Effect of oxidation-reduction potential on the growth of starter and nonstarter lactic acid bacteria

Cheddar and other bacterial-ripened cheeses commonly contain high numbers of nonstarter lactic acid bacteria (NSLAB) that enter cheese through processing equipment or milk. Although NSLAB can have a significant effect on flavor development, little is known about the factors that influence the growth and composition of the nonstarter biota in cheese. Thus, the complexity and numbers of NSLAB in cheese, and their effect on cheese quality, are largely a matter of chance. One factor that may affect NSLAB population dynamics is oxidation-reduction potential (Eh). This study examined the relationship between starter or NSLAB growth and medium Eh in a laboratory-scale bioreactor. Results showed growth of Lactococcus lactis S2, Lactobacillus casei Lila, and Lb. casei ATCC 334 produced a steady increase in medium Eh, whereas Eh fluctuated during growth of L. lactis SCO 213 or Lb. casei M36. Lactobacillus curvatus S76 had little effect on medium Eh. Growth of two Lb. casei nonstarter strains, ATCC 334 and M36, was also examined at two pre-selected Eh values (150 and -50 mV). In those experiments, a positive Eh (150 mV) had no effect on growth of Lb. casei ATCC 334, but retarded Lb. casei M36 growth in early log phase. In contrast, a negative Eh environment (-50 mV) retarded growth of Lb. casei ATCC 334 in early log phase and also hindered growth of Lb. casei M36 in late log phase. Overall, these results suggest it may be possible to select starter/adjunct combinations that predictably alter E h in a manner that favors dominance of the adjunct culture and helps control "wild" NSLAB populations.