Effects of Different Freezing Temperatures and Freeze-thaw Cycles on Quality Characteristics of Blueberries
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Abstract:
The effects of freezing temperature and freeze-thaw cycles on blueberry fruit quality were studied. Using refrigeration at 4 ℃ as the control group, the short-period changes in the quality indexes of blueberry such as firmness, soluble solid content, titratable acid content, ascorbic acid content, anthocyanin content and malondialdehyde content were investigated at freezing temperatures of -10 ℃, -18 ℃, -25 ℃ and -80 ℃. One, two, three and four freeze-thaw cycles were carried out, and the above quality indexes and physical indicators such as fruit cracking rate and thawing loss rate were determined repeatedly. The results showed that compared with the control group, the soluble solid content of the -80 ℃ freezing group increased by 0.10% on average, whilst the -10 ℃ freezing group decreased by 0.17% on average. During the storage period, the titratable acid content of the control group decreased by 0.35%, whilst the -80 ℃ freezing group decreased by only 0.15%. The number of freeze-thaw cycles was significantly and positively correlated with the anthocyanin content, malondialdehyde content and fruit cracking rate, and significantly and negatively correlated with the firmness and ascorbic acid content. The regression equations of the quality indexes and the number of freeze-thaw cycles was constructed. After the blueberries were subjected repeatedly to freeze-thaw cyclefor more than twice, the changing trend of the regression equation became obvious. Blueberries are suitable for frozen storage, but -10 ℃ is not a suitable freezing temperature for blueberries. The quality of quick-frozen blueberries at -80 ℃ is better, and the number of repeated freeze-thaw cycles during actual frozen storage and processing should not exceed twice.
