Bioactive Properties and Phenolic Composition of Wood-Aged Beers: Influence of Oak Origin and the Use of Pale and Dark Malts

Abstract

Ageing beer in contact with wood is a common technological procedure that has been used for centuries to improve colour, structure, and certain flavours. Herein, the impact of the addition of French and American oak wood to two beer styles, pale and dark, on beer phenolic composition (total phenolics, total flavonoids, and HPLC-DAD) and bioactivity (FRAP, DPPH, anti-inflammatory activity in RAW 264.7, and antiproliferative in Caco-2 cells) was assessed. Thirteen phenolics were quantified with values according to previous reports. Dark malt resulted in higher values of total phenolics, to which m-hydroxybenzoic, syringic, p-coumaric acids, and xanthohumol contributed considerably; the exception was (+)-catechin and salicylic acid, which were found to be higher in pale beers. American oak significantly increased 3,4-dihydroxyphenylacetic, vanillic, and syringic acids up to roughly 3, 2, and 10 times, respectively, when compared with French wood. FRAP and DPPH values varied between pale and dark beers, with a less pronounced effect after wood addition. All samples presented considerable cellular antioxidant and anti-inflammatory as well as antiproliferative activity, but differences were found only for the antiproliferative activity, which was higher for the dark beers, which reached about 70% inhibition. Overall, the influence of malts was more pronounced than that of wood, in the studied conditions, highlighting the overwhelming impact of malts on the bioactivity of beer.

Keywords: FRAP; HiVan; MTT; beer maturation; wood chips.

Figure 1

Antioxidant activity assessment through the FRAP (A)—expressed in mg of ferrous sulphate equivalents per litre of beer sample (mg FSE·L⁻¹), and DPPH (B)—assays presented in mg of Trolox equivalents per litre of beer sample (mg TE·L⁻¹). Significant differences are indicated over the bars (compared to the respective P and S controls) and over the brackets (comparing the same treatments with different woods). **** Significant at p < 0.0001, ** significant at p < 0.01, and * significant at p < 0.05. ns: not significant. Values expressed as mean ± SEM (n = 3).

Figure 2

Cellular antioxidant, anti-inflammatory, and antiproliferative activities assessed through the determination of intracellular reactive oxygen species (ROS) levels in beer samples vs. LPS stimulated control (A); the determination of extracellular NO levels in cells exposed to beer vs. LPS control (B); and cell viability measured after exposure of cells to 20% sample (beer in CM) vs. medium control after 48 h exposure (C). ns: not significant. **** Significant at p < 0.001. * Significant at p < 0.05.

Figure 3

Principal Component Analysis (PCA) biplots of polyphenol composition (red) of beers (blue) used as active variables. Data from bioactivity assays (grey) used as passive supplementary variables (1 = FRAP, 2 = DPPH, 3 = antioxidant, 4 = anti-inflammatory, and 5 = antiproliferative). In green, the type of malt and wood origin are explored as supplementary factors.