Analysis Of Apple Juice Microorganism And Flavor

Concentrated apple juice has the largest consumption in the world and China is the largest exporter of concentrated apple juice.The flavor compounds and microbial controlling is an important research direction in concentrated apple juice industry.Volatile flavor compounds are very important indicator when evaluating quality of fruit juice.This thesis mainly focused on the change of flavor compounds in the producing process of concentrated apple juice and the microbial distribution was also evaluated using methods of microbiology and molecular biology.This thesis provided the theoretical basis to improve the operation regulation and quality control of concentrated apple juice.The changes of the amount and species of microorganisms in the producing process were analyzed under the direction of national standard of food microbiological examination.After the enzymolysis of pulp,the number of aerobic microorganisms decreased by 19.51%.The number of aerobic plate and yeasts after pasteurization was reduced to almost zero,but they increased to 2.9×104CFU/g and 2.6×104CFU/g after pectin enzymolysis treatment indicating enzymatic hydrolysis process is the most susceptible to microorganisms.After concentration treatment there is no microorganism detected.Microorganisms during producing process of concentrated apple juice were separated using the method of.microbiology and 83 strains were obtained,including 11 strains of aerobic bacteria,10 strains of anaerobic bacteria,35 strains of yeast,27 strains of mould.According to the growth characters 11 isolates were closed for identification.One mould was identified as Aspergillus terreus,which could produce patulin.Four strains of Saccharomyces cerevisiae from the samples of pulp enzymolysis treatment were identified.Two strains of Acinetobacter johnsonii from the samples of pulp enzymolysis treatment were identified.Lactobacillus casei and Lactobacillus paracasei from the samples of pulp enzymolysis treatment were identified.Two strains of thermo tolerant yeasts were identified as Ogataea polymorpha from the samples of pectin enzymolysis treatment,which could grow at 50?.The volatile flavor composition and changes during the producing process was detected using the headspace solid phase microextraction combined with gas chromatography-mass spectrometry.Volatile flavor compounds in apple juice were mainly composed with alcohols,esters,aldehydes,ketones,olefins and other substances.There were 33 kinds of esters,10 kinds of aldehydes and 7 kinds of alcohols.The number and amount of flavor compounds changed apparently during enzymolysis,pasteurization,ultrafiltration and concentration treatment.The amount of alcohols and esters increased after pectin enzymolysis.However,the total amount of volatile flavor compounds decreased after pasteurization,ultrafiltration and concentration treatment.A total 19 volatile flavor compounds were identified from the concentrated apple juice.