Temporary Low Temperature Accumulates Antioxidant Phenolic Compounds in Kale

Various environmental factors are known to induce the accumulation of health-promoting phytochemicals in plant-based food. The objective of this study was to determine the effect of temporary low temperature on the concentration of antioxidant phenol compounds in kale (Brassica oleracea var. acephara). Fourteen day-old kale seedlings of two cultivars (‘Manchoo Collard’ and ‘TBC’) were transplanted and cultivated in a growth chamber (20°C, 12 h photoperiod, Red:White:Blue LEDs = 8:1:1, 142±10 µmol·m^-2·s^-1) for 3 weeks. For low-temperature treatment, kale plants at 3 weeks of transplanting were subjected to 4°C low temperature for 3 d and subsequently recovered for 2 d under normal growth conditions. Fresh and dry weights of shoots and roots, Fv/Fm ratio, total phenolic concentration and antioxidant capacity were measured before the treatment and 2 d of recovery. As a result, Fv/Fm ratio of kale leaves started to decrease at 15 h of low temperature treatment. No significant difference was observed between control and low temperature treatment in fresh and dry weights of shoots and roots of both cultivars. However, two cultivars showed opposite trends in total phenolic concentration and antioxidant capacity. ‘Manchoo Collard’ exposed to low temperature had 15% higher total phenolics than control, whereas TBC under low temperature showed 16% lower total phenolics than control. Similar trends were observed in antioxidant capacity. In conclusion, these results suggested that temporary low temperature treatment would be a potential strategy to improve nutritional quality of kale without growth inhibition.