Effect of radiation processing on physico-chemical quality and inhibition of yeast and mold and aerobic bacterial count in natural plum juice during refrigerated storage

Abstract

Fully red plums (Cv. Santa Rosa) harvested at proper maturity were processed into juice and packed in polypropylene (PP) bottles. The packaged juice was irradiated at 0.5 kGy and stored at 3 ± 1 °C for 50 days. Samples were evaluated at intervals of 10 days for physico-chemical, microbiological and sensory quality attributes. Results indicated that dose of 0.5 kGy maintained higher levels of total soluble solids, sugars and total ascorbic acid in juice towards later storage periods compared to control. Dose of 0.5 kGy significantly (p ≤ 0.05) enhanced total phenols in plum juice by 2.3 % following irradiation. Anthocyanins content of plum juice decreased both with dose and storage, however after 50 days decrease in anthocyanin content was 30.8 % in un-irradiated juice compared to 23.3 % in 0.5 kGy treated juice. Among individual anthocyanins, monoglycoside anthocyanins especially cyanidin-3-rutinoside was less stable to irradiation compared to diglycoside anthocyanins. DPPH and hydroxyl radical scavenging activity of juice increased by 6.8 % and 4.9 % above control after irradiation at 0.5 kGy. Microbial populations significantly reduced by irradiation at 0.5 kGy and about 1 log reduction in yeast and mold count was observed after irradiation. Dose of 0.5 kGy was sufficient to reduce total bacterial levels below detection limit up to 20 days of storage. Sensory analysis indicated that un-irradiated plum juice was unacceptable within 20–30 days while 0.5 kGy treated juice was acceptable up to 50 days of refrigerated storage.