Research Article

Behavior and viability of spontaneous oxidative stress-resistant Lactococcus lactis mutants in experimental fermented milk processing

Abstract

Previously, we isolated two strains of spontaneous oxidative (SpOx2 and SpOx3) stress mutants of Lactococcus lactis subsp cremoris. Herein, we compared these mutants to a parental wild-type strain (J60011) and a commercial starter in experimental fermented milk production. Total solid contents of milk and fermen­tation temperature both affected the acidification profile of the spon­taneous oxidative stress-resistant L. lactis mutants during fermented milk production. Fermentation times to pH 4.7 ranged from 6.40 h (J60011) to 9.36 h (SpOx2); Vmax values were inversely proportional to fermentation time. Bacterial counts increased to above 8.50 log10 cfu/mL. The counts of viable SpOx3 mutants were higher than those of the parental wild strain in all treatments. All fermented milk prod­ucts showed post-fermentation acidification after 24 h of storage at 4ºC; they remained stable after one week of storage.

Previously, we isolated two strains of spontaneous oxidative (SpOx2 and SpOx3) stress mutants of Lactococcus lactis subsp cremoris. Herein, we compared these mutants to a parental wild-type strain (J60011) and a commercial starter in experimental fermented milk production. Total solid contents of milk and fermen­tation temperature both affected the acidification profile of the spon­taneous oxidative stress-resistant L. lactis mutants during fermented milk production. Fermentation times to pH 4.7 ranged from 6.40 h (J60011) to 9.36 h (SpOx2); Vmax values were inversely proportional to fermentation time. Bacterial counts increased to above 8.50 log10 cfu/mL. The counts of viable SpOx3 mutants were higher than those of the parental wild strain in all treatments. All fermented milk prod­ucts showed post-fermentation acidification after 24 h of storage at 4ºC; they remained stable after one week of storage.