Examination of the Microbiome and Slit Defects in Hard Cheddar Cheese During 12 Months of Storage

To Chiu

doi:10.7273/000005052

Late blowing defect (LBD) and slit formation in Cheddar cheese during aging cause substantial loss to the cheese industry. Cheese flavor adjunct cultures were tested for their inhibitory effects over LBD spoilers. Clostridium butyricum, Cl. pasteurianum, Cl. tyrobutyricum, and Paucilactobacillus wasatchensis are known causes of LBD. Spoilers were inoculated in cell-free supernatant (CFS) from the commercial lactic acid bacteria (LAB) to test the inhibitory effects of metabolites from adjuncts, pH adjusted to 5 or 7. While metabolites can inhibit spoiler growth, their inhibitory abilities depend on LAB strains and pH. At pH 5, CFS of CR540, Flavogard 360, MC 71, and SCP5 completely reduced Cl. tyrobutyricum and Plb. wasatchensis to below detection, while 2.31-2.50 log10 CFU/ml of Cl. butyricum and Cl. pasteurianum survived. ADD EZ-AGE inhibited Cl. tyrobutyricum to 0.88 CFU/ml and completely inhibited Plb. wasatchensis at pH 5. At pH 7, CFS of CR540, Flavogard 360, MC 71, and SCP5 reduced all four spoilers to below detection, while CFS of ADD EZ-AGE could not completely inhibit spoilers. For the cheese storage experiment, cheeses were made with four different formulas: bulk starter (MC 58 or MC71, Flavobac 302, and Flavogard 360); bulk starter with Delvo Added Salvory, with SCP5, or with CR 540. The cheeses were subjected to 14.1 hours of cooling at 4°C and part of the CR 540 treatment was subjected to 22.8 hours of cooling. Cheese samples were taken to enumerate spores and LAB and to elucidate their microbiome. The V1-V3 region of the 16S rRNA gene was sequenced for analysis of the cheese’s microbiome. Low and decreasing spore counts in all treatments suggested that Clostridium species were not the spoiler. Streptococcaceae and Lactobacillaceae dominated the cheeses’ microbiome at the family level, while Lactococcus and Lactobacillus dominated the genus level. Lactococcus lactis is the dominant species and decreased with aging for all treatments. Adjunct cultures shared the unique microbe community of each cheese. The slit portion of SCP5 had higher alpha diversity than the intact part at 3 and 6 months. The start of slit formation coincided with the decrease of LAB count on MRS count and >2% decrease of relative abundance of Lactobacillus helveticus, suggesting their relations. Cheese with extra cooling had significantly fewer slits. Further studies are recommended to analyze the effects of Lb. helveticus reduction and gas production by the spoiler during cheese aging, and their roles in LBD.

Examination of the Microbiome and Slit Defects in Hard Cheddar Cheese During 12 Months of Storage

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