Department of Food Science
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Browsing Department of Food Science by browse.metadata.advisor "Britz, T. R."
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- ItemCritical evaluation of the accuracy of the enumeration methodology of Coliforms and E. Coli in water from rivers used for the irrigation of fresh produce(Stellenbosch : Stellenbosch University, 2012-12) Brand, Amanda Salome; Britz, T. R.; Sigge, G. O.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: The accuracy of methods for the enumeration of coliforms and Escherichia coli present in river water intended for the irrigation of fresh produce has been critically evaluated to determine whether the results of the traditional method were reliable in indicating faecal pollution. The potential of rapid alternative methods were also explored. Baseline monitoring of the Berg River showed the presence of potential pathogens such as Salmonella, and also that E. coli levels exceeded international guidelines for the safe irrigation of minimally processed foods (MPFs) in 20.5% of cases, which indicated faecal intrusion. An exploratory study into the use of microbiological and physico-chemical parameters in predicting E. coli numbers, as a rapid alternative to direct enumeration, was conducted. These measurements, neither individually nor in combination, could accurately predict the E. coli numbers. The rapid method Colilert-18 was compared against multiple tube fermentation (MTF) for the enumeration of coliforms and E. coli. Spearman rank correlation coefficients showed that Colilert-18 had acceptable (r2=0.69) and fair (r2=0.74) correlations with MTF for coliform and E. coli enumeration, respectively. Bland and Altman statistics were used to determine pollution influence, and Colilert-18 showed increasing disagreement with MTF at very high concentrations of coliforms and E. coli. Bacterial isolates obtained from MTF reactions were identified using biochemical and mass spectrometry methods. These identifications revealed that the greatest contributors to inaccurate coliform enumeration by MTF were false negative coliforms which fail to produce gas from lactose. Numerical biochemical data suggested that these isolates may be able to use other carbohydrates preferentially over lactose. Inaccurate E. coli enumeration was caused by E. coli strains which could not utilise lactose or 4-methylumbelliferyl- -D-glucuronide (MUG), as well as non-E. coli isolates which were able to hydrolyse MUG. The method of transfer of bacteria between MTF media was also identified as problematic for accuracy. Monoplex polymerase chain reaction (PCR) differentiation of MTF isolates showed that detection of the uidA gene showed the greatest accuracy in the detection of E. coli, while the multiplex PCR protocol for detecting diarrheagenic E. coli pathotypes identified one strain of enteroaggregative E. coli (EAEC). A qualitative methodological risk classification was used, in combination with the individual reactions of MTF isolates, to elucidate their contribution to enumeration inaccuracy and to evaluate the effect of MUG and Levine-eosin methylene blue (L-EMB) agar. The classification indicated that inaccurate enumeration of E. coli was more problematic than that of coliforms, but revealed that the exclusion of MUG from MTF may increase the accuracy of E. coli enumeration. The omission of L-EMB would have very little effect on E. coli enumeration accuracy. This work confirmed that MTF is fairly reliable in the enumeration of coliforms and E. coli. Inaccuracies are primarily attributable to atypical organisms which are considered to make up a small proportion of the total bacterial population. Colilert-18 was shown to be an acceptably accurate alternative, and its rapid production of results can be highly advantageous in the monitoring of irrigation water used for MPFs.
- ItemThe effect of carbon monoxide on the colour stability and quality of yellowfin tuna (Thunnus Albacares) muscle(Stellenbosch : Stellenbosch University, 2013-03) Neethling, Nikki E.; Hoffman, Louwrens C.; Britz, T. R.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: Processors face the problem of extending the shelf-life of yellowfin tuna, while still maintaining the desirable bright red colour. Methods which have commonly been applied to meats and fish for shelf-life extension, such as ultra-low temperature freezing and vacuum packaging, have proved ineffective for tuna as these methods result in undesirable colour changes. Another method is the use of a carbon monoxide (CO) treatment, which results in tuna muscle with a desirable cherry-red colour that is stable during freezing and vacuum packaging. It is generally used in conjunction with freezing and vacuum packaging and can be used as a single gas (100% CO) or at varying concentrations in a mixture of gases. Other benefits of the use of CO include the potential inhibition of protein and lipid oxidation which would result in shelf-life extension. Its use with tuna has been criticised as it could mask spoilage indicators such as discolouration which could be misleading to consumers. Two pilot studies established that the tuna would be treated (+CO) for 150 min at 3 bar pressure to attain the desired surface colour development and colour penetration. Untreated samples were used as a control (-CO). In accordance to industry practices, the tuna was also subjected to both aerobic (overwrap) (OP) and anaerobic (OI) conditions and either one (Fx1) or two (Fx2) freeze/thaw cycles. It was found that the CO treatment did enhance, maintain and stabilise the surface colour of the tuna muscle during freezing and thawing. The carboxymyoglobin of the OP samples, however, rapidly oxidised to metmyoglobin, resulting in an undesirable brown discolouration. The OI samples maintained the colour throughout the shelf-life trial. The enhanced damage caused by the second freeze/thaw cycle was not apparent in the OP +CO treatments but the effect was seen in the OI +CO treatments. The CO treatment had no effect on either the lipid or protein oxidation. The number of freeze/thaw cycles also had no effect on the lipid oxidation but accelerated the protein oxidation to such an extent that the carbonyls being measured had reacted with other biological constituents and could no longer be detected. The packaging had an effect on both the protein and lipid oxidation with less lipid oxidation and retarded protein oxidation being observed in the OI treatments. A correlation was observed between myoglobin oxidation and protein oxidation in the tuna muscle with all the treatments. In the OI +CO samples, however, the a* values remained high even as the b* values and TBARS values increased. Thus the CO treatment of the tuna masked the visible indicator (browning) of lipid oxidation. It was concluded that overall the OI +CO Fx1 treatment resulted in the best quality product with regards to colour stability, colour maintenance, and lipid and protein oxidation. The results from this study reiterated the concerns regarding the use of CO with tuna as it can mask visible spoilage indicators which raise food safety concerns.
- ItemInvestigating the efficacy of hydrogen peroxide agaisnt isolated environmental Escherichia coli strains(Stellenbosch : Stellenbosch University, 2015-04) Giddey, Kirsten Francis; Lamprecht, Corne; Sigge, G. O.; Britz, T. R.; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.ENGLISH ABSTRACT: Surface water used for irrigation is often highly contaminated on a microbial level. Using contaminated surface water for the irrigation of fresh produce can lead to foodborne disease outbreaks and Escherichia coli has been a major cause of foodborne outbreaks associated with fresh produce over the past few years. There are many possible on-farm treatment options available to decrease the high microbial loads present in surface water, one of these is H2O2 and various factors can influence its use. The aim of this study was to determine the efficacy of H2O2 on different E. coli strains. Water from the Plankenburg River was sampled and treated with (250, 300 and 350 mg.L-1) H2O2 and the impact at 0, 30, 60, 90 and 120 min was then evaluated. It was found that the log reductions differed between samples. Log reductions ranged between 1.60 – 2.63 for Aerobic colony counts (ACC), total coliforms and Escherichia coli. The water was not considered safe for irrigation use although it had been treated with H2O2. Reference (ATCC) and environmental E. coli strains were individually treated with H2O2 (250, 300 and 350 mg.L-1) at 0, 30, 60, 90 and 120 min. Log reductions for the ATCC strains ranged between 2.13 – 5.48. This indicated a variation in H2O2 resistance between the different reference strains tested. Log reductions for the environmental E. coli strains ranged between 2.17 – 3.93. Escherichia coli M53 and MJ56 were the most resistant and most sensitive environmental strains to the H2O2 treatment, respectively. Once again it was observed that variations existed between the log reductions achieved for different strains. Overall, it was observed that the ATCC E. coli strains were more sensitive to the H2O2 treatments when compared the environmental strains. This indicates that ATCC strains should not be used for H2O2 treatment optimisation. Certain factors can influence the efficacy of H2O2 such as concentration and organic matter (chemical oxygen demand) present in the water. Different H2O2 concentrations were evaluated (50, 350, 700 and 1 000 mg.L-1) on two E. coli strains (M53 and W1371). Results indicated that 50 mg.L-1 was not effective as less than 1 log reduction was achieved after 120 min. When 350 and 700 mg.L-1 were used similar log reductions were achieved (1.78 – 2.27), which was not expected. Using 1 000 mg.L-1 was considered an effective concentration that resulted in no growth present after 120 min. Escherichia coli strain W1371 carried EPEC virulence factors (potential pathogen). This was included in the study in order to determine how a strain carrying virulence factors would react to H2O2. Escherichia coli W1371 was considered resistant to the H2O2 treatment and log reductions were similar to that achieved for M53. The catalase activity of the E. coli strains was studied to determine if a link existed between catalase activity and H2O2 resistance. Although a trend was observed between heat-stable catalase activity and H2O2 resistance, there were exceptions. It was concluded that high catalase activity does not always coincide with H2O2 resistance and that other mechanisms might also contribute to E. coli survival. Overall, it was observed that there are certain factors that influence the efficacy of H2O2 as a treatment option. It can be concluded that environmental E. coli strains are generally more resistant to the H2O2 treatment compared to ATCC E. coli strains, this needs to be considered when using H2O2 or other chemical disinfectants as a treatment option.