Response of Chlorophyllase and Magnesium Dechelatase Enzymes in Yellow- and Green-Fleshed Kiwifruit to Degreening at Different Temperatures

Kiwifruit cultivars include fruit having a diversity of flesh colors in the range red to yellow to green, associated with specific pigment accumulations. In the yellow-fleshed cultivars, chlorophyll degradation is necessary to unmask the underlying carotenoid pigments, which are responsible for the yellow color. This study aimed to confirm the enzyme activity involved in chlorophyll degradation using different degreening temperatures in the yellow-fleshed kiwifruit (cv. ‘Kiss’, Actinidia chinensis var. chinensis) and in the contrasting green-fleshed kiwifruit (cv. ‘Hayward’, Actinidia chinensis var. deliciosa). Cultivar ‘Kiss’ was harvested at hue angle 106.9° and degreening was carried out at 0, 5, 10 or 15 °C for 41 d. Additionally, one week later, a second batch of the same cultivar was subsequently treated at 30 °C for one week to explore the inhibitory effect on degreening and to elucidate the roles of chlorophyllase and magnesium dechelatase enzymes in the process. Fruit degreened at 30 °C was maintained at 15 °C for 23 d afterward and was compared with fruit stored at 0 °C or at 15 °C for 30 d. Similar degreening treatments were applied to cv. ‘Hayward’ at commercial maturity. Every seven days, flesh color, pigment concentrations and the activities of chlorophyllase and magnesium dechelatase in the flesh were evaluated. Degreening of ‘Kiss’ kiwifruit was enhanced by 15 °C treatment or by 30 °C treatment for seven days and was associated with increasing carotenoids and decreasing chlorophyll a. The magnesium dechelatase activity was greater in fruit degreening at 15 °C, which was consistently maintained throughout the degreening period; however, the activity remained low at very high temperature (30 °C). Regardless of the above, degreening at 30 °C was not inhibited, showing faster color change and high chlorophyllase activity during the exposure time. In contrast, ‘Hayward’ maintained its green color with high concentrations of chlorophylls and carotenoids. However, the high chlorophyllase and the low magnesium dechelatase activities found in ‘Hayward’, suggest that chlorophyllase enzymes are not the only ones involved in flesh degreening.