Effects of White and Red Light Photoperiods on Physiology and Biochemistry as well as Glucoraphanin Metabololism of Broccoli Sprouts

In this study, the effects of white light and red light at different photoperiods (0, 4, 8, 12, 16 and 20 h·d⁻¹) on growth, contents of soluble sugar, soluble protein, ascorbic acid, anthocyanins as well as glucoraphanin metabolism of broccoli sprouts were studied. The results showed that the growth of broccoli sprouts was inhibited by light treatment, but red light promoted the growth compared with white light. With the increasing of light photoperiods, the content of soluble sugar, soluble protein, ascorbic acid, glucoraphanin and total glucosinolates, myrosinase activity as well as sulforaphane formation firstly increased, then decreased. Compared with white light, red light significantly enhanced soluble sugar, soluble protein, ascorbic acid and glucoraphanin content in broccoli sprouts. However, higher anthocyanin content was observed in white light treated broccoli sprouts rather than red light treated broccoli sprouts. In addition, when photoperiod was less than 12 h, red light resulted in higher sulforaphane formation than white light (P<0.05). When photoperiod was more than 12 h, red light did not affect even decreased sulforaphane formation compared with white light treatment. In conclusion, red light treatment was beneficial to the enhancement of yield and nutritional quality of broccoli sprouts compared with white light, and 12 h·d⁻¹ was the appropriate photoperiods.