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Raw milk cheese has unique flavor and textural characteristics not obtainable in cheese from pasteurized milk. Several specialty cheeses made from raw milk are marketed worldwide, especially in Europe. However, because of safety concerns, many countries have imposed stringent restrictions on production and sale of raw milk cheeses. The purpose of this thesis research was to use high pressure (HP) treatment as a novel alternative for conventional pasteurization so that raw milk quality cheese could be produced without compromising food safety. The specific objectives of this research were to evaluate (i) the effect of HP treatment of milk on its coagulation and gelation characteristics, (ii) the destruction kinetics of microorganism and enzymes in milk, (iii) cheese making characteristics of HP treated milk as compared to the raw, pasteurized and micro-filtered milk (controls) and, finally (iv) to evaluate ripening characteristics of cheddar cheese made from HP treated milk in comparison with the controls. / Three coagulation parameters of milk---lag time, mean coagulation rate, and inflexion time (time for reaching the point of maximum coagulation rate)---were evaluated as a function of pressure (200--400 MPa), temperature (3--21°C) and holding time (10--110 min) using a response surface methodology. In general, the lag time and inflexion time decreased while the mean coagulation rate increased with an increase in pressure, holding time or a decrease in temperature: The rennet gel characteristics were evaluated as gel strength (GS) and water-holding capacity (WHC). With a decrease in pressure level, temperature and holding time, there was a decrease in water-holding capacity and an increase in the gel-strength of the rennet curd. (Abstract shortened by UMI.)

The application of high pressure (HP) processing on raw milk cheese was investigated in order to assure safety and improve quality. Fresh raw milk cheese inoculated with contaminant, spoilage and pathogenic microorganisms (Escherichia coli K-12, E. coli O157:117 and Listeria monocytogenes), as well as natural micro-flora, were subjected to UP treatment at selected pressures (200--400 MPa) for various holding times (0 to 100 min), or number of pulses. HP destruction of microorganisms followed the dual effect destruction behavior involving a step change in the population due to a pressure pulse (pulse effect, PE) and a first order rate log-linear kinetics during the pressure hold. The pressure dependency of kinetic parameters followed the pressure destruction time (PDT) and Arrhenius type models. / The results suggest that high pressure treatment as a powerful tool for microbial control do not result in major change in raw milk cheese quality properties (color and texture). It would thus be an effective method of inactivation of spoilage bacteria and pathogens for ensuring safety and keeping the quality of raw milk cheese.

High pressure (HP) kinetics of the microbial destruction and changes in the physicochemical characteristics of milk and pork were studied. Raw milk samples containing indigenous microflora of approximately 106 CFU/mL were heat sealed in dual peel sterilization pouches and subjected to HP treatment from 150--400 MPa with holding times ranging 5--120 min. The kinetic parameters (rate constant, k and decimal reduction time, D) for the microorganisms, alkaline phosphatase, color and viscosity were evaluated, based on first order kinetics and the pressure dependence of kinetic parameters was evaluated using pressure destruction time (PDT) and Arrhenius models. Kinetic data was well described by the first order model (R 2 > 0.90). / The application of pressure pulse was explored for pressure destruction of microorganisms as well as changes in physical-chemical characteristics of pork chops. Pork chops (2 days post-rigor) were subjected to HP treatment from 200--350 MPa for 0--120 min. Results showed that pressure changes of pork variables followed a dual effect consisting of an instantaneous pressure kill (IPK) with the application of pressure pulse (no holding) and a subsequent first order rate of destruction during the pressure hold time. The IPK values were pressure dependent and increased with pressure level. Parameters k and D indicated a higher rate of pressure destruction of microorganisms compared to quality attributes. / Kinetics of pressure destruction of Listeria monocytogenes Scott A were studied in relation to those of indigenous microorganism of milk and pork. The IPK was more pronounced with L. monocytogenes than with indigenous microflora. However, the kinetic parameters (k and D values) indicated a larger pressure resistance for L. monoctyogenes. HP processes were developed based on the standard plate count (SPC) kinetic data for indigenous microflora of milk as well as L. monocytogenes in milk and pork. The results showed that SPC kinetics permitted good estimation of microbial destruction in low pressure-lethality processes of milk and pork but its application at higher pressure-lethality levels were inaccurate. On the other hand, processes established based an destruction of L. monocytogenes were more predictable. Pressure pulse application to microbial lethality was also well predicted. / The shelf-life of milk and pork increased with the level of applied pressure lethality, but Q10 values suggested that low storage temperature was nevertheless required to control microbial growth and maintain quality. Storage of HP treated park offered some improvement in the texture but resulted in large color changes and drip losses. L. monocytogenes were not detected in any of the stored milk samples HP treated to achieve a lethality ≥10D.

Thesis (MScVoedselwet)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Milk has been identified as having the potential of being a carrier of human pathogens, and it is thus essential to eliminate or reduce the likelihood of milk borne contamination. This problem of milk contamination is generally solved by the process of pasteurisation which is achieved by heating the "raw" material for a sufficient period of time to destroy any pathogenic and spoilage bacteria which may be present at a temperature of below 100°C. Presently, there are two basic methods of pasteurisation in use in the dairy industry, the LTLT and the HTST methods, where the applied heat treatment is considered sufficient to ensure public safety and adequate keeping quality. In addition to these, there is another method, the "pot" pasteurisation, to be found in Southern Africa that was designed to eliminate potential pathogenic and spoilage bacteria present in raw milk. As far as it is known no thermal studies have been done on the "pot" pasteurisation method. The objectives of this study were to determine the impact of different milk pasteurisation temperature and time combinations on the survival of selected microbes. The accuracy of the "pot" pasteurisation method and how it differs from the other pasteurisation methods was also determined using the same selected microbes. The six selected microbes were thermally inactivated by using the LTLT, HTST and the "pot" pasteurisation methods at low and high inoculum levels of 104 and 106 cfu.ml-1. The thermal death curves were constructed for each selected species. The selected microbes included the strains Bacillus cereus (S4), Chryseobacterium meningosepticum (S5), Pseudomonas putida (S6), Acinetobacter baumannii (C3), Escherichia coli (58) and Candida lipolytica (G1). Survivors were enumerated after heating for 0, 5, 10, 15, 20, 25, 30, 35 and 40 min for both the LTLT and HTST pasteurisation methods and after heating for 0, 10, 20 and 30 min for the "pot" pasteurisation method. The results from this study showed that with the exception of the B. cereus strain, the other selected microbes at both high and low concentration levels did not survive the LTLT or the HTST pasteurisation methods. It was found that for all the organisms used in this study, there was a rapid initial death rate just before the required pasteurisation temperatures of 63°, 72° and 90°C were reached, during the "come-up" period. In contrast, the results from the "pot" pasteuriser showed that theB. cereus (S4), Chr. meningosepticum (S5), P. putida (S6), A. baumannii (C3) and E. coli (58) strains survived the pasteurisation conditions applied. From these results it was thus concluded that the "pot" pasteuriser under the conditions evaluated in this study, did not pasteurise effectively. Therefore, it is recommended that the manufacturer improves the heating quality of the "pot" pasteuriser. As it was found that only the B. cereus (S4) strain survived all the different pasteurisation methods, future research needs to be done to determine at which temperature this heat resistant bacterial strain will be destroyed. This is very important because there is a need to destroy all the spoilage microorganisms that can lead to the deterioration of food products. / AFRIKAANSE OPSOMMING: Melk is 'n potensiële draer van mikrobes wat patogenies is vir die mens. Dit is dus essensiëel om die besmetting van melk te verlaag of te elimineer. Die probleem van melkbesmetting word opgelos deur die proses van pasteurisasie. Die proses word toegepas deur verhitting van die rou material vir 'n voldoende periode om patogeniese en bederf organismes te vernietig. Temperature onder 100°C word gebruik. In die suiwelbedryf word twee basiese metodes gebruik: die LTLT (lae temperatuur, lang tyd) metode en die HTKT (hoë temperatuur, kort tyd) metode. Albei hittebehandelings is voldoende om publieke veiligheid en 'n genoegsame rakleeftyd te verseker. 'n Derde metode, "pot" pasteurisasie, word in Suidelike Afrika gebruik. Die metode is ontwikkel om potensiële patogene en bederf organismes in rou melk te elimineer. Die probleem is dat daar geen navorsing op die temperatuur eienskappe van die “pot" metode gedoen is nie. Die doelwitte van hierdie navorsing was om die effek van verskillende temperatuur:tyd kombinasies op die oorlewing van sekere mikrobes te bepaal. Die akkuraatheid van die "pot" metode en die manier hoe dit van ander metodes verskil, is ook in ag geneem. Die navorsing is ten alle tye gebaseer op die geselekteerde mikroorganismes. Die ses geselekteerde spesies van mikrobes is vernietig deur middel van die LTLT, HTKT en "pot" pasteurisasie metodes. Die mikrobes is geïnaktiveer teen lae en hoë inokulums van 104 en 106 kve.ml-1. Terminale dodings kurwes is opgestel vir elke geselekteerde spesie. Die mikrobes van belang is Bacillus cereus (S4), Chryseobacterium meningosepticum (S5), Pseudomonas putida (S6), Acinetobacter baumannii (C3), Escherichia coli (58) en Candida lipolytica (G1). Die oorlewende mikroorganismes is na hitte behandelings van 0, 5, 10, 15, 20, 25, 30, 35 en 40 minute vir beide die LTLT en die HTKT pasteurisasie metodes en na hitte behandelings van 0, 10, 20, en 30 minute vir die "pot" pasteurisasie metode getel. Die resultate van die navorsing dui aan dat, behalwe vir B. cereus, die geselekteerde mikrobes teen beide lae en hoë konsentrasies nie die LTLT en die HTKT metodes oorleef het nie. Daar is gevind dat, vir al die organismes, vinnige aanvanklike dodingstempos teenwoordig was net voor die noodsaaklike pasteurisasie temperatuur van 63°, 72° en 90°C bereik is, gedurende die "come-up" periode. Inteenstelling hiermee het die resultate van die "pot" metode bewys dat B.cereus (S4), Chr. meningosepticum (S5), P. putida (S6), A. baumannii (C3) en E. coli (58) stamme die pasteurisasie toestande oorleef het. Uit die resultate is ’n gevolgtrekking gemaak dat die "pot" pasteurisasie metode nie effektief was nie. Daar word dus aanbeveel dat die vervaardiger die verhittings-kwaliteit van die "pot" pasteurisasie apparaat verbeter. Aangesien net die B. cereus (S4) stam al drie pasteurisasie metodes oorleef het, moet toekomstige navorsing gedoen word om die vernietigings temperatuur van dié hittebestande stam te bepaal. Die navorsing is van belang weens die behoeftes om alle bederf mikroorganismes wat tot die agteruitgang van voedsel produkte kan lei, te vernietig.

A bovinocultura de leite vem se estabelecendo como importante atividade socioeconômica na agricultura familiar em todo o país. Tal atividade tem sido considerada como garantia de sobrevivência de famílias no campo promovendo sua reprodução social. Como um dos principais alimentos disponíveis para a humanidade, a produção de leite tem exigido tecnologias para garantir sua qualidade sob aspectos físico-químicos e microbiológicos, entre outros. Dentro deste contexto, esta pesquisa apresenta uma abordagem socioeconômica de agricultores produtores de leite bovino que residem em uma comunidade do interior do município de Pato Branco na Região Sudoeste do estado do Paraná, buscando conhecer as características das famílias e aspectos específicos na produção de leite e o que a atividade tem representado nas referidas famílias em termos socioeconômicos, bem como a qualidade do leite produzido. O presente estudo compreendeu três fases de trabalho. Inicialmente foi realizado um diagnóstico de 26 famílias da comunidade Independência, com o intuito de obter informações referente a realidade social, econômica e aspectos de desenvolvimento da atividade leiteira. Na segunda fase, foram coletadas amostras de leite nas propriedades com o objetivo de avaliar a qualidade físico-química, microbiológica, bem como, pesquisa de resíduos fármacos de uso veterinário, resíduos antibióticos e aflatoxinas. A qualidade microbiológica da água, usada na atividade leiteira, também foi avaliada. A terceira fase compreendeu a elaboração de queijos artesanais análogo ao Boursin, como proposta de aproveitamento tecnológico do leite, sendo feita pesquisa de avaliação sensorial e intenção de compra dos produtos desenvolvidos. A comunidade pesquisada tem potencial para a atividade de bovinocultura de leite, apresentando elevada produtividade leiteira. No que se refere à qualidade do leite, a pesquisa demonstrou necessidades de melhorias no manejo e higiene na realização das ordenhas dos animais, entre outros fatores relacionados ao uso dos conhecimentos tecnológicos disponíveis. Foi possível o desenvolvimento de um produto diferenciado, o qual pode ser considerado uma alternativa de renda e resgate da cultura da comunidade na fabricação de queijos, consistindo em uma proposta de desenvolvimento econômico e social para as unidades de produção de base familiar. / The dairy cattle has been established as an important socioeconomic activity in family farms across the country. Such activity has been considered as warranty of survival of families in the country region promoting their social reproduction. As one of the main food available for people, the production of milk has been demanding technologies to guarantee its quality under physicochemical and microbiological aspects, among others. Within this context, this research presents a socioeconomic approach of bovine milk farmers who live in a community in the interior of Pato Branco district, in the southwest area of Paraná state, with the intention of understanding the families’ characteristics, specific aspects in the production of milk, and what this activity has represented concerning socioeconomic terms for these families, as well as the quality of the produced milk. The present study carried out three work phases. Initially, a diagnosis of 26 families of the Independence community was accomplished, with the intention of obtaining information regarding their social and economic reality, and important aspects regarding the development of dairy activity. In the second phase, samples of milk were collected in the properties with the objective of evaluating its physicochemical, microbiological quality, as well as in relation to the presence of residues of medicines for veterinary use, antibiotic residues and aflatoxins. Water used in the dairy was also collected to evaluate its microbiological quality. The third phase involved the elaboration of handmade cheeses similar to Boursin, as a proposal of technological use of the milk, together with a research of sensorial evaluation and intention of purchase of the developed products. The researched community has potential for the dairy cattle activity, presenting high dairy productivity. Regarding the quality of the milk, the research demonstrated needs of improvements in the handling and hygiene concerning the milking of the animals, among other factors related to the use of the available technological knowledge. The development of a differentiated product was possible, which can be considered as an alternative of income and rescue of the community's culture in the production of cheeses, consisting of a proposal of economic and social development for the family based production units.

A bovinocultura de leite vem se estabelecendo como importante atividade socioeconômica na agricultura familiar em todo o país. Tal atividade tem sido considerada como garantia de sobrevivência de famílias no campo promovendo sua reprodução social. Como um dos principais alimentos disponíveis para a humanidade, a produção de leite tem exigido tecnologias para garantir sua qualidade sob aspectos físico-químicos e microbiológicos, entre outros. Dentro deste contexto, esta pesquisa apresenta uma abordagem socioeconômica de agricultores produtores de leite bovino que residem em uma comunidade do interior do município de Pato Branco na Região Sudoeste do estado do Paraná, buscando conhecer as características das famílias e aspectos específicos na produção de leite e o que a atividade tem representado nas referidas famílias em termos socioeconômicos, bem como a qualidade do leite produzido. O presente estudo compreendeu três fases de trabalho. Inicialmente foi realizado um diagnóstico de 26 famílias da comunidade Independência, com o intuito de obter informações referente a realidade social, econômica e aspectos de desenvolvimento da atividade leiteira. Na segunda fase, foram coletadas amostras de leite nas propriedades com o objetivo de avaliar a qualidade físico-química, microbiológica, bem como, pesquisa de resíduos fármacos de uso veterinário, resíduos antibióticos e aflatoxinas. A qualidade microbiológica da água, usada na atividade leiteira, também foi avaliada. A terceira fase compreendeu a elaboração de queijos artesanais análogo ao Boursin, como proposta de aproveitamento tecnológico do leite, sendo feita pesquisa de avaliação sensorial e intenção de compra dos produtos desenvolvidos. A comunidade pesquisada tem potencial para a atividade de bovinocultura de leite, apresentando elevada produtividade leiteira. No que se refere à qualidade do leite, a pesquisa demonstrou necessidades de melhorias no manejo e higiene na realização das ordenhas dos animais, entre outros fatores relacionados ao uso dos conhecimentos tecnológicos disponíveis. Foi possível o desenvolvimento de um produto diferenciado, o qual pode ser considerado uma alternativa de renda e resgate da cultura da comunidade na fabricação de queijos, consistindo em uma proposta de desenvolvimento econômico e social para as unidades de produção de base familiar. / The dairy cattle has been established as an important socioeconomic activity in family farms across the country. Such activity has been considered as warranty of survival of families in the country region promoting their social reproduction. As one of the main food available for people, the production of milk has been demanding technologies to guarantee its quality under physicochemical and microbiological aspects, among others. Within this context, this research presents a socioeconomic approach of bovine milk farmers who live in a community in the interior of Pato Branco district, in the southwest area of Paraná state, with the intention of understanding the families’ characteristics, specific aspects in the production of milk, and what this activity has represented concerning socioeconomic terms for these families, as well as the quality of the produced milk. The present study carried out three work phases. Initially, a diagnosis of 26 families of the Independence community was accomplished, with the intention of obtaining information regarding their social and economic reality, and important aspects regarding the development of dairy activity. In the second phase, samples of milk were collected in the properties with the objective of evaluating its physicochemical, microbiological quality, as well as in relation to the presence of residues of medicines for veterinary use, antibiotic residues and aflatoxins. Water used in the dairy was also collected to evaluate its microbiological quality. The third phase involved the elaboration of handmade cheeses similar to Boursin, as a proposal of technological use of the milk, together with a research of sensorial evaluation and intention of purchase of the developed products. The researched community has potential for the dairy cattle activity, presenting high dairy productivity. Regarding the quality of the milk, the research demonstrated needs of improvements in the handling and hygiene concerning the milking of the animals, among other factors related to the use of the available technological knowledge. The development of a differentiated product was possible, which can be considered as an alternative of income and rescue of the community's culture in the production of cheeses, consisting of a proposal of economic and social development for the family based production units.

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The efficacy of six sanitizers, [chloline (200 ppm), iodophor (2S: ppm), acid anionic (200 ppm), peracetic acid (200 ppm), and fatty acid sanitizer (200 ppm)], was evaluated against bacteria attached to gasket materials. Pseudomonas fluorescens, Yersinia enterocolitica, Bacillus cereus, and Listeria monocvtogenes were capable of significant attachment to both buna-N nlbber and Teflon® gasket surfaces in either pure or mixed cultures. Differences in initial attachment rates were evident in a mixed culture of P. fluorescens, Y. enterocolitica, and Listeria monocytogenes in vitro. Sanitizer effectiveness depended upon the bacterium being enumerated, the type of surface, if the bacterium was attached in pure culture or as part of a mixed culture, and the system of evaluation, (i.e. whether or not sanitizer was used alone or as part of a cleaning system). Peracetic acid was the most effective. Removal of bacteria was more pronounced on the Te'f1on® surface with all sanitizers used. The cleaning system, which consisted of a pre-rinse with warm water, application of the cleaning solution, post-rinse with warm water, and application of the sanitizing solution, allowed microorganisms to remain, when the bacteria were present as a pure culture, but resulted in the complete removal of bacteria in mixed culture. / Ph. D.