Screening Of Lactic Acid Bacteria From Prunes Puree And Development Of Fermented Low Sugar Prunes Jam

As one of the characteristic fruits and vegetables in Xinjiang,prunes have abundant yields,but prunes are relatively unstorable,and some prunes are not suitable for fresh eating.At present,there are few processed products of prunes in the market,and the resource advantages and value of prunes are not fully reflected and utilized.The development and utilization of products using prunes as raw materials can improve the economic benefits of the prunes industry.In this study,the lactic acid bacteria which suitable for prunes fermentation were screened,and the performance of the fermentation of prunes by self-derived lactic acid bacteria and some heterogenous lactic acid bacteria was explored.At the same time,the fermentation substrate and fermentation process were optimized.And on the basis of the optimal fermentation process,the production process of low-sugar prunes jam was optimized.The main findings are as follows:(1)The lactic acid bacteria in the puree of prunes were separated and purified by the traditional method of streaking.Five strains with good acid production performance and suitable for prunes fermentation were initially screened through bromocresol purple MRS solid medium and prunes juice solid medium.Through preliminary physiological and biochemical identification and further molecular biological identification,it was finally determined that the strains C2,D2,M2,and P1 were Enterococcus faecium,and the strain E2 was Leuconostoc mesenteroides.After that,the growth performance and acid production performance of 5 strains of lactic acid bacteria in MRS broth,as well as the bacteria's own antioxidant performance were determined.The results showed that Leuconostoc mesenteroides E2 grew rapidly in MRS broth and had good acid production performance.The intact lactic acid bacteria cell suspension of Leuconostoc mesenteroides E2 and Enterococcus faecium C2 had good antioxidant capacity.Finally,the p H,total acid content,total sugar content,color difference,DPPH free radical scavenging rate and ABTS~+free radical scavenging rate were used as indexes to compare the fermentation performance of five lactic acid bacteria in prunes pulp.Leuconostoc mesenteroides E2 was more suitable for the fermentation of prunes pulp.(2)This chapter used prunes,the"Empress"of Xinjiang,as raw materials to explore the changes of titratable acid content,color difference,total phenol content,DPPH free radical scavenging rate etc.during the fermentation of prunes pulp by Lactobacillus bulgaricus JYLB-19,Streptococcus thermophilus JYSR-26,Lactobacillus plantum JYLP-326 and Lactobacillus Switzerland A25.The results showed that Lactobacillus plantarum JYLP-326 and Lactobacillus bulgaricus JYLB-19 had better acid production and could maintain high reddness in the fermented prunes pulp.Lactobacillus plantarium JYLP-326 and Streptococcus thermophilus JYSR-26 had better antioxidant capacity.In the process of fermentation,although the DPPH free radical scavenging rates and ABTS~+free radical scavenging rates of the four heterogenous lactic acid bacteria decreased with the increase of fermentation time,they were all higher than those of the control group.By comprehensive comparison,Lactobacillus plantarum JYLP-326 was more suitable for the fermentation of prunes pulp.(3)Based on the p H value,total sugar content,total phenol content and other indicators,it was determined that the best bacterial mixture ratio for fermented prunes pulp was Leuconostoc mesenteroides E2 and Lactobacillus plantarum JYLP-326 at a ratio of 3:1.Afterwards,using sensory evaluation,p H,total acid content,total sugar metabolism rate and total phenol content as indicators,glucose was determined as the best supplementary carbon source,and the initial sugar content adjusted to 10°Brix was the most suitable for compound lactic acid fermentation.Through single factor and response surface experiments,the optimal fermentation conditions were as follows:the amount of bacteria added was 5%,the fermentation time was 24 h,and the fermentation temperature was 34?.At this time,the sensory score was91.21 points and the total phenol content was 815.199 mg/L.(4)The sensory evaluation,gel strength and other indicators were used to explore the characteristics of pectin,xanthan gum,CMC-Na and guar gum in different amounts of jam.Finally,pectin and xanthan gum were selected for compounding,and the optimal ratio of thickener was determined.The best ratio of thickener was that the ratio of pectin to xanthan gum was 2:1.According to the single factor and response surface results,the optimal process of low-sugar prunes jam was as follows:citric acid content was 0.3%,sucrose solution concentration was 30%,compound thickener content was 0.4%,and the sensory score at this time was 90.35 points.