Bitter Taste Impact and Thermal Conversion of a Naringenin Glycoside from Cyclopia genistoides

Abstract

A naringenin derivative, isolated from Cyclopia genistoides, a bitter tasting herbal tea, especially when in green (unoxidized) form, was identified as (2S)-5-[α-L-rhamnopyranosyl-(1→2)-β-D-glucopyranosyloxy]naringenin (1). The compound partially epimerizes to (2R)-5-[α-L-rhamnopyranosyl-(1→2)-β-D-glucopyranosyloxy]naringenin (2) when heated at different temperatures (80, 90, 100, 110, and 120 °C) for a prolonged period in a phosphate buffer at pH 5. The fractional conversion model predicted the decrease in the concentration of compound 1 the best. The activation energy of the conversion reaction was calculated as 99.16 kJ mol −1 . Prolonged heating resulted not only in formation of compound 2 but eventually a decrease in its concentration and the formation of another conversion product, (E)-2′-[α-L-rhamnopyranosyl-(1→2)-β-D-glucopyranosyloxy]-4′,6′,4-trihydroxychalcone (3). In contrast, naringin, glycosylated at C-7, remained stable when heated under the same conditions (100 °C for 6 h at pH 5). The bitter intensity of compound 1 was substantially less than that of naringin, both tested at 0.04 mM, a concentration typical of compound 1 in an herbal tea infusion of green C. genistoides. This comparison indicates that the position of the sugar moiety plays an important role in determining both bitter intensity and heat stability of naringenin glycosides.

Heat treatment improves the sensory properties of the ultrafiltration by‐product of honeybush (Cyclopia genistoides) extract

“…Heating of the retentate reduced the concentration of most of the phenolic compounds, with 90 °C/4 h having a greater impact, in particular on mangiferin, isomangiferin, 2RNAR and 2SNAR (Table 2). Previous studies [39][40][41] provided insight into the relative heat stability of the compounds as determined by structure, as well as their likely degradation products. Alexander et al 9,31 demonstrated that mangiferin is a major contributor to the bitter taste of C. genistoides, that the ratio of mangiferin to isomangiferin might play a role, and that IDG and 2SNAR could suppress and enhance the bitter intensity of a xanthone fraction, respectively.…”

Comprehensive off‐line CCC × LC‐DAD‐MS separation of Cyclopia pubescens Eckl. & Zeyh. phenolic compounds and structural elucidation of isolated compounds

“…Compounds O , Q and AD were tentatively identified as naringenin‐ O ‐(hexose‐ O ‐deoxyhexose) isomers due to the neutral loss of a hexose‐deoxyhexose [M − H − 162 − 146] − moiety 33 . Compounds O and Q were identified as (2 S )‐5‐ O ‐[α‐ l ‐rhamnopyranosyl‐(1 → 2)‐β‐ d ‐glucopyranosyl]naringenin and (2 R )‐5‐ O ‐[α‐ l ‐rhamnopyranosyl‐(1 → 2)‐β‐ d ‐glucopyranosyl]naringenin, respectively, based on their relative elution times in the first and second dimension and comparison of data to those of authentic reference standards 16,33,40 . Compound AD was identified as a related naringenin‐ O ‐(hexose‐ O ‐deoxyhexose) derivative, which showed identical MS behaviour to O and Q 33 …”

“…From Fraction D, compound 1 was identified as (2 S )‐5‐ O ‐[α‐ l ‐rhamnopyranosyl‐(1 → 2)‐β‐ d ‐glucopyranosyl]naringenin, previously isolated from Cyclopia genistoides. 16 From Fraction E, four compounds were identified as R ‐neo‐eriocitrin ( 2 ), 45,46 3‐ O ‐α‐ l ‐arabinopyranosyl‐3,4‐dihydroxybenzoic acid ( 5 ), 47 4‐ O ‐β‐ d ‐glucopyranosyl‐ Z ‐4‐hydroxycinnamic acid ( 6 ) 48 and 4‐(4′‐ O ‐β‐ d ‐glucopyranosyl‐4′‐hydroxy‐3′‐methoxyphenyl)‐2‐butanone ( 7 ) 49,50 . Compound structures are shown in Figure 5.…”

“…Authentic phenolic reference standards (purity ≥ 95%) were purchased from Extrasynthese (Genay, France; narirutin), Sigma‐Aldrich (mangiferin, hesperidin, 3‐β‐ d ‐glucopyranosyliriflophenone) and Chemos GmbH (Regenstauf, Germany; isomangiferin). 3‐β‐ d ‐Glucopyranosylmaclurin, (2 S )‐5‐ O ‐[α‐ l ‐rhamnopyranosyl‐(1 → 2)‐β‐ d ‐glucopyranosyl]naringenin and (2 R )‐5‐ O ‐[α‐ l ‐rhamnopyranosyl‐(1 → 2)‐β‐ d ‐glucopyranosyl]naringenin were isolated from Cyclopia genistoides (L.) Vent 15,16 . Stock solutions of the phenolic standards (ca.…”

β-Selective Glycosylation Using Axial-Rich and 2-<i>O</i>-Rhamnosylated Glucosyl Donors Controlled by the Protecting Pattern of the Second Sugar

“…1a). These compounds exhibit various biological activities, [3][4][5][6][7] and the novel glycosides of flavones, [8][9][10][11][12] terpenes, [13][14][15][16][17] and steroids [18][19][20][21][22] are naturally occurring; therefore, they have attracted attentions of the pharmaceutical chemists. The synthesis of 2-O-α-L-rhamnosyl-β-O-glucosidic structure involves the rhamnosylation of 2-O in a glucosyl donor bearing an aglycon at the β-anomeric oxygen.…”