Effect of pasteurization and high pressure in donkey milk and colostrum

• Autor(a) principal: Gonçalves, Mafalda Sofia Mendes
• Data de Publicação: 2013
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/12599
• topic: Biotecnologia; Leite; Pasteurização; Microorganismos

When breast-feeding is not possible or after weaning, finding an adequate alternative nourishment becomes mandatory. Commercial infant formulas have been developed as nutritional substitutes for breast milk. Actually, clinical studies have demonstrated that donkey milk could substitute breast feeding in infants affected by severe IgEmediated cow milk allergies, whose composition is very similar to breast milk. High-pressure processing (HPP) is a non-thermal technology that can provide safe foods with similar characteristics to the unprocessed foods, causing microbial inactivation while maintaining its nutritional and functional properties. The main goal of this work was to investigate and compare the effect of thermal pasteurization and HPP (400, 550 and 625 MPa for 2.5, 10 and 30 min at 8 °C) on microbial quality, in immunoglobulin A, M and G (IgA, IgM and IgG) concentrations and lysozyme activity in donkey milk and colostrum. The microbiological results indicated that the log of CFU/mL of the raw milk were already above the maximum values allowed at the 6th day of storage, while total aerobic mesophilic bacteria, Enterobacteriaceae and Coliforms for the thermal pasteurized milk were 4.21, 3.0 and 4.04 log CFU/mL at the 30th day of storage, respectively. In raw colostrum total aerobic mesophilic bacteria and Enterobacteriaceae, were detected above the maximum values allowed at the 4th and 7th day, respectively. HPP (400 and 550 MPa at 8°C, for 10 min) inactivated all the quantified microorganisms to values below the detection levels up to at least the 30th day for milk and 40th for colostrum. Regarding the activity of lysozyme it was observed that in the milk its activity was kept in all AP treatments used for pressurization for 2.5 and 10 min. At 30 min occurred a decrease of about 30 to 40%. In the case of colostrum there was a greater reduction at 625 MPa, 10 and 30 min (40%). The thermal pasteurization, on the other hand, resulted in significant loss of the activity, especially in the colostrum (40%). In relation to the content of IgA in both the colostrum and milk, it was observed only in samples not processed. At 625 MPa (10 and 30 min) IgM was not detected in colostrum and IgG not detected. In colostrum, IgG values were higher than the unprocessed sample at 550 (2.5 and 10 min, 208% and 143%) and at 625 MPa (10 and 30 min, 412% and 260%). This work demonstrates that pressure treatments at the level necessary for milk pasteurization (up to 550 MPa/10 min) can guarantee microbial safety and preserve lysozyme activity and IgG content, being a good alternative to thermal pasteurization.