During ripening, tissues soften and starch is degraded into sugars. At the same time the strength of the fruit and peel cell wall deteriorates.
Starch declines from around 20-23% at harvest to 1-2% in ripe fruit. Sugars increase in roughly the same proportions. Plantains, however, have higher starch contents of 50-60% prior to cooking, at full ripening.
If ripening is controlled at temperatures of between 14.5-18 °C, then the fruit turns a 'ripe yellow'. If this process is allowed to take place at temperatures above 25°C, 'green-ripe' bananas are produced. Retailers have a 7-stage color chart for ripening bananas. At Stage 1, fruit is hard, and green, with a high starch content. At Stage 4 there is more yellow than green fruit.
Then by Stage 7, fruit is soft, yellow with brown flecks, and has a high sugar content. Processed banana products represent less than 0.005% of the total world production. The most important products are canned banana puree used predominantly for baby food and dried banana chips or slices.
Banana bunches need to be protected from damage during fruit-fill, at harvest and during shipment. The use of bunch covers is increasingly common practice.
Cutting and handling of the banana crop during harvest needs to be carefully monitored to minimize damage.
Timing of harvest is critical. Plantation managers need to ensure the banana fruit is at the right stage for the market. This is normally based on color, physical length, and ridge characteristics.
Fruit should also have accumulated a desired level of sugars and have a long green-life potential, thus meeting the required storage requirements.
Control of pests and diseases is particularly important during flowering and fruit-fill. The use of a balanced fertilizer programme is important to ensure nutrients don't limit fruit quality.
Nitrogen influences fruit quality, improving sweetness by increasing the level of Total Soluble Solids (TSS), sugars and the TSS/Acid Ratio.
Potassium is needed for the transfer of carbohydrates from the leaf to the fruit, improving pulp content and fruit size as well as starch to sugar conversion in the fruit. Potassium is very important in maintaining or improving banana fruit quality. As with other nutrients, plant crops generally require more potassium than ratoon crops.
Nitrogen and potassium supplies need to be in balance. For example, over-use of nitrogen can lead to bunches with extended fingers and smaller fruit. Over-use of potassium may restrict uptake of other nutrients – e.g. calcium and magnesium.
Calcium has a major role to play in strengthening the peel, minimizing bruising, splitting and transport damage. It also reduces maturity spot/staining of fruit. Quality is also improved through good calcium nutrition.
Calcium is particularly important for extending storage quality and green life, by improving the integrity of the peel and the fruit, minimizing cracking and damage.
There is some evidence that soil applied calcium nitrate combined with calcium fruit sprays will improve 'green life' and hence fruit quality.
Zinc and boron are important in minimizing flower disorders and ensuring good bunch formation. Boron is particularly important in sugar transportation and translocation and along with zinc and iron improves the TSS content of the fruit.