Effects of electron-beam irradiation on blueberries inoculated with Escherichia coli and their nutritional quality and shelf life

Fresh blueberries have become a popular new functional food because of their remarkably high levels of antioxidant phytonutrients and health benefits. However, the potential prevalence of human pathogens on blueberries has become an increased concern because they are consumed fresh. Procedures effective in decontamination and extending shelf life without affecting fruit quality are needed. Electron-beam irradiation was applied to fresh blueberries at the doses ranging from 0.5 to 3.0 kGy and its effectiveness for inactivating Escherichia coli (E. coli) K-12 and extending shelf life were investigated. The decimal reduction dose, D₁₀ values, of E. coli in cultural medium and blueberries were 0.43 ± 0.01 kGy and 0.37 ± 0.015 kGy, respectively. Irradiation reduced bacteria inoculated on blueberries from 7.7 × 10⁸ CFU/g to 6 CFU/g at 3.13 kGy and decreased the decaying of blueberries stored at 4 °C up to 72% and at room temperature up to 70% at this dose. No significant effect on the total monomeric anthocyanins, antioxidant activity, and l-ascorbic acid content of blueberries was observed from irradiation at doses ≤3 kGy. However, significant decreases in the antioxidant activity and l-ascorbic acid content were found in both control and irradiated blueberries after storage at 4 °C for 7 and 15 d. Information obtained in this study indicates that low dose electron-beam irradiation is effective in reducing E. coli and extending shelf life while maintaining the antioxidant properties of blueberries.