Cooling characteristics of different precooling methods for litchi

To study the cooling characteristics of different precooling methods for litchi.

A pressure-difference precooling test chamber was established. Four precooling methods, including ice water(L1), cold storage(L2), pressure-difference(L3) and forced-air pressure-difference with high humidity (L4), were adopted for "Huaizhi" litchi.

The results showed that L1, L2, L3 and L4 spent 35, 55, 64 and 345 min respectively to precool the litchi down to the target temperature (5 ℃). The cooling procedure of litchi fruit at different positions for L1 performed no significant difference. L2 took 195, 258 and 228 min to precool litchi at left and right positions and top layer respectively. However, the fruit temperature at middle and bottom layer and middle position were still up to 5.37, 6.16 and 7.37 ℃ respectively after 345 min precooling; and the cooling procedure of litchi fruit showed significant differences between the left, right position and its middle position. L3 took 39, 52, 42 min to precool litchi at the left and right positions and top layer respectively. However, the fruit temperature at middle and bottom layers and middle position were still up to 6.03, 5.67 and 9.03 ℃ respectively after 55 min precooling. The cooling procedure of litchi fruit showed significant difference among the top layer, left position and its middle and bottom layers. L4 spent 39 and 41 min to precool litchi at the left position and top layer respectively. However, the fruit temperature at the middle and bottom layers, middle and right positions were still respectively up to 5.86, 8.83, 7.87 and 6.63 ℃ after 64 min precooling. The cooling procedure of litchi fruit showed a significant difference between the left position and its middle position. L1 has high cooling efficiency and good fruit temperature uniformity, which is suitable for cooling litchi.