This study investigated the effect of the Lactoperoxidase system (LPS) alone and in combination with pasteurisation, on the growth of Listeria monocytogenes (LM) ATTC 7644 in goat milk and goat milk cottage cheese during a shelf life of 10 days at 4 °C. Goat milk was inoculated with LM ATTC 7644 and divided into two samples, one the control and Lactoperoxidase (LP) was activated in the other sample. Both the control and LP activated samples were kept at ambient temperature for 6h. After 6h the control and LP activated samples were again divided into two and one of the respective samples was pasteurised at 72 °C for 15 s. All the four samples were analysed for LM ATTC 7644 immediately after LP activation at 0h, after 6h of LP activation and after pasteurisation. Goat milk cottage cheese was made with all four samples, i.e. control raw, control pasteurised, LP activated raw and LP activated pasteurised goat milk and analysed for LM ATTC 7644 on days 1, 2, 5, and 10. Six hours after LP activation the mean LM ATTC 7644 count for the LP activated milk decreased by log 0.5 cfu/ml where as the LM ATTC 7644 for the control increased by log 0.5 cfu/ml. The reduction of LM ATTC 7644 count in LP activated milk when compared to the control shows that goat milk lactoperoxidase is capable of reducing L. monocytogenes when stored at ambient temperatures. Furthermore, LM ATTC 7644 count in LP activated pasteurised goat milk decreased by log 1.1 cfu/ml more, compared to the control pasteurised goat milk. Therefore, pasteurisation together with LP activation may be more effective than pasteurisation alone in controlling the growth of L. monocytogenes in goat milk. For the control raw goat milk cottage cheese on day 10, the LM ATTC 7644 count was 90 % less than on first day of storage. The LP activated raw goat milk cottage cheese count followed a similar trend to the control raw goat milk cottage cheese, and reached levels of log 2.9 cfu/g on the last day of storage. The control pasteurised goat milk cottage cheese LM ATTC 7644 count on day 10 was 92 % lower compared to day 1 where as the LP activated pasteurised goat milk cottage cheese LM ATTC 7644 count was 98 % less than on day 1. The results of this study indicate that the activation of the LPS significantly (p≤0.05) decreased the LM ATTC 7644 count in goat milk, during a period of 6h. Combined pasteurisation and LP activation had a synergistic effect on the LM ATTC 7644 count in goat milk. The LM ATTC 7644 count declined in cottage cheese made from both control and LP activated goat milk. A greater decrease was observed in LP activated pasteurised goat milk cottage cheese over the storage period of 10 days at 4 °C. This combination may be used to reduce the multiplication of LM ATTC 7644 for production of safer products like goat milk and goat milk cottage cheese. / Dissertation (M Inst Agrar (Food Production and Processing))--University of Pretoria, 2007. / Food Science / M Inst Agrar / unrestricted

Submitted by (edna.saturno@ufrpe.br) on 2017-03-28T13:22:55Z No. of bitstreams: 1 Chiara Rodrigues de Amorim Lopes.pdf: 1063652 bytes, checksum: 6655c28f0a035e0d1cca00a02296e5fc (MD5) / Made available in DSpace on 2017-03-28T13:22:55Z (GMT). No. of bitstreams: 1 Chiara Rodrigues de Amorim Lopes.pdf: 1063652 bytes, checksum: 6655c28f0a035e0d1cca00a02296e5fc (MD5) Previous issue date: 2010-02-24 / This study was to evaluate, through 3 trials, the efficiency of the lactoperoxidase system (LPS) activation on the preservation of refrigerated and non-refrigerated cow milk in Havana, Cuba. In the first and second trial was used raw milk stored at environmental temperature for 0, 4, 8 and 12 hours of storage and the SLP has been activated in the laboratory and camp, respectively. In the third trial was used raw milk refrigerated for 0, 24, 48, 72 and 120 hours of storage. SLP has been activated by the product STABILAK®, a commercial activator containing sodium thiocyanate and Sodium percarbonate. There was observed effect of treatment (activated and not activated) of storage time (P < 0.01) and of interaction treatment x time (P < 0.05) on the acidity in the three trials, effect of storage time on the lactose (P < 0.05) and total solids (P < 0.01) in trial II and effect of treatment on fat, protein, total solids (P < 0.01) and lactose (P < 0.05 ) in trial III. For the coliforms count, was observed effect of treatment (P < 0.01, trial I; P < 0.01, trial III), of storage time (P < 0.05, trials I and II; P <0.01, trial III) and treatment x time interaction (P < 0.05, trial III). For the psychrotrophic count was observed effect of treatment (P < 0.05) and storage time (P < 0.01). SLP inhibited the growth of coliforms population in raw milk non-refrigerated and kept the normal level of acidity up to 8 hours depending on the initial quality of milk. In refrigerated raw milk the inhibitory effect of SLP on the coliforms count was extended to 120 hours and the acidity was kept the normal level up to 48 hours after activation. There was no effect of SLP on the psychrotrophic population over the storage times. The SLP did not alter the initial concentrations of fat, protein, lactose and solids in all trials, and managed to prevent the degradation such components for periods of up to 120 hours in refrigerated raw milk. / Foram realizados três ensaios com o objetivo de avaliar a eficiência do sistema lactoperoxidase (SLP) na conservação do leite cru refrigerado e não-refrigerado no estado de Havana, Cuba. No primeiro e no segundo ensaio utilizou-se leite cru armazenado sob temperatura ambiente durante 0, 4, 8 e 12 horas de conservação e o SLP foi ativado em condições de laboratório e de campo, respectivamente. No terceiro ensaio foi utilizado leite cru, refrigerado durante 0, 24, 48, 72 e 120 horas de conservação. Para ativação do SLP utilizou-se um ativador do SLP composto por tiocianato e percarbonato de sódio conhecido como STABILAK®. Houve efeito de tratamento (ativado e não-ativado), de tempo de conservação (P < 0,01) e da interação tratamento x tempo (P < 0,05) sobre a acidez titulável nos três ensaios; efeito de tempo sobre o nível de lactose (P < 0,05) e os sólidos totais (P < 0,01) no ensaio II e, efeito de tratamento sobre os níveis de gordura, a proteína, os sólidos totais (P < 0,01) e a lactose (P < 0,05) no ensaio III. Para a contagem de coliformes totais, houve efeito de tratamento (P < 0,01, ensaio I; P < 0,01, ensaio III), de tempo de conservação (P < 0,05, ensaios I e II; P < 0,01, ensaio III) e da interação tratamento x tempo (P < 0,05, ensaio III). Para a contagem de psicrotróficos observou-se efeito de tratamento (P < 0,05) e de tempo de conservação (P < 0,01). O SLP inibiu o crescimento da população de coliformes em leite cru não-refrigerado e manteve o nível de acidez dentro dos limites aceitáveis até 8 horas, dependendo da qualidade inicial do leite. Em leite cru refrigerado o efeito inibitório do SLP sobre a contagem de coliformes totais foi prolongado até 120 horas e a acidez foi mantida dentro dos limites aceitáveis até 48 horas pós-ativação. Não foi observado efeito do SLP sobre a população de psicrotróficos ao longo dos tempos de conservação. O SLP não alterou as concentrações iniciais de gordura, proteína, lactose e sólidos totais, em todos os ensaios realizados, e conseguiu evitar que ocorresse degradação de tais componentes por períodos de até 120 horas, em leite cru refrigerado.