Hot air treatment decreases chlorophyll catabolism during postharvest senescence of broccoli (Brassica oleracea L. var. italica) heads

Abstract

AbstractA hot air treatment was applied to broccoli (Brassica oleracea L. var. italica) florets and its effect on chlorophyll catabolism during postharvest senescence was analyzed. Florets were treated at 48 °C for 3 h and then placed in darkness at 20 °C. During storage, the yellowing of florets occurred simultaneously with a decrease in chlorophylls and an increase in pheophytins. Heat treatment delayed the appearance of yellowing by 2–3 days and a similar extension of shelf‐life could be inferred. Also, the treatment delayed the onset of chlorophyll catabolism and slowed both the rate of chlorophyll a degradation and pheophytin accumulation. No effect on chlorophyll b degradation was found. Chlorophyllase and Mg‐dechelatase activities increased from the first day of storage in untreated florets, whereas peroxidase‐linked chlorophyll bleaching activity increased from day 3. In heat‐treated florets, chlorophyllase activity did not increase until day 2 and then increased at lower rate than in controls. Mg‐dechelatase and peroxidase‐linked chlorophyll bleaching activities were similar in treated and control florets during the first 2 days of storage, but thereafter the activity of both enzymes was lower in heat‐treated samples. In conclusion, a treatment at 48 °C for 3 h delayed chlorophyll a catabolism in broccoli during postharvest senescence and decreased the activities of chlorophyllase, Mg‐dechelatase and peroxidase, three of the enzymes probably involved in chlorophyll degradation in plants. Copyright © 2006 Society of Chemical Industry