Changes in Amylase Activity, Soluble Sugars and Proteins of Unripe Banana and Plantain during Ripening

Abstract

The profiles of amylase activity, soluble sugars and proteins in unripe plantain (Musa paradisiaca) and for a comparison, unripe banana (Musa sapientum), from harvest to ripening were investigated to provide basic information about their nutritional status at the different stages of the ripening process. Unripe plantain contained about a quarter of the soluble sugars found in ripe plantain. Conversion of the insoluble sugar (starch) to soluble sugar by amylase during ripening was an almost linear process. And as such, activity of amylase in plantain was highest at the ripe stage (2400 ± 120 Units/mg protein) and lowest immediately after harvest when it was still green (700±100 Units/mg protein). The soluble proteins increased from first day when it was harvested, at maximum around the third day and began to decline gradually. In contrast, amylase activity was highest in unripe banana (3900 ± 310 Units/mg protein) and decreased rapidly to a very low value (100 ±15 Units/mg protein) when it was fully ripened. The soluble sugar level in unripe banana was 3.8 ±0.5 mg/ml and around 6.0 ±1.0 mg/ml of extract when fully ripened. The soluble protein was 3 ± 1.0 mg/ml of extract when unripe and increased nine folds to a value of 27± 3.0 mg/ml of extract when fully ripened. The overall results suggest that the highest amount of starch, and the lowest amount of soluble sugars were present on the day when the mature plantain was just harvested.