Resistant starch in various starchy vegetables and the relationship with its physical and chemical characteristics

Starch is a complex carbohydrate consisting of numerous glucose units joined by glycosidic bonds. According to digestibility, starch has been categorized into rapidly digestible starch that takes 20 minutes after consumption to be fully digested, slow digestible starch which takes between 20 and 120 minutes to be fully digested in the small intestines, and resistant starch (RS) which resists digestion in the small intestine and undergoes fermentation in the large intestines, hence producing beneficial products for the human health. The study was carried out to compare the contents of RS in different starchy vegetables and analyze the physicochemical properties such as moisture content, amylose content, swelling, and water absorption capacity (WAC) of the chosen food samples and explain the relationship between the physicochemical properties and RS content of the food samples. Potato starch recorded a high resistant starch content at 56.43%, while corn starch was low at 2.82% RS. There was a positive correlation between RS and amylose content. However, there was a negative correlation between swelling capacity and WAC. The RS content of potato starch recorded the least swelling at 1.49 g/g compared to the high value of yellow sweet potatoes of 8.47 g/g. Water absorption capacity presented a similar trend to swelling. In six out of the eight samples analyzed, a high amylose content in starchy foods was an indication of high RS in the food, attributed to its long chain and double helices it forms after gelatinization. A high RS content in foods leads to low swelling capacity and low WAC. Therefore, low swelling in potato starch indicated a high RS content.