After-Effect of Biogas Digestate Used for Growing Seedlings on the Antioxidant System of Tomato (Solanum lycopersicum) Fruits

Digestate is primarily a by-product of anaerobic digestion, where organic waste is converted into biogas. Also, digestate has become an excellent tool for enriching the eroding and disappearing fertile soil and restoring its fertility over the past two decades. The research applying digestate as a fertilizer includes outdoor and greenhouse vegetables such as tomatoes. Antioxidants are one of the most useful substances in tomatoes. Therefore, this work aimed to evaluate the residual effect of solid grain waste digestate (below digestate) used for seedling production on the response of the antioxidant capacity of tomatoes of different fruit maturity with other assays. Tomato seedlings were grown in a peat substrate (control) and peat mixed with 5%, 10%, 15%, and 20% biogas digestate addition; fruits were harvested at three maturity levels: green growth, half-ripe, and fully ripe. From each treatment, five fruits were randomly selected at different maturity stages. This research shows that both the maturity stage and the addition of digestate may influence the antioxidant activity and total phenolic contents in tomato fruit. The digestate addition shows a significant increase in phenolics; all treatments resulted in the highest amounts during full ripening. The percentage of digestate in peat substrate and peat mixture did not have such a uniform effect as fruit maturity. The addition of 20% digestate significantly increased antioxidant activity and total phenol content in green and medium-ripe fruit; however, fully ripened fruits had similar antioxidant system responses under all digestate treatments.