Identification of hydroxycinnamic acid derivatives of selected canadian and foreign commercial beer extracts and determination of their antioxidant properties

Highlights

• Stir stick stout, a local beer, had the highest content of total phenolics and flavonoids.

• The major hydroxycinnamic acids were identified and quantified by HPLC-DAD.

• 4-Vinylguaiacol, (4VG), a derivative of ferulic acid, was identified first time in Canadian beer.

• A positive correlation was reported for the first time between 4-VG and radical scavenging assays.

• Local Canadian beer showed higher and strong free radical scavenging activities.

Abstract

Phenolic compounds in beer are derived from grains and hops during processing and production. Thus, the total phenolic content (TPC) of beer extracts, from selected Canadian and foreign commercial, and laboratory produced beers were examined and ranged from 3.72 ± 0.23 to 13.73 ± 0.49 mg GAE/100 mL beer. The total flavonoid content (TFC) of the same beer extracts varied from 0.82 ± 0.02 to 5.28 ± 0.04 mg CE/100 mL beer. Of particular interest were the hydroxycinnamic acids (HCAs) and derivatives in beer extracts because of their antioxidant properties. Main HCAs and a key derivative of ferulic acid, 4-vinylguaiacol (4-VG), were identified in beer extracts by high performance liquid chromatography (HPLC). Significant variations in TPC, TFC, HCAs and 4-VG content were observed among the beer extracts. Antioxidant activities of beer extracts, determined by radical scavenging and ferric-reducing assays, were positively correlated (p < 0.05) with TPC, TFC, and 4-VG but observed negative correlation with individual HCAs (p > 0.05). The positive correlation of 4-VG with ABTS radical cation scavenging and reducing power assays is reported first time. These findings suggest that phenolic compounds and a key derivative of the hydroxycinnamic acid, 4-VG, may have the protective role in the beer as an antioxidant.

Introduction

Beer is the most commonly consumed alcoholic beverage in the world (Stewart, 2013). Canadians drink more beer (51%) than wine (28%) and spirits (27%) (WHO, 2014). The flavor stability and shelf life of beer still remain as a big challenge to brewers (Leitao et al., 2011; Zhao, Chen, Jian Lu, & Zhao, 2010). Different beers have distinct flavors that popularizes a specific brand while their shelf life is important for preserving flavor quality and nutritional value. Oxygen content and oxidation are the main cause of flavor and quality deterioration of commercial beers (Zhao et al., 2010). A number of natural antioxidants, for example, phenolics, sulfite, and Maillard reaction products, are present in beer (Guido, Boivin, Benismail, Goncalves, & Barros, 2005; Zhao et al., 2010). Of these, phenolics are of particular interest to brewers because they can delay, retard and/or prevent oxidation during brewing process (Guido et al., 2005).

Phenolics are secondary metabolites widely distributed in plant foods. They display a wide range of antioxidant and biological activities in food and biological systems which is mostly dependent on their structures and the number of functional groups (Rahman, de Camargo, & Shahidi, 2017, 2018). The major phenolics in beer are phenolic acids, flavonoids and stilbenes (Callemien & Collin, 2009; Wannenmacher, Gastl, & Becker, 2018). Many of these phenolics act as flavor precursors and antioxidants. For example, hydroxycinnamic acids (HCAs) and their decarboxylated derivatives such as 4- vinyl guaiacol, 4-vinyl phenol, and 4-vinyl syringol can impart a very strong flavor to beer (Callemien & Collin, 2009; Vanbeneden et al., 2006, 2008). These derivatives are produced in beer during wort boiling and fermentation by decarboxylation (Vanbeneden et al., 2006, 2008).

Many studies have been conducted on beer phenolics and their antioxidant activities (Leitao et al., 2011; Lugasi, 2003; Piazzon, Forte, & Nardini, 2010; Zhao et al., 2010). These studies mainly focused on the relationship between total phenolic content and antioxidant activities of beer extracts with identification of individual phenolic compounds. Very limited data are available, however, on the profiles of hydroxycinnamic acids (HCAs) and their derivatives in commercial beers and their identification (Vanbeneden et al., 2006, 2008). In fact, the profiles of phenolics, individual HCAs, and their derivative phenols in local Canadian beer, have not been extensively studied. These compounds could be important to enhance the shelf life of beer, because of their antioxidant properties (Richard- Forget et al., 1995), which still remains to be examined. Therefore, the aim of this study was to investigate the major HCAs and their derivatives, in a laboratory produced beer and selected Canadian and foreign beers consumed in Canada using HPLC-DAD. In addition, the antioxidant activities of all beer extracts were studied using in vitro screening assays. A Pearson correlation statistical analysis was conducted between antioxidant screening assays and total phenolic content (TPC), total flavonoids content (TFC), HCAs and 4-VG to establish the antioxidant properties of beer extracts and individual HCAs and 4-VG.