Typescript (photocopy). / Digitized by Kansas Correctional Industries

Call number: LD2668 .T4 1963 D48 / Master of Science

Thesis (BTech (Food Technology))--Cape Technikon, 1999. / The Dairy industry, one of the larger food industries in South Africa processes probably the most perishable and possibly the most regulated foodstuff, namely mille The unique combination of vitamins, proteins, carbohydrates, lipids, moisture and near neutral pH, offers a suitable environment for the proliferation of microbes. Milk is therefore highly susceptible to microbiological activity resulting in the irreversible spoilage of this food (Frazier & Westhoff, 1988). The coliform group of organisms comprises all aerobic and anaerobic, gram-negative, non-spore-forming rods that are able to ferment lactose with the production of acid and gas at 32°C within 48 hours (Richardson, 1985). The primary purpose of the coliform detection test is to measure the quality of the practices used to minimise bacterial contamination of processed dairy products (Richardson, 1985). IDF Standard 132A: (1991) defines psychrotrophic organisms as organisms forming countable colonies when incubated aerobically at 6.5°C for 10 days under the conditions specified in IDF standard 101A. Shelf-life tests conducted in the fresh milk laboratory of a processing plant, revealed significant growth of coliforms in samples stored at 5°C. Luch, (1985) reported that other contaminating psychrotrophs together with the coliforms reduce the shelf-life of the milk when the storage temperature thereof is above 10°C.

Graduation date: 1995

Selected public health criteria of pasteurised milk available to the consumer from milk -shops in a selected area of Pretoria compared with a national distributor's milk were evaluated. Pasteurised milk samples were obtained from five randomly selected milk-shops in the northwestern part of Pretoria over a six-week period from June to August 1998. Milk from a wellknown national distributor was also obtained from three supermarkets in the same area during the same time period to act as the control milk. Mean total aerobic bacterial counts, coliform counts and psychrotrophic bacterial counts were determined. The presence of Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Salmonella species, staphylococcal enterotoxins, inhibitory substances, alkaline phosphatase and somatic cells in milk were also determined. Of the 135 milk samples purchased from milk-shops, 87% were not fit for human consumption on the basis of the minimum standards prescribed in the Foodstuffs, Cosmetics and Disinfectants Act (Act 54 of 1972). In contrast, 100% of the 79 control milk samples passed all the safety criteria laid down in the Act. x Milk-shop milk quality varied between milk-shops and between sampling days. All milk-shop milk was sold as having been pasteurised, yet 38.5% of milk samples purchased failed the alkaline phosphatase test, indicating that they had not been pasteurised correctly or were contaminated with raw milk. The total aerobic plate counts were generally high for all milkshop milk samples ranging from 1.0 x 102 to 2.7 X 107 CFU/mQ with a median value of 41000 CFU/mQ, whereas for the control milk it ranged from 7.0 x 102 to 8.7 X 103 CFU/mQ, with a median value of 2 200 CFU/mQ. Coliform counts varied from 0 to 3.4 X 104 per mQ in milk-shop milk, with 68% of samples having counts lower than 20 coliforms/mQ, which is the maximum number allowed when the Petrifilm method of counting is used. Coliforms could not be detected in 1 mQ of control milk samples. E. coli was detected in 1 mQ of 17% of milkshop milk, 95% of which originated from milk which was alkaline phosphatase positive. Salmonella spp. could not be detected in 1 mQ in any of the E. coli-positive milk tested. Psychrotrophic bacterial counts done after pre-incubation of milk-shop milk were extremely high, and ranged from 3 x lOS to 2.2 X 108 CFU/mQ, with a median value of 2.4 x 107 CFU/mQ. In Europe the psychrotrophic count may not be greater than 100 000 CFU/mQ. None of the milk-shop milk passed this European standard, whereas 98.7% of the milk obtained from the national distributor fell within the prescribed parameters. S. aureus was isolated from 54 (40%) milk-shop milk samples, and four (7.8%) of 51 isolates tested produced staphylococcal enterotoxins A (SEA), B (SEB), D (SED) or a combination. Control milk did not contain any S. aureus and 15 milk samples tested for the enterotoxin gave a negative result. All control milk was negative for inhibitory substances, but these were detected in 54.1 % of milk-shop milk. Somatic cell counts varied between 1.2 x 104 and 1.6 x 106 cells/mQ in the milk-shop milk, with a median count of 4.2 x 105 cells/mt Only 18.7% of samples had counts above the legal limit of 500 000 cells/mQ. The national distributor's milk always had counts less than 150 000 cells/mQ. xi The results showed that milk-shop milk differed significantly (p < 0.05) from the national distributor's milk, and that the quality of milk purchased from milk-shop outlets was generally of a poor bacteriological quality. The presence of inhibitory substances, and the isolation ofE. coli and S. aureus (some of which were able to produce enterotoxins) indicated potentially unsafe milk and posed a serious public health risk to consumers. / Dissertation (MMed Vet (Hyg))--University of Pretoria, 2000. / Production Animal Studies / unrestricted

The effectiveness of an adsorption filter in retaining bacteria present in milk was examined. Skim milk and whole milk (100ml) were separately filtered through a 47mm adsorption filter. No significant change in total solids, total fat, and solids-not-fat percentages of skim and whole milk permeates was observed after filtration. Adsorption of Pseudomonas fluorescens at target concentrations of 103 , 102 , and 101 cells/ml was determined in 100ml of dairy standard methods buffer, nutrient broth, whole milk, and skim milk. The average percentage bacterial retentions were 95 ± 5.5%, 95 ± 2.6%, 28 ± 22.1%, and 62 ± 15.5%, respectively. A treatment was developed for milk to increase the bacterial retention of ~ fluorescens after filtration. The preferred treatment for 100ml of skim milk involved the following final concentrations (v/v): 0.80% disodium ethylenediamine-tetraacetic acid, 0.02% sodium dodecyl sulfate, pH to 7.5 with 1N sodium hydroxide. The average bacterial retention of ~ fluorescens using the treatment was 91 ± 7.1%. Enumeration of bacteria adsorbed to the filter was then conducted using impedance microbiology. When milk was inoculated with ~ fluorescens at target concentrations of 103 , 102 , and 101 cells/ml, an average log bacterial increase of 1.4 ± 0.1 (25x) was obtained. This method will allow for rapid detection of microorganisms in milk by increasing microbial load in the tested sample and eliminating the need for pre-enrichment. / Ph. D.

no abstract provided by author / Master of Science

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: This study describes: the evaluation of the current, and potential assay methods for the quantification of cholesterol, cholesteryl esters and free fatty acids in milk and the application thereof ; an account of the difficulties associated with the usage of FoodPro® Cleanline, an enzyme preparation used as processing aid, during ultra-high temperature processing of milk ; the development of activity assays which can be used for the kinetic characterization of glycerophospholipid cholesterol acyltransferase, the active enzyme in FoodPro® Cleanline ; the development of an accurate and facile activity assay, and the validation thereof, which can be used for the validation of enzyme activity prior to dosage of milk with FoodPro® Cleanline. / AFRIKAANSE OPSOMMING: Hierdie studie beskryf: die evaluering van die huidige, en potensiële, metodes vir die kwantifisering van cholesterol, cholesteriel esters en vryvetsure in melk, sowel as die toepassing van hieridie metodes ; 'n verduideliking van die moeilikhede wat ondervind word gedurende die gebruik van FoodPro® Cleanline, 'n ensiempreparaat vir gebruik as 'n verwerkingshulpmiddel, tydens ultrahoë-temperatuurprosessering van melk ; die ontwikkeling van aktiwiteitsbepalings metodes vir gebruik in kinetiese karakterisering van gliserofosfolipied cholesterol asieltransferase, die aktiewe ensiem in FoodPro® Cleanline ; die ontwikkeling van 'n akkurate, eenvoudige aktiwiteitsbepalings metode, en bevestiging van hierdie metode, wat gebruik kan word vir kwalitieitskontrole alvorens die dosering van melk met FoodPro® Cleanline.

Several lactic acid bacteria (LAB) of the Lactococcus, Lactobacillus, Leuconostoc and Pediococcus genera were screened for inhibition of food-borne pathogens and spoilage microorganisms in raw milk and dairy products. Listeria monocytogenes was killed by Lactococcus lactis subsp. lactis and Pediococcus pentosaceus due to their production of bacteriocin-type inhibitors. Staphylococcus aureus was not able to grow in raw milk at temperatures below 5°C even without LAB being present. Gram negative Salmonella enteritidis. Salmonella typhimurium and Escherichia coli, along with spoilage bacteria of the genus Pseudomonas were dramatically inhibited by a Lactobacillus species, designated AS-1, in raw and pasteurized milk as well as in cottage cheese. However, other LAB were not able to inhibit these organisms. Lactobacillus AS-1, did not produce hydrogen peroxide but carbon dioxide was produced. The AS-1 strain was a gram positive coccobacillus, catalase and oxidase negative and produced DL-lactic acid. It deaminated arginine and grew over a temperature range of 5°C to 45°C. It was also able to ferment glucose, galactose, fructose and lactose in addition to 17 other carbohydrates. High numbers (107 CFU/ml) of AS-1 were required to obtain complete inhibition of gram negative bacteria. A selective medium (ASLM) for Listeria monocytogenes was developed to follow the fate of this particular pathogen in association with LAB in raw milk; other selective media were not able to inhibit the growth of background flora of raw milk. ASLM was superior to four other media in allowing only the growth of the target pathogen. For the Lactococcus genus, a selective and differential agar medium (Alsan) was formulated to selectively allow growth of Lactococcus spp. and to differentiate between Lactococcus lactis subsp. lactis and the biovariety diacetylactis, based on citrate utilization. / Graduation date: 1993

"Ititu" is a concentrated fermented milk utilized by Borana pastoralists in Southern Ethiopia. The effect of types of container used (glass, fibrous), smoking (smoked, non-smoked) and whey withdrawal (whey, non-whey withdrawn) treatments on the microbiological and chemical compositions of the fermented milks were investigated over a storage period of 28 days. Microbiological results indicated that the type of container used had significant effect (p $>$ 0.05) on total bacterial count (TBC) and lactic acid bacterial counts (LAB) for Weeks 1, 2, 3 and 4 and on coliform count (COLI) for Weeks 3 and 4. These counts determined for the fermented milks in the glass containers were found to be significantly lower compared to those in the fibrous vessels. There was significant difference (p $>$ 0.05) in the overall proximate composition for container and whey withdrawal treatments compared to smoking treatment. / An increased breakdown of the major caseins ($ alpha sb{ rm s1}$ and $ beta$) over the storage period was indicated. / A significant increase was noted on the content of the free amino acids compared to the total amino acids over the storage period.