Flavonoid bitterness

Naringin is by far the most predominant flavonoid bitter principle in grapefruit (Hagen et al. 1966) and pummelo, while neohesperidin is slightly more predominant in sour orange (Castillo et al. 1992). Neoeriocitrin and poncirin occur in only relatively minor amounts in juices. 

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Assessment of taste is achieved by sensory analysis, from very simple experiments such as triangular tests aiming at determining detection thresholds to complex descriptive analysis approaches. A method referred to as time-intensity that consists in recording continuously the intensity of a given sensation over time under standardized conditions has been applied to study flavonoid bitterness and astringency properties. 

Direct ultraviolet spectrophotometric methods have been developed to measure naringin in grapefruit (19J and hesperidin in orange juice (20, 21j. While these methods are rapid, they are also nonspeciTTc for flavonoid bitterness. 

In addition to the bitter acids and essential oils, the flowers of hops offer a rich array of polyphenolic compounds, primarily chalcones and their accompanying flavanones, many of which are prenylated derivatives (Stevens et al., 1997,1999a, b). The most prominent flavonoid in all plants studied was xanthohumol [342] (3 -prenyl-6 -0-methylchalconaringenin chalconaringenin is 2, 4, 6, 4-tetrahydroxychalcone) (see Fig. 4.11 for structures 342-346). Several additional chalcones—variously adorned with 0-methyl and/or C-prenyl functions—were also encountered, along with their respective flavanones. Three new compounds were described in the Stevens et al. 

Frydman A, Weisshaus O, Bar-Peled M, Huhman D, Summer L, Matin F, Lewinsohn E, Fluhr R, Gressel J, Eyal Y (2004) Citrus fruit bitter flavors isolation and functional characterization of the gene Cml,2RhaT encoding a 1,2rhamnosyltransferase, a key enzyme in the biosynthesis of the bitter flavonoids of Citrus. Plant J 40 88-100... 

We know of thousands of flavonoids. They have a C6-C3-C6 skeleton and are responsible for the bright colors in flowers. The bitter taste in citrus fruits is caused by flavonone glycosides. 

Quinolizidine alkaloids are non-toxic to the legumes which produce them. On the other hand, the quinolizidine alkaloids can be toxic and in some cases very toxic to other organisms. The biotoxicity of alkaloids has for some time been considered to be connected with their bitter taste" ° ". The quinolizidine alkaloids are certainly bitter in taste to humans. However, not all alkaloids are. Literature states that some pyrrolizidine and indolizidine alkaloids are not bitter in their pure forms" Furthermore, there are many non-alkaloid compounds, such as flavonoids, that are bitter in taste but non-toxic. Therefore, although quinolizidine alkaloids are bitter, the connection between biotoxicity and bitter taste is not absolute. 

Noble, A.C., Astringency and bitterness of flavonoid phenols. In Chemistry of Taste Mechanisms, Behaviors, and Mimics (eds P. Given and D. Paredes), American Chemical Society, Washington, DC, 2002, p. 192. 

N.A. Meliacins, triterpenoid bitters, tannins, flavonoids.100 For hemorrhoids, malaria, peptic ulcers, intestinal worms. Antifungal, antiviral, antiinflammatory, antibacterial. 

Proanthocyanidins are polymeric flavonoid compounds composed of flavan-3-ol subunits (unitii.3), and are responsible for bitterness and astringency in some foods and beverages. This unit describes methods for extracting and purifying proanthocyanidins, and for determining their subunit composition by HPLC. Based upon HPLC results, the average degree of polymerization and the conversion yield for purified proanthocyanidins can be determined. 

Proanthocyanidins are polymeric flavonoid compounds composed of flavan-3-ol subunits (Fig. II. 4.1), and are widely distributed in the plant kingdom, including plants that are important as a source of food (Santos-Buelga and Scalbert, 2000). They impart bitter and astringent properties. In addition, these compounds may have potential health effects (Santos-Buelga and Scalbert, 2000). 

Main actives The aerial parts contain flavonoids and the root contains bitter components and inulin. 

Main actives Sesquiterpene lactones, which are bitter flavoured, triterpenes, steroids, flavonoids, mucilages and an inulin content that varies from 2 to 40% in the autumn. Benefits The bitter components were used to promote the flow of digestive juices in the upper intestinal tract. 

Main actives Diteipene bitter components including marrubiin (c.1%), caffeic acid derivatives including chlorogenic acid, flavonoids and a trace of volatile oil. 

The olives themselves contain many phenolic compounds with antioxidant properties. Bouaziz et al. (2005) investigated the olive cultivar Chemlali from Tunisia. Oleuropein (7.14), a bitter glycoside esterified with a phenolic acid, was the major compound present. Phenolic monomers and twelve flavonoids were also identified. The antioxidant activity of the extract was evaluated. Acid hydrolysis of the extract enhanced its antioxidant activity. / -Hydroxyphenyl-cthanol (7.12) and quercetin (1.43) showed antioxidant activities similar to that of 2,6-di-fert-butyl-4-methyl phenol (7.15), a reference compound with known antioxidant properties. It was suggested that a hydroxyl group at the ortho-position on the flavonoid B ring could contribute to the antioxidant activity of the flavonoids. 

Flavan-3-ols represent the most common flavonoid consumed in the American and, most probably, the Western diet and are regarded as functional ingredients in various beverages, whole and processed foods, herbal remedies, and supplements. Their presence in food affects quality parameters such as astringency, bitterness, sourness, sweetness, salivary viscosity, aroma, and color formation [Aron and Kennedy, 2007]. Flavan-3-ols are structurally the most complex subclass of flavonoids ranging from the simple monomers ( + )-catechin and its isomer (—)-epicatechin to the oligomeric and polymeric proanthocyanidins (Fig. 1.10), which are also known as condensed tannins [Crozier et al., 2006b]. 

Chromatographic methods were developed to separate a few of the citrus flavonoids from the complex mixture of citrus flavonoids. The early paper chromatographic methods for flavanones (22, 23) were difficult to quantitate because of band broadening and uneven solvent development. Several thin layer chromatographic (TLC) methods were developed to separate the bitter from the nonbitter flavanone glycosides (24, 25, 26, 27). 

Gas-liquid chromatography (GLC) has notTeen employed for the analysis of flavanone glycosides because they are non-volatile and thermally unstable. One GLC method (28) has been developed for the analysis of the flavanone aglycones. However, the method is extremely time consuming in that the samples must be extracted, hydrolyzed and derivatized before analysis. Furthermore, the procedure cannot distinguish between bitter and nonbitter flavonoids. 

Flavonoids have no odor or mouth feel and, in general, do not contribute significantly to the color of most citrus juices. Their primary effect on citrus quality is due to the bitter taste of certain flavanone glycosides. Thus, quantitative descriptions of desirable citrus qualities are usually based on the absence or maximum concentration limits for these compounds. 

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