Resistant starch in plantain (Musa AAB) and implications for the glycaemic index

Consumption of foods rich in resistant starch and slowly digestible starches has been associated with lower postprandial glycaemic responses. The need to identify and quantify resistant starch in potential resistant starch sources and optimise processing conditions to maximise their benefit is vital in the quest for more healthy diets required for the control and management of diabetes and related conditions. Significant quantities of three types of resistant starch were identified in plantains: these are physically entrapped starch (RS1), native resistant starch (RS2) and retrograded starch (RS3). However, the relative quantities of each type vary with the conditions/state of processing/storage conditions applied to the food before consumption. The high correlation (r2 = 0.8) obtained between increased total resistant starch content of plantain products and reduced glycaemic index suggests that factors which promote the formation of enzyme resistant starch in plantain can also influence the glycaemic response to the available carbohydrates. Apart from native resistant starch which has been commonly reported for the Musa ssp, our data suggest that some alcohol extractable components of plantain may act as enzyme inhibitors. The presence of these components resulted in an increase in the value of RS2 in flours when compared to the starch isolates. It may be necessary therefore to distinguish between resistant starch type 2 (RS2), which is due to the inherent nature of starch and resistant starch produced from the interference from other food components such as enzyme inhibitors. This type of resistant starch may not be present in all foods and its properties need to be further investigated.