Screening and Validation of Flavor-forming Starter Bacteria for Korean Gouda-type Cheese Model

Abstract

Lactic acid bacteria (LAB) have an important role in dairy fermentations, notably as cheese starter cultures. They cause not only rapid acidification and coagulant of milk through the production of lactic acid, but also flavor formation. Cheese flavor results from a complex combination of flavor compounds. The flavor compounds in cheeses are derived from milk composition which is mainly composed of lactose, milk casein, and milk fat. During cheese production and ripening period, various enzymes from milk, rennet, starter cultures, and non-starter LABs are involved in the flavor formation pathways

glycolysis, proteolysis, and lipolysis. Among these three pathways, starter LABs are especially related into amino acids degradation, presumably the origin of major flavor compounds. Therefore, specific key enzymes (AdhE

Bifunctional Alcohol/Aldehyde dehydrogenase, BcaT

Branched chain aminotransferase, AraT

Aromatic aminotransferase, EstA

Esterase, Adh

Alcohol dehydrogenase, CitP

Citrate permease, KdcA

Keto acid decarboxylase) appear to be major criteria for the selection of flavor-forming starter bacteria. By using the multiplex PCR assay for detection of genes for those enzymes, 44 of flavor-forming LAB strains were screened. Among them, the most putative strains which have a possibility to flavor formation in cheese were selected. They were four of Lactococcus lactis subsp. lactis strains and one of Lactococcus lactis subsp. cremoris strain. Each of five strains were further characterized and assessed for industrial use. The combinations of starter bacteria were validated in miniature Gouda-type cheese model. Flavor compounds of tested miniature cheeses were analyzed and profiled by using the Hercules Ⅱ electronic nose (Alpha M.O.S., France). Compared to industrial cheese starter (CHN-11, Chr.hansen, Denmark), selected flavor-forming starter bacteria showed more variety flavor profile. Methylbutanone and 1-propanol, 2-methyl- was only found in test groups. Among the test groups, flavor profile of Test 1 evolved most at the last day of ripening.