Effects of low temperature pre-cooling on the inner temperature and mass loss of longan fruits treated with SO2 fresh-keeping paper before and during storage at normal atmospheric temperature

This paper aimed to study the effects of low temperature pre-cooling in refrigeration room at 5℃ on the inner temperature and mass loss of longan fruits covered with SO2 fresh-keeping paper and stored in sealed foam boxes at 25℃ . With longan cv. Chuliang used as materials, a L9（34） orthogonal design was used to test the effects of different factors including dosage of compound preservative （factor A）, pre-cooling method （factor B） and duration of pre-cooling （factor C） on the fruit inner temperature and mass loss rate of longan fruits before and during storage at 25℃ . The results showed that all the treatments had a significantly lower fruit temperature when packed （T1）, the lowest temperature during storage （T2） and the temperature when unpacked （T3） than the control by 10~20℃ （P ﹤ 0.05）, 5~10℃ （P ﹤ 0.05） and 1~4℃ respectively, and a much longer duration of fruit warming-up by 2~3 times. Meanwhile, the mass loss rates of treatments after pre-cooling and storage and on 4d-shelf were all increased, but decreased during storage. The cooling rate of naked fruits without any covering （abbreviated as NC） was higher than that of fruits covered with single layer newspaper （PC） and wet cloth after wrung out （WC）, the latter two were similar. Among the three pre-cooling methods, the inner temperature of fruits after NC was significantly lower than that of PC and WC by 3~4℃ （P ﹤ 0.05）, and the PC lower than WC. The longer the pre-cooling duration, the lower the T1 and the fruit temperature during the whole storage. Furthermore, the effects of factor B on the fruit temperature and mas loss rate was the most significant （P ﹤ 0.05）, followed by factor C and A, and factor A has little effect. Combined with the mean value comparison, it was concluded that A1（or A2） B1C1（or C2） is a recommended combination for the longan fruits within foam box stored at 25℃ , which can result in a better shelf performance in the range of 0.18~0.22% factor A along with NC and 4~13 h pre-cooling duration.