Effects of Pre-Harvest Supplemental UV-A Light on Growth and Quality of Chinese Kale

The effects of supplemental UV-A (385 nm) period and UV-A intensity for 5 days before harvest (DBH) on growth, antioxidants, antioxidant capacity, and glucosinolates contents in Chinese kale (Brassica oleracea var. alboglabra Bailey) were studied in plant factory. In the experiment of the UV-A period, three treatments were designed with 10 W center dot m(-2) UV-A supplement, T1(5 DBH), T2 (10 DBH), and no supplemental UV-A as control. In the experiment of UV-A intensity, four treatments were designed with 5 DBH, control (0 W center dot m(-2)), 5 w (5 W center dot m(-2)), 10 w (10 W center dot m(-2)), and 15 w (15 W center dot m(-2)). The growth light is as follows: 250 mu mol center dot m(-2)center dot s(-1); red light: white light = 2:3; photoperiod: 12/12. The growth and quality of Chinese kale were improved by supplemental UV-A LED. The plant height, stem diameter, and biomass of Chinese kale were the highest in the 5 W center dot m(-2) treatment for 5 DBH. The contents of chlorophyll a, chlorophyll b, and total chlorophyll were only highly increased by 5 W center dot m(-2) UV-A for 5 DBH, while there was no significant difference in the content of carotenoid among all treatments. The contents of soluble sugar and free amino acid were higher only under 10 DBH treatments than in control. The contents of total phenolic and total antioxidant capacity were the highest in 5 W center dot m(-2) treatment for 5 DBH. There was a significant positive correlation between total phenolic content and DPPH and FRAP value. After 5 DBH treatments, the percentages and contents of total aliphatic glucosinolates, sinigrin (SIN), gluconapin (GNA), and glucobrassicanapin (GBN) were highly increased, while the percentages and contents of glucobrassicin (GBS), 4-methoxyglucobrassicin (4-MGBS), and Progoitrin (PRO) were significantly decreased, especially under 10 W center dot m(-2) treatment. Our results show that UV-A LED supplements could improve the growth and quality of Chinese kale, and 5 W center dot m(-2) UV-A LED with 5 DBH might be feasible for Chinese kale growth, and 10 W center dot m(-2) UV-A LED with 5 DBH was better for aliphatic glucosinolates accumulation in Chinese kale.

Automated summary

The effects of supplemental UV-A LED on the growth and quality of Chinese kale were studied. The results showed that 5 W UV-A LED with 5 days before harvest (DBH) had a positive effect on the growth of Chinese kale, while 10 W UV-A LED with 5 DBH was better for the accumulation of aliphatic glucosinolates in Chinese kale.