During ripening, the decline in acidity is due to the respiration of which acid?

• A. Tartaric acid
• B. Citric acid
• C. Malic acid
• D. Ascorbic acid

Answer: (C)

During ripening the fruit’s metabolism uses stored acids as fuel, and the acid that is actively consumed through respiration is malic acid. Malate is oxidized in the mitochondria to oxaloacetate, feeding the TCA cycle and releasing energy. As this malic acid pool shrinks, titratable acidity drops and the fruit becomes less tart. Tartaric acid tends to stay relatively constant during ripening, so it doesn’t drive the acidity decline. Citric acid can vary but isn’t the main acid being metabolized in most ripening grapes, and ascorbic acid isn’t a primary determinant of acidity changes in this context. So the decline in acidity is best explained by the respiration of malic acid.