Light spectrum combinations and intensity effects on Brassicaceae microgreen biomass yield and secondary metabolite accumulation: a review

Microgreens are gaining increasing attention because of their short production cycle and their beneficial attributes such as high nutritional content, secondary metabolite production, and gastronomic applications. Among the key production parameters for microgreen production under controlled environments, light quality and quantity are key factors affecting beneficial attributes. Hence, the objective of this study was to synthesize the effects of light on outcomes in Brassicaceae microgreens. Therefore, we carried out a literature review from 36 different studies to collect, harmonize, and synthesize information on the effects of light spectrum combinations and intensities on 12 commonly grown Brassicaceae microgreens. We have presented results on the influence of light intensities and spectrum combinations on biomass and secondary metabolite production. For instance, results showed that there was a positive nonlinear correlation between the amount of light (cumulative light integral (CLI)=daily light integral * growing period in days) and dry weight (DW). We showed that an increase in CLI corresponds to an increase in DW (kg m^‑2) production up to 300 mol m^‑2 (R²=0.88), beyond which gains are minimal. Furthermore, we used multilinear regression models to show that more variation in DW, Carotenoid, and Anthocyanin outcomes was explained by the light spectrum combinations than light intensity. Furthermore, Brassicaceae microgreens showed a higher content of Carotenoids and Anthocyanins where multiple light spectra combinations were significantly associated with secondary metabolite production. Our results show that there are valuable benefits from including UV, far-red, and green spectra when producing microgreen biomass, carotenoids, or anthocyanins. The results provide a summarized overview on light intensity and spectrum combination effects on microgreens with a focus on accounting for variety-specific variation in microgreens which can inform future research designs and production environments based on desired outcomes.