Galactose-positive adjunct cultures prevent gas formation by Paucilactobacillus wasatchensis WDC04 in a model gas production test

摘要

Gas production by obligatory heterofermentative lacticacid bacteria such as Paucilactobacillus wasatchensisis a sporadic problem in Cheddar cheese and results inundesired slits and cracks in the cheese. Growth of Pa.wasatchensis is not rapid, which makes investigationsof gas production difficult to consistently execute. Aprimary objective of this study was to develop a modelgas production test that could be used to investigatethe effect of galactose and ribose utilization on gasproduction by Pa. wasatchensis and determine whethergalactose-fermenting adjunct cultures could prevent gasformation. Paucilactobacillus wasatchensis WDC04 wasinoculated at 10~1 to 10~6 cfu/mL into carbohydrate-restrictedMRS broth containing different ribose and galactoselevels and incubated for up to 21 d at 23°C. Gasproduction in the broth was detected using a Durhamtube inverted on a 6-cm-long capillary tube; cells wereenumerated at 4, 8, and 12 d; and residual galactosewas also measured. Gas production was sporadic exceptfor when 10~5 cfu/mL of Pa. wasatchensis WDC04 wasinoculated into broth containing 0.3% ribose and 0.7%galactose. In those tubes, gas production was consistentlyobserved after 8-d incubation, by which timegalactose levels had decreased to 0.15%. Co-inoculationof Pa. wasatchensis WDC04 with as few as 10~3 cfu/mLof a lactose-negative galactose-positive adjunct culture(Pediococcus acidilactici 23F, Lacticaseibacillus paracaseiUW4, or Lactobacillus helveticus 7995) resultedin galactose depletion by d 4 and no observable gasproduction by d 12. With less galactose available to theslower-growing Pa. wasatchensis WDC04, its growthwas limited to 10~8 cfu/mL when any of the adjunctcultures was co-inoculated, compared with 10~9 cfu/mLwhen grown on its own. We concluded that galactosefermentingadjunct cultures have potential for preventingunwanted gas production in cheese by competitionfor resources and especially by removing the 6-carbongalactose before it can be utilized for energy by anobligatory heterofermentative lactobacilli such as Pa.wasatchensis and produce carbon dioxide.