| Dioscorea opposita Thunb,also known as yam,has high nutritional value and contains a variety of functional active ingredients such as polysaccharides.In China,yam is a kind of medicine and food resource which is loved by consumers and mainly eaten as a vegetable.Thequalityofyam includes sensoryquality,nutritionquality,antioxidant and textureproperties.However,there are few investigations on the effects of structure properties of cooking on yam.In this paper,the effects of different cooking methods such as boiling,steaming,hot frying and microwave on sensory quality,nutritional components,functional components,structure and gelatinization properties of yam were studied.The following conclusions are drawn:The effects of different cooking methods such as boiling,steaming,stir-frying and microwave on sensory quality,nutritional and functional components of yam were studied.The results showed that under the four cooking conditions,the cooking time had a significant effect on the sensory quality of yam(P<0.05).Under the conditions of this study,the optimal cooking time of the four cooking methods of boiling,steaming,hot frying and microwave was 11 min,12min,9min and 6.5min,respectively.Each cooking method had a significant effect on the color of yam(P<0.05).After cooking,the brightness of yam decreased and the whiteness value decreased.There was no significant difference between the whiteness value of yam samples cooked by microwave and steaming and that of fresh yam samples(P >0.05).The values of L * value and whiteness were the lowest,and those of a *value and b * value were the highest(P<0.05)when hot-fried.After cooking,the hardness of yam samples was significantly reduced(P<0.05),After microwave cooking,the chewability of yam samples increased significantly(P<0.05),The chewability of steamed and boiled yam decreased significantly(P<0.05),Compared with fresh samples,the chewability of hot-fried yam was not significant(P>0.05).After cooking,the contents of protein,allantoin,flavonoids,polyphenols and polysaccharides in yam decreased significantly(P < 0.05),but the influence of different cooking methods on the protein content was not significant(P > 0.05).The change trend of the four active ingredients was the same.The loss degree of the four active ingredients,followed by steaming,boiling,microwave and hot frying,ranged from low to high,the antioxidant activity of steamed cooking samples was the highest.The effects of different cooking methods such as boiling,steaming,stir-frying and microwave on the structure and gelatinization of yam were studied by SEM,FTIR and RVA.The results showed that the starch of yam was gelatinized to different degrees in the samples processed by steaming,boiling and stir-frying,the intact starch granules cannot be seen in the scanning electron microscope by those three treatments.The degree of starch gelatinization in yam is the lowest during microwave cooking.Under the four cooking methods,the infrared spectrum waveform of the starch was basically consistent with that of the fresh yam sample,but there were differences in the positions and intensities of the absorption peaks of the starch in different cooking methods,indicating that no new groups were produced in the cooking process.The crystal structure of starch in the steamed samples was damaged to different degrees after cooking,and the order degree of starch granules was the lowest.The gelatinization temperature significantly increased after microwave cooking.Boiled cooking process of yam has the highest peak viscosity,valley viscosity,final viscosity,breakdown and setback value,peak viscosity,trough viscosity and final viscosity of microwave and steamed yam were both significantly increases,while the breakdown value were significantly reduced compared with the fresh yam,The retrogradation value was not significant.However,the peak viscosity and valley viscosity of hot frying decreased significantly,while the final viscosity and rejuvenation value did not change significantly. |
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