Abstract:The effect of Lactobacillus acidophilus KLDS 1.0901 on the characteristics and antioxidant activity of yoghurt during fermentation was studied，and a yoghurt starter with strong antioxidant activity was developed.Yogurt was prepared by fermentation of Streptococcus thermophilus S1 and Lactobacillus germanica subspecies KLDS 1.0207 and by co-fermentation of Lactobacillus acidophilus KLDS 1.0901. The acidity and viable bacteria were evaluated，and the physical properties，acetaldehyde and diacetyl production of the yogurt were analyzed.Sensory evaluation was carried out.Finally，the antioxidant activity of yogurt in vitro was explored and studied，and then the fermentation performance and antioxidant ability of Lactobacillus acidophilus KLDS 1.0901 to fermented yogurt were compared. The yoghurt fermented with Streptococcus thermophilus S1，Lactobacillus germanica subspecies KLDS 1.0207 and Lactobacillus acidophilus KLDS 1.0901 had fast acidification rate and curd milk for 5 hours.Compared with yoghurt fermented without Lactobacillus acidophilus KLDS 1.0901，the number of live Lactobacillus bacteria was 3.55× 108 CFU/g and the content of acetaldehyde，the flavor substance.The content of diacetyl was 7.5 ug/mL，22.8 ug/mL，and the sensory score was 86 points，which was second only to Hansen Fermentation No.3.Compared with No.3 Hansen starter，the addition of No.2 starter KLDS 1.0901 has similar antioxidant activity in vitro，which can play an important role in scavenging free radicals and has potential for industrial development.