Natural Milk lipase: influence of its activity on the free fatty acids and volatile compounds profiles of cheeses during ripening.

PEROTTI MARÍA CRISTINA; VÉLEZ MARÍA AYELÉN; WOLF IRMA VERÓNICA; CANDIOTI MARIO CÉSAR; HYNES ERICA RUT; ZALAZAR CARLOS ANTONIO

Praga, República Checa.

Congreso; 4th International Symposium on Recent Advances on Food Analysis.; 2009

Institute of Chemical Technologi Prague, International Association of Environmental Analytical Chemistry, Rikilt Institute of Food Safety

Moderated lipolysis is a desirable event during ripening of hard cooked cheeses, as it increases piquant taste and genuine flavour. Milk possesses an indigenous lipolytic enzyme, the lipoprotein lipase (LPL), which is associated to casein micelle. However, its activity on triglycerides is limited because milk fat is protected by the milk fat globule membrane (MFGM). 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 accessibility enzyme-triglycerides. These factors were studied by comparing pasteurized milk and non thermally-sanitized milk, and milk with native and damaged MFGM. The free fatty acids (FFA) were assessed by gas chromatography (GC-FID) as ethyl esters and quantified with the internal standard method at the beginning and the end of the ripening. Volatiles compounds were isolated by microextraction 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 similarly during ripening. However, the profiles of FFA showed differences in the relative proportions of the FFA groups. In particular, the proportion of short chain fatty acids (SCFA) was higher in cheeses made with no-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 triglyceride, where SCFA are esterified. Similar results were obtained for most volatile compounds in the groups of ketones, alcohols, esters and acids. In cheeses made with non-heated milk and with native fat, the proportion of SCFA and the levels of the volatile compounds were in general higher than those found in cheeses made with milk in which the MFGM was damaged. However, the opposite behaviour was found for some compounds derived from fat lipolysis, in cheeses 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.