Exploring Hydroxytyrosol-Enriched Commercial Formulations: Effects on Tomato Yield and Quality Under Greenhouse Conditions

Agro-food processing by-products represent valuable sources of bioactive compounds with potential applications in sustainable crop production. This study evaluated the agronomic and postharvest responses of greenhouse-grown tomato to two commercial formulations enriched in hydroxytyrosol (Formula A and Formula B) and derived from olive oil processing by-products. Plants were grown in a soilless coco-peat system, and the formulations were applied manually to the root system according to their respective manufacturer-recommended regimes. The substrate bag was considered the experimental unit (n = 6 per treatment), with the greenhouse block retained in the statistical model. Formula A and Formula B increased total yield by 9.6% and 15.7%, respectively, and marketable yield by 14.5% and 21.0%. Both formulations increased fruit firmness, whereas total soluble solids remained unaffected. Shelf life increased from 23 days in control fruit to 32 and 38 days following Formula A and Formula B application, respectively. Antioxidant-related responses were treatment-dependent: Formula B increased DPPH radical-scavenging capacity and total and reduced vitamin C, whereas lycopene increased significantly with Formula A and showed an intermediate response with Formula B; total polyphenols and anthocyanins were unaffected. The treatments also modified fruit primary-metabolite profiles, including sugars, organic acids, and amino acids, and both formulations increased fruit Ca, K, and N concentrations at the final sampling. Overall, these findings demonstrate the potential of hydroxytyrosol-enriched commercial formulations to improve tomato productivity and selected postharvest-quality traits while providing a valorization route for olive oil processing by-products. However, because the formulations differed in composition, hydroxytyrosol concentration, dose, and application frequency, the specific contribution of hydroxytyrosol cannot be isolated from that of the complete formulations.