Research On Breeding High-resistance Lactobacillus And Freeze-drying Technology

Lactobacillus rhamnosus GG was discovered from healthy person.It is a probiotic strain that has attracted most attentions and the best documentated in this field.It can tolerate intestinal conditions and adhere both to intestinal mucus and to pithelial cells.The functional properties of LGG include balance the ubjects' intestinal microflora,reduce the risk of diarrhoea,bind and eliminate toxins,lower the risk of dental caries and enhance the immunity.The fermentation productions of lactic acid which are currently commercially available mayor in lactobacillus acidophilus and Bulgaria bacilli,few of lactobacillus rhamnosus.In this study,efficient starter culture is hoped obtained through studies on direct-to-vat of lactobacillus hamnosus,which provide the lactobacillus rhamnosus yogurt products with direct-to-vat cultures.Probiotic properties of multi Lactobacillus rhamnosus preserved in the lab were evaluated in my study.We screened a strain of L.plantarum with excellent performance,named as L.rhamnosus LGG-QF-3.We optimised culture conditions using raw materials of industrialization,improved the fermentation cell density and decreased the cost of production.The main results are as follows:1.Screening of Lactobacillus rhamnosus strainsWe isolated 8 Lactobacillus rhamnosus strains from traditional Xinjiang yogurt.By detecting the growth and acid production capacity,the ability of antioxidant stress,the ability of acid stress and the ability of anti-freeze stress,we screening two strains in which LGG-QF-3 with the strongest anti-stress and LGG-QF-7 with the strongest anti-freeze H2O2 stress.L.rhamnosus LGG-QF-3 and L.rhamnosus LGG-QF-7 were excellent yogurt fermentation starter culture and has the potential application value.2.The vitro evaluation of probiotic properties of Lactobacillus rhamnosusThrough screening to the laboratory 8 strains for their resistance to bile salts,gastrointestinal fluid resistance,degradation of cholesterol and other probiotic properties,we screened a L.rhamnosus strain with good probiotic properties,andnamed as L.rhamnosus LGG-QF-3.The probiotic characteristics performance of the strain are as follows: In the p H2.5 environment the viable counts of strain decreased only one magnitude after 6h cultured;In the 0.3% bile salt cultured after 6h,there are still about 104 survival cell;It has strong tolerance to the artificial gastric juice and artificial intestinal juice,under the both of the conditions,it was cultured after 6h the viable count of strain decreased about two orders of magnitude;It has the good cholesterol removal ability,cholesterol removal rate reached more than 60%.3.Optimization of culture conditions of L.rhamnosus LGG-QF-3The strain of L.rhamnosus LGG-QF-3 high density fermentation conditions were optimized.Through the orthogonal test and other optimization method we obtained the optimum formula and culture conditions: 0.5% soybean meal,1% yeast powder,4%brown sugar and inorganic salt,37? 60r/min shaking culture by 24 h,viable count can reach 109 orders of magnitude.The experiments showed that in the culture medium added 0.5% fructooligosaccharides or 0.5% of oligo isomaltose sugar,L.rhamnosus LGG-QF-3 in optimizing cultivation of 37? cultured after 24 hours,the maximum cell density increased 1.5.4.Choose and optimize the best cryoprotectant for L.rhamnosus LGG-QF-3Taking L.rhamnosus LGG-QF-3 as study objects,the survival rates and viability have been investigated in the presence of cryoprotectants after freeze-drying.Activities of sugar metabolic enzymes and changes of cell membrane have been determined immediately following the freeze-drying.The results showed that the cryoprotectants can significantly improve the survival rate and vitality of Lactobacillus,but the effects of cryoprotectants were differencent to some extent.The best cryoprotectant for L.rhamnosus LGG-QF-3 was 10 % skim milk.5.The yogurt fermented using this strain L.rhamnosus LGG-QF-3Sensory evaluation shows that the yogurt fermented using the strain L.rhamnosus LGG-QF-3 has appropriate acidity,delicate taste and rich aroma.L.rhamnosus LGG-QF-3 is an excellent yogurt fermentation starter culture and has the potential application value.