Growth and Activity of Lactococcus lactis ssp. cremoris in Ultrafiltered Skim Milk

Abstract

Ultrafiltration of milk causes physico-chemical and compositional changes in the concentrated product. Ultrafiltration of skim milk to give concentration factors 1 to 5 caused an increased buffer capacity as concentration increased. Milk proteins (casein and whey proteins) and minerals (calcium, phosphorus, magnesium, potassium, and sodium) increased with the increased concentration, NPN remained fairly constant, and lactose content decreased slightly. The effect of concentration of UF retentate on growth, lactic acid production, and proteolytic activity of Lactococcus lactis ssp. cremoris strains 103, 108, and 208 was determined. By using large inocula to overcome high buffer capacity of higher concentration retentates, there was an uncoupling of growth from lactic acid production. Although large amounts of lactic acid were produced in higher concentration retentates, the high buffer capacity resisted the change of pH. A simulated Cheddar cheese manufacturing test was used to determine inoculum size of starter cultures necessary to give the desired pH change in UF retentates. It was possible to overcome the effect of buffer capacity up to concentration factor 4 by use of increased inoculum size of strongly proteolytic strains, but for retentate of concentration factor 5 the use of a 10% inoculum failed to overcome the buffer effect.