Abstract
Processing methods affect starch hydrolysis, digestibility, absorption and glycaemic index (GI) of food. Although some studies have reported on the effect of boiling, frying, roasting and baking on glycaemic index of traditional staples, there is limited information on the contribution of drying, fermentation, boiling and steaming on starch bioavailability and glycaemic index. This research work aimed at determining the effect of fermentation, steaming, boiling and drying on starch bioavailability and predicted GI of some cassava-based traditional foods consumed in Ghana. The total starch, amylose, amylopectin, dietary fibre and predicted glycaemic index of the intermediate and finished products were determined according to standard protocols. The analysis established that steaming and boiling increase GI of foods, fermentation has no significant influence on predicted GI of fermented steamed products, and drying has no substantial effect on predicted GI of cassava flour. However, staples or products prepared from solar dried cassava flour would have higher predicted GIs than those of sun dried cassava flour. This work has also provided evidence in support of the fact that total starch and amylopectin give rise to an increase in GI whereas amylose and dietary fibre contents contribute to a decrease in GI of foods. The predicted GIs of raw cassava, boiled cassava (<i>ampesi</i>), <i>akyeke</i>, cooked <i>kokonte</i> with sun dried flour and cooked <i>kokonte</i> with solar dried flour were found to be (47.75%), (77.30%), (79.05%), (40.20%) and (61.11%), respectively. Temperature plays a significant role in breaking hydrogen bonds in food molecules causing the release of glucose and subsequently affecting GI. The GI data of these staples may be used in conjunction with other food composition tables for healthy food choices and nutritional counselling. Processors can incorporate more fibre or amylose-containing crops into food products as well as ensure the use of sun or solar drying to produce low glycaemic index food products.
Highlights
Many processed and traditional foods go through succession of processing operations which may affect their digestibility, absorption and glycaemic index
The decrease in total starch content of the samples may be attributed to the different processing methods employed in the study [14]
The analysis revealed that, fresh cassava has high amount of starch and amylopectin than amylose and dietary fibre, and was expected to have a glycaemic index (GI) value more than what was reported in the study
Summary
Many processed and traditional foods go through succession of processing operations which may affect their digestibility, absorption and glycaemic index. Processing of cassava involves methods such as cleaning, size reduction, drying, fermentation, cooking methods, heat treatment (pasteurization and sterilization) and many others [1, 2]. These processes improve eating quality, reduce cyanogenic glucosides concentration and its toxicity [3], their effects on glycaemic index need to be comprehensively studied. The glycaemic index (GI) of foods is the measure of the rate of absorption of carbohydrate into the blood after consumption of a meal and is significantly affected by the processing operations [4] This is because these operations are suggested to cause cell wall disruption, depolymerization, retrogradation, gelatinization and hydrolysis of the carbohydrate to facilitate enzymatic reaction or digestion, for the release of glucose into the blood after consumption or eating [5, 6]
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