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Ua ANSWER ^*^
Citrus fruits: all of 'em. It's strongest in lemons and limes, which are up to 8% citric acid by weight and can even be used to extract the chemical from; sour oranges can also be used, so we assume that the more sour the fruit the higher the citric acid content.
Berries and soft fruit: Almost all berries with the possible EXCEPTION of blueberries. Certainly found in: strawberry, raspberry, gooseberry, cranberry, redcurrant, blackcurrant. Redcurrants are one of the worst offenders - redcurrant juice can be used to replace lemon juice in jam recipes!
Exotic fruits: Pineapple, tamarind
Stone fruits: Cherries (apparently only a small amount)
Vegetables: Tomatoes, cayenne peppers (not the same as sweet peppers), Jerusalem artichoke, lettuce (!)
Wine - as a by-product of fermentation, and to improve clarity
Cheese - Citric acid is used in the manufacturing process to help clot the milk FASTER. It may be an integral part of making certain CHEESES, especially mass-produced mozzarella, but appears to be a by-product of industrialisation for most British cheeses: the traditional method of adding BACTERIAL culture to the milk and allowing it to act slowly does not use added citric acid as far as I know. I don't, however, know whether citric acid also appears naturally in cheese as a by-product of the bacterial reactions. Conclusion: traditional (read: expensive) cheeses are likely to be safer, but the jury's out overall.
Sourdough breads eg. rye bread - as a by-product of fermentation.
Hope This will help
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