Heat Shock Treatments Induce the Accumulation of Phytochemicals in Kale Sprouts

Abstract

The objective of this study was to determine the effect of heat shock treatments on the phytochemicals including antioxidants and anticancer materials in kale (Brassica oleracea L. var. acephala) sprouts. In study I, kale sprouts grown under the growing system for four days were soaked at 40, 50, or 60℃ distilled water for 10, 30, or 60 seconds, and in study II, kale sprouts were soaked at 50℃ distilled water for 10, 20, 30, 45, or 60 seconds. After the heat shock treatments, the sprouts were transferred into normal growing conditions and recovered there for two days. Fresh and dry weights, electrolyte leakage, total phenolic concentration, antioxidant capacity, total flavonoid concentration, phenylalanine ammonia-lyase (PAL) activity, and glucosinolates content of the sprouts were measured before and after the heat shock treatments. As a result, there was a significant decrease in the fresh and dry weight of kale sprouts treated with heat shock compared with control at harvest in study I. Especially, heat shock at 60℃ lead to more pronounced growth inhibition compared with heat treatments at 40 and 50℃. Electrolyte leakage by cell collapse was the highest in the sprouts exposed to 60℃ distilled water, which agreed with the growth results. Heat shock at 50℃ significantly induced the accumulation of phenolic compounds. In study II, fresh weight of kale sprouts at 50℃ heat shock showed a significant decrease compared with the control at one and two days after the treatment. However, the decrease was minimal and dry weight of kale sprouts was not significantly different from that in control. In contrast, the heat shock-treated kale sprouts had higher level of total phenolic concentration than control at harvest. Heat shock treatments at 50℃ for 20 seconds or more showed at least 1.5 and 1.2 times higher total phenolic concentration and antioxidants capacity than control, respectively. The change of the total flavonoid concentration was similar with that of antioxidants. PAL activity after 24 hours of heat shock was higher in all the heat shock-treated sprouts than that in control suggesting heat shock may stimulate secondary metabolic pathway in kale sprouts. Seven glucosinolates were identified in kale sprouts and soaking the sprouts with 50℃ water for 20 seconds had a pronounced impact on the accumulation of total glucosinolates as well as two major glucosinolates, progoitrin and sinigrin, at harvest. In conclusion, this study suggests that heat shock using hot water would be a potential strategy to improve nutritional quality of kale sprouts by inducing the accumulation of phytochemicals with antioxidant and anticancer properties.

The Influence of Physical Treatments on Phytochemical Changes in Fresh Produce after Storage and Marketing

“…Kale (Brassica oleracea) sprouts were immersed in hot water at 40, 50, and 60 • C for 10, 30 or 60 s and then kept for 2 more days at ambient temperature. Treatment at 50 • C for at least 20 s significantly induced the accumulation of phenolic compounds and glucosinolates, as well as antioxidant capacity, as compared to the untreated control [35].…”

Optimal Duration of Drought Stress Near Harvest for Promoting Bioactive Compounds and Antioxidant Capacity in Kale with or without UV-B Radiation in Plant Factories

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