Bitterness in alcoholic beverages: The profiles of perception, constituents, and contributors

Highlights

• The bitterness profile in alcoholic beverages was described.

• Polyphenols, iso-α-acids, higher alcohols, and bitter peptides are the major bitter compounds.

• Raw materials and microbial metabolism were the major contributor to bitterness.

• Improvement on bio-electronic sensor to identify bitter components was suggested.

• The bitterness metabolic mechanism is needed further microbial exploration.

Abstract

Background

Bitterness is a basic flavor in alcoholic beverages (beer, wine, liquor, and rice wine) and has physiological significance, although excessive and disharmonious bitterness is unpleasant. Current research on flavor in alcoholic beverages is primarily focused on volatile constituents and distinctive flavor compounds. However, studies on the recognition, identification, and metabolic mechanism of bitter substances are still in the preliminary phase.

Scope and approach

This review provides an integrated account of the signal transduction and recognition, composition and sensory properties of bitterness in alcoholic beverages. Abiotic and biotic factors within fermentation systems that may influence the bitterness of the fermented beverages are summarized. Future research on the molecular characteristics, taste attributes, and metabolic pathways of bitterness are discussed herein.

Key findings and conclusions

Polyphenol and iso-α-acid extracted from grapes and hops are the typical bitter substances in wine and beer. Microbial metabolites, including bitter peptides and higher alcohols, are the primary contributors to bitterness in liquor and rice wine. These compounds can activate one or more specific bitter taste receptors. Manufacturing processes and sensory interactions also influence the perception of bitterness. Establishing normative bitterness scoring methods and distinguishing acceptable and unacceptable bitterness based on sensory physiology will continue to be the goals of bitterness research. Further elucidation of the metabolic mechanism underlying bitterness through a combination of omics and synthetic microbiology will allow for taste characteristics of alcoholic beverages to be manipulated.

Introduction

Alcoholic beverages are hedonic goods that have been consumed in societies for a long time and may also have an important role on diets by providing polyphenols and bioactive peptides (Cai et al., 2019; Jin, Zhu, & Xu, 2017). Wine, beer, liquor, and rice wine are alcoholic beverages that are popular worldwide and whose global prevalence has increased over thousands of years due to their excellent aroma and taste (de Freitas, 2019; H.; Liu & Sun, 2018; S.; Soares, Brandao, Mateus, & de Freitas, 2017). The effect of consumption preferences on sensory interactions indicates that unpleasant flavors are a significant barrier to product acceptance (Prescott, 2015). To be successful in the modern alcoholic beverage marketplace, a producer must have a comprehensive understanding of the science underlying the choices of customers. Bitterness perception is considered a defense mechanism against toxicants that activates central warning signals to regulate food intake (Peng et al., 2015). Differences in physiological mechanisms among individuals, various environmental factors, and the interaction of functional groups between substances affect bitter perception (Spence, 2015). Additionally, short periods of repeated intake of alcoholic beverages will enhance the bitter sensation and may have a negative impact on the acceptance of a product.

In recent decades, the flavor chemistry of alcoholic beverages has primarily focused on volatile components and the compounds, i.e. dried fruit (raisins), red berries, honey, chocolate, and vanilla, that significantly contribute to their distinctive sensory properties (Maarse, 2017), with some research on bitterness having also been conducted. It is generally accepted that phenols are the primary bitter irritants in wine, and the chemical structural characteristics of phenols, including the degree of polymerization, galloylation, B-ring trihydroxylation and stereochemistry of the subunits results in different bitter sensations (Ma et al., 2014). Analogously, the specific bitterness qualities that hop acid isomers impart to beer have been described as ‘harsh’, ‘instant’, and ‘rounded’ (Oladokun et al., 2016). Little information on bitterness in liquor is available, while the bitter peptides of rice wine have been previously described (Maeda et al., 2011). However, the receptor-binding mechanism of bitter agonists in alcoholic beverages remains unclear.

The time to reach maximum intensity in the mouth is greater for bitterness than for other basic tastes. There are many types of bitter substances, which mostly contain groups of –NO₂, =N-, –SH, -S-, –SO₃H, -S-S, =C = S, etc. (Jaggupilli, Howard, Upadhyaya, Bhullar, & Chelikani, 2016). These compounds are used as ligands to form signal molecules with bitter taste receptors or hydrophobic compounds to directly activate the messenger system to participate in bitterness conduction (Devillier, Naline, & Grassin-Delyle, 2015). The Bitter Database (BitterDB) has gathered information regarding the chemical characteristics, receptors, and identifiers of more than 1000 bitter compounds (Dagan-Wiener et al., 2019). Despite recent advances in decoding bitter sensation, the structural diversity of compounds and polymorphisms of human bitter receptors make the identification and screening of natural and synthetic bitter compounds in alcoholic beverages an arduous task (Carleton, Accolla, & Simon, 2010). Moreover, there are technical limitations to the definition of bitter characteristics through the use of electronic tongue (ET) sensors.

The construction of bitter taste perception is a highly complex process that depends on individual bitterness receptors, the existence of an independent bitter component and interactions between flavor components. Research on the structures, characteristics, and mechanisms of bitterness in alcoholic beverages has been insufficient. In the present review, the transduction and evaluation of bitterness in alcoholic beverages is described, followed by a discussion on the aspects of the chemical composition, sensory characteristics, as well as biotic and abiotic factors that may affect bitterness formation. The goal of this review is to elucidate possible challenges to identifying bitterness characteristics in alcoholic beverages and provide an outlook concerning the further research to regulate the bitterness characteristics and improve flavor of alcoholic beverages.