Changes In Basic Components And Antioxidant Activity In The Process Of Lactic Acid Bacteria Fermentation Of Apple Puree

Fermented juices from fruits and vegetables by lactic acid bacteria have recently been received more and more attentions of the customers,due to their nutrition and flavor.Apple is one of the biggest yield fruits in China,with high nutritive value.In the study,the changes of primary components and antioxidant activities of fermented apple juices were studied,in order to obtain the optimal fermentation parameters and apple cultivar.(1)The fermentations of apple juice by L.plantarum,L.paracasei,L.acidophilus and S.thermophiles were investigated.A basic stability and then sharp decrease of pH was found,indicating that there was a long lag phase(2d)for lactic acid bacteria to adapt to apple juices before rapid growth.DPPH free radical scavenging ability of each fermented apple juice was lowed compared with its unfermented juice,along with the decrease in total phenol contents.Based on pH,DPPH free radical scavenging ability and sensory evaluation,L.plantarum was selected as the suitable lactic acid bacteria for apple juice fermentation.(2)Single factor experiments were used to analyze the effects of initial pH,bacterial adding amount,temperature and time on fermented apple juice by L.plantarum.Based on pH,DPPH free radical scavenging ability and sensory evaluation,the optimal fermentation parameters were obtained as follows: initial pH 4.5,bacterial adding amount 8mg/100 mL,fermentation at 37°C for 5d.After the fermentation,fermented apple juice had good sensory evaluation;in which,the pH was 2.58,and the total phenolic content was increased from 4.95mg/100 mL to 6.42mg/100 mL,and DPPH free radical scavenging ability was improved by 1.5 folds.(3)The effects of different cultivars on primary components and antioxidant activities of apple juice fermented by L.plantarum were investigated.Four apple cultivars including Gala,Red Fuji,Golden Delicious and Green delicious were used in the study.pH and total sugar contents of apple juices from the above cultivars were decreased significantly to 2.72~3.54 and 72~102 g/L,while their reducing sugar contents were first decreased and then increase during fermentation.Total phenolic contents were increased by 1.33~2.24-folds after 10 d fermentation.DPPH free radical scavenging ability,ABTS free radical scavenging ability and ferrous ion reducing power of apple juices from Gala,Red Fuji,Golden Delicious and Green delicious were almost steady in the first 5d fermentation,and then obviously increased in the late stage(5-10d).At the end of fermentation,the abilities of each system to scavenge DPPH and ABTS free radicals was increased by 1.67~2.31-folds and 1~1.63-folds,respectively;and ferric reducing antioxidant power were increased by 1.5~1.59-folds.Among them,antioxidant activity of fermented juices from Gala and Red Fuji were significantly higher than the others.(4)Volatile substances and their relative contents of apple juices from different cultivars before and after the fermentation by L.plantarum were studied using solid phase microextraction(HS-SPME)and gas chromatography-mass spectrometry(GC-MS).75 volatile substances were detected in the unfermented and fermented apple juices.Esters were the main volatile substances.Some esters were formed in fermented apple juices,including methyl acetate,propyl acetate,phenylethyl acetate,ethyl octanoate,γ-butyl esters,propyl 2-methylbutyrate,vinyl 3-methylbutyrate,methyl octanoate,isoamyl acetate,2-methylbutyl acetate.Principal component analysis(PCA)indicated that the difference was increased between volatile substances of unfermented and fermented juices from Gala,Red Fuji,Golden Delicious and Green delicious,especially the former two apple juices.