Enzymatic Preparation of Purple Potato Juice and Its Fermentation Characteristics of Lactic Acid Bacteria

In this paper,purple potato juice rich in anthocyanins was prepared by enzymatic method. Lactobacillus casei,Lactobacillus bulgaricus and Lactobacillus plantarum were used to ferment purple potato juice. The effect of blanching time,high temperature α-amylase dosage on the yield and anthocyanin content of purple potato juice and changes of pH,anthocyanin,total phenol content,sugar component,organic acid and DPPH scavenging capacity during fermentation were studied. The results showed that the purple potato had the highest juice yield after blanching and color protection for 2.5 min. The blanching time had a significant effect on the anthocyanin content of purple potato juice. The anthocyanin content was 7.7 times higher than that without blanching when blanching for 2.5 min. With the treatment of high temperature α-amylase(20 U/g)and saccharification enzyme(200 U/g),the yield of purple potato juice was 69.80%±3.85%,the total phenol content was 1136.67±33.76 mg/L,and the anthocyanin content was 218.25±1.89 mg/L. The pH value of purple potato juice gradually decreased after fermentation by lactic acid bacteria,and a large amount of lactic acid was produced. The acid production capacity was in the order of Lactobacillus bulgaricus > Lactobacillus plantarum > Lactobacillus casei. Sucrose,glucose and fructose were consumed by lactic acid bacteria as substrates during fermentation.The anthocyanin,total phenol and DPPH·clearing ability decreased by 11.33%~17.82%,6.22%~7.73%,24.23%~27.62%,respectively after 48 h of fermentation. The decrease of antioxidant activity is associated with that of anthocyanin and total phenolic content.