Lipolysis during Ripening of Emmental Cheese Considering Organization of Fat and Preferential Localization of Bacteria

Abstract

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 degrees C, 28 days at 21 degrees C, and 8 days at 4 degrees C. Lipolysis, which corresponded to 1.56% of fat, mainly occurred in the 21 and 4 degrees 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 > or =1%. 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.

Spatial Distribution of Bacterial Colonies in a Model Cheese

“…The addition of fat will create a heterogeneous matrix with two phases. Colonies may not be evenly distributed, as it was previously shown that bacterial colonies were located at the fat-protein interface (8,19), and these were not spherical. The interfacial area would also be increased because of their shape.…”

“…Consequently, the ripening process must take place on a microscopic scale around colonies. Only studies showing microscopic examinations of bacterial colonies in cheese either by electronic microscopy (24) or, more recently, by confocal laser scanning microscopy (7,19) have been reported.…”

Effect of Wild Strains Used as Starter Cultures on Free Fatty Acid Profile of Urfa Cheese

“…All these factors activate the membrane-bound lipoprotein lipase and thus trigger enzymatic hydrolysis of milk fat [Hassan et al, 2013;Lopez et al, 2006].…”

“…Lipolysis in cheese is a result of action of biolytic enzymes called hydrolases (lipases and esterases) that split the ester linkage between a fatty acid and the glycerol moiety of the triacylglycerol [Lopez et al, 2006;McSweeney, 2004]. Among the short-chain free fatty acids propionic, butyric, isobutyric and iso-valeric acids play active role in aroma formation; the medium-chain free fatty acids, such as hexanoic, octanoic and decanoic acids, are visibly arisen from the lipolytic breakdown of milk fat [Randazzo et al, 2008].…”

Following Pathogen Development and Gene Expression in a Food Ecosystem: the Case of a Staphylococcus aureus Isolate in Cheese

“…Fluorescence in situ hybridization with 16S rRNA provides microbial identification and physical detection of uncultivable microorganisms in fragile matrices like cheese (32), and its use is being expanded to pathogens in different environments (33)(34)(35). The spatial distribution of bacterial flora in cheese has also been explored by using scanning electron mi-croscopy, fluorescence and light microscopy, and laser scanning microscopy (36)(37)(38)(39)(40). An in situ approach used to investigate the spatial distribution of bacterial colonies of fluorescent Lactococcus lactis in a solid-food matrix with a model system has been recently developed (41), demonstrating that live cells can be visualized in cheese.…”