6.7.3. Phenolic Acids

The presence of phenolic acids is associated with astringency, discoloration and inhibition of enzymatic activity and antioxidant properties. Phenolic acids identified in almond kernel have been ca ffeic, p-coumaric, ferulic, sinapic, syringic, vinyl, gallic, protocatechuic and p-hydroxybenzoic, which are fundamentally derivated from benzoic acid or cinnamic acid.

Senter and Horvat [131] found that protocatechuic acid is the dominant phenolic acid in the edible part of almond kernel, followed by p-hydroxybenzoic acid and vinyl acid. Wijeratne et al. [108] observed that the total quantity of free phenolic acids was 163 mg/100 g in the skin, while total quantities of esterified phenolic acids obtained from skin, shell and whole seed were 2796, 1671 and 400 mg/100 g, respectively. Monagas et al. [111] compared the polyphenol concentration in the almond skin of Spanish and American almonds (Table 6).

Bolling [107] reported the almond skin content of protocatechuic acids. The hydroxycinnamic acids, chlorogenic acid, ferulic acid, caffeic acid, sinapic acid and two diferulates have been identified in almond skin, although only chlorogenic acid, caffeic acid and p-coumaric acid have been quantitated.
