Identification of buckwheat (Fagopyrum esculentum Moench) aroma compounds with GC–MS

Buckwheat has a strong characteristic aroma, but its phytochemical background has not yet been fully elucidated. The aims of this study were identification and quantification of individual compounds responsible for the buckwheat aroma. Volatiles from a freshly ground buckwheat flour were extracted by different methods: direct extraction with petroleum ether, pentane or methanol, distillation with Clevenger apparatus and a headspace solid-phase microextraction method. The extracts were analysed by GC–MS with electron ionisation. Compounds were identified by MS and by comparison of retention times with reference compounds. Direct extraction with methanol and distillation proved to be very efficient. In these extracts twenty-five and thirty-five compounds were identified, respectively. The first extract contained more hydrophilic compounds and the latter more volatile compounds. Most of the compounds were quantified and their odour activity value (OAV) calculated. Only two compounds (salicylaldehyde and phenylacetaldehyde) were found in both extracts. The compounds with the highest contribution to the buckwheat aroma were: 2,5-dimethyl-4-hydroxy-3(2H)-furanone, (E,E)-2,4-decadienal, phenylacetaldehyde, 2-methoxy-4-vinylphenol, (E)-2-nonenal, decanal, hexanal and salicylaldehyde (2-hydroxybenzaldehyde).     

Contribution of dynamic headspace GC–MS analysis of aroma compounds to authenticity testing of honey

The volatile profiles of 43 authentic honey samples of different botanical and geographical origins were obtained by means of gas chromatography–mass spectrometry. A qualitative analysis of the volatile compounds identified was performed in order to assess the marker compounds (if/when existing) for both botanical and geographical origin. The results seem to indicate the existence of certain marker compounds for the floral origins assessed (e.g. acacia, chestnut, eucalyptus, heather, lavender, lime, rape, rosemary and sunflower). Also such compounds for two geographical origins (e.g. Denmark and England) seem to exist and possible marker compounds could also be found for the honeys from The Netherlands, Spain and Portugal.     

Bound aroma compounds of Marmajuelo and Malvasía grape varieties and their influence on the elaborated wines

Marmajuelo and Malvasía are two white grape varieties grown in Spain (Canary Islands), the former only in the Canary Islands, while the latter is a variety widely spread throughout the world. At the present time, the oenological potential of these varieties grown in the Canaries has not yet been studied. Aroma precursors in musts and skins, and free volatiles in wines were determined in samples of both varieties. Aroma precursors of must and skins were isolated by absorption on XAD-2 resin, and the aglycone liberated by means of acid hydrolysis. Free volatiles from wines and from aroma precursors were extracted with dichloromethane and then analysed by GC–MS. The analysis of glycosidic aroma precursors showed that Malvasía variety presented higher contents of terpenes in grapes than those of Marmajuelo variety. In addition, some precursors of benzenic compounds presented higher contents in the musts of Malvasía with respect to those in the musts of Marmajuelo. The main difference in wine volatile composition was that cis-3-hexen-1-ol, ethyl acetate and γ-nonalactone compounds showed a significantly higher mean content in Malvasía wines than in Marmajuelo wines. Among the aroma precursors analysed, only α-terpineol, linalool oxides, 4-allyl-2,6-dimethoxyphenol, 2-methoxy-4-vinylphenol, 4-hydroxybenzaldehyde, vanillin and benzyl alcohol showed contents in grapes comparable to the levels observed in wine volatile compounds.     

Retention of aroma compounds by β-lactoglobulin in different conditions

This contribution to the study of the retention and the release of aroma compounds was conducted on model systems in the presence or absence of β-lactoglobulin. To know the interactions between the aroma compounds and this protein we studied the hydration of the protein and the effect of water activity on the sorption of the volatiles. It has been shown that water is necessary in the formation of aroma–protein interactions. The presence of β-lactoglobulin in aqueous solution increased the retention of the four aroma compounds considered. They modify the flux at the interface air–aqueous solution. These results could be applied in the technology of foods such as emulsions which could be stabilized with proteins, and particularly in dairy products which are generally flavored.     

Sensory characteristics of wholegrain and bran-rich cereal foods – A review

BackgroundWholegrain foods are known to be health-beneficial but their sensory characteristics may be a limiting factor for consumption. The scientific literature of factors influencing sensory quality of wholegrain foods is rather scarce.Scope and approachMany cereals like rye, oats, barley and sorghum are actually used mainly as wholegrain, whereas for wheat the situation is the opposite. This review deals with factors that differentiate the sensory properties of wholegrain and bran-rich foods from those of refined cereal foods.Key findings and conclusionsWholegrain and bran contain flavour-active compounds, flavour precursors and resistant cell wall structures causing changes in flavour and texture during processing. In wholegrain foods, different chemical constituents contribute to bitterness. Increased knowledge on flavour formation has led to the possibility to not only measure but actually also design the flavour. Structure and texture are also important determinants underlying eating quality and stability of cereal foods. Hitherto established means of modulating sensory quality and thus improving acceptability of wholegrain foods are presented.     

Comparison on aroma compounds in Chinese soy sauce and strong aroma type liquors by gas chromatography–olfactometry,chemical quantitative and odor activity values analysis

In order to elucidate the differences on aroma compounds in Chinese liquors with different aroma styles and the reasons, aroma compounds of Xijiu in soy sauce aroma and strong aroma type were investigated in the research. By gas chromatography–olfactometry (GC–O), aroma compounds in Chinese liquor were chosen for quantitative and odor activity value (OAV) analysis. Ethyl hexanoate, butanoic acid, 3-methylbutanoic acid, hexanoic acid and dimethyl trisulfide were considered to be the most powerful odorants in both liquor samples (aroma intensity ≥3.5) by GC–O. As important aroma compounds (OAV ≥10) in the liquors, ethyl propanoate, ethyl 2-methylpropanoate and 1-propanol were considered with much higher OAVs in soy sauce aroma type liquor, while OAVs of ethyl pentanoate, ethyl hexanoate, ethyl heptanoate, ethyl octanoate, ethyl lactate, hexyl acetate, butyl hexanoate, hexyl hexanoate and hexanoic acid were far lower in strong aroma type liquor. The OAV of ethyl hexanoate in strong aroma type liquor exceeded 50,000, which explained the reason why strong aroma liquor was considered with prominent fruity aroma. The odor differences between the liquors were mainly caused by the manufacturing practices.     

Invited review: Use of infrared technologies for the assessment of dairy products—Applications and perspectives

Dairy products are important sources of nutrients for human health and in recent years their consumption has increased worldwide. Therefore, the food industry is interested in applying analytical technologies that are more rapid and cost-effective than traditional laboratory analyses. Infrared spectroscopy accomplishes both criteria, making real-time determination feasible. However, it is crucial to ensure that prediction models are accurate before their implementation in the dairy industry. In the last 5 yr, several papers have investigated the feasibility of mid- and near-infrared spectroscopy to determine chemical composition and authenticity of dairy products. Most studies have dealt with cheese, and few with yogurt, butter, and milk powder. Also, the use of near-infrared (in reflectance or transmittance mode) has been more prevalent than mid-infrared spectroscopy. This review summarizes recent studies on infrared spectroscopy in dairy products focusing on difficult to determine chemical components such as fatty acids, minerals, and volatile compounds, as well as sensory attributes and ripening time. Promising equations have been developed despite the low concentration or the absence of specific absorption bands (or both) for these compounds.     

Ochratoxin A in liquorice products – a review

Liquorice is a herbal medicine produced mainly in China and Iran. This plant is suspected to contain ochratoxin A (OTA), a secondary metabolite produced by fungi. Although liquorice is not included in the daily dietary of humans, the high levels of OTA reported in this product have concerned consumers. Registration of a standard method for measuring the amount of this mycotoxin in liquorice-derived products is an important challenge and requires the introduction of a reliable, simple, fast-performance and reproducible technique. This review examines studies carried out concerning the occurrence of OTA in liquorice products. Recent information regarding contaminated liquorice, the regulatory framework and methods to degrade OTA in liquorice are discussed.     

Ultrahigh pressure extraction of bioactive compounds from plants—A review

Extraction of bioactive compounds from plants is one of the most important research areas for pharmaceutical and food industries. Conventional extraction techniques are usually associated with longer extraction times, lower yields, more organic solvent consumption, and poor extraction efficiency. A novel extraction technique, ultrahigh pressure extraction, has been developed for the extraction of bioactive compounds from plants, in order to shorten the extraction time, decrease the solvent consumption, increase the extraction yields, and enhance the quality of extracts. The mild processing temperature of ultrahigh pressure extraction may lead to an enhanced extraction of thermolabile bioactive ingredients. A critical review is conducted to introduce the different aspects of ultrahigh pressure extraction of plants bioactive compounds, including principles and mechanisms, the important parameters influencing its performance, comparison of ultrahigh pressure extraction with other extraction techniques, advantages, and disadvantages. The future opportunities of ultrahigh pressure extraction are also discussed.     

Solvent assisted flavour evaporation – a new and versatile technique for the careful and direct isolation of aroma compounds from complex food matrices

 A compact and versatile distillation unit was developed for the fast and careful isolation of volatiles from complex food matrices. In connection with a high vacuum pump (5×10^–3 Pa), the new technique, designated solvent assisted flavour evaporation (SAFE), allows the isolation of volatiles from either solvent extracts, aqueous foods, such as milk or beer, aqueous food suspensions, such as fruit pulps, or even matrices with a high oil content. Application of SAFE to model solutions of selected aroma compounds resulted in higher yields from both solvent extracts or fatty matrices (50% fat) compared to previously used techniques, such as high vacuum transfer. Direct distillation of aqueous fruit pulps in combination with a stable isotope dilution analysis enabled the fast quantification (60 min including MS analysis) of compounds such as the very polar and unstable 4-hydroxy-2,5-dimethyl-3(2H)-furanone in strawberries (3.2 mg/kg) and tomatoes (340 μg/kg). Furthermore, the direct distillation of aqueous foods, such as beer or orange juice, gave flavourful aqueous distillates free from non-volatile matrix compounds. Received: 4 December 1998 / Revised version: 22 January 1999     

α-Dicarbonyl compounds in food products: Comprehensively understanding their occurrence,analysis, and control

α-Dicarbonyl compounds (α-DCs) are readily produced during the heating and storage of foods, mainly through the Maillard reaction, caramelization, lipid-peroxidation, and enzymatic reaction. They contribute to both the organoleptic properties (i.e., aroma, taste, and color) and deterioration of foods and are potential indicators of food quality. α-DCs are also important precursors to hazardous substances, such as acrylamide, furan, advanced lipoxidation end products, and advanced glycation end products, which are genotoxic, neurotoxic, and linked to several diseases. Recent studies have indicated that dietary α-DCs can elevate plasma α-DC levels and lead to “dicarbonyl stress.” To accurately assess their health risks, quantifying α-DCs in food products is crucial. Considering their low volatility, inability to absorb ultraviolet light, and high reactivity, the analysis of α-DCs in complex food systems is a challenge. In this review, we comprehensively cover the development of scientific approaches, from extraction, enrichment, and derivatization, to sophisticated detection techniques, which are necessary for quantifying α-DCs in different foods. Exposure to α-DCs is inevitable because they exist in most foods. Recently, novel strategies for reducing α-DC levels in foods have become a hot research topic. These strategies include the use of new processing technologies, formula modification, and supplementation with α-DC scavengers (e.g., phenolic compounds). For each strategy, it is important to consider the potential mechanisms underlying the formation and removal of process contaminants. Future studies are needed to develop techniques to control α-DC formation during food processing, and standardized approaches are needed to quantify and compare α-DCs in different foods.     

Gas chromatographic–olfactometric characterisation of headspace and mouthspace key aroma compounds in fresh and frozen lamb meat

Two different techniques for obtaining extracts representing the most relevant aroma chemicals from grilled lamb have been developed and applied to the elucidation of the gas chromatographic−olfactometric (GC−O) profiles of grilled lamb from fresh or frozen samples. The first technique attempted to collect the aroma released during grilling; and the second one, the aroma released during eating. The GC–O work was complemented with a thorough isolation and identification study comprising liquid chromatography and dual gas chromatography with simultaneous MS and olfactometric detection. Eight different aroma compounds with meaty odours were detected of which (Z)-2-heptenal, 2,5-dimethylpyrazine, (Z)-2-decenal, 2-butyl-2-octenal, 2-acetyl-2-thiazoline and (E,E)-2,4-decadienal could be identified. Moreover, 2-isopropyl-3-methoxypyrazine, 2-methylbenzaldehyde and 4-hydroxy-3-methoxybenzaldehyde (vanillin) were described for the first time in lamb. Frozen samples contained higher levels of ethyl hexanoate and butanoic and 3-methylbutanoic acids, while samples obtained directly from the grill were richer in pyrazines. Furaneol was only important in samples directly collected from the mouth.     

Impact of ‘oxidizing’ and ‘reducing’ buckwheat sourdoughs on brown rice and buckwheat batter and bread

The influence of reducing and oxidizing buckwheat sourdoughs on the rheological, protein, and bread properties of buckwheat and brown rice flour was investigated. Batters and breads prepared with chemically acidified doughs, fresh pre-doughs, and fresh pre-doughs containing glutathione (3 mM) were used as controls. No significant differences were observed after the addition of reducing and oxidizing sourdoughs in all trials. Proteolysis was observed after proofing time in buckwheat and brown rice batters, respectively. Acidified doughs increased the elasticity and the gelatinization temperature of buckwheat batters. No notable microstructure changes were detected in brown rice batters. The extension of fermentation time in sourdough caused a slight decrease in bread volumes in all trials. Sourdoughs increased the bread volume and decreased the crumb hardness of buckwheat breads. In trials with brown rice flour, the addition of sourdough did not show relevant volume differences as compared to the controls, except big voids in sourdough bread crumb. Linear correlations between hardness, volume, and cells’ density were observed. However, no clear correlations among rheological parameters and bread characteristics could be detected. These results indicated that the applied strains were responsible for the leavening capacity of the yeast during the proofing time and for crumb structure in trials with buckwheat and brown rice flour. Applied sourdoughs were able to change the molecular, and bread properties of buckwheat and brown rice bread.     

Fat crystals and emulsion stability — a review

The effects of fat crystals in food emulsion formation and stability are reviewed. Topics discussed in detail include fat crystal wettability, interfacial rheology, crystal microstructure, and particle location. Specifics on the potential future direction of the field are discussed.     

Small and large deformation rheology and microstructure of κ-carrageenan gels containing commercial milk protein products

The rheological behaviour of commercial milk protein/κ-carrageenan mixtures in aqueous solutions was studied at neutral pH. Four milk protein ingredients; skim milk powder, milk protein concentrate, sodium caseinate, and whey protein isolate were considered. As seen by confocal laser microscopy, mixtures of κ-carrageenan with skim milk powder, milk protein concentrate, and sodium caseinate showed phase separation, but no phase separation was observed in mixtures containing whey protein isolate. For κ-carrageenan concentrations up to 0.5 wt%, the viscosity of the mixtures at low shear rates increased markedly in the case of skim milk powder and milk protein concentrate addition, but did not change by the addition of sodium caseinate or whey protein isolate. For κ-carrageenan concentrations from 1 to 2.5 wt%, small and large deformation rheological measurements, performed on the milk protein/κ-carrageenan gels, showed that skim milk powder, milk protein concentrate or sodium caseinate markedly improved the strength of the resulting gels, but whey protein isolate had no effect on the gel stength.     

Interactions between aroma compounds and β-lactoglobulin in the heat-induced molten globule state

The present study aims to elucidate the binding of small hydrophobic ligands onto the molten globule state of β-lactoglobulin (BLG). The conversion of the native BLG into a molten globule state was induced by heat treatment at acidic pH. The molten globule state was evidenced by far and near-UV circular dichroism spectra. β-Ionone and guaiacol exhibited a higher binding ability to BLG in the heat-induced molten globule state compared to unheated BLG, as assessed by protein surface hydrophobicity measurements, using 6-propionyl-2-(dimethylamino)naphthalene (PRODAN) fluorescent probe. The binding sites of the two aroma compounds were determined by 2D nuclear magnetic resonance (NMR) spectroscopy. The less tightly packed structure of the molten globule favoured ligand binding, in particular within the central cavity. The greater flexibility of the calyx entrance, and the conformational change of loop EF induced an easier access of the central cavity after the thermal treatment.