A comparative study on flavor trapping techniques from the viewpoint of odorants of hot-pressed rapeseed oil.

Rapeseed oil, as one of the three major vegetable oils in the world, its matrix effect makes the decoding flavor a challenge. Solid-phase microextraction (SPME), SPME-Arrow, headspace stir bar sorptive extraction (HSSE), direct thermal desorption (DTD), and solvent-assisted flavor evaporation (SAFE) were compared based on the odorants in hot-pressed rapeseed oil. Besides, methodological validation for 31 aroma standards was conducted to compare reliability and robustness of these approaches. DTD showed the largest proportion of acids, while the other techniques extracted a majority of nitriles. The highest number of odorants was detected by SAFE (31), followed by HSSE (30), SPME-Arrow (30), SPME (24), and DTD (14). SPME-Arrow showed the best performance in linearity, recovery, and reproducibility followed by SPME, HSSE, DTD, and SAFE. Results reveal the advantages and limitations of diverse methodologies and provide valuable insights for the selection of extraction methods in an oil matrix and flavor decoding.

Effect of glucose oxidase treatment on the aroma qualities and release of cooked off-odor components from heat-treated Hami melon juice.

Melon juice produces strong cooked off-odors during heat processing, leading to serious deterioration of aroma quality. In this work, the aroma quality of melon juice, the changes in GOD reaction products, and the interactions of reaction products and cooked off-odor components were analyzed by sensory evaluation, gas chromatography-mass spectrometry/olfactory, ultraperformance liquid chromatography-triple quadrupole mass spectrometry, and isothermal titration calorimetry to study the effect mechanism of glucose oxidase (GOD) on the release of cooked off-odor components from heat-treated melon juice. The results showed that GOD treatment improved the aroma quality mainly by controlling off-odor attributes and maintaining characteristic odor attributes. This was because the reaction products (hydrogen peroxide and gluconic acid) of GOD treatment inhibited the release of cooked off-odor components from heat-treated melon juice through oxidation and hydrophobic effects. Furthermore, these products reduced the loss of characteristic odor compounds by restraining Maillard, degradation, and oxidation reactions during heat processing.

Isolation and identification of putative precursors of the volatile sulfur compounds and their inhibition methods in heat-sterilized melon juices.

Volatile sulfur compounds, such as dimethyl sulfide, dimethyl disulfide and dimethyl trisulfide, cause the off-flavor in heat-sterilized juices and limit the commercial production of juices. In this study, we investigated the precursors for these volatile sulfur compounds and analyzed the potential inhibition methods. Upon separation of melon juice components using resin column, the dimethyl sulfide precursor was present in the acidic fraction whereas the dimethyl trisulfide precursor was present in neutral and acidic fractions. Exogenous addition experiments indicated S-methyl methionine was the precursor of dimethyl sulfide, and methionine was the precursor of dimethyl disulfide and dimethyl trisulfide. The release of volatile sulfur compounds was reduced by decreasing the pH to 2.0, or by adding epicatechin. We concluded S-methyl methionine and methionine were degraded into volatile sulfur compounds through nucleophilic substitution and Strecker degradation. This study can help establishing protocols for controlling the release of volatile sulfur compounds in heat-sterilized juices.

Application of volatile and spectral profiling together with multimode data fusion strategy for the discrimination of preserved eggs.

The maturity level of eggs during pickling is conventionally assessed by choosing few eggs from each curing batch to crack open. Yet, this method is destructive, creates waste and has consequences for financial losses. In this work, the feasibility of integrating electronic nose (EN) with reflectance hyperspectral (RH) and transmittance hyperspectral (TH) data for accurate classification of preserved eggs (PEs) at different maturation periods was investigated. Classifier models based solely on RH and TH with EN achieved a training accuracy (93.33%, 97.78%) and prediction accuracy (88.89%; 93.33%) respectively. The fusion of the three datasets, (EN + RH + TH) as a single classifier model yielded an overall training accuracy of 98.89% and prediction accuracy of 95.56%. Also, 52 volatile compounds were obtained from the PE headspace, of which 32 belonged to seven functional groups. This study demonstrates the ability to integrate EN with RH and TH data to effectively identify PEs during processing.

Comprehensive investigation on volatile and non-volatile metabolites in broccoli juices fermented by animal- and plant-derived Pediococcus pentosaceus.

A metabolomics approach was employed to investigate differences and correlations among key odorants and non-volatile metabolites in broccoli juices fermented by plant- and animal-derived Pediococcus pentosaceus. Forty volatile metabolites were identified by headspace solid-phase microextraction/gas chromatography-mass spectrometry. According to orthogonal projections to latent structures-differential analysis, 24 and 21 differential volatiles were detected after fermentation by plant- and animal-derived P. pentosaceus, respectively. The concentrations of 10 odorants (OAV ≥ 1) detected by gas chromatography-olfactometry changed significantly after fermentation by P. pentosaceus. Using ultrahigh-pressure liquid chromatography/quadrupole time-of-flight mass spectrometry, 49.47% of the non-volatile metabolites were classified as lipids and lipid-like molecules. The relative expressions of five non-volatile metabolites that exhibited significant correlations with odorants using Spearman correlation analysis changed significantly after fermentation. Fermentation with animal- and plant-derived P. pentosaceus can therefore change key odorants and non-volatile metabolites in broccoli juice that contribute to the characteristic organoleptic properties of products.

Characterization of the aroma-active compounds in black soybean sauce, a distinctive soy sauce.

Black soybean sauce's (BSS) aroma was scarcely investigated, which seriously affected BSS's quality and consumers' preference. Thus the aroma compounds in BSS were characterized using gas chromatography-mass spectrometry/gas chromatography-olfactometry coupling with recombination and omission experiments. Sensory evaluation showed the fruity odor was increased by 63% and the malty, alcoholic, floral, smoky, caramel-like and sour odors were decreased by 24-35% when compared to the control soy sauce (SS, p < 0.05). Totally, 126 volatile compounds, 44 aroma-active compounds and 22 vital aroma-active compounds were identified in BSS. Compared to SS, BSS exhibited a distinctive aroma characteristics which was caused by significantly higher odor activity values (OAVs) of 3-methylbutyl acetate (357%), ethyl propanoate (144%), ethyl 3-methylbutanoate (70%), ethyl 2-methylbutanoate (102%) and lower OAVs of 4-hydroxy-2,5-dimethyl-3(2H)-furanone (52%), 4-hydroxy-2-ethyl-5-methyl-3(2H)-furan-3-one (50%), ethanol (48%), 4-vinylguaiacol (41%), 3-methylthiopropanal (37%), 3-methylbutanol (33%), 4-ethylguaiacol (28%). The results would contribute to BSS's quality control and aroma improvement.

Volatile biomarkers for early-stage detection of insect-infested brown rice: Isopentenols and polysulfides.

To reduce food loss from stored products by insect attack, monitoring and early detection of insects are essential. Presently, monitoring with pheromone traps is the primary method for detection; however, traps are effective only after the insects propagate. Detection and identification of the early volatile biomarkers arising from insect-infested brown rice was performed in this study to develop an alternative detection strategy. Brown rice was infested with eggs of seven insect species, including Sitophilus zeamais and Plodia interpunctella. Infested rice emitted at least one of the volatile compounds prenol, isoprenol, dimethyl disulfide, and dimethyl trisulfide (DMTS). In particular, isopentenols were generated by moths within one week of infestation, whereas they were not released from non-infested rice. DMTS was detected from all insect-infested brown rice, especially S. zeamais and P. interpunctella. These volatiles are potential early biomarkers for the presence of insects in brown rice.

Untargeted and targeted metabolomics strategy for the classification of strong aroma-type baijiu (liquor) according to geographical origin using comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry.

A metabolomics strategy was developed to differentiate strong aroma-type baijiu (SAB) (distilled liquor) from the Sichuan basin (SCB) and Yangtze-Huaihe River Basin (YHRB) through liquid-liquid extraction coupled with GC×GC-TOFMS. PCA effectively separated the samples from these two regions. The PLS-DA training model was excellent, with explained variation and predictive capability values of 0.988 and 0.982, respectively. As a result, the model demonstrated its ability to perfectly differentiate all the unknown SAB samples. Twenty-nine potential markers were located by variable importance in projection values, and twenty-four of them were identified and quantitated. Discrimination ability is closely correlated to the characteristic flavor compounds, such as acid, esters, furans, alcohols, sulfides and pyrazine. Most of the marker compounds were less abundant in the SCB samples than in the YHRB samples. The quantitated markers were further processed using hierarchical cluster analysis for targeted analysis, indicating that the markers had great discrimination power to differentiate the SAB samples.

Characterization of volatile sulfur compounds in soy sauce aroma type Baijiu and changes during fermentation by GC × GC-TOFMS, organoleptic impact evaluation, and multivariate data analysis.

An analytical method based on headspace solid-phase microextraction (HS-SPME) combined with comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOFMS) was developed to characterize volatile sulfur compounds (VSCs) in soy sauce aroma type Baijiu (SSAB) and soy sauce aroma type rounds Baijiu (SSARB). Using this method, 19 VSCs were identified and quantified. The aroma contribution of VSCs was evaluated by odor activity values (OAVs) and perceptive interactions. Seven VSCs had concentrations higher than their corresponding odor thresholds. In particular, the presence of methyl furfuryl disulfide (OAV: 7-11) and 2-methyl-3-(methyldisulfanyl)furan (OAV: 9-18) with relatively high OAVs in Baijiu was reported for the first time, and they could be the important aroma contributors to SSAB. Moreover, sensory analysis revealed that dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide enhanced the perception of fruity aromas in the matrices studied. Partial least-squares discriminant analysis (PLS-DA) analysis indicated that the VSCs could be used to distinguish SSARB.

Characterization of key aroma-active sulfur-containing compounds in Chinese Laobaigan Baijiu by gas chromatography-olfactometry and comprehensive two-dimensional gas chromatography coupled with sulfur chemiluminescence detection.

Volatile sulfur-containing compounds (VSCs) often exist at extremely low concentrations, making them difficult to be determined. The VSCs in Laobaigan (LBG) Baijiu were analyzed by headspace solid-phase microextraction (HS-SPME) coupled with GC × GC-SCD, by which 12 VSCs were identified. Among the 65 odor-active compounds that were determined by GC-O with the aid of aroma extract dilution analysis (AEDA), benzenemethanethiol and 2-methyl-3-furanthiol were found to possess the highest FD values of 6561. The limits of detection (LODs) of the identified VSCs determined by GC × GC-SCD were found to be extremely low at 0.05-1.53 ng/L, with their analytical recoveries from 85% to 116%. The VSCs in the LBG samples were determined in a range of concentrations from 0.77 ±â€¯0.02 µg/L to 60.04 ±â€¯2.32 µg/L. Benzenemethanethiol, dimethyl trisulfide, 2-methyl-3-furanthiol and 2-furfurylthiol exhibited odor activity values (OAVs) > 100 and significantly contributed to the overall aroma of LBG Baijiu.

Identification of the cooked off-flavor in heat-sterilized lychee (Litchi chinensis Sonn.) juice by means of molecular sensory science.

The main contributors to the cooked off-flavor in heat-sterilized lychee juice (HLJ) were studied by means of molecular sensory science. The HLJ which elicited cooked cabbage/potato and onion/garlic off-flavor was compared with fresh lychee juice (FLJ) having desired sensory attributes via chemical analysis and sensory evaluation. Aroma extract dilution analysis, quantitative analysis and calculation of odor activity values (OAVs) were conducted on both FLJ and HLJ. The results showed that compared with FLJ, 15 compounds had increased OAVs in HLJ, among which, dimethyl sulfide (DMS), methional, dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS) and 2,4-dithiapentane presented cooked cabbage/potato, garlic/onion and sulfurous impression. The omission experiment proved that DMS, methional, DMTS, DMDS, 3-methylbutanal and 2,4-dithiapentane had significantly negative effects on the overall aroma of HLJ. Further studies on HLJs from other varieties of lychee confirmed that DMS, methional, DMTS, DMDS and 3-methylbutanal were responsible for the cooked off-flavor of HLJ in general.

Method for sampling and analysis of volatile biomarkers in process gas from aerobic digestion of poultry carcasses using time-weighted average SPME and GC-MS.

A passive sampling method, using retracted solid-phase microextraction (SPME) - gas chromatography-mass spectrometry and time-weighted averaging, was developed and validated for tracking marker volatile organic compounds (VOCs) emitted during aerobic digestion of biohazardous animal tissue. The retracted SPME configuration protects the fragile fiber from buffeting by the process gas stream, and it requires less equipment and is potentially more biosecure than conventional active sampling methods. VOC concentrations predicted via a model based on Fick's first law of diffusion were within 6.6-12.3% of experimentally controlled values after accounting for VOC adsorption to the SPME fiber housing. Method detection limits for five marker VOCs ranged from 0.70 to 8.44ppbv and were statistically equivalent (p>0.05) to those for active sorbent-tube-based sampling. The sampling time of 30min and fiber retraction of 5mm were found to be optimal for the tissue digestion process.

Static headspace analysis of odorants in commercial rice proteins.

Accurate identification of the odor-contributing compounds in aqueous slurries of rice proteins is necessary to improve their overall flavor characteristics. The objective of this study was to identify the primary odorants in rice protein slurries using static headspace analysis. Five commercial rice protein (RP) products, RP-G, RP-O, RP-RM, RP-RS1, and RP-RS2, were analyzed. RP-G contained the lowest levels of most of the odorants. Acetaldehyde was present in the highest amount in RP-O (0.434mg/m3). RP-RM had the highest levels of hexanal (5.907mg/m3), methanethiol (0.138mg/m3), pentanal (1.575mg/m3), and 2-pentylfuran (5.702mg/m3). Corresponding odor values were, 111, 86, 22 and 21, respectively. In RP-RS1 and RP-RS2, the predominant odorants were dimethyl disulfide, dimethyl trisulfide, and hexanal. The results showed the importance of the volatile compounds produced from amino acids, including the sulfur-containing compounds and acetaldehyde, as well as lipid oxidation derived odorants to the overall odor of rice proteins.

Potential of different mechanical and thermal treatments to control off-flavour generation in broccoli puree.

The aim of this study was scientifically investigate the impact of the sequence of different thermo-mechanical treatments on the volatile profile of differently processed broccoli puree, and to investigate if any relationship persists between detected off-flavour changes and microstructural changes as a function of selected process conditions. Comparison of the headspace GC-MS fingerprinting of the differently processed broccoli purees revealed that an adequate combination of processing steps allows to reduce the level of off-flavour volatiles. Moreover, applying mechanical processing before or after the thermal processing at 90°C determines the pattern of broccoli tissue disruption, resulting into different microstructures and various enzymatic reactions inducing volatile generation. These results may aid the identification of optimal process conditions generating a reduced level of off-flavour in processed broccoli. In this way, broccoli can be incorporated as a food ingredient into mixed food products with limited implications on sensorial consumer acceptance.

Impact of processing on odour-active compounds of a mixed tomato-onion puree.

Gas chromatography-olfactometry revealed thirty-two odour-active compounds in a heat-processed tomato-onion puree, among which twenty-seven were identified by gas chromatography-olfactometry-mass spectrometry (GC-O-MS) and comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC-TOF MS). Based on the results of two olfactometric methods, i.e. detection frequency and aroma extract dilution analysis, the most potent aroma components include: dipropyl disulfide, S-propyl thioacetate, dimethyl trisulfide, 1-octen-3-one, methional, dipropyl trisulfide, 4,5-dimethylthiazole, 2-phenylacetaldehyde and sotolone. Processing of mixed vegetable systems can add complexity in their aroma profiles due to (bio)chemical interactions between the components. Therefore, the impact of different processing steps (i.e. thermal blanching, all-in-one and split-stream processes) on the volatile profile and aroma of a mixed tomato-onion puree has been investigated using a GC-MS fingerprinting approach. Results showed the potential to control the aroma in a mixed tomato-onion system through process-induced enzymatic modulations for producing tomato-onion food products with distinct aroma characteristics.

A novel method for beef bone protein extraction by lipase-pretreatment and its application in the Maillard reaction.

Five beef bone hydrolysates were obtained by different enzyme treatment schemes, including papain (M), combination of porcine pancreatic lipase and papain (Z+M, combination of lipase and papain (Y+M), Protamex (F), combination of porcine pancreatic lipase and Protamex (Z+F). The degree of hydrolysis (DH), free amino acids and molecular weight distribution of these hydrolysates were evaluated. To further explore the differences between these five hydrolysates, Maillard reaction products (MRPs) were prepared using a xylose/cysteine/hydrolysate model. It was found that the DH, content of low molecular weight peptides and amino acids of hydrolysates increased significantly after lipase pre-treatment. GC-MS showed that the total content of furans, pyrroles and thioethers in MRPs Y+M increased by 78.0% compared with MRPs M, while in MRPs Z+F, pyrazines increased by 44.1% compared with MRPs F. Examining the sensory characteristics of the MRPs, the MRP from the hydrolysate of Y+M had the best mouthful, umami and meaty characteristics. The correlation analysis further confirmed that an appropriate lipase pre-treatment could improve the flavour of MRPs.