DETERMINATION OF GROWTH-PARAMETERS OF LACTOCOCCI IN MILK AND ULTRAFILTERED MILK

Fresh skim milk and a highly standardized skim milk powder (Nilac) wer e ultrafiltrated at 50-degrees-C to concentration factors of approxima tely 2, 2.5, 3.5, and 4.5, based on total protein. Growth characterist ics of Lactococcus lactis ssp. cremoris E8 and the mesophilic mixed-st rain Bos starter culture were investigated in the UF retentates and no n-UF skim milk under conditions of regulated pH. The maximum specific growth rate and the maximum specific acidification rate showed extreme variation and, therefore, could not be used to measure the effect of UF on the growth characteristics of L. lactis ssp. cremoris. The mean total growth of strain E8 and the Bos mixed-strain starter after 22 h decreased by 25 and 40%, respectively, in UF retentate with a concentr ation factor of 3.6 compared with growth reached in regular skim milk. Part of this effect could be explained as growth inhibition from the higher concentration of whey proteins in the UF retentates.