Abstract
In the present study, we report on the nutrient composition, amylase titer and superoxide anion-scavenging activity (SOSA) of Chinese yam (Dioscorea opposita Thunb., nagaimo) tubers harvested in Hokkaido, in comparison with those, previously published, of potato (May queen variety), a major crop, from the same district. Nagaimo had high contents of water and calcium compared to potato, and was expected to be a good supplier of some vitamins, such as α -tocopherol, vitamins B1 and B6, and ascorbic acid. The total dietary fiber content was lower in nagaimo, but it had a high proportion of water-soluble dietary fiber, compared to potato. Moreover, nagaimo possessed a lower starch content compared to potato, with 25% amylose and a high proportion of resistant starch. As for free sugars, nagaimo had higher contents of glucose and fructose, its sucrose level being almost the same as in potato. It was confirmed that the major amino acids in nagaimo were glutamic acid and arginine, dissimilar to those in potato. Determination of the amylase titer in tubers showed that nagaimo had almost the same activity compared to potato, leading to the presumption that eating raw tubers of nagaimo causes no intestinal problems directly related to its amylase activity. A notable SOSA was also found in nagaimo, but the antioxidant activity was slightly weaker compared to potato.
