New Volatile Sulfur-Containing Constituents in a Simultaneous Distillation−Extraction Extract of Red Bell Peppers (Capsicum annuum)

Abstract

An extract of red bell peppers ( Capsicum annuum) was prepared by simultaneous distillation-extraction (SDE, Likens-Nickerson). In addition to the already known (3 E)-3-hepten-2-one ( 1), the unsaturated C9-ketones 1-nonen-4-one ( 2), (2 E)-2-nonen-4-one ( 3), and (2 E,5 E)-2,5-nonadien-4-one ( 4), 2-methoxy-3-isobutylpyrazine ( 5), and heptane-2-thiol ( 6), we identified 19 new thiols (the aliphatic saturated and unsaturated thiols 14- 16, and 22- 27, the mercapto-ketones 12 and 13, the mercapto-alcohols 17, 18, and 30, the dithiols 19 and 28, the methylthio-thiols 20 and 21, and the thiophene-thiol 31) and the two new dithiolanes 10 and 29. All of them are structurally related to the unsaturated C7- and C9-ketones 1- 4. The free thiols were enriched using Affi-Gel 501 ( p-aminophenyl-mercuric acetate grafted on an agarose gel). The new compounds were confirmed by syntheses and were organoleptically evaluated.

Influence of the Stereochemistry on the Sensory Properties of 4-Mercapto-2-heptanol and Its Acetyl-Derivatives

“…19,20 The reaction mixture was stirred at room temperature overnight. After careful quenching with 100 mL of distilled water under ice-cooling, the aqueous phase was adjusted to pH 2, using hydrochloric acid (5%) and extracted with dichloromethane (3 × 20 mL).…”

“…The chromatographic and mass spectrometric data were in agreement with those previously reported. 19 Capillary gas chromatographic analysis of 3 using heptakis(2,3-di-O-acetyl-6-O-tert-butyl dimethylsilyl)-β-cyclodextrin as chiral stationary phase enabled the separation of the four stereoisomers ( Figure 2B). The assignment of the order of elution was based on a two-step procedure: (i) separation of the two diastereoisomers via HPLC and comparison of the NMR data to those reported for anti-(2S,4S)-4-mercapto-2-heptanol, the product obtained from 3-hepten-2-one utilizing tandem Michael addition-MeerweinPonndorf-Verley reduction, and (ii) preparation of the (4S)-configured stereoisomer via lipase-catalyzed resolution of 4-acetylthio-2-heptanone 2 and subsequent reduction of the remaining substrate with lithium aluminum hydride.…”

The Significance of Volatile Sulfur Compounds in Food Flavors

“…Elution of beverages (e.g., wine) through a column containing a pHMB absorbent is an alternate approach (14). Thiols in flavor extracts can also be enriched on agarose gel grafted with p-aminophenyl-mercuric acetate, then desorbed with a 10 mM dithiothreitol solution (15).…”

“…Subsequently, a series of newly-reported thiols, mercapto ketones, mercapto alcohols, and methylthio-thiols were identified in red bell pepper which cover a palette of organoleptic properties (15). Their flavor descriptors range from "berry/tropical fruit", to "green/vegetable-like, meaty, onion-like, sesame, peanut, coffee, and roasted."…”

Preparation and Odour Properties of (S)-3-Mercapto-1-Heptyl Acetate

“…Asymmetric epoxidation of 3 under the Sharpless conditions using D-(-)-diethyl tartrate afforded (2R,3R)-4 (94% ee) which was treated with thiourea in the presence of Ti(OPr i ) 4 to give (2S,3S)-5 (92% ee), a thiirane of inverted absolute configuration.…”