The Effect of Light Intensity and Photoperiod on the Yield and Antioxidant Activity of Beet Microgreens Produced in an Indoor System

Abstract

Microgreens are immature and tender edible vegetables that have become relevant in the market due to their contribution to human health as “functional food”. They can be produced in controlled environments, allowing more efficient use of space and resources and facilitating the management of environmental conditions, such as light, temperature, and relative humidity. The study’s objective was to evaluate the impact of photoperiod and light intensity on red beet microgreens’ yield and the antioxidant compound content. LED growth lamps (spectrum of 75% red, 23% blue, and 2% far-red) under two photoperiods were evaluated: 12 and 16 h, and three intensity levels: 120 (low), 160 (medium), and 220 (high) µmol m−2 s−1. The largest photoperiod raised 32, 49, and 25% on phenolic compounds, total betalains, and antioxidant capacity, respectively, but a 23% reduction in microgreens yield was obtained compared with the shortest photoperiod. The low and medium intensities promoted the highest yield, reaching 460 g m−2; yield decreased significantly by 22.1% at high intensity compared to low and medium intensity. Contrastingly, no effect on antioxidant activity was observed with the evaluated range intensities, except for the betalains concentration, which was reduced by 35% under the highest intensity compared to low intensity. On the other hand, resource use efficiency (energy and water) improved under the shortest photoperiod. Thus, an intensity between 120 and 160 µmol m−2 s−1 and a photoperiod of 12 h favored the microgreen’s beet growth and saved electricity; meanwhile, a 16 h photoperiod ameliorated the beet microgreens antioxidant activity under a light spectrum composed of blue:red:far-red = 23:75:2.