The comparative study of the quality characteristics of frozen litchi under different thawing temperatures and heat-transfer coefficient: Effects on thawing characteristics, physicochemical properties, nutritional characteristics, and eating quality

Thawing temperature and heat-transfer coefficient are important factors affecting the quality of thawed food, and are also essential parameters for thawing process optimization. The quality characteristics of frozen litchi under different thawing temperatures (4 °C, 12 °C, 25 °C, 37 °C, 50 °C) and heat-transfer coefficient (air thawing and still water thawing) were studied. The results showed that compared with air thawing, still water thawing could significantly shorten thawing time ( p < 0.05) by 67.86–90.49%. 12 °C and 25 °C were considered the reasonable temperature for thawing litchi which was specifically manifested less drip loss (0.93–1.41%), better texture profile and sensory evaluation, higher content of cell wall water and ascorbic acid (13.28-19.75 mg/100g). The slower the thawing rate, the more complete the microstructure of litchi. However, there was no significant difference ( p > 0.05) in the content of total soluble solids (TSS) and titratable acidity (TA) between different groups. The total viable bacteria in litchi thawing at 12 °C showed a relatively low level. There was a strong correlation between drip loss and texture profile, the content of ascorbic acid, and overall acceptability. At thawing temperatures of 4 °C and 50 °C, changes in heat-transfer coefficient would significantly affect the thawing quality characteristics of litchi. In summary, 12-25 °C is the appropriate temperature for thawing litchi. Within this temperature range, still water thawing can shorten the thawing time while maintaining the quality of litchi. • 12∼25 °C was suitable temperature for thawing frozen litchi. • Still water thawing was an effective way to improve heat-transfer coefficient. • The slower the thawing rate, the more complete the microstructure of litchi. • Reducing drip loss was necessary for thawing litchi. • Water content and integrity of cell wall help maintain hardness of litchi.