A Combination of LED and Compost to Improve Spinacia oleracea L. Quality and Chemical Composition

Background: Spinach has a high content of nutrients, proteins, carbohydrates, and vitamins beneficial for human health, that are closely associated with the type of crop, the growing media, the temperature, and lights used for growing. Methods: Two types of light were used: white light (WL) and red light (RL), and also three different growing media: compost without additives (CB), compost with coffee additive (CC), and compost with rockrose additive (CR). Results: Spinach grown under WL, regardless of the treatment, showed greater plant growth than that grown under RLP. Furthermore, treatments WLCC and WLCR increased by 90% and 95%, respectively, compared to WLP; similarly, treatments WLCB, WLCC, and WLCR increased by 179%, 174%, and 205%, respectively, compared to the RLP control. The protein content of spinach leaves from growing media WLCB and WLCC increased by 50 and 46% respectively compared to WLP; similarly, growing media RLCB and RLCC increased by 82 and 57% respectively compared to RLP. This contrasted with the carbohydrate content, which was higher in spinach grown under WLP and RLP. Spinach grown under WLP and RLP showed significantly more free sugars. On the other hand, spinach grown under WL had a higher concentration of organic acids than that grown under RL, regardless of the growing media used. The content of fatty acids, phenolic compounds, and antioxidant activities did not follow a clear pattern with respect to the type of light and growing media. Conclusions: Overall, compost-based substrates combined with white LED light enhanced spinach growth and nutritional quality through a synergistic effect. However, compost reduced phenolic compounds, while red LED light increased phenolic content and antioxidant activity, indicating contrasting effects on spinach quality.