Lipolysis during ripening of emmental cheese considering organization of fat and preferential localization of bacteria
Résumé
This study followed the progression of lipolysis in Emmental cheese by quantifying the concentrations of individual free fatty acids (FFA) released during ripening in each of the different rooms: 12 days at 12 °C, 28 days at 21 °C, and 8 days at 4 °C. Lipolysis, which corresponded to 1.56% of fat, mainly occurred in the 21 and 4 °C rooms, with 68 and 16.5% of total FFA, respectively. The nonselectivity of lipolytic enzymes was evidenced: all fatty acids were released with level of g1%. Differential scanning calorimetry experiments showed that the thermal properties of cheese were affected by (i) lipolysis of fat, that is, the monoacylglycerols, diacylglycerols, and FFA that may be localized at the fat/whey interface, and/or by (ii) hydrolysis of high-melting-point triacylglycerols constituted mainly by long-chain saturated fatty acids (e.g., palmitic acid). Analysis of the cheese microstructure was performed using confocal laser scanning microscopy. Fat globules were mainly disrupted after pressing of curd grains, leading to the release of the milk fat globule membrane (MFGM); fat inclusions were surrounded by pockets of whey, delimited by casein strands. Moreover, colonies of bacteria were preferentially localized in situ at the fat/protein interface. This study showed that both the localization of bacteria and the supramolecular organization of fat which was not protected by the MFGM can help the accessibility of milk fat to lipolytic enzymes and then contribute to the quality of cheese.