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Natural Milk lipase: influence of its activity on the free fatty acids and volatile during ripening
Praga, República Checa
Simposio; Recent Advances in Food Analysis; 2009
Moderated lipolysis is a desirable event durig ripening of hard cooked cheeses, as it increases piquant taste and genuine flavour. Milk possesses an indigenous lipolytic enzyme, the lipoprotein lipase, which is associated to casein micelle. However, its activity on triglycerides is limited because milk fat is protected by the milk fat globule membrane. This work was aimed at increasing fat hydrolysis and flavour compounds production in hard cheeses by increasing LPL activity and improving its access to milk triglycerides. For this purpose, hard cheeses (Reggianito type) were produced in pilot plant and ripened during 90 days. The influence of two different factors was studied: the method of milk sanitization and the accesibility enzyme-triglycerides. These factors were studied by comparing milk with nativ and damaged MFGM, and pasteurized milk with non-thermally sanitized milk. The free fatty acids (FFA) were assessed by gas chromatography (GC-FID) as ethyl esthers and quantified with the internal standard method at the beggining and the end of the ripening. The volatile compounds were isolated by microestraction in solid phase (SPME) and analysed by GC-FID/MS. The areas were quantified in arbitrary units. For all cheeses, it was observed that the degree of lipolysis increased during ripenig, being similar for all treatments. However, the profiles of FFA showed differences in the relative proportions of the FFA groups. In particular, the percentage of short chain fatty acids (SCFA), was higher in the cheeses made with non-thermally treated milk than in those made with pasteurized milk. This fact suggests that LPL played a role in lipolysis, as it has a positional specificity to the sn-3 position of the trigliceryde, where SCFA are estherified. Similar results were obtained for most of the volatile compounds that constitute the groups of ketones, alcohols, esthers (derivated of FFA catabolism) and the group of acids (derivated of lipolysis). Overall, the greatest area values were obtained for the cheeses made with no pasteurized milk. In cheeses made with no heated milk and with native fat, the percentage of SCFA and the levels of the volatile compounds were in general higher than those found in cheess made with pasteurized milk. In the conditions of the study, results suggest that thermal treatment had a higher impact on cheese lipolysis and volatile compounds production than the destabilization of the fat emulsion.