| The dried longan is high nutritional value and easy to save. But its added value is low. Lactic acid bacteria (LAB) fermentation helps to strengthen nutrition, improve the flavor and the utilization rate of bioactive components. This study was that longan flesh fermented Lactic acid bacteria was made, with the purpose of providing accessories for the machining process of functional beverage. Oat contains abundant of β-glucan, dietary fiber. Oat has multiple physiological functions, such as preventing obesity. So oats were used for the development of corn beverage, which were favored by the market.β-glucan and dietary fiber were bonded in oat. Poor solubility leaded to low utilization rate of β-glucan in oat. Predecessors mainly used the process of extrusion or enzyme to enhance the content of soluble β-glucan in oat, but the effect was not ideal. At present, the process of extrusion and enzymolysis coordinated were not reported. Therefore, the use of high temperature amylase assisted extrusion technology to improve the content of soluble β-glucan in oat, which helped for the research and development of the different types of oat products, widening the utilization way of oats. From the above, this study was that the effect of LAB fermentation on free and bound phenolics and flavonoids and antioxidant activity of dried longan flesh was investigated. to optimize the process of longan flesh fermented by lactic acid bacteria. The main composition of longan flesh were compared before and after fermentation of lactic acid bacteria. To compare different pretreatment methods on the influence of the content of soluble β-glucan in oat. Optimize the process of oat enzymatic preparation. Through the sensory evaluation and stabilizer screening, a kind of functional beverage with good taste and good flavor and low sugar content were prepared.(1) Optimization of the process of longan flesh fermented by mixed LAB. Effect of seven LAB fermentation on lactobacillus colonies, pH and total acid, reduced sugar content, free and bound phenolics, flavonoids, FRAP value and ORAC value in dried longan flesh were compared. Leuconostoc mesenteroides GIM 1.473 and Lactobacillus plantarumsubsp-Plantarum GIM 1.380 were selected. The conditions of longan flesh fermented by mixed LAB were optimized through the single factor experiment with Box-Benhnken central composite experimental design based on the indicators of the free phenolics and sugar content. A regression model of four factors including the fermentation time, the mixed lactobacillus inoculation, solid-liquid ratio and the fermentation temperature was established. Through regression analysis and validation test, the optimum conditions were solid-liquid ratiol:7, fermentation temperature 37℃, fermentation time 53h, mixed lactobacillus inocuation 1.4%. These four factors which impacted on the free phenolics and sugar content in descending order were fermentation time, fermentation temperature and mixed lactobacillus inoculation。The free phenolics and sugar content which prepared under the optimum conditions respectively were 141.34±1.68 mg GAE/100 g DW,235.20±3.54 mg/g DW.(2) Comparison of Composition of dried longan flesh fermented by mixed LAB. Dried longan flesh was fermented by mixed LAB, under the optimum fermented conditions, comparing the content of organic acids, phenolics changes of free amino acids and volatile flavor materials in dried longan flesh. After fermentation, free phenolics and flavonoids content increased significantly (P< 0.05), increased by 17.32% and 33.11% respectively, comparing with before fermentation; bound phenolics and flavonoids content significantly decreased (P<0.05), respectively, decreased by 57.17% and 46.56%. After fermentation, lactic acid, acetic acid and succinic acid content increased significantly (P<0.05), comparing with non-fermentation, oxalic acid and malic acid content decreased obviously (P<0.05). After fermentation, free amino acid in longan flesh reduced 5 species, and added 1 specie-bird glycine, comparing with non-fermentation; 17 kinds of amino acid content declined, and the content of 5 kinds of amino acid increased. After fermentation, the eight new flavor substances appeared, including three esters and two mushroom olefins, three alcohols.(3) Optimization of the process of enzymatic preparation oat hydrolysate. Oats were used as material, comparing different pretreatment processes on soluble β-glucan content in oat on soluble β-glucan content. Results show that the bake, extrusion, high temperature of a-amylase assisted extrusion and superfine grinding significantly improved soluble β-glucan content (P<0.05). Among them, the effect of the high temperature of a-amylase assisted extrusion is best, soluble β-glucan content in oat increased by 83.73%; the effect of superfine grinding was the worst, soluble β-glucan content in oat increased by 21.13%. Four kinds of pretreatment technology improved soluble β-glucan content in oat in descending order were high temperature of a-amylase assisted extrusion, extrusion, roast and superfine grinding, with soluble β-glucan content and free phenol content for the indicators, comparing the effects of different enzyme on the oat. The conditions of enzymatic preparation oat hydrolysate were optimized through the single factor experiment based on the indicators of soluble β-glucan content and free phenolics content. The results showed that the neutral protease can significantly increase the soluble β-glucan content in oat hydrolysate (P<0.05), medium temperature of α-amylase and cellulase enzyme can significantly increase free phenolics content in the oat hydrolysate (P<0.05). Through analysis, the optimum conditions were temperature 51℃, pH 6.6, time 2h, and solid-liquid ratio 1:8.(4) The preparation of oat-longan beverage fermented by lactic acid bacteria. The ratio of enzyme solution and longan broth was optimized based on the indicators of sensory evaluation; effect of 4 kinds of stabilizer on the stability of oat-longan beverage fermented by lactic acid bacteria based on the centrifugal sedimentation rate; the main nutrient of the beverage was analyzed. Results show that when The ratio of enzyme solution and longan broth was 80:20, the sensory score of the beverage was the highest, and it was 90.4. Effect of 4 kinds of stabilizer on the stability of the beverage was different, and Effect of pectin on the stability of the beverage was significant (P<0.05). When the content of pectin was 0.15%, the centrifugal sedimentation rate is the lowest, and it was 9.44%, thus 0.15% pectin was the optimal additive amount of the stabilizer. There were β-glucan 38.29±1.98 mg/100 mL, free phenol 6.78±0.54 mg/100 mL, protein 1.28±0.09 mg/mL, fat 5.35±0.12 mg/mL, dietaru fiber 7.63±0.24 mg/mL solids 82.8±3.27 mg/mL, reducing sugar±2.0318.96 mg/mL, and ash content of 3.52±0.28 mg/mL in the beverage. |
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