Enhancing Antioxidant, Antiproliferation, and Free Radical Scavenging Activities in Strawberries with Essential Oils

Abstract

Several natural antimicrobial compounds derived from essential oils of plants were investigated for their efficacies in inhibiting decay and extending the shelf life of strawberries (Fragaria x ananassas Duch.). The severity of decay in strawberries stored at 10 °C was significantly reduced by treatment with thymol. Treatments with menthol or eugenol also suppressed the fungal growth, but to a lesser extent. All of these three natural antimicrobial compounds extended shelf life of strawberries as compared to the control. Strawberries treated with thymol, menthol, or eugenol also maintained better fruit quality with higher levels of sugars, organic acids, phenolics, anthocyanins, flavonoids, and oxygen radical absorbance capacity than the untreated fruits. The free radical scavenging properties of strawberry fruit were evaluated against 2,2-diphenyl-1-picryhydrazyl (DPPH^•), hydroxyl (HO^•), and superoxide radicals (O₂^•-) using electron spin resonance measurements. Higher radical scavenging capacities were found against DPPH^• and HO^• in all treated fruit, particularly in berries treated with thymol, compared to those in the control groups. In addition, strawberry extracts were evaluated for their antiproliferative activities using HT-29 colon cancer cells. Extracts from all treated fruit exhibited significantly stronger inhibition on HT-29 cell proliferation than those from the control fruit. These data provide evidence that, in addition to possessing antimicrobial activity, the essential oils also increase free radical scavenging capacity and antiproliferative activity in fruit and, in turn, enhance the resistance of fruit tissues to deterioration and spoilage. Keywords: Strawberries; eugenol; menthol; thymol; antioxidant; antiproliferation