Riley, Cliff K.; Adebayo, S.A; Wheatley, Andrew O.; Asemota, Helen N.
Author Affiliation, Ana.
The correlation between granular properties and the in vitro digestion of native starches extracted from yams (Dioscorea spp.)
Date of Publication
Yam (Dioscorea spp.) is a monocotyledous tuber bearing plant belonging to the family Dioscoreacea within the genus Dioscorea. Yams are consumed in the tropical and subtropical regions as a primary source of digestible carbohydrate. The effect of starchy foods on blood glucose and insulin responses may vary significantly, which could be attributed to the physiochemical properties of the starches. The degradability of starch when consumed is important especially among diabetics and hyperlipidemic individuals, as starches that are easily degraded tend to have a higher insulin demand than slower degrading starches. This can significantly affect insulin sensitivity, and influence the development of type II diabetes. The diet of diabetics is of concern; especially in the Caribbean where in Jamaica alone over 300,000 cases of diabetes is reported in a population of just over 2.7 million. Understanding the properties of starches from carbohydrate rich foods consumed and how it relates to digestibility may impact the level of control over blood glucose responses. This study was designed to investigate the relationship between granule properties and the in vitro digestibility of starches extracted from Dioscorea cayenensis cultivar (cv) Round leaf yellow yam, Dioscorea polygonoides (cv) Bitter yam and Dioscorea esculenta (cv) Chinese yam. Significant variations were observed in the particle properties of the different yam starches studied (p<0.05). The projected mean granular diameter ranged from 5.4 µm (Chinese yam) to 34.5 µm (Round leaf yellow yam). The variations observed in the granular size may have influenced the surface properties of the starches, as Chinese yam and Bitter yam were found to have the largest specific surface area (625.91 m2/kg and 258.76 m2/kg respectively) while Round leaf yellow yam (117. 4 m2/kg). The results also showed a direct correlation between the particle size and specific surface area on the digestibility of the various starches. Chinese yam and Bitter yam starches, with the smallest mean granule diameters and highest specific surface areas, were found to be the most digestible (21.27 ± 0.01 and 18.11 ± 0.02 % respectively), while Round leaf yellow yam with the largest mean granule diameter and lowest specific surface area was the least digestible (13.74 ± 0.03 %) at 37 °C under in vitro conditions. Starches with small granules and large specific surface areas may be more digestible than those with larger granules. This suggest that these starches may be digested and absorbed at different rates when consumed, which could be of importance to diabetic and hyperlipidemic individuals as the differences in digestibility of the different yam starches could affect post-prandial blood glucose levels.....