Short-term cold pretreatment accelerates ethephon-induced postharvest kiwiberry ripening

Rapid and uniform ripening is important for the postharvest processing and utilization of kiwifruit ( Actinidia arguta ). Ethephon-induced ripening, however, is often accompanied by excessive softening and oxidative deterioration. This study investigated the effects of short-term temperature pretreatment before ethephon application on the subsequent ripening process. Fruit received ethephon alone (Et), cold pretreatment at 0 °C for 8 h before ethephon application (CEt), or heat pretreatment at 35 °C for 8 h before ethephon application (HEt); untreated fruit served as a natural-ripening reference. CEt fruit attained a soluble solids content of 16.39% and a firmness of 9.48 N at 24 h, when respiration and ethylene evolution rates also peaked. Fructose and glucose accumulated earlier, whereas malic and quinic acid contents declined. The accelerated decrease in firmness was accompanied by greater losses of Na₂CO₃-soluble and CDTA-soluble pectins, an earlier peak in pectin methylesterase activity, and higher polygalacturonase and β-galactosidase activities during late ripening. At 48 h, malondialdehyde content and electrolyte leakage in CEt fruit were 9.0% and 8.9% lower than those in HEt fruit and 5.4% and 4.2% lower than those in Et fruit, respectively. Antioxidant enzyme activities increased earlier, and several in vitro antioxidant-capacity indices remained higher through late ripening. CEt reached the predefined sensory threshold at 16 h, and its mean sensory scores at 24 and 36 h both exceeded 8.4. The principal CEt-versus-Et response pattern was also observed in an independent second-year validation. Under the present conditions, cold pretreatment before ethephon application accelerated the ripening of hardy kiwifruit, while the measured membrane-injury indices remained lower than those of Et and HEt fruit at 48 h.