Effects of ripening stage and cooking methods on available glucose, resistant starch and estimated glycemic index of bananas (Musa sapientum; Nam-wa variety)

Abstract

© 2018, Malaysian Journal of Nutrition. Introduction: Resistant starch (RS) has been associated with health benefits including reduced cholesterol absorption, and also been considered as a prebiotic. Little is known of the RS contents of bananas from Thailand. Methods: This study determined the digestibility of starch in bananas (Nam-wa variety) at different ripeness stages, based on roasting and boiling. In vitro glycemic response of the bananas was also investigated. Based on peel colour, banana maturity stages were classified into 8 stages namely, unripe (stages 3-5) and ripe (stages 6-8). Analysis methods used were in-vitro enzymatic digestion and HPLC analysis. Results: Unripened bananas contained less total sugar compared to ripened bananas. Rapidly Available Glucose (RAG) and Slowly Available Glucose (SAG) contents increased in tandem with progression of the ripening stage. However, there was no significant difference in the RS content with ripening stage (p>0.05). The RS content also did not show significant difference between the cooking methods. Boiling of banana at the same ripening stage considerably reduced the estimated glycemic index (eGI) (34-56), whilst roasting did not produce any marked changes in pGI (53-56). Conclusion: The RAG and SAG amounts in the bananas studied were found to be directly related to ripening stage. Boiling was shown to be a better cooking method for lowering the pGI of bananas compared to roasting.