Analysis Of Main Components Of Longan Pulp Fermentated By Lactic Acid Bacteria And The Development Of Its Beverage

Longan,one of the tropical and subtropical fruits,is full of nutrition.Because of the maturity concentration and the short storage period,longan is mainly consumed by fresh eating,the variety of processed products is very few.Therefore,it is necessary for longan to broaden processing pathway and develop different types products to meet consumer demand.This is significant for broadening the utilization and increasing the economic value of longan.Lactic acid bacteria have bioactive activity including improve gastrointestinal,enhance immunity and anti-oxidation.However,there is a little attention on fruit pulp fermented lactic acid bacteria.Phenolic compounds are the main active ingredient in fruits and vegetables.Only free phenolics were reported in the previous study of phenolic compounds during the processing of fruit and vegetable,whereas bound phenolics were ignored in the research.In this paper,longan(Chuliang)was used as materials,and the conditions of longan pulp fermentation by lactic acid bacteria were optimized.Furthermore,the main components in longan pulp fermented by lactic acid bacteria were analyzed including sugar,phenolics,flavonoids,form of existence,phenolic compositions,antioxidant activity,and flavor component.Finally,the beverage of longan pulp fermented by lactic acid bacteria was developed.The main results are presented as follows.(1)Optimization of the conditions of longan pulp fermentation by lactic acid bacteria:Using fresh longan pulp as raw materials,lactic acid bacteria was domesticate to adapt to the high concentrations of longan pulp.The conditions of longan pulp fermentation by lactic acid bacteria process were optimized through the single factor experiment with Box-Benhnken central composite experimental design based on the indicators of total acid and pH value.A regression model of four factors was established including the fermentation time,fermentation temperature,amount of skim milk powder and inoculation amount of the bacteria.Through regression analysis and validation test,the optimum conditions are as follows:fermentation time 12h,fermentation temperature 45? 5%the amount of skim milk powder and 3%inoculation amount of the bacteria.The acidity of fermented fruit pulp is 105.1°T under the optimum condition.The impact of various factors on the acidity are in the following order;the amount of skim milk powder>fermentation time>fermentation temperature>inoculation amount of the bacteria.(2)Analysis of the main components in longan pulp fermented by lactic acid bacteria:Living bacteria number,pH value,total sugar,reducing sugar,total phenolics,flavonoids,phenolic composition,antioxidant activity were analyzed during the process of fermentation.The results showed that live bacteria number in the process of longan pulp fermentation was increased at first and then fluctuation around in 2.0×108cfu/mL value,when 4h viable count reaches a maximum value of 4.65×108cfu/mL.The pH value decreased significantly(p<0.05),drops from 7.07 to 4.40.Total sugars and reducing sugar content decreased significantly(p<0.05),total sugar dropped from 36.42mg/g to 70.84mg/g,reducing sugar dropped from 26.34mg/g to 42.77mg/g.In the process of longan pulp fermentation,total phenol and flavonoids content declined firstly and then rised,total phenol increased from 46.9 mg GAE/100g to 47.8 mg GAE/100g,the total flavonoids content increased from 10.7 mg CE/100g to 13.7mg CE/100g;After the fermentation,the proportion of bound phenolics increased,but the difference is not obvious in different fermentation time.The proportion of the bound flavonoids reached maximum level(23.7%)after 6h of fermentation.Phenolic compositions were analyzed by HPLC in longan pulp fermentation.11 phenolic compositions were detected including gallic acid,protocatechuic acid,vanillic acid,clove,epicatechin,four methyl catechol,ferulic acid,coumarin,resveratrol,rutin and quercetin.Longan pulp in the process of fermentation,the protocatechuic acid,syringic acid,epicatechin,four methyl catechol,coumarin,and resveratrol.Total FRAP and ORAC antioxidant activity value was significantly increased(p<0.05),the total FRAP value increased from 152.9 mg TE/100g to 201.1 mg TE/100g,total ORAC value increased from 703.1?mol TE/100g to 861.5?mol TE/100g;the bound FRAP value almost had no changed,and the proportion of bound ORAC antioxidant capacity significantly increased(p<0.05).(3)Analysis of the flavor components in longan pulp fermented by lactic acid bacteria:Research longan fruit purees volatile substances before and after fermentation,found before puree fermentation has the flavor components in longan pulp fermented by lactic acid bacteria were also investigated by GC-MS.There were 53 kinds of flavor components through fermentation,including 15 kinds of terpene hydrocarbons,6 kinds of alcohols,18 kinds of esters,7 kinds of ketones,3 kinds of aldehydes,2 kinds of acids and 2 other types.Lactic acid bacteria fermentation can produce unique flavor of milk products,mainly including acetaldehyde,3-hydroxy-2-butanone,ethyl acetate and their contents were 1.953?g/g?1.085?g/g?2.193?g/g,respectively.(4)Development of the beverage of longan pulp fermented by lactic acid bacteria:The process of beverage of longan pulp fermented by lactic acid bacteria was optimized by the response surface experimental design,and the response value is comprehensive score that weighted with two indexes like stability and sensory evaluation.Through the regression analysis and verification test,the optimum condition for the production of the beverage was as follows:pectin 0.04%,sodium alginate 0.3%,xanthan gum 0.02%,sugar acid ratio 25.Under the optimum condition,centrifugal sedimentation rate of the beverage was 7.36%,the sensory score was 89.3,and the comprehensive score was 98.97.The impact of various factors on the score was as follows:sugar-acid ratio>pectin content>sodium alginate content>xanthan gum content.