Characterization of the Glycemic Index of Raw and Thermally Processed Sweet Potatoes (Ipomea batatas L.)

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Diabetes mellitus is one of the more common and serious chronic diseases across the globe. There are 20.8 million children and adults in the United States, or 7% of the population, who have diabetes. While an estimated 14.6 million have been diagnosed, 6.2 million people are unaware that they have the disease. Type-2 non insulin-dependent diabetes mellitus diabetes (NIDDM), formerly adult-onset diabetes, is a disease that occurs when the body produces enough insulin but cannot use it effectively. This form of diabetes has primarily been observed to develop in adults over the age of 40, but is gradually becoming a threat across all age groups. About 90% to 95% of people with diabetes have type 2; of which 80 percent are overweight. Diabetes is a life-long disease, but it can be self-managed if people take responsibility of their daily care. Through diet management, exercise, self-testing of blood glucose and in many cases oral medication and/ or insulin, people with diabetes can assist their bodies to keep blood glucose near normal levels. The objective of our study was to investigate the short term glycemic effect of Beauregard sweet potato impomea batatas in normal subjects through measuring the glucose response of sweet potato with and without skin, and of skin alone, in comparison with the more commonly consumed white potato. The study investigated the decrease in glycemic response of white potato vs. white potato plus Caiapo, an antidiabetic acidic glycoprotein component in Japanese sweet potato cultivars. The first study focused on C-peptide and insulin analysis via ELISA (ALPCO Diagnostics) from subjects at 0, 60, and 120 minutes after consumption of potato samples. Glucose levels were measured at times 0, 30, 60, 90, 120 minutes post prandially with glucometers (Freestyle). These data illustrated that differences in insulin, C-peptide response due to potato were constant over time resulting in graph parabola trends similar to glucose response. The comparison of C-peptide, serum insulin, and glucose response showed that the mechanism for the hypoglycemic effect in sweet potato or Caiapo is not due to improved insulin production, response to blood glucose, or increased insulin uptake by target cells. The study suggested that the blood glucose lowering effects occur in the small intestine (duodenum) by retarding absorption of glucose to the bloodstream. The subsequent study investigated the thermo-stability, through cooking, of the low glycemic index effect previously determined in Beauregard sweet potato by measuring the glycemic index after baking at 375o F for 1 hour, steaming at 100o C for 45 minutes, dehydration at 40o C overnight, and microwaving for 5 minutes. Participants consumed 25g of available carbohydrate, determined through AOAC proximate analysis of lipid, ash, moisture, and total dietary fiber levels in each preparation method. Comparing the heat treatments (steaming, baking, dehydrating, and microwaving) of Beauregard sweet potato skin and flesh illustrated the extent to which cooking affects the glycemic index. Results showed that steamed skin, baked skin, and dehydrated flesh do not have statistically different glycemic indices (p> 0.05) from those of raw sweet potatoes (n=12). Dehydrated sweet potato flesh, along with the aforementioned cooked sweet potatoes, retained the low glycemic index of raw sweet potatoes. The glycemic index of steamed flesh elevated to that of a medium glycemic index food. Baked and microwaved flesh also elicited blood glucose responses to those of medium glycemic index foods. This information will lead to further understanding of preferred foods for diabetics to assist in blood glucose management. Understanding the glucose response and glycemic index elicited by NC sweet potatoes will improve recommendations for their health promoting properties, such as reducing the risk of diabetes or insulin resistance.



sweet potatoes, glycemic index, processed