Study On Processing Technology Of Blueberry Juice Fermented By Lactic Acid Bacteria

As a new drink, blueberrey juice fermented by lactic acid bacteria can improve flavor and medical health function of blueberries, this is an extension of the blueberry deep processing technology. The research of blueberry juice fermented by lactic acid can provide theoretical basis for industrialized production of blueberry industry and has a positive practical significance.The raw material of this drink is blueberries, plus suitable amount of glucose and skimmed milk as supplementary materials.Then a high nutritional value and flavor of new drink is developed using lactobacillus casei and lactobacillus plant.The main results of this paper are as follows:(1) Optimization of the fermentation proportion of lactic acid bacteria:through the changes of pH, lactic acid content and the number of living bacterium in the fermentation process, it shows that lactobacillus casei and lactobacillus plants have cooperative fermentation ability for the proportion of 1:2. The number of living bacterium achieves 1.3 × 109 CFU/mL and lactic acid content in fruit juice is 7.63 g/kg after 24 h fermentation.(2) The filter of carbon and nitrogen source that promote lactic acid bacteria fermentation in blueberry juice. The utilization of different carbon and nitrogen source is studied by comparing the pH and lactic acid content in the fermentation process.The result shows that the best utilization of carbon and nitrogen source are glucose and skim milk when the fermentation proportion of lactobacillus casei and lactobacillus plants is 1:2.(3) The processing crafts of blueberry juice fermented by lactobacillus casei and lactobacillus plants are optimizated:lactic acid content and sensory score as the main indexs, the optimum raw material proportion of blueberry juice fermented by lactic acid bacteria is studied through the single factor and orthogonal experiment analysis.The optimum raw material proportion of blueberry juice with good flavor is the concentration 30%, glucose 8%,and skim milk 3%, the sensory score of the product is 94 and lactic acid content 8.07 g/kg.The best fermentation parameters of blueberry juice is studied by single factor and response surface experiments through the lactic acid content and total antioxidant capacity.The result shows that the inoculum dose is 4.9%, the lactic acid content is 8.33 g/kg and total antioxidant capacity is 229.93 U/mL afer fermentation 23h at 36℃.The optimal compound stabilizers is determined by the rate of layered in blueberry juice, the best stabilizer combination is add 0.12% PGA,0.07% CMC- Na and 0.07% xanthan gum, the rate of layered is 2.41%.(4) The research of lactic acid bacteria in vitro gastrointestinal digestion:the torlence of lactobacillus casei and lactobacillus plants in the environment of artificial gastric fluid, intestinal fluid, bile salts and high salt fluid are studied. The results show that:the number of living bacterium are 6.5×106,1.8×107 and 5.2×107 CFU/mL after 2 h in the pH value of 1.5, 2.5,3.5 artificial gastric fluid; the number of living bacterium are 1.3×106 CFU/mL after 3 h in the artificial intestinal fluid.The number of living bacterium is 2.7×107 CFU/mL when the Ox-gall salt content reach 0.50 g/100 mL in MRS liquid medium; the number of living bacterium is 6.4×107 CFU/mL when the NaCl content reach 6 g/100 mL in MRS liquid medium. The results indicate that lactobacillus casei and lactobacillus plant have strong tolerance in artificial gastric, intestinal fluid, bile salts and high salt environment.(5) The kinds of blueberry juice aroma components increase from 25 to 38, including acids, esters, ketones, but alcohols, alkenes material reduced after fermentation. New materials are generated such as methyl formate,2-undecanone, beta-myrcene and 3-methyl-1-butanol.The changes of blueberry volatile aroma compositions are obvious after fermentation.The pH value drop by 22.94%, lactic acid content is 2.06 times of the original juice, anthocyanins content in blueberry juice decrease by 5.36%, polyphenol content increase by 15.05% and total antioxidant capacity increase by 34.87% after fermented. Blueberry juice fermented by lactic acid bacteria has pleasant sweetness and sourness and improve its nutritional value.(6) The storage stability of fermented blueberry juice is studied,the experiment results as follows:the numbers of living bacterium in fermented blueberry juice are 6.6×107 CFU/mL at room temperature after 4 days, the numbers of living bacterium are still 2.3 × 106 CFU/mL after 6 days, above the national standard requirements, but the juice taste sour. It means that the juice can be saved for 4 days at room temperature. The lactic acid bacteria show a slow growth and high number of living bacterium at 4 ℃.The numbers of living bacterium are 3.1 × 107 CFU/mL after 4 weeks, it indicates that the product can be preserved for 28 days under the condition of cold storage.