English abstract
The present study analyzed microbial groups, physico-chemical characteristics, proteolysis, lipolysis and rheological properties over a 30-day ripening period of a standard semi hard cheese made from pasteurized goat's milk. The cheese was manufactured from pasteurized milk by a standard method and ripened over a 30-day period at controlled temperature and humidity.
The microbial groups of technological interest (aerobic mesophilic , flora, lactococci, lactobacilli, micrococcaceae, coliforms and molds and yeasts) were enumerated. With the exception of coliforms and micrococaccacea, high counts of all other microbial were observed. The total bacteria counts were high in cheese throughout ripening, with lactic acid bacteria being the main microbial group. Total and faecal coliforms were completely absent throughout ripening indicating that they do not play any role in the development of the cheese characteristics. Microcaccacea showed initial low counts but maintained their levels relatively constant during the ripening period.
The main biochemical modification of cheese during ripening was related to the extent of proteolysis. The water soluble nitrogen (WSN) and non-protein nitrogen (NPN) (trichloroacitic acid nitrogen (TCAN)) in the semi hard cheese increased during ripening; after 1 month, the percentage of (WSN) was 40.6 % and the NPN fraction accounted for 11.04 % of the total nitrogen. Lipolysis was insignificant and remained constant throughout the ripening period studied. The total FFA content at the end of ripening was 9.87 g oleic acid / 100 g fat. A fast decrease in the pH of the cheese was observed during the ripening period.
The rhelogical study suggested that the most important factors that may influence the texture of the goat cheese is the level of total solids and the extent of protein degradation recorded as soluble nitrogen during the ripening period. Rheological properties of goat's cheese showed a transformation from a soft and elastic consistency to a hard and brittle body as a function of aging from day 8 to day 30 of production.
This study will contribute to the general knowledge of cheese made of pasteurized goat's milk. It also will help the Omani farmers to apply the new technology of making cheese and to control the conditions of production and storage.
