DFT study of the radical scavenging activity of isoxanthohumol, humulones (α-acids), and iso-α-acids from beer

Ilija Cvijetić,Dušanka Milojković-Opsenica,Petar Ristivojević,Mire Zloh,Miljan Bigović,Maja Vitorović-Todorović

doi:10.1007/s11224-021-01780-4

Abstract

Humulones and iso-humulones are potent natural antioxidants found in beer. In this study, density functional theory (DFT) method was applied for elucidating the structure-antioxidant activity relationship and molecular mechanism of antioxidant activity of eight bioactive humulones previously identified in different beer samples: isoxanthohumol, (R)- and (S)-adhumulone, cis- and trans-iso-adhumulone, cis- and trans-iso-n-humulone, and desdimethyl-octahydro-iso-cohumulone. The calculated bond dissociation enthalpies (BDEs) suggest that desdimethyl-octahydro-iso-cohumulone was the most potent compound with BDEs 5.1 and 23.9 kJ/mol lower compared to the values for resveratrol in gas phase and water, respectively. The enolic –OH is the most reactive site for hydrogen atom transfer (HAT). The presence of β-keto group with respect to enolic –OH diminishes the HAT potency via the formation of a strong intramolecular hydrogen bond. Another common antioxidant mechanism, single electron transfer followed by proton transfer (SET-PT), is only feasible for isoxanthohumol. The results of this study indicate a strong correlation between the increased antioxidant activity of beer products and the higher content of reduced iso-α-acids.

Highlights

Beer is the second most-consumed low alcoholic beverage in Europe, accounting for 37% of the total EU alcohol consumption [1]
The pharmaceutical properties of beer mainly depend on the chemical composition of hops and malt, as well as parameters involved in brewing, e.g., the variety of barley and hops, temperature, and pH during mashing, sparing, boiling, as well as yeast fermentation
About 70–80% of beer polyphenols originate from malt, and the remaining fraction belongs to bitter acids from hops

Summary

Introduction

Beer is the second most-consumed low alcoholic beverage in Europe, accounting for 37% of the total EU alcohol consumption [1]. Beer contains a wide range of compounds such as proteins, carbohydrates, B vitamins (niacin, riboflavin, folate, cobalamin, and pyridoxine), amino acids, phenolic. The harmful effects associated with the increased alcohol intake are wellknown, the effects of moderate consumption of beer (one glass for woman and two for a man per day) require further study. These effects mainly vary for diverse alcoholic beverages due to their heterogeneous content of non-alcoholic components. About 70–80% of beer polyphenols originate from malt, and the remaining fraction belongs to bitter acids from hops. Hops contains about 14.4% of polyphenols such as phenolic acids, prenylated chalcones, flavonoids, catechins, and proanthocyanidins [3].

Objectives

Methods

Results

Conclusion