Physicochemical Properties of Repetitive Heat-treated Ginger and Its Quantitative Conversion of Gingerol to Shogaol

Abstract

Ginger was steamed at 121 o C and 1.5 lb/in 2 for 30 min, dried at 60 o C for 12 h, and each step was repeated nine times. During processing, the lightness (L* value) and yellowness (b* value) decreased from 85.65±0.33 and 26.99±0.20 in the non-treated ginger to 56.91±0.25 and 16.69±0.06 in ginger treated for the ninth treatment. On the other hand, redness (a* value) increased from -1.51±0.03 to 7.34±0.08 on the eight treatment and then decreased to 7.21±0.04 on the ninth theatment. The contents of 6-gingerol decreased from 3.257±0.067 mg/g in the non-treated ginger to 0.567±0.036 mg/g on the theatment, whereas the contents of 6-shogaol increased from 1.299±0.050 mg/g to 2.999±0.089 mg/g on the sixth treatment and decreased to 2.099±0.039 on the ninth treatment. The contents of 10-gingerol decreased slightly from 1.106±0.125 mg/g to 0.806±0.026 mg/g. Unlike the 6- and 10-gingerol, the contents of 8-gingerol did not change greatly, with values between 0.916±0.005 mg/g and 1.106±0.005 mg/g being observed during processing. The tyrosinase inhibitory activities were increased from 43.42±11.45% in the non-treated ginger to 100% on the sixth treatment and then decreased to 51.98±7.36% on the theatment. The antioxidative activity was retained during processing.