Garrido, I., M. Urpi-Sarda, M. Monagas, C. Gómez-Cordovés, P.J. Martín-Álvarez, R. Llorach, B. Bartolomé, C. Andrés-Lacueva, 2010. Targeted analysis of conjugated and microbial-derived phenolic metabolites in human urine after consumption of an almond skin phenolic extract. J. Nutr. 140:1799–807.
A single-blind, placebo-controlled, and randomized trial study was carried out with 16 healthy volunteers (7 men and 5 women). The test group ingested an encapsulated almond skin phenolic extract (884 mg of total polyphenols/dose) containing flavan-3-ols, flavonols, and flavanones, whereas the placebo group ingested microcrystalline cellulose. Our aim in this study was to determine changes in the urinary excretion of conjugated and microbial-derived phenolic metabolites before (-2 to 0 h) and after (0–2, 2–6, 6–10, and 10–24 h) intake of the almond polyphenols compared with the placebo group. For the test group, maximum urinary excretion of (epi)catechin and naringenin conjugates derived from phase II metabolism was attained at 2–6 h after consumption of the almond skin extract and excretions differed from the placebo group during this time period (P ≤ 0.0001). However, excretion of conjugated metabolites of isorhamnetin was highest at 10–24 h and did not differ from the placebo group during this time (P > 0.05). Hydroxyphenylvalerolactones reached maximum urinary levels at 6–10 h after consumption of almond polyphenols, and excretion differed from the placebo group during this time period (P = 0.0004). For the test group, excretions of phenolic acids (hydroxyphenylpropionic, hydroxyphenylacetic, hydroxybenzoic, and hydroxycinnamic acids) did not differ from the placebo group at any time period of urine collection (P > 0.05). The findings presented in this work provide evidence concerning the bioavailability of almond skin polyphenols considering the effects of both phase II and microbial metabolism.