Why does unripe fruit taste sour, but ripe fruit usually tastes sweet?

Video：Why does unripe fruit taste sour, but ripe fruit usually tastes sweet?

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Why does unripe fruit taste sour, but ripe fruit usually tastes sweet? Where the sourness went?

The difference in taste between unripe and ripe fruit largely boils down to their chemical composition, primarily their sugar and acid content.

Unripe fruits are typically sour due to the higher concentrations of various organic acids, such as malic, citric, and tartaric acids, among others. These acids are important for the initial stages of fruit development. They act as natural preservatives that protect the fruit from microbial attack, and they also help in the transportation of minerals during the early growth phase.

As a fruit ripens, a process called the climacteric phase takes place, which is a stage of increased metabolic activity. This is typically characterized by a burst in respiration and often coincides with a rise in ethylene production, a plant hormone that triggers the ripening process. Many complex biochemical changes occur during this stage.

One of the major changes is the conversion of starches into sugars. Many fruits store energy in the form of starches during the growth phase. As the fruit ripens, these starches are broken down into simpler sugars such as glucose and fructose. This process is known as starch hydrolysis and is facilitated by enzymes like amylases and glucosidases. This conversion contributes to the sweetness that characterizes ripe fruit.

Simultaneously, the organic acids that make the fruit sour are used up in respiration and other metabolic processes during ripening, or they may be converted into other compounds that do not taste sour. This results in a decrease in the fruit’s overall acidity, reducing the sourness.

Also, there are changes in tannin and pectin content in the fruit. Tannins contribute to astringency in unripe fruit and are broken down during the ripening process. Pectin, which helps maintain firmness in unripe fruit, is broken down by the enzymes known as pectinases, making the fruit softer.

Ripening also causes other changes that contribute to the fruit’s appeal, such as a change in color due to the breakdown of chlorophyll and an increase in aroma due to the production of volatile compounds.

In summary, the sourness in unripe fruit is largely due to organic acids and other compounds. During ripening, these are reduced or transformed into other substances, while starches are converted into sugars, resulting in the sweet taste characteristic of ripe fruit.