PRODUCTION OF MIXED CULTURES OF NON-ISOGENIC LACTOCOCCUS-LACTIS SSP CREMORIS USING IMMOBILIZED CELLS

Mixed cultures of non-isogenic proteinase-positive (E8) and proteinase -negative (HP) strains of Lactococcus lactis ssp. cremoris containing a variety of strain ratios were prepared using either released or free cells. After 10 h of fermentation in skim milk and milk-based medium, the growth of released proteinase-positive E8 cells was higher than p roteinase-negative HP resulting in an increase in the relative proport ion of proteinase-positive E8. The strain ratio of the mixed culture p repared with released cells remained constant during 6-h activity test in skim milk, whereas with the mixed culture prepared with free cells , the proportion of proteinase-positive E8 decreased. Maximum specific growth rates for strain E8 and specific productivity of lactic acid w ere higher, and lactic acid production was lower with released cells h arvested in the fermented milk-based medium compared to free cells obt ained in fermented milk-based medium. The technique of cell immobiliza tion could be used to produce active mixed starter cultures with the d esired proportion of strains.