Studies on the Flavour of Yogurt Fermented with Bifidobacteria

Significance of Volatile Components and Organic Acids in the Sensory Acceptance of Yogurt

Abstract

Fermented milk was prepared by incubating sterilized milk with a single starter culture consisting of one of 5 strains of Bifidobacterium, Lactobacillus bulgaricus or Streptococcus thermophilus, or with their mixed starter culture in a sealed vessel. The volatile components in the top gas space in the vessel were analyzed directly by capillary gas chromatography. Acetaldehyde and diacetyl were commonly produced in all the fermented milk, while only a few bacterial strains produced ethanol. In the single starter culture study, the highest activity in acetaldehyde evolution was recognized in the case of fermentation with B. breve ATCC 15700, whereas the fermentation of milk with B. longum BB-536 caused outstanding ethanol production. Incubation with the mixed starter culture stimulated the production of acetaldehyde and diacetyl. Ethanol production was, on the other hand, lower than via fermentation with the single starter culture with the mixed starter culture of bifidobacteria, S. thermophilus and L. bulgaricus. Milk products fermented with the mixed starter culture achieved a higher score in the sensory acceptance evaluation than did those fermented with the single starter culture of bifidobacteria. In order to exhibit favorable palatability for yogurt fermented with bifidobacteria, it is desirable to employ additional the starter cultures of S. thermophilus and L. bulgaricus which are broadly used in yogurt manufacturing.