826 18 Fruits and Fruit Products
(18.15)(18.16)in Formula 18.15. They have been found in vari-
ousRosaceae, e. g., raspberries and blackberries,
and contain the structural elements mentioned
above.
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). Hydroxycin-
namic acid biosynthesis starts with phenylalanine
[cf. Reaction route 18.16: a) phenylalanine-
ammonia 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 hy-
droxycinnamic acids by a pathway analogous to
β-oxidation of fatty acids:(18.17)