Microbial inhibition and shelf-life extension of longan (Dimocarpus longan) juice by UV radiation

Abstract

This study aimed to investigate the effects of UV radiation at different doses (0–149.8 J/cm2) and pasteurization process (72 ± 1 °C, 1 min) on the quality preservation of longan juice. Longan juice was inoculated with Escherichia coli and subjected to UV and pasteurization process. UV-149.8 J/cm2, and pasteurized longan juice samples had higher log reduction values of total microbial (2.80 and 3.63), yeast/mold (4.14 and 4.56), and E. coli (2.76 and 4.13) log CFU/mL, respectively, compared to untreated control and other UV treated samples. The first order kinetic model potentially inhibited total microbial count, yeast/molds and E. coli in UV-149.8 J/cm2 sample. pH, total solids, total acidity, and turbidity showed no difference in UV and pasteurized samples. However, color values were affected in pasteurized sample than the UV treatments. Total phenolic content (TPC), total flavonoid content (TFC) and antioxidant (DPPH and FRAP) values were highest in untreated control, followed by the UV-74.88 J/cm2 than that of UV-149.8 J/cm2 and pasteurized samples. Based on the highest bioactivity, UV-74.88 J/cm2 and pasteurized samples were compared for quality changes during 15 days of storage at 4 °C. The selected UV-74.88 J/cm2 sample had higher TPC, TFC, DPPH, and FRAP values than the pasteurized sample up to 12 days of cold storage. Additionally, total plate count and yeast/mold were lowest in UV-74.88 J/cm2 sample in comparison with untreated control. Color values were stable in UV-74.88 J/cm2 sample, compared to pasteurized sample. Pasteurized longan juice showed no growth of yeast/mold during the entire storage period. Therefore, shelf life of UV-74.88 J/cm2 sample was prolonged to 12 days compared to the control sample that became unacceptable after 6 days during storage at 4 °C. UV treatment of longan juice could be considered a promising non-thermal additive free technology for reducing microbial load, improving quality characteristics, and extending shelf life.