4. Conclusions
Here we have performed a comparison of frozen litchi fruits
which have undergone either immersion or air-blast freezing. An
analysis of the quality changes of frozen litchi fruit during its
refrigerated storage was done for 6e12 months post-freezing. IF
was found to be a greatly superior freezing method, with quality
similar to fresh litchis, whereas AF led to deterioration of the fruits.
The higher freezing rate and the better integrity of microstructure
of IF litchis likely explained the higher preservation quality in terms
of reduced drip loss, color retention, and texture quality. The
freezing procedure must be an integrated and systematic process
for optimal quality preservation incorporating a series of treat-
ments including color-protecting, vacuum packaging, precooling,
immersion freezing, frozen storage and quick thawing. Among
these treatments, the high freezing rate in IF played the most
important role in guaranteeing good quality during frozen storage
because of the small size of ice crystals and reduced damage to the
fruit microstructure. A constant long-term storage temperature
followed by a quick and uniform thawing process ensured the
maintenance of these advantages through inhibiting ice crystal
growth and recrystallization. These processes were indispensable
for the good quality preservation of litchi fruit during storage. IF has
clear and demonstrable advantages in enhancing the quality of
frozen litchis. Since further studies and optimization efforts will be
carried out in the future, immersion freezing technology could be a
novel application for long term storage of litchi fruits as well as for
all other frozen food with very promising industrial potential