Streptococcus thermophilus in Cheddar cheese - production and fate of galactose

The behaviour of Streptococcus thermophilus in combination With Lactococcus lactis subsp. cremoris or subsp. lactis mesophilic starters in experimenta l Cheddar cheese is reported. In a standard manufacturing procedure employi ng a 38 degreesC cook temperature. even very low levels (0.007%) of Str. th ermophilus; combined with normal levels of the mesophilic starter (1.7%) re sulted in increased rates of acid production, the formation of significant amounts of galactose (similar to 13 mmol/kg cheese), and populations nearly equivalent to those of the mesophilic lactic starter iii the curd before s alting. At a 41 degreesC cook temperature. the Str. thermophilus attained a higher maximum population (similar to log 8.2 colony forming units (cfu)/g ) than the Lc. lactis subsp. cremoris (similar to log 6.8 cfu/g) and formed more galactose (similar to 28 mmol/kg). Lactobacillus rhamnosus, deliberat ely, added to a cheese made using Str. thermophilus starter and which conta ined 24 mmol galactose/kg at day one, utilized all the galactose during the first 3 months of cheese ripening. Adventitious non-starter lactic acid ba cteria had the potential to utilize this substrate too, and a close relatio nship was demonstrated between the increase in this flora and the disappear ance of the galactose. Some possible consequences for cheese quality of usi ng Str. thermophilus as a starter component are discussed.