|
New, healthier alternatives to processed food starches with a lower GI, or glycaemic index, may soon be on the menu, thanks to scientists in China and the US. Genyi Zhang and Mahesh Venkatachalam of the Southern Yangtze University, and Bruce Hamaker of Purdue University, Indiana, have begun to unlock the secrets of starches that make dehusked grains, potatoes, and processed foods such as biscuits and breakfast cereals less healthy compared with low GI foods. Their statistical analysis of starchy data could lead to new processed carbohydrates that do not cause the worrying blood sugar spikes associated with conventional processed starch. Blood sugar spikes caused by ingestion of rapidly digestible carbohydrates (RDS), as opposed to slow carbohydrates (SDS) have been associated with metabolic disorders and diabetes by nutrition scientists in recent years. However, discovering what exactly it is about RDS and SDS that makes them so different in terms of the body's response and more specifically the pancreatic response has been difficult. Now, Hamaker and his colleagues have looked at the various physical properties of RDS and SDS to try and determine the underlying differences. The shape, size, surface pores and channels, and degree of crystallinity of starch granules, they have found, are not the direct cause of slow digestion of carbohydrates. Rather, the semicrystalline structure is, they explain, critical to the beneficial slow digestion property. Cook, or otherwise process, an SDS, however, and this semicrystallinity can be lost and a once-slow starch becomes an RDS. With this information in hand, the researchers have compared cereal and potato starches, the former are SDS, while potatoes are notoriously RDS. The study revealed that cereal starches have a higher proportion of A-type crystalline structure but are less structurally perfect and that this is related to the degree of polymerization of the starch chains. These structural characteristics are all but absent in potatoes. It is this supramolecular semi-crystalline structure seen in native cereals and not potatoes and processed carbohydrates that, the team suggests, makes SDS so slow to digest and so healthier and gives RDS much faster access to the bloodstream following digestion. Related links:
|
|
