Sweetening of fruits
QUESTION: How do fruits acquire sweetness?
N. Balasubramaninan, Chennai
ANSWER: As the fruit reaches the end of its growth period, it may undergo some characteristic qualitative changes. These changes are collectively referred to as ripening. The three essential steps in the fruit ripening process are a respiratory raise of energy for ripening, providing the fuel, so as to speak for the synthesis of new sets of enzymes and the action of these enzymes in bringing about the changes characteristic of ripening. These changes are softening of the fruit flesh, the hydrolytic conversion of storage materials and quality changes which include marked changes in pigmentation, production of flavour materials and depletion of astringent substances. Among these the hydrolytic enzymes, which are responsible for the conversion of storage materials into sugars play a major role in adding sweetness to the ripening fruit. The major enzyme, which helps for sweetening in majority of fruits is invertase.
Many enzymes involved in the ripening process would spring from the activity of protein synthesis during early climateric rise than before the rise begins. It implies that biosynthesis of new proteins is essential for hydrolytic conversion of storage products during ripening.
Various fruits show widely different rates and extents of such hydrolytic activities. For example banana ripens extremely fast and the hydrolysis of starch is precipitous. Apples are more gradual in hydrolytic as well as in other ripening actions and citrus fruits such as orange and lemon are ponderously slow, sometimes taking months. Hydrolytic activities can give rise to increase in sugars not only from starch but also from fats.
S. Palaniappan, Pudukkottai, T. N.
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