Effect of drying method and temperature on powder characteristics and polyphenol content of Strawberries

The effect of the freeze- drying,blast- drying,vacuum- drying and drying temperature on powder characteristics and polyphenol content of strawberries was studied in this paper. Extractable polyphenols( EPP)were obtained with 50% methanol and 70% acetone,and non- extractable polyphenols( NEPP) were hydrolyzed by methanol / H2SO4.Polyphenol content was determined by the Folin- phenol reagent method. The values of L*,a*,b*of the strawberry powder were measured by using a color meter.And the transmittance of the supernatant was observed at 665 nm.The results showed that the highest yields of EPP and proanthocyanins were obtained in the freeze- dired strawberry,and EPP in the strawberry powder was significantly decreased with the increasing of drying temperature and the NEPP showed the opposite trend. But there was no significant effect of the drying treatment on the TPP yield.There was no obvious change of index of the strawberry powder among different drying method and temperature. But the transmittance of the supernatant,the values of L*,a*and b*of strawberry powder decreased with the increasing of the drying temperature.In all,freeze- dried retained the EPP and original color in strawberries.