Formulation of a Corn Starch and Thyme Extract–Based Natural Spray for Postharvest Preservation and Insect Control, Applied to Tomato Fruits and Aphis gossypii

Abstract

This study aimed to develop a natural bio-spray for postharvest fruit preservation with dual functionality, combining postharvest preservation and insecticidal activity, and to evaluate its effectiveness under room-temperature storage conditions as a natural alternative to conventional chemical products. The bio-spray was formulated using the hydroethanolic extract of Thymus vulgaris and corn starch, together with other auxiliary ingredients to obtain a stable formulation. The plant extract was prepared by cold maceration using a hydroethanolic solvent (80:20, v/v), yielding an extraction efficiency of 9.96%. Three bio-spray formulations containing 0.375 g, 0.750 g, and 1.125 g of thyme extract per 250 mL were prepared while maintaining the same proportions of the other formulation components. The insecticidal activity of the extract and the formulated sprays was evaluated using a direct contact bioassay against the cotton aphid (Aphis gossypii). In addition, the efficacy of the bio-spray in preserving tomato fruits was assessed over a 15-day storage period. The results showed that aphid mortality increased progressively with increasing extract concentration and exposure time. The highest concentration (1.125 g/250 mL) achieved 100% mortality after 15 min, whereas the same mortality rate was reached after 20 and 25 min with the 0.750 g and 0.375 g formulations, respectively. Regarding tomato preservation, the untreated control fruits exhibited the first signs of deterioration from the fifth day, with pronounced deterioration on days 10 and 15. In contrast, all treatments containing thyme extract delayed fruit deterioration and maintained fruit quality throughout the storage period. Among the tested formulations, T2 showed the best performance in preserving fruit firmness, external appearance, and overall quality, followed by T1 and T3. These findings indicate that combining the hydroethanolic extract of Thymus vulgaris with corn starch represents a promising strategy for developing a natural bio-spray or edible coating capable of extending the postharvest shelf life of fruits while controlling certain agricultural pests, with strong potential for future commercialization as an environmentally friendly postharvest preservation product.