Abstract:

Co-culture of Lactobacillus plantarum (L.p) with antioxidant ability and Streptococcus thermophilus (S.t) was
used to produce yogurt with antioxidant activity. The culture conditions temperature, inoculum size, and L.p to S.t ratio
were examined. By measuring the inhibition of thiobarbituric acid reactive substances (TBARS), reducing power, metal ion
chelating capacity and 1,1-diphenyl-2-tridinitrophenylhydrazine (DPPH) radical scavenging capacity, the antioxidant activity
of yogurt was evaluated, and the control of its postacidification by temperature was also discussed. The results showed that
a yogurt with the best quality and controlled postacidification at 5 ℃ was obtained when the fermentation was carried out at
43 ℃ using an inoculum size of 2% at an L.p to S.t ratio of 1:1.5. The yogurt fermented by L. p and S. t at the ratio of 1:1.5
had the highest antioxidant activity.

Key words: antioxidant activity, yogurt, fermentation conditions, optimization