Shelf-Life Extension of Dried Kaempferia parviflora Rhizomes by Gamma Irradiation

Abstract

Kaempferia parviflora rhizomes exposed to gamma irradiation at doses of 0, 5, and 7.5 kGy were evaluated every 3 months for their microbial loads, contents of 5,7-dimethoxyflavone (DMF), total phenolic contents, and antioxidant activities (DPPH and FRAP assays) during 12 months of storage at 25 °C. After gamma irradiation, microbial loads were reduced below acceptable limits. Phytochemical contents in irradiated samples were significantly increased as compared to those of the control (0 kGy) while DPPH radical scavenging activities were significantly decreased. However, gamma irradiation had no effect on FRAP values. During storage of irradiated samples, phytochemical contents and antioxidant activities were gradually decreased whereas microbial loads were progressively increased. Even so, microbial quality of irradiated samples was less than acceptable limits through 12 months' storage. Gamma irradiation at doses of 5 and 7.5 kGy was sufficient to control microbial growth and T. castaneum infestation of K. parviflora rhizomes within acceptable limits for at least 12 months at 25 °C. Additionally, 5 and 7.5 kGy were effective doses to retain DMF and phenolics in K. parviflora rhizomes.