Temperature and duration of water dips influence chilling injury, decay and polyamine content in 'Fortune' mandarins

Late-ripening mandarin (Citrus reticulata, Blanco, cv. 'Fortune') is appreciated for its quality, but the high sensitivity of this cultivar to chilling injury (CI) limits its marketability. In this study, the effect of postharvest hot-water dip (HWD) treatments on chilling tolerance and polyamine (PA) induction in flavedo tissue was investigated. After HWD treatments (44 degrees C for 3, 9 and 15 min; 47 degrees C for 3, 6 and 9 min; and 50 degrees and 53 degrees C for 3 min), fruits were stored for 45 days at 2 degrees or 12 degrees C, and CI development, decay, weight loss, and PA content were evaluated. After 45 days at 2 degrees C, the major reduction in CI was found in fruit dipped for 6 min at 47 degrees C or 3 min at 53 degrees C. Under these treatments, the CI index was 0.8 and 0.75, respectively, as compared with 1.5 in untreated fruit. Fruit stored at 12 degrees C did not develop any CI symptoms. The different HWDs also reduced fruit decay, bur did not alter the rate of water loss during cold storage at both temperatures. Immediately after HWDs, PA content increased in flavedo with temperature and exposure time. The most important relative increase occurred in spermine (spm), despite being the minor PA. The HWD-induced spm content decreased about two-fold after 28 days of cold storage. Spermine reduction was more important than that observed in spermidine (spd) and putrescine (put). This pattern of change in PA content does not appear to be related to the HWD-induced cold tolerance.