Question

1) Is there a relationship between starch and sugar contents and the degree of ripening of bananas ? Explain in detail

2) starch should give a negative result in benedicts (or fehling's) test; however , it usually shows a trace of simple sugars present . Explain that result .

3) Based on what you have learned , explain why over-ripened bananas are turning mushy and the pulp becomes sweet . ( The browing is a different process that has to do with oxidation )

Answer 1

1) Green banana contains sugar 0.94% and starch 22.26%. Ripe bananas contain 18.87% sugar and 0.82% starch. In bananas ripening invoves reduction in starch content. During the early part of ripening sucrose is the predominant sugar but in the later stage glucose and fructose predominates. Hence, starch is converted to sugars of 66% sucrose, 14% fructose, and 20% glucose. So unripen bananas have more of starch than sugars and as bananas ripen starch content decrease and sugar content increase.

2) Starch is a non reducing sugar and fructose and glucose are reducing sugars.i.e they will give a positive Benedict's test because banana has some free sugars as well.

3) Over- ripened bananas turn mushy and the pulp becomes sweeter because of decrease in starch content and increase in sugar(glucose , fructose,sucrose) of banana on ripening. Stach content, which ,provides firmness and structure to the banana decreases on ripening and hence bananas become mushy and pulpy. Since sugar content increases on ripening , so the pulp becomes sweeter.