Effects of different household cooking methods on the biological properties of Chinese yam

Yam (Dioscorea opposite Thunb) is used as a staple food and a traditional medicine in China. This study investigated the effects of different household cooking methods on the bioactive components (phenolic compounds, diosgenin and allantoin) and their bioaccessibility as well as the biological properties (antioxidant activity, hypoglycemic activity, anti-angiotensin I-converting enzyme (ACE) or anti-acetylcholinesterase (AChE)) of Chinese yam using an in vitro simulated digestion model. The results demonstrated that cooking caused significant losses of total soluble phenolic compounds (lowest loss of 20% for boiling at atmospheric pressure) and diosgenin content (lowest loss of 27.37% for microwaving) but no changes in the allantoin content. The cooking methods affected the bioaccessibility of the bioactive components differently. Normal steaming resulted in the highest amount of bioaccessible phenolic compounds (71.21%) and allantoin (79.07%), whereas high-pressure boiling in the highest content of diosgenin (75.58%). The concentration of bioactive components in the digesta fluid was correlated with the antioxidant activity and enzymatic inhibitory activities. Overall, household cooking processes allow the biological activity of yam to be retained by changing the profile of bioactive components potentially available for intestinal absorption. Thus, a household cooking method such as normal pressure steaming appeared to be most suitable for achieving the expected health benefits of yam.