Effects of gamma irradiation under vacuum and air packaging atmospheres on the phytochemical contents, biological activities, and microbial loads of Kaempferia parviflora rhizomes

Abstract

Kaempferia parviflora is a traditional herb for health promotion and therapy attributed to its methoxyflavone and phenolic constituents. This study was performed to determine the effects of gamma irradiation (0, 5, 7.5, and 10 kGy) under vacuum and air packaging atmospheres on the phytochemical contents, biological activities, and microbial loads of K. parviflora rhizomes. The optimal extraction condition for achieving high antioxidant activity was: ethanolic concentration, 40% v/v; solid/solvent ratio, 1 : 10 g/ml; extraction temperature, 30 °C; and extraction time, 1 h. This condition was used to prepare extracts of K. parviflora rhizomes for further determination. The high performance liquid chromatography-diode array detector method was employed for the determination of methoxyflavones in rhizome extracts. The contents of methoxyflavones and phenolic compounds were found to increase with increasing gamma irradiation dose. In contrast, the antioxidant activities decreased with increasing gamma radiation dose. However, all three doses applied did not affect total flavonoid contents and albumin denaturation inhibitory activities in all extracts. The highest contents of methoxyflavones and phenolic compounds were observed in 7.5 kGy irradiated rhizomes packaged under air atmosphere. Irradiation treatment at doses of 5–10 kGy was sufficient to control microbial contamination and Tribolium castaneum infestation in dried rhizomes. This study suggests that 7.5 kGy irradiation is the effective treatment to improve the quality of K. parviflora rhizomes.