2009_Book_FoodChemistry

826 18 Fruits and Fruit Products
(18.15)
The phenolic acids develop differently during
the ripening of fruits. In apples, they reach
a maximum in June and then decrease, e. g., from
mid-June to the beginning of October (mg/kg):
p-coumaric acid (460 → 15), caffeic acid
(1270 → 85), ferulic acid (95 → 4). Subsequent
storage results in further losses. In contrast,
the concentrations in strawberries of, e. g., β-
coumaric acid (69 → 175), caffeic acid (15→39),
gallic acid (80 →121) and vanillic acid (3 → 34)
increase from the beginning of June till ripening
in the beginning of July (mg/kg). Hydroxycinnamic
acid biosynthesis starts with phenylalanine
[cf. Reaction route 18.16: a) phenylalanineammonia
lyase; b) cinnamic acid 4-hydroxylase;
c) phenolases; d) methyl transferases, R: OH and
OCH 3 in various positions].
The hydroxybenzoic acids are derived from hydroxycinnamic
acids by a pathway analogous to
β-oxidation of fatty acids:
(18.16)
in Formula 18.15. They have been found in various
Rosaceae, e. g., raspberries and blackberries,
and contain the structural elements mentioned
above.
(18.17)