| Asparagus(Asparagus officinalis L.)is a Liliaceae Asparagus plant,rich in polysaccharides,saponins,flavonoids,amino acids,dietary fiber,vitamins and minerals and other nutrients,with high edible value.At present,the research on asparagus is focused on the separation,purification and determination of asparagus components,while the research on improving the nutrition and function of asparagus by bio-fermentation technology is rare.Lactobacillus play an important role in protecting and improving the nutritional value,sensory flavor and storage safety of fruit and vegetable juice.In this study,asparagus juice was prepared by pretreatment.Different L.plantarum was used to ferment asparagus juice.The preparation conditions of asparagus juice fermented by L.plantarum S7 were optimized,and the flavor substances and biological functions of the fermented asparagus juice were analyzed.The main research contents are as follows:(1)Study on the preparation conditions of asparagus juice.The green asparagus was blanched,the asparagus mud was squeezed by water bath,microwave,ultrasonic I and ultrasonic II.Finally,the asparagus juice was pasteurized.The results showed that the best blanching condition was blanching for 1 minute at 95?,which made the asparagus juice have the best color protection effect and less loss of components in asparagus juice.At this time,the color a value of the asparagus juice was-2.853,and the content of flavone,saponin,reducing sugar and free amino acid in asparagus juice were 0.392 mg/g.38.259 mg/g,7.267 mg/g and 8.374 mg/g respectively.The best assistant treatment was ultrasonic II treatment that was 60 ? and 50 W ultrasonic assisted treatment for 30 min,which increased the content of each component in the asparagus juice.At this time,the content of flavone,saponin,reducing sugar and free amino acid in asparagus juice were 0.499 mg/g,38.307 mg/g,8,383 mg/g and 8.374 mg/g respectively.The best sterilization condition was pasteurization at 95 0C for 15 minutes.At this time,the total number of colonies,coliforms,fungi and yeasts in asparagus juice all were not detected..(2)Study on the effects of different Lactobacillus plantarum on the composition of asparagus juice.Based on the 18 hour fermentation process of asparagus juice by 11 strains of L.plantarum screened in our laboratory,it was found that 11 strains of L.plantarum could grow well in asparagus juice.The maximum viable number of L.plantarum was between 108-109 CFU/mL,the lowest pH value was between 3.00-3.20,and the final total acid content was between 6.30-9.27 g/kg,indicating that L.plantarum could grow and ferment well in asparagus juice.The organic acid content of 11 strains of L.plantarum fermented asparagus juice changed significantly.(P<0.05),lactic acid content increased rapidly,oxalic acid content decreased rapidly and increased slowly,tartaric acid increased and decreased,malic acid and ascorbic acid content decreased rapidly,citric acid content fluctuated,succinic acid content increased first,then increased and then decreased,acetic acid content increased and then decreased,indicating that 11 strains of L.plantarum could be separated by the change of organic acid content.The changes of active components in asparagus juice fermented by 11 strains of L.plantarum showed that the contents of reducing sugar,polysaccharides,saponins and free amino acids decreased rapidly,while the content of flavonoids increased first and then decreased.The final content of reducing sugar was between 0.653-2.461 mg/g,the content of polysaccharides was between 1.626-7.561 mg/g,and the content of saponins was between 5.774-9.218 mg/g,and the free amino acid content is between 6.123-6.688 mg/g(except L.plantarum S7).The content of saponins,flavonoids and free amino acids in the asparagus juice of L plantarum S7 was significantly higher than that of other fermented asparagus juices(P<0.05),which were 9.218 mg/g,0.613 mg/g and 7.499 mg/g,respectively.(3)Optimizing the preparation conditions of asparagus juice fermented by L plantarum S7.Three significant factors of asparagus juice fermentation were screened out by Plackett-Burman test.The best fermentation conditions of asparagus juice were determined by Box-Behnken test:the ratio of material to liquid was 1:1,the addition of whey powder was 1.59 g/100g,and the addition of sugar was 4.00 g/100g.Under these conditions,the flavonoid content in L.plantarum S7 fermented asparagus juice was 1.12 mg/g and the saponin content was 19.67 mg/g.The number of viable bacteria was 7.21×109 CFU/mL and the sensory score was 94.00.Box-Behnken test was conducted to determine the optimum stabilizer dosage:xanthan gum 0.25 g/kg,carrageenan 0.14 g/kg,pectin 1.27 g/kg.Under these conditions,the centrifugal precipitation rate of fermented asparagus juice was 8.51%.(4)Composition and function analysis of asparagus juice fermented by L.plantarum S7.The physical and chemical indexes of L.plantarum S7 fermented asparagus juice were determined as follows:soluble solids content 11.383%,total acid content 5.646 g/kg,reducing sugar content 3.887 mg/g,saponin content 19.675 mg/g,flavone content 1.142 mg/g,free amino acid content 8.713 mg/g.Flavor substances in asparagus juice were determined by solid phase microextraction(SPME)and GC-MS.It was found that 41 kinds,45 kinds and 33 kinds of flavor substances were detected in fresh asparagus juice,natural fermented asparagus juice and L.plantarum S7 fermented asparagus juice,totaling 88 kinds.The relative contents were 94.58%,95.00%and 94.25%,respectively.L.plantarum S7 fermentation increased ketones,acids and other flavor substances in asparagus juice,decreased esters and hydrocarbons flavor substances,and there was no significant difference in alcohols and aldehydes flavor substances.The total antioxidant capacity of L.plantarum S7 fermented asparagus juice was 1.133 U/mL,hydroxyl radical scavenging rate was 89.135%,cholesterol micelle solubility inhibition rate was 95.294%,nitrite scavenging rate was 69.141%and nitrosamine synthesis blocking rate was 76.190%,which were significantly higher than that of natural fermented asparagus juice and fresh asparagus juice,while the total reducing power of 0.432 was significantly lower than that of natural fermented asparagus juice and fresh asparagus juice,indicating that fermentation of L.plantarum S7 increased the antioxidant,cholesterol lowering,nitrite removal and nitrosamine removal abilities of asparagus juice. |
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