Encapsulated essential oil blend of thyme, cloves and rosemary oils as natural preservative: A sustainable solution to post-harvest food and fruit spoilage in Uganda

Abstract

Post-harvest spoilage of fruits, particularly tomatoes, accounts for up to 40% annual losses in Uganda, mainly due to microbial contamination, ethylene-induced ripening, and oxidative degradation. Conventional chemical preservatives reduce spoilage but raise health and environmental concerns, necessitating natural, eco-friendly alternatives. Essential oils (EOs) from thyme (Thymus vulgaris), clove (Syzygium aromaticum), and rosemary (Rosmarinus officinalis) are reported to possess antimicrobial, antioxidant, and ethylene-inhibiting properties. However, their direct application in food systems is constrained by high volatility, poor solubility, and undesirable sensory effects. In this study, a preservative blend of the three EOs was encapsulated using ionic gelation of carboxymethyl cellulose (CMC) with calcium chloride to achieve controlled release and improved stability. Antimicrobial activity of the encapsulated blend was evaluated against Escherichia coli and Staphylococcus aureus using Compact Dry plates. Preservative efficacy was further assessed by monitoring tomato firmness and color (USDA color scale) over a 14-day storage period at room temperature (25±2 °C). Results demonstrated that encapsulation enhanced both safety and functionality. The EO blend at 10% (v/v) completely inhibited E. coli growth and reduced S. aureus colonies by 95.6% relative to the untreated control (Table 1). In storage trials, untreated tomatoes reached full ripeness (USDA color score 6; firmness score 1) by day 9. In contrast, tomatoes treated with encapsulated oils retained higher quality, maintaining a lighter red stage (score 5) and improved firmness (score 2) even at day 14 (Table 4: color progression; Table 5: firmness comparison). Unencapsulated oils delayed ripening only until day 9, after which protection significantly declined. In conclusion, encapsulated EO blends substantially reduced microbial spoilage and delayed ripening, thereby preserving tomato quality and extending shelf life. This eco-friendly strategy offers a viable alternative to synthetic preservatives, with the potential to reduce post-harvest losses and improve food security in Uganda.