When peanuts germinate, bioactive compounds such as resveratrol (RES), γ-aminobutyric acid (GABA), isoflavones, and polyphenol compounds are generated. Peanut kernels were germinated in the dark for two days, and stimuli including soaking liquid, rice koji, high-pressure processing (HPP), and ultrasonic treatment were tested for their ability to activate the defense mechanisms of peanut kernels, thus increasing their bioactive compound content. The results of this study indicate that no RES was detected in ungerminated peanuts, and only 5.58 μg/g of GABA was present, while unstimulated germinated peanuts contained 4.03 µg/g of RES and 258.83 μg/g of GABA. The RES content of the germinated peanuts increased to 13.64 μg/g after soaking in 0.2% phenylalanine solution, whereas a higher GABA content of 651.51 μg/g was observed after the peanuts were soaked in 0.2% glutamate. Soaking peanuts in 5% rice koji produced the highest RES and GABA contents (28.83 µg/g and 506.34 μg/g, respectively). Meanwhile, the RES and GABA contents of HPP-treated germinated peanuts (i.e., treated with HPP at 100 MPa for 10 min) increased to 7.66 μg/g and 497.09 μg/g, respectively, whereas those of ultrasonic-treated germinated peanuts (for 20 min) increased to 13.02 μg/g and 318.71 μg/g, respectively. After soaking peanuts in 0.5% rice koji, followed by HPP treatment at 100 MPa for 10 min, the RES and GABA contents of the germinated peanuts increased to 37.78 μg/g and 1196.98 μg/g, while the RES and GABA contents of the germinated peanuts treated with rice koji followed by ultrasonic treatment for 20 min increased to 46.53 μg/g and 974.52 μg/g, respectively. The flavonoid and polyphenol contents of the germinated peanuts also increased after exposure to various external stimuli, improving their DPPH free radical-scavenging ability and showing the good potential of germinated peanuts as functional products.
Keywords: HPP; antioxidant; germination; peanut; resveratrol; rice koji; ultrasonic.