Natural Preservation Strategy for Green Olives: Effects of Thyme Oil-Enriched Chitosan Edible Films on Physicochemical, Microbiological, and Sensory Attributes

Edible film-coating technology is an innovative approach to help maintain food quality and inhibit microbial growth in place of synthetic preservatives. This study focused on evaluating the effects of chitosan (CS) films (2%) contained with thyme essential oil (TO) at 0.2, 0.5, and 1% on the microbiological changes, sensory, and quality attributes of green olives stored at 4 °C for 90 days. Table olive samples, which were covered with chitosan solutions containing different concentrations of thyme oil, were assessed for physicochemical (% moisture, pH, titratable acidity, color (L*, a*, b^*, and ΔE*)) and microbiological (total viable count and yeast and mold count) and sensory properties. During the storage period, moisture loss was more evident in the control group, decreasing to 53.62 ± 0.33% by day 90. In contrast, the CS and CS+TO coatings significantly reduced moisture loss. Specifically, the CS+0.2% TO, CS+0.5% TO, and CS+1% TO treatments maintained moisture levels around 57-58% at the end of storage. The overall sensory results indicated that edible coatings, particularly those containing thyme oil, effectively preserved the visual and textural quality of green olives throughout storage. However, high concentrations of thyme oil slightly reduced taste acceptability. Therefore, CS+0.2% TO and CS+0.5% TO formulations appear to offer the most balanced performance, combining effective antimicrobial protection with favorable sensory properties. The maximum reduction in total viable count (TVC) and yeast-mold was observed in the CS+1% TO group, with values of 4.36 and 3.07 log CFU/g, respectively. It has been determined that chitosan films containing thyme oil have an inhibitory effect on microbial activity. Overall, these results demonstrate the usability of edible films as synthetic preservatives and edible coating systems offer promising potential for preserving both the safety and quality of table olives, while also supporting consumer acceptance.