Abstract:

Lactobacillus reuteri with antimicrobial activity against Penicillium as spoilage bacteria in yoghurt was screened
and the major antimicrobial substances produced by the dominant strain were determined by exclusion tests. Then, the
dominant strain was applied as an adjunct culture to fermented milk. Meanwhile, physical and chemical properties and
sensory quality of the yoghurt as well as the antiseptic effect of the dominant strain on it were studied. Results showed
that Lactobacillus reuteri CICC6121 was the dominant strain against Penicillium. The antimicrobial substance in cellfree
supernatant was reuterin. CICC6121 did not show any antagonism against Lactobacillus bulgaricus or Streptococcus
thermophilus during yoghurt fermentation. The physicochemical properties and sensory quality of yoghurt inoculated and
not inoculated with CICC6121 were nearly the same. During 21 days of cold storage, CICC6121 could inhibit the growth of
Penicillium significantly and avoid yoghurt spoilage via contamination.

Key words: yoghourt spoilage organisms, bacteriostatic effect, Lactobacillus reuteri, sensory quality of yoghourt, biopreservation