Effect of Cooking Temperature and Cooking Style on the Resistant Starch Content of Chinese Yam （Dioscorea polystachya Turcz.）

Abstract

The Chinese yam (Dioscorea polystachya Turcz.) is a common starchy component of the Japanese diet and is often eaten raw. We evaluated resistant starch (RS) content of the Chinese yam and also investigated the effects of cooking temperature and cooking style on RS. The Chinese yams were cut into half-moon slices or grated, and both types of cuts were studied in the raw as well as cooked forms. They were heated to 70°C or boiled, and then analysed for the RS content. The RS content was found to be five-to-six-fold higher in raw Chinese yam than that in the cooked one. Furthermore, the RS content was 1.7-fold higher in half-moon slices of the raw Chinese yam than that in the grated yam. These results suggest that raw Chinese yam contains a large amount of RS2, which is highly resistant to enzymatic hydrolysis, and that much of this starch is gelatinised when cooked. Furthermore, it was suggested that the cooking style of the Chinese yam might also affect the amount of RS within.