Ultrastructural and Starch Digestibility Characteristics of Sweet Potato Spaghetti: Effects of Edible Gums and Fibers

Abstract

Considering the importance of pasta as a food having low starch digestibility, and the global increase in diabetes, an attempt was made to develop low glycaemic spaghetti from sweet potato incorporating gums and fibers. Gums such as guar, xanthan, and locust bean were incorporated at 0.5, 1.0, and 1.5 g/100 g mix while the fibers such as apple, oat, and wheat were incorporated at 10 and 20 g/100 g mix levels along with 1.0 and 1.5 g/100 g of xanthan gum, respectively. Gum fortified spaghetti retained more protein on cooking than fiber + xanthan gum fortification. Higher swelling index was observed for gum fortified spaghetti than fiber + xanthan gum fortification, whereas cooking loss followed a reverse pattern. Lowest in vitro starch digestibility was observed for xanthan gum (1.5%) fortification, which was significantly less than the fiber + xanthan gum fortification. Resistant starch was retained to a high extent in the fortified spaghetti. The estimated glycaemic index for control spaghetti was 66.62, which could be reduced to 58–60 and 57–59 through 1.5% gum 20% fiber + xanthan gum fortification, respectively. Gums increased the firmness (N) and decreased the toughness (Ns) of dry spaghetti, while cooking drastically reduced the firmness. Formation of starch-gum-protein network was evident in the scanning electron microscopic pictures of most of the gum fortified samples. Ultrastructural studies showed that fiber + xanthan gum fortification had less firm structure of cooked spaghetti than xanthan gum alone. The study showed that guar gum and xanthan gum (1.5%) fortification can produce sweet potato spaghetti with medium glycaemic index of 58.