difference between the four sludge sampling sites. A major difference was found between the activity of the microbial populations during the peak and off-peak seasons. The overall trend regarding the biogas production rate (SB) and the methane production rate (SM) values showed an increased activity during peak-season and a decreased activity during off-peak season. For the biogas formation test the highest incubation temperature (25°C) resulted in the most biogas being produced, followed by 18°C, and with 10°C resulting in the lowest biogas volume. The biogas formation tests indicated that microbial activity and therefore biogas production was dependent on especially favourable temperature conditions. The pond and activity of the microbial populations are therefore influenced by factors like environmental changes such as decreased air temperatures and substrate changes such as decreased COD concentrations during the off-peak season. This in turn influences the rate of biogas production as well as the methane production rate. The theoretical CH4 calculations and estimates based on the results obtained during the biogas formation tests indicated that CH4 recovery from the anaerobic pond would definitely be a worthwhile consideration. If it were assumed that the estimated CH4 volumes (based on only 15% of the pond volume for practical reasons) obtained could be applied as an energy source, the minimum yearly savings in coal usage would amount to about R 665 000. This study was valuable in evaluating the factors such as pond conditions, pond activity and air temperatures and the effect on the biogas production potential as well as more importantly, CH4 production for the purpose of energy recovery.
- ItemDevelopment of technology for the production of stable high moisture dried fruit(Stellenbosch : Stellenbosch University, 2003-12) Erwee, Anton; Joubert, E.; Hansmann, C. F.; Britz, T. J.; Stellenbosch University. Faculty of AgriSciences . Dept. of Food Science.ENGLISH ABSTRACT: Dried fruit is a well-known food product that has been produced for many years. The product characteristics have remained constant throughout this time with a moisture content of ca. 18 - 26% (mlm). However, in recent times there has been a definite trend towards a fmal dried fruit product in the intermediate moisture range with a moisture content of ca. 36%. The high water activity (aw) of the product (ca. 0.85) makes the product susceptible to microbiological spoilage and the product therefore requires a subsequent pasteurisation step to ensure a safe product. A further consequence of the increased moisture content, higher aw and the temperature of the pasteurisation step, is the increased rate of non-enzymatic browning reactions. Currently the shelf life is only 15 weeks while a minimum shelf life of 30 weeks is required to enable product export. Moisture sorption isotherms may be used to depict the relationship between moisture content and aw. Moisture sorption isotherms were thus determined for Royal type apricots and nectarines at 25° and 40°C. Samples, equilibrated at relative humidities in the range of 11-97%, were obtained using saturated salt solutions and a static gravimetric method. Isotherms were found to be of type I, typical of dried fruit. Six mathematical models namely; BET, GAB, Iglesias and Chirife, Halsey, Henderson, and Chung and Pfost, were fitted to experimental data. The GAB model predicted the aw of both apricots and nectarines the best at 25° and 40°C with the Henderson equation second best in all instances. The binding energy, as a function of moisture content, was calculated to determine energy requirements for drying. At low moisture contents « 20%) an increase of energy was required for drying. Discolouration of macerated dried Royal type apricots and nectarines during accelerated storage as affected by moisture (32, 36, and 40%, mlm) and sulphur dioxide (S02) content (2500, 3000 and 3300 mg.kg" for apricots; 1800, 2200 and 2600 mg.kg" for nectarines) was investigated. The macerated samples were stored at 30°, 40°, 50° and 60°C. Colour was quantified in terms of the L* value of the CIELab system (used throughout the study). Moisture and S02 contents affected both the initial fruit colour and the rate of discolouration. The highest L* values, i.e. lightest fruit colour, were obtained for fruit at 40% moisture content and the highest S02 levels. Increasing storage temperature accelerated the loss of moisture and S02. The influence of a 10°C increase in storage temperature on the rate of browning and thus shelf life was described in terms of the QIO value. QIO and aw values of apricots ranged from 1.96 - 2.47 and 0.833 - 0.890, respectively, while QIO values of 1.50 - 4.61 and aw values ofO.844 to 0.890 were obtained for nectarines. Discolouration of dried nectarine halves during accelerated storage at 40°C as affected by rehydration method, moisture content, packaging atmosphere and pasteurisation method, was investigated. The fruit halves were rehydrated using three different methods to obtain moisture contents of 36 and 40%, respectively. Dry heat and steam pasteurisation techniques were used to render a microbiologically safe product. Commercial packaging material was used and the atmosphere was modified with CO2 to lower the O2 concentration in the headspace. A two-step rehydration at 45°C, steam pasteurisation at 90°C for 150 minutes and packaging under a high CO2 atmosphere rendered a product with the best colour retention under accelerated storage conditions of 40°C for eight weeks. To confirm the results obtained with accelerated storage at temperatures that the product would normally be retailed at, shelf life tests were also performed at 5° and 25°C. Discolouration of whole dried Royal type apricot and nectarine halves as affected by rehydration method, moisture content, packaging atmosphere and pasteurisation method was investigated. The methodology for rehydrating, pasteurising and packaging the high moisture dried fruit developed in this study was compared against the standard method used by the industry. The new processing method increased shelf life. Samples were stored for a period of 30 weeks and were tested every five weeks to determine CO2 concentration in headspace, colour retention and S02 concentration of the fruit. Both apricots and nectarines achieved a shelf life of 30 weeks at both storage temperatures and an extrapolated shelf life of 89 weeks at 5°C, but only 32 weeks at 25°C.
- ItemThe effect of region, yeast strain and ascorbic acid on the development of a sulphur-like aroma and on Sauvignon blanc wine quality(Stellenbosch : Stellenbosch University, 2000-12) Swart, Ewarda; Marais, Jeannine; Britz, T. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: Highly valued Sauvignon blanc wines, with the distinctive cultivar-typical aromas, reminiscent of grassy, green pepper or asparagus-like, are produced in some South African regions. Quite often, however, neutral and sulphur-like, low quality Sauvignon blanc wines are produced and this phenomenon is of great concern to wine producers and consumers, and affects our competition on overseas markets, negatively. The aim of this study was to investigate the effect of region, ascorbic acid/S02 treatments and yeast strain on Sauvignon blanc wine aroma and quality. Wines were produced from grapes obtained from the warmer Robertson and the relatively cooler Stellenbosch regions (1998 season). The juices were treated with different combinations of ascorbic acid/S02 treatments [commercially available ascorbic acid/meta preparate, S02 (control), pure ascorbic acid/S02] and Saccharomyces cerevisiae yeast strains (Vin 13, VL3C, NT 116). The wines were analysed for esters, higher alcohols, monoterpenes and 2-methoxy-3-isobutylpyrazine (ibMP). The wines were also sensorially evaluated for wine aroma intensities (fruity/ester, sulphur-like, grassy/green pepper) and overall quality. Additionally, the synergistic action of ibMP and the sulphur-containing component, 4-mercapto-4-methylpentan-2- one (MMP), considered to be the most important impact components of Sauvignon blanc, was studied. The two components were added, separately and in combinations at increasing concentrations, to different media. The nuances perceived, varied from dusty, grassy to green pepper for ibMP and from guava, sulphur-like to cat urine or "conifer" for MMP. Significant differences were observed between the wines treated with the different combinations of ascorbic acid/S02 treatments and fermented with different yeast strains, irrespective of region. The highest quality, cultivar-typical Sauvignon blanc wines were produced from the pure ascorbic acid/S02 treatment in combination with yeast strains Vin 13 and NT 116. This coincided with high ester and low higher alcohol concentrations, which did not overpower the typical Sauvignon blanc character. The treatments had, in some cases, a significant effect on monoterpene levels, but it was concluded that these differences were not big enough to affect wine quality. Levels of ibMP were too low and could not be reliably measured. Low quality wines, with prominent, undesirable sulphur-like aromas, were produced from juices, treated with the commercially available ascorbic acid/meta preparate and the French yeast strain, VL3C. Techniques, followed to identify the aroma components causing the sulphur-like offflavours, as MMP or as other sulphur-containing components, were gas chromatography/mass spectrometry, solid phase microextraction and sniffing. However, these tests were not successful and studies to identify these off-flavours should be continued. It was succeeded in this study to produce Sauvignon blanc wines without the undesirable, sulphur-like aromas. Although this investigation showed that a newly developed, commercially available ascorbic acid/meta preparate did not yield any sulphur-like off-flavours, quite often Sauvignon blanc wines with such off-flavours are still produced. Further research is needed to clarify this phenomenon.
- ItemThe effects of hot-deboning on the physical quality characteristics of ostrich (Struthio camelus) Muscularis gastrocnemius, pars interna and Muscularis iliofibularis(Stellenbosch : University of Stellenbosch, 2005-03) Botha, Sune St.Clair; Hoffman, Louwrens C.; Britz, T. J.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Food Science.The aim of this study was to investigate the effects of hot-deboning (1 h post-mortem) on the shelf-life and the physical meat quality characteristics, including tenderness, pH, purge (%), cooking loss (%), and raw meat colour of vacuum packed ostrich (Struthio camelus var. domesticus) meat cuts from the M. gastrocnemius, pars interna and the M. iliofibularis during post-mortem refrigerated aging for respectively 21 d at 4ºC and 42 d at -3º to 0ºC.
- ItemEvaluation of agricultural effluents and irrigation water as sources of antimicrobial resistant Escherichia coli(Stellenbosch : Stellenbosch University, 2013-12) Romanis, Marco; Britz, T. J.; Lamprecht, Corne; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: Food-borne disease outbreaks caused by Escherichia coli have been linked to the use of faecally-polluted irrigation waters. Thus the overall aim of this research was to evaluate irrigation water and agricultural effluents as sources of antibiotic resistant E. coli in the Western Cape. The aim of the first study was to enumerate and characterise E. coli present in irrigation water and in potential contamination sources. Maximum total coliform and E. coli counts for irrigation sites was log 7.862 and log 5.364 MPN.100 mL-1, respectively. Five out of seven irrigation sites had E. coli counts exceeding national and international guidelines for ‘safe’ irrigation water (<1 000 counts.100 mL-1), making it unsafe for the irrigation of fresh produce. In this study, 46.6% of the E. coli strains were characterised in phylogenetic group B1. It has been shown that E. coli in group B1 have the ability to survive and persist in the external environment. Group B1 was also the most common group among isolates from irrigation sites (79.4%), while isolates from environmental sites grouped mainly in group A0 (54.1%). It was concluded that the wide variation of E. coli types present in irrigation water is a concern that should be further investigated. This raises human health implications since the increased exposure to faecal organisms increases the risk of food-borne outbreaks. The E. coli isolates (n = 120) and the marker (n = 37) and reference strains (n = 6), were evaluated for antibiotic resistance to seven medically-important antibiotics from different classes using the Kirby-Bauer disc diffusion method. Thirty-five strains (35/163 = 21.5%) exhibited resistance to one or more antibiotics. Piggery effluent was found to harbour the most antibiotic resistant E. coli isolates (9/35 = 25.7%). Among the resistant E. coli strains, the highest occurrence of antibiotic resistance was to trimethoprim (2.5 μg) (68.6%), tetracycline (30 μg) (57.1%), ampicillin (10 μg) (45.7%) and chloramphenicol (30 μg) (34.3%). Seventy-four percent (26/35) exhibited multiple antibiotic resistances to two or more antibiotics. The antibiotic resistant E. coli strains were evaluated for the presence of pathotypes using Polymerase Chain Reaction analysis to detect Intestinal Pathogenic E. coli (InPEC) and Extra-intestinal Pathogenic E. coli (ExPEC). Five InPEC strains were characterised as four Entero-Pathogenic E. coli (EPEC) strains resistant to three or four antibiotics and one Entero-Aggregative E. coli (EAEC) strain resistant to trimethoprim. The antibiotic resistant EAEC strain also possessed the ExPEC-related gene iutA. Two E. coli isolated from the Mosselbank River were both resistant to chloramphenicol and trimethoprim and also possessed the ExPEC-related gene iutA. It was concluded that the diverse antibiotic resistances of E. coli pathotypes present in irrigation water is a concern that should be further investigated.
- ItemEvaluation of hot water and hot air heat shock treatments on South African avocados to minimise the occurrence of chilling injury(Stellenbosch : Stellenbosch University, 2002-12) Kritzinger, Madeleine; Britz, T. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: The South African avocado fruit industry is export driven and the successful storage of fruits for extended periods is, therefore, essential. It was recorded that 7.7 million cartons were exported during the 1995 season. The shipping of the avocados takes approximately 15 days and the fruits are being stored at low temperatures to minimise the possibility of fruits softening. Unfortunately low temperature storage results in chilling injury. A possible method to increase avocado resistance to chilling injury is to administer a heat shock treatment. In this way the fruits are protected from chilling injury by inducing the formation of so-called heat-shock proteins which render the cell membranes more resistant to chilling injury. The objective of this study was to evaluate different heat shock treatment protocols as a method of preventing or minimising chilling injury and to extend the shelf-life of avocado fruits while exporting at the lowest possible temperature. Examining the effect of different temperatures and exposure times on the quality of the different avocado cultivars pursued this. The exterior chilling injury on each fruit was quantified and the firmness and internal quality parameters evaluated. A total of 32 Experimental Studies were conducted. The results showed that the Hot Water Heat shock Treatment (HWHST) worked effectively for the South African 'Fuerte' cultivar between 40° and 42°C for exposure times of between 20 and 30 min. The 'Edranol' cultivar also showed promising results between 40° and 42°C for exposure time of between 8 and 22 min. The HWHST was not effective on the South African 'Hass' cultivar. The 'Ryan' cultivar with its thick skin made this cultivar less susceptible to chilling injury and therefore HWHST would be unnecessary. The 'Pinkerton' cultivar had a lot of factors that influenced the results. Therefore, more research needed to be done on the 'Pinkerton' cultivar, before any conclusions could be obtained from this cultivar, although it showed potential. Hot air treatment worked fairly well, but unfortunately the long exposure time needed made this treatment unpractical. Throughout the whole study the importance of maturity surfaced as a major role in all the aspects of post harvest quality.
- ItemExtracellular polymer extraction and analysis from UASB granules and batch produced anaerobic granular sludge(Stellenbosch : Stellenbosch University, 2002-03) Van Eeden, Alida Elizabeth; Britz, T. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: The start-up period of Upflow Anaerobic Sludge Bed (UASB) reactors can significantly be reduced by enhancing the time-consuming granulation process through the batch cultivation of anaerobic granular sludge and thus seeding the reactor with this cultivated granular sludge, instead of raw anaerobic sludge. The precise mechanism for granule formation is not well known, but it is believed that extracellular polymers (ECP) play a critical role in the granulation process. Information on the precise role of ECP is also limited and no universal standardised method for ECP extraction is used at present. Therefore, comparison of results from different researchers has to be made with great caution. The objectives of this study were to evaluate an ECP extraction methód so as to optimise the extraction time, and then to correlate ECP composition of UASB granules with granule metabolic activity. The impact of changes in the environmental conditions, such as sludge sources (Paarl and Kraaifontein-sludge), carbon growth substrates (yeast extract lactate, glucose medium and fruit cocktail effluent) and batch cultivation techniques (roller-table and shake-waterbath), on batch cultivation studies was also evaluated in terms of granule activity, ECP composition and granule formation. A physical extraction method was used to quantify the ECP content of UASB granules from six different sources. The optimal extraction time was taken as the time needed before cell lysis took place, and before intracellular material started contributing to the ECP content of the granules. It was concluded that the ECP composition was affected by the wastewater composition fed to the original UASB reactors, It was also found that the activity test results could be used to indirectly predict the activity of the different trophic groups present in the UASB granules. A correlation was found between the activity test results and the total ECP content, and this showed that the granules with the higher ECP yields exhibited greater biogas (SB) and methanogenic (SM) activities. However, based on the activity data and total ECP content, it appeared that a protein:carbohydrate ratio < 1 affected the activity of the granules, The sludge source used as inoculum for batch cultivation of anaerobic granular sludge had a significant effect on granule formation. The use of a pre- granulated raw anaerobic sludge, such as the Paarl-sludge, resulted in a greater increase in granule numbers at the end of the cultivation period. The acetic acid activity profiles showed that the acetoclastic methanogens that are involved in initiation of granulation by nucleus formation, were inactive or absent in the different batch systems, with the exception of the roller-table glucose cultivated Kraaifontein-sludge (RKG) batch system. The addition of glucose as carbon growth substrate for batch cultivation not only enhanced the activity of the acidogenic population, but also led to the establishment to a greater variety of granule trophic groups within all the glucose cultivated batch systems. The addition of fruit cocktail effluent as carbon substrate enhanced ECP production in the Paarl-sludge cultivated batch systems. However, the addition of carbon substrates showed no discernible trend on granule formation itself. The roller-table cultivation technique resulted in the higher increase in granule numbers, and it was speculated that the more vigorous shake-waterbath technique probably shortened the contact time between biomass and substrate. Large variations in the ECP composition of the different batch systems were found, and these were ascribed to the composition heterogeneity of different sludges. For future studies, it is advisable to characterise sludge, both chemically and microbiologically before using as inoculum. The selection of an appropriate sludge inoculum should then lead to optimisation of the granulation process.
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