The colour switch of banana

SCIENCE FOR YOUTH

by Hiya Islam

scienceSlice a couple of bananas and plop them in the cold milk waiting in your blender. Hey, add in those diced strawberries. Mangoes go equally great too! A minute of mechanic whirlpool and your smoothie is ready. You pour the ever-so-healthy drink in a glass. Drizzle some honey and garnish it with bits of cashew and mint leaves, don’t forget to squeeze those few drops of fresh lime on top. And of course, post it on Instagram with #freshlyblended. Literally, so many recipes insist on these tropical fruits, it’s hard to ignore. Bananas are on top of the priority list of many nutritionists. But why can’t they forever stay yellow? How far would you go to keep your bunch as yellow as possible?

The answer is simple. As the fruit ripens, it passes through a number of colors which is basically a chemical change. It starts out as green slowly turning to yellow, progressing to a mottled skin and lastly, a jet-black trash material. Chlorophyllase is the enzyme that breaks down the green chlorophyll in the peel revealing yellow. But, is it time to eat? Often, this yellow tricks us into eating only to find it bitter and waxy. It is because pectinase and amylase are yet to act. Pectinase digests pectin in cell walls and amylase converts starch into sugars. As a result, the fruit becomes softer and sweeter. These enzymes are activated by a gaseous hormone, ethylene, released by the fruit itself. Another enzyme, polyphenol oxidase is why we see the brown spots. Polyphenol oxidase helps in the oxidation of organic compounds, phenols giving rise to melanin, the same pigment found in our hair, eyes and skin. These melanin spots found are in fact a part of banana’s defense mechanism. When bruised, it helps to prevent potential infections and rotting. This ethylene production never ceases. Once it starts to ripen, grab yours before it turns too mushy to eat.

Nonetheless, sometimes you just need to get done with ripening and move on to the next step of the recipe. For this, pack some bananas loosely in a paper bag. Accumulation of ethylene and its circulation will speed up the ripening process. Alternatively, poke the banana on all sides and place it in the microwave oven for 30 seconds. Repeat until desired texture is achieved. On the other hand, many face the dilemma of maintaining the freshness. Wrapping the stem with aluminium foil or plastic wrap is effective as it prevents the escape of ethylene. Or, refrigerate them when your perfect ripe stage has arrived. Although this makes the skin unappetizingly dark, the fruit inside remains intact and edible. This method can save your bananas for up to a week.

In case your bananas are overripe, muffins, pancakes and banana bread are yearning to be baked into life.

Hiya Islam is a student of BRAC University.

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