The changes in nutritional quality of frozen litchis could be determined by comparing key quality indices. This study analyzed vitamin C and TSS to determine the effect of freezing methods on nutrient preservation in frozen litchis. It was
found that little drip loss occurred in the IF samples (p < 0.05) during the whole storage time, while drip loss increased to 4% in AF samples after 180 days of storage (Fig. 6a). This can be easily explained in the light of the relationship between drip loss and microstructure integrity. The vitamin C content and TSS decreased gradually in both IF and AF samples of vitamin C was detected in AF samples,likely due to rapid leaching out via drip loss, whereas less than 20% loss occurred in the IF samples. It was noticed that most of the vitamin C loss in IF samples occurred before and during the freezing
process rather than storage time, indicating that optimization of pretreatment and freezing processes are the key steps to preserving vitamin C levels, as well as the other nutrients. Additionally, the application of microwave thawing played a critical role in minimizing nutrient loss due to rapid and uniform thawing and reduced thawing time. This could
effectively avoid the damaging effects of increased temperature,
enzymatic activity and microbe growth on loss of vitamin C, sugar
and other nutrients during thawing. Also, microwave thawing itself
also has a sterilizing effect and can reduce enzyme activity. As a
result, application of IF process plus water shift microwave thawing
radically resolved the problem of drip loss in frozen litchi fruit.
With the same thawing method, the quality changes obtained from
AF and IF were different. It therefore can be concluded that the
main differences of quality changes obtained from IF and AF litchis
with the same storage and thawing processes were due to the
different freezing procedures.