Evaluation of pungency in the diploid and tetraploid types of ginger (Zingiber officinale Roscoe) and antioxidative activity of their methanol extracts

The diploid and tetraploid types of the ginger cultivars, Kintoki, Oshoga and Sanshu, were studied in relation to the gingerol content, antioxidative activity and pungency sensory evaluation. The tetraploid ginger type was derived from the respective diploid ginger type by shoot tip culture. Gingerols are major pungent constituents in natural ginger. Among the three ginger cultivars, the total gingerol content of the tetraploid type was much higher than that of the respective diploid type and, especially, the 10-gingerol (10G) content of the tetraploid type showed a remarkable increase. Both diploid and tetraploid types of the cultivar Kintoki contained the highest level of gingerol among the respective types of the three ginger cultivars studied. Sensory evaluation of the pungency of ginger using a triangle test showed that the pungency of all the tetraploid types was distinctly higher than that of the diploid ones and that the pungency intensity decreased in the order Kintoki Oshoga Sanshu. The pungency intensity of the five samples except for the diploid type of the cultivar Kintoki was correlated with the gingerol content. The antioxidative activity of the methanol extracts from the ginger cultivars used was measured by the weighing, ferric thiocyanate and deoxyribose oxidation methods. Both diploid and tetraploid types displayed the highest antioxidative activity based on the determination by the ferric thiocyanate method. Although the antioxidative activity measured by the deoxyribose oxidation method varied among the diploid and tetraploid types tested, all the tetraploid types inhibited deoxyribose oxidation by 40%. These results demonstrated that in the tetraploid types of ginger the gingerol content, antioxidative activity and pungency intensity were higher than in the diploid ones