Stereoisomeric flavour compounds

The enantiomeric distribution of 3-mercaptohexanol (1) and 3-methylthiohexanol (2) in yellow and purple passion fruits was determined by capillary gas chromatography (GC) using two different chiral stationary phases and a flame photometric detector. The results were confirmed by enantioselective capillary GC combined with mass spectrometric detection.1 shows an enrichment of the (S)-enantiomer, but the enantiomeric purity varies in a wide range. Irrespective from the enantiomeric distribution of1, 2 was detected with high enantiomeric purity in favour of the (S)-enantiomer. Using the method presented the addition of synthetic, racemic2 is easily detected.     

Stereoisomeric flavour compounds LXXI: determination of the origin of aroma-active dihydrofuranones

The odour characteristics of chiral 3[2H]-furanones, which are important aroma compounds, have been evaluated by sniffing the separated enantiomers through the port of a gas chromatograph (gc-sniffing). The results revealed great differences in the odour quality and thresholds of the single enantiomers. The determination of the origin of 2,5-dimethyl-4-hydroxy-3[2H]-furanone and 2,5-dimethyl-4-methoxy-3[2H]- furanone from strawberries, pineapples and commercial samples has been achieved using GC-isotope ratio mass spectrometry (GC-IRMS). For this technique to be successful, it is essential that preparative and storage procedures should not influence the isotope ratio of compound analysed; this is demonstrated to be the case for 2,5-dimethyl-4-hydroxy-3[2H]-furanone.     

Stereoisomeric flavour compounds LXXV: synthesis and structure–function relationship of 3-methylthiobutanal enantiomers

 The synthesis of enantiopure 3-methylthioalkanals, in particular of 3-methylthiobutanal enantiomers, is described. Elucidation of the structure was achieved by aldehyde-evoked reduction to 3-methylthiobutanol of a known absolute configuration. The odour characteristics of the enantiomers were determined by enantioselective gas chromatography/ olfactometry using octakis(2,3-di-O-butyryl-6-O-tert-butyldimethylsilyl)-γ-cyclodextrin as the chiral stationary phase. Exclusively, the (R)-configured 3-methylthiobutanal exhibits the odour typical of cooked potatoes, whereas the (S)-configured stereoisomer is odourless. Received: 24 May 1996     

食品风味物质的分离研究进展与应用

介绍了一些常用食品风味物质的分离抽提方法,主要包括分子蒸馏法、超临界流体抽提法、超滤法、直接萃取法,并举实例说明这些方法的应用。     

金华火腿特征风味物质研究进展

金华火腿是我国传统的干腌火腿,以其特殊的风味而著称。通过对金华火腿及其它干腌火腿主要风味物质、形成机理、提取及鉴定方法等研究现状的综述,表明对金华火腿特征风味物质的深入研究有利于了解风味物质形成规律,为金华火腿加工工艺控制及火腿调味料开发应用提供理论基础。     

Stereoisomeric flavour compounds LXXX: alkyl-branched alkanals – stereodifferentiation, structure elucidation and structure – function relationship

The direct enantioseparation of 2-methylbutanal, 2-methylpentanal, 2-ethylhexanal, 3-methylpentanal and 4-methylhexanal was achieved using enantioselective gas chromatography and the chiral stationary phase heptakis-[2,3-di-O-acetyl-6-O-tert.butyldimethylsilyl]-β-cyclodextrin (DIAC-TBDMS-β-CD). Odour characteristics and threshold values of detection for compounds were evaluated by enantioselective gas chromatography/olfactometry. Enantiopure reference compounds with defined absolute configurations were synthesized starting from the corresponding alcohols or acids which were commercially available or prepared in the laboratory.     

Volatile flavour substances of apricot and their changes during ripening

Aroma content and composition of different Hungarian and foreign apricot cultivars were studied. Volatile flavour substances were isolated by simultaneous steam distillation-extraction. GC and GC/MS analysis of the aroma extracts revealed 40 components, 12 of them have been reported for the first time in apricots. The changes in the aroma composition of the cultivar “Hungarian kajszi” during ripening were also studied.     

Stereoisomeric flavour compounds LXXVI: direct enantioseparation, structure elucidation and structure-function relationship of 4-tert-butyl-α-methyldihydrocinnamaldehyde

 Using enantioselective gas chromatography and heptakis(2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin (DIAC-TBDMS-β-CD) as the chiral stationary phase, the direct enantioseparation of 4-tert-butyl-α-methyldihydrocinnamaldehyde was achieved. The threshold values and odour characteristics of the enantiomers were investigated by enantioselective gas chromatography/olfactometry. In order to elucidate stereochemical features, the carbonyl-function was oxidized to the corresponding acid and diastereomeric amides were generated with (S)-2-amino-2-phenyl-ethanol [L(+)-α-phenylglycinol] as the enantiopure reagent. After separation and isolation by high-performance liquid chromatography, absolute configurations were deduced from X-ray structure elucidation of a pure stereoisomer. Amide cleavage, reduction and selective oxidation yielded the enantiomers of 4-tert-butyl-α-methyldihydrocinnamaldehyde. Received: 7 October 1996 / Revised version: 18 November 1996     

Stereoisomeric flavour compounds LXXIV: 2-phenylpropanol, 2-phenylpropanal and 2-phenylpropanal dimethyl acetal: structure elucidation and structure-function relationship

The direct enantioseparation of 2-phenylpropanol, 2-phenylpropanal and 2-phenylpropanal dimethyl acetal was achieved, using enantioselective gas chromatography and heptakis-[2,3-di-0-acetyl-6-0-tert.butyldimethylsilyl]--cyclodextrin (DIAC--CD) or octakis-[2,3-di-0-acetyl-6-0-tert.butyldimethylsilyl]--cyclodex-trin (DIAC--CD) as the chiral stationary phase. Their odour characteristics and threshold values were investigated by enantioselective gas chromatography/olfactometry. Starting from commercially available (R)-2-phenylpropionic acid, enantiopure (R)-configured reference compounds were synthesized.     

Stereoisomeric flavour compounds LXIX: stereodifferentiation of δ(γ)-lactones C8–C18 in dairy products,margarine and coconut

The enantiomeric distributions of δ- and γ-lactones from dairy products are determined by enantioselective multidimensional gas chromatography. By using heptakis(2,3-di-O-acetyl-6-O-TBDMS)-β-cyclodextrin as the chiral main column, the simultaneous stereodifferentiation of the δ- and γ-lactones C₁₃–C₁₈ is reported for the first time. Genuine lactones of dairy products preferably occur as (R)-enantiomers. Flavoured margarine and coconut are analysed and discussed. Reference compounds are synthesized as racemates and separated by enantioselective HPLC into the enantiomers. Chiral compounds of characteristic enantiomeric ratios are detected irrespective of the manufacturing processes used.     

A study of volatile flavour substances in Dalmatian traditional smoked ham: Impact of dry-curing and frying

Volatiles from Dalmatian prosciutto were isolated by solvent extraction (SE), simultaneous distillation extraction (SDE) and nitrogen purge and steam distillation (NPSD) and analyzed by GC and GC–MS. In all, 46 compounds were identified by SDE and SE (including fatty acids, aldehydes, phenols, esters, ketones and others), while 81 compounds were identified by NPSD (headspace volatiles including phenols, aldehydes, hydrocarbons, ketones, alcohols, esters and heterocyclic compounds). Regarding the impact of dry curing period on the volatiles, an increase in the percentages of aldehydes and esters during the ripening of the prosciutto was observed. Quantitative percentage differences among fried and raw samples were particularly evident in respect of aldehydes (SDE and SE). The NPSD method provided additional information of the volatiles from fried ham, since the pyrazines and most of the lower aldehydes that are important thermally derived flavour compounds were only isolated by NPSD (not by SE and SDE).     

Beef broth flavour: study of flavour development

Of the range of preparation conditions studied here, the beef broths with the most favourable sensory characteristics (P ≤ 0.05) were those manufactured with minced meat in a 7.5 g l⁻¹ NaCl solution in proportions of 1:2 (w/v), heated at 85 °C for 60 min (the beef broth flavour was clean, clear, without any off‐flavour). Our data indicate the importance of accurately determining the heat treatment, since intermediate treatments yielded beef broths of good quality, whereas less intense treatments produced broths with raw meat and bloody and metallic flavours, and intensely heated broths had a warmed‐over or sour and astringent flavour. At higher temperatures the cooking time required to obtain a good‐quality broth decreased. From the analysis of variance of the sensorial data, temperature plays a more important role than cooking time in the development of the sensory properties of beef broths. © 2000 Society of Chemical Industry     

The effect of flavour modulators on chewing gum flavour duration

This study investigated the impact of flavour modulators on dynamic flavour perception, salivation and chewing behaviour of chewing gum. Thirty-nine participants chewed gum for 15 min while assessing flavour intensity, chewing patterns and saliva flow rate. Four flavour modulators (Cooling, Tingling, Salivating and Warming) were added to a citrus-flavoured gum and compared with a control gum, citrus flavour only. Flavour modulators increased flavour duration as measured by flavour intensity half-time; the time needed to reduce the flavour intensity by half. The ‘Salivation’ modulator had the smallest effect and ‘Warming’ had the largest effect on flavour duration. Salivary flow rate was significantly increased by the flavour modulators and was highly correlated with the flavour duration. Chewing behaviour was not affected by the modulators. We conclude that the interaction between the citrus flavour, saliva and flavour modulators (Intensates® flavours) increased the perceived flavour duration during chewing by up to 86% compared with Control.     

酒花多酚-潜在的啤酒风味和风味稳定物质

从CO2萃取后的废酒花中获得的多酚提取物，可以在啤酒生产中评价它们的抗氧化力和潜在的风味特征。由LC-MS和LC-UV的分析数据可知获得的多酚提取物具有较高的选择性，且含有所有的多酚物质。采用固相萃取技术，提取的总多酚物质可以进一步被分级为原花青素、黄酮苷和异戊烯基黄酮。除原花青素外，所有多酚溶液都有很强的风味活性且对口感有利。在啤酒酿造过程中添加这些多酚提取物可以明显延长啤酒的风味稳定性？这些新的酒花制品能赋予啤酒独特的风味并提高啤酒的风味稳定性。     

Stereo-isomeric flavour compounds

2-Alkyl-substituted 4-methyl(4,5-dimethyl)-1,3-dioxolanes are synthesized by the cyclization of propan-1,2-diol and butan-2,3-diol with “Strecker aldehydes” as the carbonyl compounds. The stereo-isomeric 1,3-dioxolanes are separated by micro-preparative multidimensional gas chromatography and their structures assigned using¹H-NMR spectroscopy (300 MHz). These references with definite stereochemistry are required for reliable interpretation of their chromatographic behaviour with Ni(II)-bis-[3-heptafluorobutanoyl-(1R,2S)-pinanoate] and Ni(II)-bis-[heptafluorobutanoyl]-(1R)-camphorate] respectively, as the chiral stationary phases.     

Physical chemistry of flavour

The sensation of flavour occurs when certain flavour-active molecules are released from food and are transported to stimulate sensors in the mouth and nose. The human brain integrates all the signals from the sensors and produces an overall flavour perception. The way in which flavour molecules are released from food during eating, and the manner in which they are retained during processing and storage, are all governed by various aspects of physical chemistry. This review describes some of the basic principles of partition, a key parameter in the physical chemistry of flavour. An overview of the theory and measurement of partition is given, along with some applications to model and real food systems.