Yongguo Liu

Rapidly Responsive and Highly Selective Fluorescent Probe for Bisulfite Detection in Food

The new fluorescent probe 4-hydroxy-3-((2E,4E)-5-phenylpenta-2,4-dienoyl)-2H-chromen-2-one (probe 1) was designed and synthesized for selective detection of sulfite. The fluorescence intensity of the probe was decreased only in the presence of HSO3-; all other anions assessed resulted in an increased fluorescence response. Hence, probe 1 acts as a highly selective sensor for HSO3-. This sulfite sensitivity can also be readily monitored visually, as once treated with sulfite the solution shows a marked color change from yellow to colorless. Moreover, probe 1 can be conveniently used as a signal tool to determine the HSO3- levels in various sugar samples.

Triple-channel comparative analysis of volatile flavour composition in raw whole and skim milk via electronic nose, GC-MS and GC-O

A novel triple-channel comparative analysis of volatile composition in raw whole and skim milk (RWM and RSM) was developed via an electronic nose (E-Nose), headspace solid-phase micro-extraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS), and gas chromatography-olfactometry (GC-O). Volatile flavour compounds from RWM and RSM caused the differences in mouthfeel characteristics by the human sensors, and also affected consumer preference. Solid state sensor technology, an E-Nose, was applied to distinguish the differences in volatiles between RWM and RSM. Headspace volatiles adsorbed by HS-SPME fiber (CAR/PDMS) were detected by GC-MS. Aroma compounds were identified by GC-O. Nine and three compounds were found to be aroma-active compounds from RWM and RSM, respectively. Octanoic acid, butanoic acid, and 3-hydroxy-2-butanone were found to be the most important aroma-active compounds in RWM, while the most important aroma-active compound of RSM was octanoic acid.

Enantioselective syntheses and sensory properties of 2-methyl-tetrahydrofuran-3-thiol acetates.

The enantioselective synthesis of four stereoisomers of 2-methyl-tetrahydrofuran-3-thiol acetate was achieved. The two enantiomers of the important intermediate cis-2-methyl-3-hydroxy-tetrahydrofuran were obtained by Sharpless asymmetric dihydroxylation (AD), whereas the two enantiomers of trans-2-methyl-3-hydroxy-tetrahydrofuran were derived from the corresponding optically active cis-isomers by Mitsunobu reaction. Each stereoisomer of 2-methyl-3-hydroxy-tetrahydrofuran went through mesylation and nucleophilic substitution to afford the corresponding product with specific configuration. (2R,3S)- and (2R,3R)-2-methyl-tetrahydrofuran-3-thiol acetate were obtained in 80% ee, whereas the (2S,3R)- and (2S,3S)-isomers were in 62% ee. The odor properties of the synthesized four stereoisomers were evaluated by gas chromatography-olfactometry (GC-O), which revealed perceptible differences among stereoisomers both in odor features and in intensities.

Highly selective and rapidly responsive fluorescent probe for hydrogen sulfide detection in wine

A new fluorescent probe 6-(2, 4-dinitrophenoxy)-2-naphthonitrile (probe 1) was designed and synthesized for the selective detection of hydrogen sulfide (H2S). The addition of H2S to a solution of probe 1 resulted in a marked fluorescence turn-on alongside a visual color change from colorless to light yellow. Importantly, this distinct color response indicated that probe 1 could be used as a visual sensor for H2S. Moreover, probe 1 was successfully used as a signal tool to determine the H2S levels in beer and red wine.

One-pot synthesis of (-)-Ambrox.

(−)-Ambrox is recognised as the prototype of all ambergris odorants. Widely used in perfumery, (−)-Ambrox is an important ingredient due to its unique scent and excellent fixative function. An environmentally friendly and practical preparation of (−)-Ambrox is still unavailable at present although a lot of attention has been paid to this hot research topic for many years. A one-pot synthesis of (−)-Ambrox was studied starting from (−)-sclareol through oxidation with hydrogen peroxide in the presence of a quaternary ammonium phosphomolybdate catalyst {[C5H5NC16H33] [H2PMo12O40]}, which gave the product a 20% overall yield.

Preparation of 2-hexyl-4-acetoxytetrahydrofuran

2-Hexyl-4-acetoxytetrahydrofuran is a flavor compound with a sweet, floral-fruity odour. Two different methods for its preparation were investigated starting from 1-decen-4-ol. 1-Decen-4-ol was transformed to 2-hexyl-4-acetoxytetrahydrofuran through mesylation, dihydroxylation, intramolecular nucleophilic substitution and acetylation in overall 70% yield; alternatively, 1-decen-4-ol was epoxidised to 1,2-epoxy-4-decanol, followed by acetylation and dehydration to produce the desired product in overall 48% yield. The two methods gave the product with poor and opposite diastereoselectivity but both routes have advantages on yield or ease of operation over the literature procedure.

Viscoelastic and Functional Properties of Cod-Bone Gelatin in the Presence of Xylitol and Stevioside

The physical, rheological, structural and functional properties of cod bone gelatin (CBG) with various concentrations (0, 2, 4, 6, 10, and 15%) of low-calorie sweeteners [xylitol (X) and stevioside (S)] to form gels were investigated. The gel strength of CBGX increased with increased xylitol due presumably to hydrogen bonds between xylitol and gelatin, but with CBGS the highest gel strength occurred when S concentration was 4%. Viscosity of CBGS samples were higher than CBGX due to Ss high molecular mass. The viscoelasticity (G′ and G′′), foaming capacity and fat binding capacity of CBGX were higher while foam stability was lower. The emulsion activity and emulsion stability of CBGX were a little lower than CBGS at the same concentration. The structure of X is linear making it easier to form a dense three-dimensional network structure, while the complex cyclic structure of S had more difficulty forming a network structure with cod bone gelatin. Therefore, X may be a better choice for sweetening gelatin gels.

Selective catalytic dehydration of furfuryl alcohol to 2, 2′-difurfuryl ether using a polyoxometalate catalyst

The spice flavour compound 2, 2′-difurfuryl ether (DFE) is widely utilised in the food industry as it has a coffee-like, nutty, earthy, mushroom-like odour. However, despite intensive research efforts, to date, an environmentally friendly and practical synthetic preparation technique for 2, 2′-difurfuryl ether is still unavailable. Here, we investigate a new approach using polyoxometalate catalysts to selectively catalytically dehydrate furfuryl alcohol to 2, 2′-difurfuryl ether. We have successfully applied this methodology using the polyoxometalate (POMs) catalyst {[(CH3CH2CH2CH2)4N]2[SMo12O40]} to produce 2,2′-difurfuryl ether in a 30.86% isolated yield.

Preparation and odour of cis - and trans -2-methyltetrahydrofuran-3-thiol acetates

The preparation of cis- and trans-2-methyltetrahydrofuran-3-thiol acetates from (E)-3-penten-1-ol is reported. The mesylate of (E)-3-penten-1-ol was converted into trans- or cis-2-methyl-3-hydroxytetrahydrofuran by oxidation with H2O2 and HCOOH or with KMnO4. cis- or trans-2-Methyltetrahydrofuran-3-thiol acetate was prepared by mesylation and an SN2 nucleophilic substitution with AcSH from trans- or cis-2-methyl-3-hydroxytetrahydrofuran respectively. The configuration of the products was confirmed by their synthesis. Olfactory evaluation of cis- and trans-2-methyltetrahydrofuran-3-thiol acetates indicated some differences both in odour feature and intensity.

Preparation and odour properties of (S)-3-mercapto-1-heptyl acetate

Synthesis of (S)-3-mercapto-1-heptyl acetate was achieved in four steps. Sharpless asymmetric epoxidation of (E)-2-heptenol yielded (2R,3R)-2,3-epoxy-1-heptanol, which was treated with thiourea in the presence of Ti(OPri)4 to give (2S,3S)-2,3-epithio-1-heptanol, reduction of which followed by acetylation afforded (S)-3-mercapto-1-heptyl acetate in 91% ee. The optically active product possessed a tropical fruit aroma reminiscent of mango and passion fruit, with berry, ester-like, sweet, and pepper-like aspects.