An overview of bitter compounds in foodstuffs: Classifications, evaluation methods for sensory contribution, separation and identification techniques, and mechanism of bitter taste transduction

Abstract

The bitter taste is generally considered an undesirable sensory attribute. However, bitter-tasting compounds can significantly affect the overall flavor of many foods and beverages and endow them with various beneficial effects on human health. To better understand the relationship between chemical structure and bitterness, this paper has summarized the bitter compounds in foodstuffs and classified them based on the basic skeletons. Only those bitter compounds that are confirmed by human sensory evaluation have been included in this paper. To develop food products that satisfy consumer preferences, correctly ranking the key bitter compounds in foodstuffs according to their contributions to the overall bitterness intensity is the precondition. Generally, three methods were applied to screen out the key bitter compounds in foods and beverages and evaluate their sensory contributions, including dose-over-threshold factors, taste dilution analysis, and spectrum descriptive analysis method. This paper has discussed in detail the mechanisms and applications of these three methods. Typical procedures for separating and identifying the main bitter compounds in foodstuffs have also been summarized. Additionally, the activation of human bitter taste receptors (TAS2Rs) and the mechanisms of bitter taste transduction are outlined. Ultimately, a conclusion has been drawn to highlight the current problems and propose potential directions for further research.

Conversion of Phytochemicals by Lactobacilli: (Phospho)-β-glucosidases Are Specific for Glucosylated Phytochemicals Rather than Disaccharides

“…56,57 Many of the bitter tastants in plants are glycosides. 3 Enzymatic deglycosylation is employed to reduce bitterness in citrus juices. 43 Food fermentations with lactic acid bacteria were also reported to reduce the bitterness of many plant foods, for example, sorghum 5 and rice wine, 58 and the deglycosylation of bitter tastants likely contributes to this effect.…”

“…2 However, phenolic compounds also contribute to the bitterness and astringency of various foods of plant origin while tannins inhibit digestive enzymes, making them undesirable or antinutritive components. 3 Humans who have been dependent on crops rich in bitter-tasting phenolic compounds evolved by mutations to bitter taste receptors. 4 Fermentation reduces the content of bitter-tasting compounds and of other adverse phytochemicals in plant foods.…”

“…13 The deglycosylation of phytochemicals profoundly alters their biological activity by either releasing toxic aglycons from cyanogenic glycosides and vicin prior to ingestion 14,15 or by reducing the bitterness of oleuropin and other bitter-tasting glycosides of phenolic compounds. 3 While the metabolism of carbohydrates by lactic acid bacteria, which are among the major food-fermenting microbes, is well understood, 16 the substrate specificity of enzymes that are active on glycosylated phytochemicals remains poorly elucidated. The metabolic characterization of a strain of L. acidophilus that encodes for two phosphotransferase (PTS) systems with cognate phosphoβ-glucosidases provided proof of concept that glycoside utilization loci in lactobacilli are specific for glycosides of small aromatic phytochemicals rather than oligosaccharides.…”

“…Consuming polyphenol-rich foods is associated with a reduced risk of diabetes and metabolic syndrome, cardiovascular disease, and colon cancer . However, phenolic compounds also contribute to the bitterness and astringency of various foods of plant origin while tannins inhibit digestive enzymes, making them undesirable or antinutritive components . Humans who have been dependent on crops rich in bitter-tasting phenolic compounds evolved by mutations to bitter taste receptors .…”

“…During fermentation, phytochemicals including polyphenols are modified by the metabolic activity of fermentation microbes and by the enzymatic activity of the plant substrate. , The first step of these conversions is the hydrolysis of ester bonds by esterases and the conversion of glycosylated phytochemicals by glycosyl hydrolases and carbohydrate lyases. − Glycosylated compounds include flavonoids, the most abundant class of polyphenolic compounds in plants, glycosinolates in Brassicaceae, cyanogenic glycosides, as well as glycosylated phytosterols and alkaloids . The deglycosylation of phytochemicals profoundly alters their biological activity by either releasing toxic aglycons from cyanogenic glycosides and vicin prior to ingestion , or by reducing the bitterness of oleuropin and other bitter-tasting glycosides of phenolic compounds . While the metabolism of carbohydrates by lactic acid bacteria, which are among the major food-fermenting microbes, is well understood, the substrate specificity of enzymes that are active on glycosylated phytochemicals remains poorly elucidated.…”