Effects of Reactive Oxygen Levels on Chilling Injury and Storability in 21 Apricot Varieties from Different Production Areas in China

The key factors for resistance to chilling injury in apricot fruits were obtained by analyzing the low-temperature storage characteristics of 21 varieties of apricot fruits in the main producing areas of China. Twenty-one varieties of apricots from different production areas in China were stored at 0 °C for 50 d and then shelved at 25 °C. The storage quality, chilling injury, reactive oxygen species (ROS), antioxidant ability, and contents of bioactive substances of the apricots were measured and analyzed. The results showed that the 21 varieties of apricot fruits could be divided into two categories according to tolerance during low-temperature storage, where there was chilling tolerance and lack of chilling tolerance. Eleven varieties of apricots, of which Xiangbai and Yunbai are representative, suffered from severe chilling injury after cold storage and shelf life. After 50 d of storage at 0 °C, the levels of superoxide anions and hydrogen peroxide accumulated in the 11 varieties of apricots with a lack of chilling tolerance during storage were significantly higher than those in the remaining 10 varieties of apricots with chilling tolerance. In addition, the activities of ROS scavenging enzymes, represented by superoxide dismutase, catalase and peroxidase, were significantly decreased in 11 varieties of apricots with a lack of chilling tolerance during storage. The contents of bioactive substances with ROS scavenging ability, represented by ascorbic acid, total phenols, carotenoids, and total flavonoids, also significantly decreased. The 10 varieties of apricots, of which Akeximixi and Suanmao are representative, were less affected by chilling injury because the production and removal of ROS were maintained at normal levels, avoiding the damaging effects of ROS accumulation in the fruit. In addition, the 10 apricot varieties with chilling tolerance during storage had higher sugar and acid contents after harvest. This could supply energy for physiological metabolism during cold storage and provide carbon skeletons for secondary metabolism, thus enhancing the chilling tolerance of the fruits. Based on the results of cluster analysis combined with the geographical distribution of the 21 fruit varieties, it was found that apricot varieties with chilling tolerance during storage were all from the northwestern region of China where diurnal temperature differences and rapid climate changes occur. In conclusion, maintaining the balance of ROS production and removal in apricots during cold storage is a key factor to enhance the storage tolerance of apricots. Moreover, apricots with higher initial glycolic acid and bioactive substance contents are less susceptible to chilling injury.