In this study, we screened eight walnut (Juglans regia L.) cultivars (‘Xifu2’, ‘Shaanhe’, ‘Weina’, ‘Xiangling’, ‘Xiluo3’, ‘Xifu1’, ‘Liaoning4’, and ‘Qingxiang’) in order to establish reliable selection criteria for storage-tolerance. Fresh walnut fruit were stored at 0 ± 0.5 °C and 70–80% relative humidity. Browning index, postharvest physio-biochemical characteristics, acid value, and sensory quality were measured. The results showed that ‘Xifu2’, ‘Shaanhe’, and ‘Weina’ developed browning early and quickly and storage was terminated for these cultivars at 60 days. ‘Xiluo3’, ‘Xifu1’, ‘Liaoning4’, and ‘Qingxiang’ had a slow browning rate and storage was terminated at 72 days. ‘Xiangling’ developed browning at a medium rate and storage was terminated at 72 days. Correlation analysis suggested that the terminal browning index of each cultivar positively correlated with lipoxygenase activity at 18 days of storage, polyphenol oxidase activity at 18–30 days, malondialdehyde content at 18 days, and the respiration rate at 42 days, while it negatively correlated with the total phenolic content at 18 days and phenylalanine ammonia lyase activity at 12 days. The storage tolerance of each cultivar was evaluated according to the terminal browning index, acid value, and sensory quality. Comprehensive evaluation and cluster analysis were performed to rank the cold storage tolerance of the eight cultivars as follows: ‘Qingxiang’ and ‘Xifu1’ > ‘Liaoning4’ and ‘Xiluo3’ > ‘Xifu2’ and ‘Xiangling’ > ‘Shaanhe’ and ‘Weina’. In conclusion, cultivars used for fresh in-husk walnut fruit with lower levels of membrane peroxidation and phenol oxidation, and higher level of phenol synthesis around 18 days of storage would be suitable candidates for cold storage. ‘Qingxiang’ and ‘Xifu1’ were selected as storage-tolerant cultivars.
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The authors are grateful for financial support from the Nationwide Extension Project of Forestry Science and Technology (44, China). We would like to acknowledge Mrs. Chaoning Zeng and Xindan Zhang for their valuable modifications on language of this manuscript.
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