Abstract: In order to identify the best thawing method to produce raspberry juice, five thawing methods were used to treat frozen raspberry, namely water bath thawing, microwave thawing, ultrasonic thawing, room temperature thawing and refrigerator thawing. This study intended to investigate if different thawing techniques could have different impacts on the thawing efficiency and drip loss. Besides, the effects of different thawing methods on 16 processing characteristics of raspberry juice were examined. Finally, we used principal component analysis, cluster analysis and grey correlation degree analysis to classify and screen the 16 indicators, and we comprehensively evaluate the 5 thawing methods. The results showed that the thawing efficiency and drip loss were highly significantly different among thawing methods (P < 0.01). The thawing efficiency followed the descending order: microwave thawing > ultrasonic thawing > water bath thawing > room temperature thawing > refrigerator thawing. The drip loss followed the ascending order: microwave thawing < room temperature thawing < refrigerator thawing < ultrasonic thawing < water bath thawing. The juice yield, sugar-acid ratio, browning degree and viscosity were representative indexes and their weight coefficients were 0.239, 0.196, 0.250 and 0.315, respectively. According to grey correlation degree analysis, the best thawing method to produce raspberry juice was microwave thawing.

Key words: raspberry, thawing, processing characteristics, principal component analysis, cluster analysis, grey correlation degree analysis