Effect of whey protein isolate on clarification of fresh Pyrus bretschneideri ‘Huangguan'pear juice

The effect of whey protein isolate( WPI) on clarification of fresh‘Huangguan'pear juice was evaluated.Based on the single factor experiments,the response surface methodology was employed to optimize the clarification conditions of pear juice and the effects of WPI and pectinase treatments alone and combined on clarity and browning degree of pear juice were also studied.The optimum conditions for clarification of pear juice were as follows: the concentration of WPI 0.69%,treatment time 90 min and treatment temperature 60 ℃.Under the conditions,the transmittance of pear juice was 87.9%.The order of clarity of pear juice treated by the three methods was WPI- pectinase > WPI > pectinase. The order of browning degree of pear juice treated by the three methods was pectinase > WPI > WPI- pectinase. The results suggested that WPI had dual effects of clarification and inhibition of browning on fresh‘Huangguan'pear juice.Moreover,WPI acted more effectively than pectinase.In addition,the effect of WPI combined with pectinase treatment was better than the effect of WPI treatment alone.