Microflora and acidification properties of yogurt and yogurt-related products fermented with commercially available starter cultures

Abstract

Yogurts and yogurt-related milk products were produced using 44 commercially available starter cultures from 8 suppliers. The yogurt starters consisted of the classical yogurt microflora and the yogurt-related cultures containing Lactobacillus acidophilus and/or Bifidobacterium spp. instead of or in addition to the yogurt bacteria. The counts of lactobacilli in the fresh yogurts varied between 5.5 × 10 7 and 6.5 × 10 8 CFU/ml, and the counts of streptococci varied from 3.5 × 10 7 to 1.2 × 10 9 CFU/ml. About 80% of the yogurts had higher counts of cocci than rods. During storage of the products for 2 weeks at 6°C the stability of the microflora differed markedly among the cultures. In the fresh yogurt-related products the L. acidophilus counts ranged from 4.0 × 10 5 to 2.6 × 10 8 CFU/ml; bifidobacteria were found at levels between 4.0 × 10 6 and 2.6 × 10 8 CFU/ml. In most products reduced viable counts of these bacteria were observed after 2 weeks. Titratable acidity increased on average by 22.3% in the yogurts, and by 14.9% in the yogurt-related products during storage. In most products a higher amount of L(+)- than D(−)-lactic acid was found.