| Ethyl esters are among the most common esters formed in cheese. Accumulation of ethyl butanoate and ethyl hexanoate in Italian cheeses, such as Parmesan and Grana Padano, contribute to the characteristic fruity flavors of these cheeses, whereas accumulation of these ethyl esters in Cheddar cheese leads to fruity off-flavors. The enzymatic and environmental parameters influencing the formation of these ethyl esters in cheese are poorly understood. Esterases and lipases are capable of both synthesizing and hydrolyzing esters. It is well established that hydrolysis of milkfat by lipases leads to the development of fatty acid (FA) flavors in cheese. However, it has not been unequivocably demonstrated that esterases and lipases from lactic acid bacteria (LAB) are responsible for ester formation in cheese.; To initiate research in this area, esterases from Lactobacillus helveticus CNRZ32 (Lbh-EstA), Lb. casei (EstB and EstC), and Lactococcus lactis (Lcl-EstA) were characterized at the nucleotide and protein level. Lbh-EstA, EstB, EstC, and Lcl-EstA hydrolyzed ethyl esters with FA chain-lengths of C2–C4, C6, C2–C6, and C4–C6, respectively. Also, Lbh-EstA, EstB, EstC, and Lcl-EstA mediated the accumulation of ethyl butanoate, ethyl pentanoate, and ethyl hexanoate in a model system simulating Parmesan cheese ripening conditions (10°C, 2–3% NaCl, pH 5.4–5.5, water activity (aw) of 0.850–0.925). Accumulation of ethyl esters by these enzymes in the model cheese system was enzyme-specific and dependent on aw. EstB and Lbh-EstA mediated the highest and lowest levels of ethyl butanoate, ethyl pentanoate, and ethyl hexanoate accumulated in the model cheese system, respectively. Enzyme-mediated accumulation of ethyl esters was higher at aw values of 0.850 and 0.900 than at 0.925. Given the selectivity of Lbh-EstA, EstB, EstC, and Lcl-EstA for both hydrolysis and synthesis of ethyl esters, it was concluded that these enzymes could influence cheese flavor development through modulation of ester profiles in cheese. |
