The Nutrient Requirements Of Lactobacillus Acidophilus LA-5 And Their Application To Fermented Milk

There are many fermented dairy products on the market that have been manufactured with a single probiotic strain such as yakult(Lactobacillus casei Shirota),Cherita(Lactobacillus rhamnosus GG ATCC 53103),and LAJOIE(Lactobacillus paracasei LPC-37),the problem of fermented milk dairy products fermented by single probiotics is that the fermentation time is longer.Streptococcus thermophilus and Lactobacillus bulgaricus are often co-fermented with probiotics in fermented milk containing the probiotic strain,however,S.thermophilus and L.bulgaricus grow faster than probiotics in the milk,which resulted viable probiotic cell counts are often low at the end of the fermentation process in fermented milk.Lactobacillus acidophilus LA-5 has many probiotic functions.In order to shorten the fermentation time of milk prepared solely by L.acidophilus LA-5 and increase its viable cell counts in fermented milk prepared by a combination of L.acidophilus LA-5,Streptococcus thermophilus,and Lactobacillus bulgaricus,this thesis studies the necessity of nutrients for the growth of L.acidophilus LA-5 and analyzes the consumption patterns and demand patterns based on the nutritional requirements of L.acidophilus LA-5,also identifies necessary nutrients,non-essential nutrients and stimulating nutrients of L.acidophilus LA-5.The types and contents of nutritional components that are lacking in the growth of L.acidophilus LA-5 in milk were obtained through analysis.Then conducting the preliminary single addition experiments evaluate the effect of nutritional factors on the fermentation time of L.acidophilus LA-5,the preliminary single addition experiments was to evaluate the effect of nutrients on the fermentation time of L.acidophilus LA-5 and select the nutrients that shorten the fermentation time of fermented milk using L.acidophilus LA-5.After these nutrients were added to milk to make fermented milk prepared by a single probiotic strain and fermented milk prepared by a combination of L.acidophilus LA-5,S.thermophilus,and L.bulgaricus,the effects of nutrients on the viable count,fermentation time,and quality of these two fermented milk were analyzed.The results of single nutrient omission showed that Cys,Glu,Ile,Leu,Lys,Met,Phe,Thr,Try,Val,Arg,and glucose are essential nutrients for the growth of L.acidophilus LA-5.Gly,Ca-pantothenate,and Mn²⁺were stimulatory nutrients that stimulated the growth of L.acidophilus LA-5.Gln,Asn,His,Pro,Ser,Asp,Gln,Tyr,Ala,Thiamine,nicotinic acid,biotin,cyanocobalamin,folic acid,inositol,riboflavin,pyridoxal,p-aminobenzoic acid,sodium acetate,ammonium citrate,NH₄Cl?KH₂PO4?K₂HPO4?Fe²⁺,Mg²⁺,Na Cl,adenine,guanine,uracil,xanthine,and thymine were non-essential nutrients that had no obvious effects on the growth of L.acidophilus LA-5.The experimental results of consumption patterns of amino acids showed that during the entire growth process of L.acidophilus LA-5,the consumption rates of Asp+Asn,Lys and Leu were the highest,which were 88.79%,81.98%,and 77.24%,respectively;followed by Tyr,Thr,Glu+Gln,and Ala,whose consumption rate all exceeded 60%.The consumption rates of Phe was the lowest,which was 17.5%.The highest and lowest consumption amounts were Asp+Asn at0.94 mmol/L and Tyr at 0.089 mmol/L.The results of the necessary profiles of amino acids showed that the proportion of Glu+Gln was 10.71%,and was higher than the amount of other amino acids demanded for the growth of L.acidophilus LA-5.Ala,Arg and Asp+Asn were next,are 9.73%,9.71%,and 8.70%,respectively.The experimental results of consumption patterns of the vitamin showed that the highest consumption rate was for riboflavin,which can reach to 61.70%,the consumption amount of p-aminobenzoic acid was the highest,which was 0.0463 mmol/L.The experimental results of the consumption pattern of base substances showed that uracil,guanine and thymine,all three consumed more than 50%of the initial addition,the highest consumption rate was uracil at65.90%,the consumption amount of uracil was the highest,which was 0.0085 mmol/L.The experimental results of consumption patterns of metal ion showed that the consumption rate of Mn²⁺was the highest,being 91.02%,the consumption amount of Na⁺was the highest,which was10.36 mmol/L.Selecting nutrients with a high consumption rate,amino acids with a high necessary rate,and essential and stimulatory nutrients which are determined according to the amino acid,vitamin,metal ion,base consumption pattern,amino acid demand pattern analysis results and single nutrient omission results of nutrients to compare with the types and contents of nutrients contained in milk,then the preliminary single addition experiments selected nutrients that shorten fermentation time of fermented milk.These nutrients are Leu,Asn,Asp,Met,riboflavin,guanine,uracil,and Mn²⁺,which were added to milk for the L.acidophilus LA-5 fermented milk test.The effect of nutrients on fermented milk prepared solely by L.acidophilus LA-5 showed that the fermentation time of fermented milk supplemented with the nutrients was shortened by 9 h,at the end of the fermentation process,the viable cell counts of fermented milk supplemented with the nutrients reached 2.17×10⁹CFU/m L,which was approximately 1.8-fold that of the fermented milk supplemented without the nutrients.The addition of nutrients had no negative effect on the titratable acidity,water-retaining capability,texture properties and sensory evaluation of the fermented milk prepared solely by L.acidophilus LA-5.The viable cell counts of L.acidophilus LA-5 in fermented milk supplemented with the nutrients was more than 10⁷CFU/m L after storage,which was higher than the fermented milk supplemented without the nutrients.The effect of nutrients on fermented milk prepared by mixed starter culture showed that there were no significant differences in fermentation time,approximately 5 h,between the fermented milk supplemented with the nutrients and fermented milk supplemented without the nutrients,the viable cell counts of fermented milk supplemented with the nutrients reached 2.93×10⁷CFU/m L,which was approximately 2.3-fold that of the fermented milk supplemented without the nutrients.The addition of nutrients had no negative effect on the titratable acidity,water-retaining capability,texture properties and sensory evaluation of the fermented milk prepared by a combination of L.acidophilus LA-5,S.thermophilus,and L.bulgaricus.The viable cell counts of of L.acidophilus LA-5 in fermented milk prepared by mixed starter culture which supplemented with the nutrients was more than 10⁶CFU/m L after storage,which was higher than the the fermented milk supplemented without the nutrients.