Studies On The Extraction Of Exopolysaccharides And High Exopolysaccharides-producing Culture Of Yoghurt

Lactic acid bacteria exopolysaccharides is produced with Lactic acid bacteriagrowing and penetrates into culture medium. It is amylose compound ofsub-metabolism and divided into capsule amylase and mucus amylose.The molecularweight of exopolysaccharides is between 4.0×10~4 and 6.0×10~6Da. Lact acid bacteriaexopolysaccharides has some characteristics of improving yoghurt qualities,such asenhancing yoghurt viscosity and rheology,prohibiting whey loss,improving yoghurttaste and increasing clabber intensity.This thesis mainly studies on the extraction ofexopolysaccharides in yoghurt and high exopolysaccharides-producing of yoghurt.This paper researches on the displacement of protein and the extraction of EPS inyoghurt,through selecting proper of TCA concentration then adjusting pH to displaceprotein by centrifugation and then through a orthogonal experiment to determine themost appropriate method of extracting EPS in yoghurt. The result indicats thatthrough selecting 20％TCA and adjusting pH value to 7.0 most of protein in yoghurtwould be removed,and the most proper means to extract EPS in yoghurt is that liquidis 75％, the time of abstraction is one day, the proportion of and solution is 1:1.Through Box-Behnken design and response surface analysis,this papers researchthe main factors of impacting on the extraction of EPS in yoghurt and determines themost appropriate conditions.The result indicates that on the condition of 82％concertation of ethanol,7.8h of extraction time, the 1.1 ratio of ethanol andsolution,the OD value of extracted EPS in yoghurt is up to 0.182,and the effect ofextraction increases by 37％.Four bacillus and two coccus are separated from seven DVS cultures.Throughappraisal and fermentation experiment, Lactobacillus delbrueckii subsp,Lactobacillushelveticus and an unknown cocci are used to constitue the high EPS-producingculture.This paper researches on three factors, including the proportion of coccus and bacillus with high capacity of producing EPS respectively, ferment temperature andthe proportion of inoculation,impact on the yoghurt production and itsquality.Through Box-Behnken design,the result indicates that the best appropriatecondition is the 80％proportion of coccus and bacillus,2.9％proportion ofinoculation,36℃ferment temperature.