Heat Shock Induces the Accumulation of Phenolic Compounds and Antioxidants In Kale Sprouts

Environmental factors are known to induce the accumulation of various health-promoting phytochemicals including phenolic compounds in vegetables. The objective of this study was to determine the effect of heat shock treatment on the concentration of phenolic compounds and antioxidant capacity in kale sprouts (Brassica oleracea var. onika). Kale sprouts grown under an auto-sprouter for 4 d were soaked at 50°C water for 10, 20, 30, 45 or 60 s. After the heat shock treatment, the sprouts were transferred to normal growing conditions (20°C, 100 µmol/m²/s, 12 h photoperiod) and recovered there for 3 d. Total phenolic concentration, antioxidant capacity, and fresh and dry weights of the sprouts were measured before and after the heat shock. As a result, the heat shock treatment significantly maintained or increased total phenolic concentration in kale sprouts during the whole recovery period while the concentration of total phenolics in control gradually decreased in the process of sprouting. Especially, 20 s heat shock treatment or over showed at least 1.5 times higher total phenolic concentration than control at 2 d after the shock treatment. The variation of antioxidant capacity in kale sprouts also showed similar trend with that of total phenolic concentration. There was a significant decrease in fresh weight of kale sprouts treated with heat shock compared with control. However, the extent of decrease was little and dry weight of kale sprouts soaked at the hot water was not significantly different from that in control. In conclusion, this study suggests that heat shock treatment using hot water would be a potential strategy to improve nutritional quality of kale sprouts by inducing the accumulation of phenolic compounds with antioxidant properties.