Variable Growth and Acid Production of Lactococci in Whole Milk Concentrated by Ultrafiltration and Diafiltration

¹ Western Center for Dairy Protein Research and Technology, Department of Nutrition and Food Sciences, Utah State University, Logan 84322-8700

Growth and acid production of several commercial strains of Lactococcus lactis ssp. were followed in whole milk, and whole milk retentate containing 32% solids, diafiltered to reduce lactose content. Generation times of some strains were longer in retentate than in whole milk.

Because of the importance of acid production rates in cheese making, increased buffer capacity of UF retentate, and the potential for bacteriophage infection, starter growth and acid production in retentate should be considered before starter blends are used to make UF cheese.

Growth rates of each strain in retentate should be considered when starter blends to be grown in UF retentate are formulated. Equal inocula of two unmatched strains can result in domination by one strain by as much as 96:4 after bulk starter has been grown to high cell density. To avoid serious problems with starters in UF retentate, blends should be formulated using strains with similar growth characteristics in UF retentate, or strain ratios should be adjusted to provide viable final numbers of all strains in a given blend.

Key Words: ultrafiltration • starter • mesophiles • retentate

Submitted on November 1, 1993
Accepted on May 31, 1994