Abstract:Lactic acid bacteria fermented fruit and vegetable juice has become an essential food in daily life because of its greenness，health and nutrition.China's pear planting industry is extensive，the yield is high，and the pear itself nutrients are comprehensive，so this study used three kinds of complex probiotics to develop a fermented pear juice beverage. Firstly，the fermentation agent of the dominant strains was prepared and the optimum process was optimized.The optimal process was as follows：feed velocity ratio of protective agent for：monosodium glutamate 2 %，trehalose 5 %，lactose 5 %，10 % skim milk，the ratio of protective agent and bacterial mud was 3∶1（mL/g），under these conditions，get bacteria powder starter bacteria live for：8.48×109 cfu/g.Secondly，the fermentation process of pear pulp was optimized，and the best process was as follows：Lactobacillus plantarum 299：Lactobacillus delbrueckii subsp.Bulgaricus 717：Streptococcus thermophilus 176（volume ratio）=4∶1∶1，inoculation amount was 8%，the fermentation temperature of 37 ℃，fermentation time 72 h.Under these conditions，pear pulp was fully fermented with outstanding taste and sour and sweet flavor.Finally，the organic acid changes of pear pulp before and after fermentation were determined the organic acids rich in pear pulp before fermentation are citric acid，malic acid，lactic acid and oxalic acid.Among them，malic acid and citric acid have dominant organic acids，with contents of 36.49 mg/100 g and 38.59 mg/100 g respectively.After fermentation by three kinds of lactic acid bacteria，the organic acid content in pear pulp changed，and the organic acid content was successively：lactic acid，citric acid，malic acid and oxalic acid. The lactic acid content increased from 1.65 mg/100 g to 116.27 mg/100 g.