Abstract:The effects of vacuum concentration, membrane concentration, freezing concentration and thermal concentration on the nutrient composition and antioxidant components of crystal pears were investigated using polyphenol oxidase (PPO), 5-hydroxymethylfurfural (5-HFM), total phenol content, titratable acidity, vitamin C (Vc) content and antioxidant activity as the indicators. The results showed that all four concentration methods increased the total phenolic content, total antioxidant activity, and ABTS+ and DPPH radical scavenging capacities of pear juice, with insignificant difference in reducing sugar content. Vacuumconcentrated pear juice had the highest sugar content (60 °Bx) and showed the greatest antioxidant effect, althoughhaving a higher PPO activity. Thermal-concentrated pear juice had the highest total phenolic content and the lowest soluble protein content (0.015 mg/mL), while causing the generation of 5-HMF (which was not detected otherwise in the juices treated by other methods). Freeze-concentration and membrane-concentration affected the titratable acid and Vc contents of pear juice to different extents. Correlation analysis showed that there were different degrees of correlation between the indicators, and the cumulative contribution of the three characteristic factors extracted from the principal component analysis reached 94.53%, reflecting the comprehensive influence of multiple indicators on the quality of pear juice. The comprehensive analysis showed that the pear juice obtained via vacuum concentration had the highest comprehensive score (1.95) and significant advantages in concentration efficiency and antioxidant activity; thermal concentration had certain advantages in improving the nutrient content of pear juice, but due to the generation of 5-HFM, its comprehensive score was the second highest. This study provides a theoretical basis for pear juice concentration and fruit deep processing.
