Development of a Simple Protocol to Assess Glucose Release After In Vitro Digestion, Allowing Comparison of Starchy Foods

Diets including foods with low glycemic index have been proposed to reverse the rising incidence of obesity and type 2 diabetes. Unfortunately, many common starchy staple foods have a high glycemic index. Several strategies for producing foods with low glycemic index have been proposed, but their application by the food industry is limited by the difficulty and cost of measuring GI in vivo. The aim of the present study was to develop a simple and reliable protocol to assess glucose release after in vitro digestion, and to use it to compare commercial starchy foods. To this purpose, a final starch digestion step was included in the INFOGEST in vitro digestion protocol by adding the enzyme amyloglucosidase, which mimicked the action of brush border enzymes. Glucose release was evaluated in five starchy foods (flour, bread, crackers, and durum wheat pasta and gluten-free pasta), available on the market in two forms produced by the same company, one standard and one rich in fiber (> 6 g/100 g). Glucose release was evaluated 0, 30, 60, and 120 min after the addition of amyloglucosidase. In all foods, glucose release at T0 was very low, confirming that starch digestion by amylases is incomplete. Excluding flours, the lowest and highest amounts of glucose release (28.29 and 49.36 g/50 g of available carbohydrates) were detected in durum wheat pasta and gluten-free pasta, respectively, confirming the high glycemic index previously detected in many gluten-free products. Notably, when glucose release was expressed as g/50 g of available carbohydrate, the impact of fiber content was negligible. Although the in vitro assessment of glucose release should not be confused with the glycemic index, the herein reported protocol can help predict the impact of foods on glycemia, facilitating the formulation of healthier products.