Odor and taste characteristics, transduction mechanism, and perceptual interaction in fermented foods: a review

Fermentation is a critical technological process for flavor development in fermented foods. The combination of odor and taste, known as flavor, is crucial in enhancing people's perception and psychology toward fermented foods, thereby increasing their acceptance among consumers. This review summarized the determination and key flavor compound screening methods in fermented foods and analyzed the flavor perception, perceptual interactions, and evaluation methods. The flavor compounds in fermented foods could be separated, purified, and identified by instrument techniques, and a molecular sensory science approach could identify the key flavor compounds. How flavor compounds bind to their respective receptors determines flavor perception, which is influenced by their perceptual interactions, including odor-odor, taste-taste, and odor-taste. Evaluation methods of flavor perception mainly include human sensory evaluation, electronic sensors and biosensors, and neuroimaging techniques. Among them, the biosensor-based evaluation methods could facilitate the investigation of the flavor transduction mechanism and the neuroimaging technique could explain the brain's signals that relate to the perception of flavor and how they compare to signals from other senses. This review aims to elucidate the flavor profile of fermented foods and highlight the significance of comprehending the interactions between various flavor compounds, thus improving the healthiness and sensory attributes.

Aroma-sensory properties of Gouda cheeses based on young Chinese consumers' preferences

The objective of this study was to examine the aroma profiles of 12 Gouda cheeses sold in China and to determine which aromas were preferred by young Chinese consumers (n = 110). The consumers selected 11 descriptors of the aromas of the Gouda cheeses in a check-all-that-apply questionnaire. These 11 descriptors were used by a panel of experts for sensory analysis to perform a quantitative descriptive analysis of the cheeses. A principal component analysis of the data from the quantitative descriptive analysis revealed that the characteristic aromas of young Gouda cheeses, medium-aged Gouda cheeses, and aged Gouda cheeses were "milky" and "whey"; "creamy" and "sour"; and "rancid" and "nutty," respectively. The results of a penalty analysis combined with the check-all-that-apply results and the preference scores showed that the 3 groups of young Chinese consumers (those who often ate cheese, occasionally ate cheese, and never ate cheese) preferred the Gouda cheeses with "milky" or "creamy" aromas and did not enjoy those with "sour" or "rancid" aromas. Occasional cheese eaters comprised the majority of the young Chinese consumers, and they were more tolerant of the Gouda cheeses with "whey" and "sulfury" aromas than those who often or never ate cheese. In addition, we identified a positive correlation between the consumers' preferences for the aromas of the Gouda cheeses and their willingness to pay for them. Overall, the results of this study should help promote the development of Gouda cheeses and associated products that meet the preferences of young Chinese consumers.

Graduate Student Literature Review: Network of flavor compounds formation and influence factors in yogurt

Yogurt is popular as a natural and healthy food, but its flavor greatly affects acceptability by consumers. Flavor compounds of yogurt is generally produced by the metabolism of lactose, protein and fat, and the resulting flavors include carbonyls, acids, esters and alcohols, etc. Each flavor compounds could individually provide the corresponding flavor, or it can be combined with other compounds to form a new flavor. The flavor network was formed among the metabolites of milk components, and acetaldehyde, as the central compounds, played a role in connecting the whole network. The flavor compounds can be affected by many factors, such as the use of different raw milks, ways of homogenization, sterilization, fermentation, post ripening, storage condition and packaging materials, etc., which can affect the overall flavor of yogurt. This paper provides an overview of the volatile flavor compounds in yogurt, the pathways of production of the main flavor compounds during yogurt fermentation, and the factors that influence the flavor of yogurt including type of raw milk, processing, and storage. It also tries to provide theoretical guidance for the product of yogurt in ideal flavor, but further research is needed to provide a more comprehensive description of the flavor system of yogurt.

Preparation of pH-responsive chitosan microspheres containing aminopeptidase and their application in accelerating cheese ripening

Microencapsulated enzymes have been found to effectively accelerate cheese ripening. However, microencapsulated enzyme release is difficult to control, often resulting in enzyme release during cheese processing and causing texture and flavor defects. This study aims to address this issue by developing aminopeptidase-loaded pH-responsive chitosan microspheres (A-CM) for precise enzyme release during cheese ripening. An aminopeptidase with an isoelectric point (pH 5.4) close to the pH value of cheese ripening was loaded on chitosan microspheres through electrostatic interaction. Turbidity titration measurements revealed that pH 6.5 was optimal for binding aminopeptidase and microspheres, affording the highest loading efficiency of 58.16%. Various characterization techniques, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy confirmed the successful loading of aminopeptidase molecules on the chitosan microspheres. In vitro release experiments conducted during simulated cheese production demonstrated that aminopeptidase release from A-CM was pH responsive. The microspheres retained the enzyme during the coagulation and cheddaring processes (pH 5.5-6.5) and only released it after entering the cheese-ripening stage (pH 5.0-5.5). By loading aminopeptidase on chitosan microspheres, the loss rate of the enzyme in cheese whey was reduced by approximately 79%. Furthermore, compared with cheese without aminopeptidase and cheese with aminopeptidase added directly, the cheeses made with A-CM exhibited the highest proteolysis level and received superior sensory ratings for taste and smell. The content of key aroma substances, such as 2/3-methylbutanal and ethyl butyrate, in cheese with A-CM was more than 15 times higher than the others. This study provides an approach for accelerating cheese ripening through the use of microencapsulated enzymes.

Generation of key aroma compounds in fat and lean portions of non-smoked bacon induced via lipid pyrolysis reaction

This study explored the evolution of key aroma compounds and their lipid precursors in the lean (LN) and fat (FT) portions of non-smoked bacon during hot air drying. The results showed that the LN portion contained most of the aroma compounds in the bacon (>88%). The volatile content of the FT portion increased as the drying time increased, whereas that of the LN portion reached a maximum within 24 h and then decreased. Based on the highest volatile contents (4889.48 ± 202.06 µg/kg) and sensory scores, 24 h was considered the optimal drying time. For key aroma compounds, hexanal and 2,3-octanedione were derived from free fatty acids and polar lipids. Notably, 1-octen-3-ol was generated only from polar lipids in the FT and LN portions. The 2-undecenal and (E, E)-2,4-decadienal were produced by the oxidation of neutral lipids in the FT portion. Dihydro-5-pentyl-2(3H)-furanone was derived from polar lipids in the LN portion. Altogether, these findings provide theoretical insights into improving the aroma of bacon by optimizing raw material selection and processing methods.

Production of a Cheese-Like Aroma via Fermentation of Plant Proteins and Coconut Oil with the Basidiomycetes Cyclocybe aegerita and Trametes versicolor

Cheese is one of the most common dairy products and is characterized by its complex aroma. However, in times of climate change and resource scarcity, the possibility to mimic the characteristic cheese-like aroma from plant-based sources is in demand to offer alternatives to cheese. Accordingly, the production of a natural cheese-like aroma via fermentation of four plant-based proteins and coconut oil with basidiomycetes has been addressed. Mixtures of soy and sunflower protein with coconut oil (15 g/L) have shown the formation of a cheese-like aroma after 72 and 56 h after fermentation with Cyclocybe aegerita and Trametes versicolor, respectively. Isovaleric acid, butanoic acid, ethyl butanoate, 1-octen-3-ol, and various ketones were identified as the key odorants. Similarities to typical cheeses were observed by the principal component analysis. Overall, the finding offered an approach to a sustainable production of a natural cheese-like aroma from a plant source, thus contributing to the development of cheese alternatives.

Investigation of the Interaction Between Lactones and Ketones in a Cheddar Cheese Matrix Using Feller's Additive Model, σ-τ Plots, U-Models, and Aroma Addition Experiments

The objective of this study was to examine the sensory interactions between lactones and ketones in a cheddar simulation matrix through perceptual interaction analysis. The olfactory thresholds of 6 key lactones had values ranging from 8.32 to 58.88 μg/kg, whereas those of the 4 key ketones ranged from 6.61 to 660.69 μg/kg. Both Feller's additive model and σ-τ plots demonstrated complex interactions in 24 binary mixtures composed of the 6 lactones and 4 ketones, including synergy, addition, and masking effects. Specifically, we found that 6 binary mixtures exhibited aroma synergistic effects using both methods. Moreover, the σ-τ plot showed a synergistic effect of aroma in 3 ternary mixtures. The U-model further confirmed the synergistic effects of the 6 groups of binary systems and 3 groups of ternary systems on aroma at actual cheese concentrations. In an aroma addition experiment, the combination of δ-octalactone and diacetyl in binary mixtures had the most pronounced impact on enhancing milk flavor. In ternary mixtures, 2 combinations, namely δ-octalactone/δ-dodecalactone/diacetyl and γ-dodecalactone/δ-dodecalactone/acetoin, significantly enhanced the milky and sweet aroma properties of cheese, while also enhancing the overall acceptability of the cheese aroma.

The Role of Autochthonous Levilactobacillus brevis B1 Starter Culture in Improving the Technological and Nutritional Quality of Cow's Milk Acid-Rennet Cheeses-Industrial Model Study

In the study, an attempt was made to develop an innovative technology for cheese manufacturing. It was hypothesized that selected autochthonous lactic acid bacteria as a starter culture are more suitable for the production of acid-rennet cheeses of good technological and sensory quality. The study aimed to assess the possibility of using the strain Levilactobacillus brevis B1 (L. brevis B1) as a starter culture to produce acid-rennet cheeses using raw cow's milk. Two variants of cheese were manufactured. The control variant (R) was coagulated with microbial rennet and buttermilk, and the other variant (B1) was inoculated with rennet and L. brevis B1 starter culture. The effect of the addition of these autochthonous lactic acid bacteria on selected physicochemical characteristics, durability, the composition of fatty acids, cholesterol, Iipid Quality Indices, and microbiological and sensory quality of acid-rennet cheeses was determined during a 3-month period of storage. The dominant fatty acids observed in the tested cheeses were saturated fatty acids (SFA) (68.43-69.70%) and monounsaturated fatty acids (MUFA) (25.85-26.55%). Significantly higher polyunsaturated fatty acid (PUFA) content during storage was observed for B1 cheeses. The B1 cheeses were characterized by lower cholesterol content compared to cheese R and showed better indexes, including the Index of atherogenicity, Index of thrombogenicity, DFA, OFA, H/H, and HPI indexes, than the R cheese. No effect of the tested L. brevis B1 on sensory quality was observed in relation to the control cheeses during 3 months of storage. The results of the research indicate the possibility of using the L. brevis B1 strain for the production of high-quality, potentially probiotic acid-rennet cheeses.

Changes in properties of human milk under different conditions of frozen storage

Human milk is the best source of nutrition for infants. Lower freezing temperatures and faster freezing rates allow for better preservation of human milk. However, research on the freezing conditions of human milk is limited. This study investigated the effectiveness of quick freezing and suitable freezing conditions for home preservation. Human milk was stored under different freezing conditions (-18 °C, -18 °C quick freezing, -30 °C, -40 °C, -60 °C, and - 80 °C) for 30, 60, and 90 days and then evaluated for changes in the microbial counts, bioactive protein, and lipid. The results showed that the total aerobic bacterial and Bifidobacteria counts in human milk after storage at freezing temperatures of - 30 °C and lower were closer to those of fresh human milk compared to - 18 °C. Furthermore, the lysozyme loss, lipid hydrolysis degree, and volatile organic compound production were lower. However, -18 °C quick freezing storage was not markedly different from -18 °C in maintaining human milk quality. Based on the results, for household and environmental reasons, the recommended temperature for storing human milk is suggested as -30 °C.

Fermentation technology as a driver of human brain expansion

Brain tissue is metabolically expensive. Consequently, the evolution of humans' large brains must have occurred via concomitant shifts in energy expenditure and intake. Proposed mechanisms include dietary shifts such as cooking. Importantly, though, any new food source must have been exploitable by hominids with brains a third the size of modern humans'. Here, we propose the initial metabolic trigger of hominid brain expansion was the consumption of externally fermented foods. We define "external fermentation" as occurring outside the body, as opposed to the internal fermentation in the gut. External fermentation could increase the bioavailability of macro- and micronutrients while reducing digestive energy expenditure and is supported by the relative reduction of the human colon. We discuss the explanatory power of our hypothesis and survey external fermentation practices across human cultures to demonstrate its viability across a range of environments and food sources. We close with suggestions for empirical tests.

Analysis of the effect of Tenebrio Molitor rennet on the flavor formation of Cheddar cheese during ripening based on gas chromatography-ion mobility spectrometry (GC-IMS)

This study aimed to evaluate the potential application of Tenebrio Molitor rennet (TMR) in Cheddar cheese production, and to use gas chromatography-ion mobility spectrometry (GC-IMS) to monitor flavor compounds and fingerprints of cheese during ripening. The results indicated that Cheddar cheese prepared from TMR (T_F) has fat content significantly lower than that of commercial rennet (C_F) (p < 0.05). However, the results of the sensory evaluation showed that there were no statistically significant differences between the two kinds of cheese (p > 0.05). Both cheeses were rich in free amino acids and free fatty acids. Compared to the C_F cheese, gamma-aminobutyric acid and Ornithine contents of the T_F cheese reached 187 and 749 mg/kg, respectively, during 120 days of ripening. Moreover, GC-IMS provided information on the characteristics of 40 flavor substances (monomers and dimers) in the T_F cheese during ripening. Only 30 flavor substances were identified in the C_F cheese. The fingerprint of the two kinds of cheese during ripening can be established by GC-IMS and principal component analysis based on the identified flavor compounds. Therefore, TMR has potential application in Cheddar cheese production. GC-IMS might be applied for the quick, accurate and comprehensive monitoring of cheese flavor during ripening.

Characteristics of Unripened Cow Milk Curd Cheese Enriched with Raspberry (Rubus idaeus), Blueberry (Vaccinium myrtillus) and Elderberry (Sambucus nigra) Industry By-Products

The aim of this study was to apply raspberry (Ras), blueberry (Blu) and elderberry (Eld) industry by-products (BIB) for unripened cow milk curd cheese (U-CC) enrichment. Firstly, antimicrobial properties of the BIBs were tested, and the effects of the immobilization in agar technology on BIB properties were evaluated. Further, non-immobilized (NI) and agar-immobilized (AI) BIBs were applied for U-CC enrichment, and their influence on U-CC parameters were analyzed. It was established that the tested BIBs possess desirable antimicrobial (raspberry BIB inhibited 7 out of 10 tested pathogens) and antioxidant activities (the highest total phenolic compounds (TPC) content was displayed by NI elderberry BIB 143.6 mg GAE/100 g). The addition of BIBs to U-CC increased TPC content and DPPH- (2,2-diphenyl-1-picrylhydrazyl)-radical scavenging activity of the U-CC (the highest TPC content was found in C-RaNI 184.5 mg/100 g, and strong positive correlation between TPC and DPPH- of the U-CC was found, r = 0.658). The predominant fatty acid group in U-CC was saturated fatty acids (SFA); however, the lowest content of SFA was unfolded in C-EldAI samples (in comparison with C, on average, by 1.6 times lower). The highest biogenic amine content was attained in C-EldAI (104.1 mg/kg). In total, 43 volatile compounds (VC) were identified in U-CC, and, in all cases, a broader spectrum of VCs was observed in U-CC enriched with BIBs. After 10 days of storage, the highest enterobacteria number was in C-BluNI (1.88 log10 CFU/g). All U-CC showed similar overall acceptability (on average, 8.34 points); however, the highest intensity of the emotion "happy" was expressed by testing C-EldNI. Finally, the BIBs are prospective ingredients for U-CC enrichment in a sustainable manner and improved nutritional traits.

Comparative analysis of the volatile components in Chinese breast milk from three regions

In this study, gas chromatography-mass spectrometry (GC-MS) coupled with Partial least squares Discriminant Analysis (PLS-DA) was used to analyze the volatiles in Chinese breast milk from different cities (Wuhan, Qingdao and Hohhot) and different lactation stages (colostrum and mature milk). The results showed that breast milk contained 122 volatile substances in 9 major groups, with the largest number of olefins (36) and the highest content of acids. The different volatile compounds of breast milk in three cities were heptanal, 2-pentylfuran, (E)-2,4-decadienal, (E)-2-heptenal, (E)-2-nonenal and 1-octen-3-one, colostrum and mature milk were (E)-2-heptenal, (E)-2-decenal, lauric acid, n-decanoic acid, (E)-2-nonenal and octanoic acid. This study might provide scientific data for the development and optimization of formulas that were more suitable for the health of Chinese infants.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-022-01235-4.

Relationship between the dynamics of volatile aroma compounds and microbial succession during the ripening of raw ewe milk-derived Idiazabal cheese

Cheese microbiota contributes to various biochemical processes that lead to the formation of volatile compounds and the development of flavour during ripening. Nonetheless, the role of these microorganisms in volatile aroma compounds production is little understood. This work reports for the first time the dynamics and odour impact of volatile compounds, and their relationship to microbial shifts during the ripening of a raw ewe milk-derived cheese (Idiazabal). By means of SPME-GC-MS, 81 volatile compounds were identified, among which acids predominated, followed by esters, ketones and alcohols. The ripening time influenced the abundance of most volatile compounds, thus the moments of greatest abundance were determined (such as 30-60 days for acids). Through Odour Impact Ratio (OIR) values, esters and acids were reported as the predominant odour-active chemical families, while individually, ethyl hexanoate, ethyl 3-methyl butanoate, ethyl butanoate, butanoic acid or 3-methyl butanal were notable odorants, which would provide fruity, rancid, cheesy or malt odour notes. Using a bidirectional orthogonal partial least squares (O2PLS) approach with Spearman's correlations, 12 bacterial genera were reported as key bacteria for the volatile and aromatic composition of Idiazabal cheese, namely Psychrobacter, Enterococcus, Brevibacterium, Streptococcus, Leuconostoc, Chromohalobacter, Chryseobacterium, Carnobacterium, Lactococcus, Obesumbacterium, Stenotrophomonas and Flavobacterium. Non-starter lactic acid bacteria (NSLAB) were highly related to the formation of certain acids, esters and alcohols, such as 3-hexenoic acid, ethyl butanoate or 1-butanol. On the other hand, the starter LAB (SLAB) was related to particular ketones production, specifically 3-hydroxy-2-butanone; and environmental and/or non-desirable bacteria to certain ketones, hydrocarbons and sulphur compounds formation, such as 2-propanone, t-3-octene and dimethyl sulphone. Additionally, the SLAB Lactococcus and Psychrobacter, Brevibacterium and Chromohalobacter were described as having a negative effect on aroma development caused by NSLAB and vice versa. These results provide novel knowledge to help understand the aroma formation in a raw ewe milk-derived cheese.

Changes in Key Aroma Compounds and Esterase Activity of Monascus-Fermented Cheese across a 30-Day Ripening Period

Monascus-fermented cheese (MC) is a new type of mold-ripened cheese that combines a traditional Chinese fermentation fungus, Monascus purpureus M1, with Western cheese fermentation techniques. In this study, the compositions of the volatile aroma compounds in MC were analyzed during a 30-day ripening period using SPME-Arrow and GC-O-MS. The activity of esterase in MC, which is a key enzyme catalyzing esterification reaction, was determined and compared with the control group (CC). Next, sensory analysis was conducted via quantitative descriptive analysis followed by Pearson correlation analysis between esterase activity and the key flavor compounds. A total of 76 compounds were detected. Thirty-three of these compounds could be smelled at the sniffing port and were identified as the key aroma compounds. The esterase activity in MC was found to be 1.24~1.33 times that of the CC. Moreover, the key odor features of ripened MC were alcohol and fruity flavors, considerably deviating from the sour and cheesy features found for the ripened CC. Furthermore, correlation analysis showed that esterase activity was strongly correlated (|r|> 0.75, p < 0.05) with various acids such as pentanoic and nonanoic acids and several aromatic esters, namely, octanoic acid ethyl ester and decanoic acid ethyl ester, revealing the key role that esterases play in developing the typical aroma of ripened MC.

The Aroma Composition of Koryciński Cheese Ripened in Different Temperatures

As a regional product, Koryciński cheese is one of the most important cheeses in the Podlasie region of Poland. In this study, the influence of technological processes, such as ripening, on shaping the organoleptic characteristics of cheese was determined. Korycin-type cheeses are produced from cow's milk according to traditional technology. The ripening process lasted 466 h at 5 °C, 10 °C, and 15 °C. The aging temperature had a decisive influence on the number of esters and organic acids formed, which were analyzed by gas chromatography-mass spectrometry (GC/MS). The organoleptic properties of the cheeses were also related to the ripening temperature.

Low-frequency ultrasonic treatment: A potential strategy to improve the flavor of fresh watermelon juice

A molecular sensory science approach was used to explore the effects of ultrasonic treatment on aroma compounds of watermelon juice. Watermelon juice was submitted to ultrasonic power at 325 W for 20 min. Ultrasonic treatment reduced odor related to cucumber and green descriptors, whilst significantly improved odors related to sweet, floral, and fruity descriptors, thus contributing to the overall flavor of watermelon juice. Compared with untreated watermelon juice, the amount and concentration of volatile compounds in ultrasonicated watermelon juice increased by 82.50% and 111.84%, respectively. Notably, 22 alkene compounds were newly formed in ultrasonicated watermelon juice, which contributed to sweet and fruity aroma of watermelon juice. The findings of the present study suggest that ultrasonic treatment may be a potential method to improve the overall flavor of watermelon juice.

Isolation, identification and sensory evaluation of kokumi peptides from by-products of enzyme-modified butter

BACKGROUND

Enzyme-modified butter is used as a common raw material to obtain a natural milk flavor. Butter protein is a by-product in butter processing that can be used as substrate to produce taste-active peptides, which can create additional value and new application opportunities, making the method more environmentally friendly.

RESULTS

Putative kokumi peptides from hydrolysates of protein by-products were isolated by gel filtration chromatography and reversed-phase high-performance liquid chromatography. The isolated peptide fraction with the most pronounced kokumi taste was screened by sensory evaluation and electronic tongue analysis. Eleven peptides were identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Six peptides were synthesized to verify their taste characteristics. Five synthetic peptides (FTKK, CKEVVRNANE, EELNVPG, VPNSAEER and YPVEPFTER) showed different intensity levels of kokumi taste. Of these peptides, the decapeptide CKEVVRNANE had the highest kokumi intensity.

CONCLUSION

The newly identified kokumi peptides increased the kokumi taste intensity and showed some synergistic effect with umami taste. Both termini of the peptides seem to play an important role in taste characteristic. Glu residue at both termini can increase the kokumi taste intensity. This work indicated that it was feasible to produce kokumi peptides by enzymatic hydrolysis of the protein by-products of butter. © 2022 Society of Chemical Industry.

Aroma classification and characterization of Lactobacillus delbrueckii subsp. bulgaricus fermented milk

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The aroma types of fermented milk produced by L. bulgaricus were divided into milky-type, cheesy-type, fermented-type and miscellaneous-type.

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The flavor fingerprints of different aroma types were established by GC-IMS.

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Acetaldehyde, 2,3-butanedione, acetic acid, butanoic acid, hexanoic acid and δ-decalactone of different aroma types were determined by Flavoromics.

The aroma of the fermented milk produced by twenty-eight Lactobacillus delbrueckii subsp. bulgaricus strains was evaluated via quantitative descriptive analysis. According to the sensory analysis results, the fermented milks were grouped into milky-type, cheesy-type, fermented-type and miscellaneous-type. The representative samples of cheese-type and fermented-type were analyzed by headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) and flavoromics. A total of 95 volatile compounds were identified and particularly, 12 aroma-active compounds were detected by using gas chromatography-olfactometry-mass spectrometry (GC-O-MS). Among the different aroma types, 2,3-butanedione, δ-decalactone, acetaldehyde, butanoic acid, acetic acid and hexanoic acid were finally screened out as the key aroma-active compounds by quantitative and odor activity value (OAV) analysis combined with aroma recombination, omission and addition experiments. These findings were valuable in developing specific fermented milk products with different aroma profiles.

Characterisation of the key volatile compounds of commercial Gouda cheeses and their contribution to aromas according to Chinese consumers’ preferences

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The aroma preference of Chinese consumers for Gouda cheese was evaluated.

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The volatile compounds in Gouda cheese were identified by GC–MS, OAV and GC–O.

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The correlation between and volatile aroma compounds were analyzed by PLS.

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Key aroma compounds were validated by aroma reorganization and omission tests.

A systematic flavoromics-based analysis of samples of 12 commercially available Gouda cheeses was performed to determine their key volatile components, the contribution of these components to the aromas of the cheeses, and which aromas were preferred by a panel of Chinese consumers. The sensory analysis results show that the Chinese consumers preferred young and medium cheeses, and that sensory attributes such as ‘milk’ and ‘cream’ were the most popular. Seventy-seven aroma compounds were identified by gas chromatography–mass spectrometry, and 28 of these were determined to be aroma-active compounds by gas chromatography–olfactometry analysis and calculation of their odour activity values. Partial least-squares analysis revealed that compounds such as diacetyl and acetoin correlated with aromas preferred by the Chinese consumers, while isobutyric acid, hexanoic acid and valeric acid correlated with aromas disliked by the Chinese consumers. Finally, the flavour contribution of each aroma-active compound was validated through aroma reorganisation and omission experiments.

Characterization of key aroma compounds in low-salt fermented sour fish by gas chromatography-mass spectrometry, odor activity values, aroma recombination and omission experiments

In this study, key aroma compounds of low-salt fermented sour fish were characterized using headspace solid-phase micro extraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS), odor activity values (OAV) and aroma recombination and omission experiments. Eighty-eight volatile compounds, including esters, aldehydes, alcohols, acids, furans and pyrazines, were identified by HS-SPME-GC-MS. Eighteen aroma-active compounds were quantified by employing calculation of OAV greater than 1. A recombination aroma model prepared using aroma-active compounds based on the odorless fish matrix sensorially matched the aroma of fermented sour fish with a score of 4.5 out of 5. The omission experiment showed that 7 out of 18 compounds had a significant contribution to the overall aroma (P < 0.05). The key aroma compounds of fermented sour fish were concluded to be ethyl acetate (OAV = 189), ethyl hexanoate (OAV = 66), isoamyl acetate (OAV = 424), ethyl butyrate (OAV = 26), hexanal (OAV = 49), 1-hexadecanal (OAV = 14) and 2-pentylfuran (OAV = 13).

Aroma Clouds of Foods: A Step Forward to Unveil Food Aroma Complexity Using GC × GC

The human senses shape the life in several aspects, namely well-being, socialization, health status, and diet, among others. However, only recently, the understanding of this highly sophisticated sensory neuronal pathway has gained new advances. Also, it is known that each olfactory receptor cell expresses only one type of odorant receptor, and each receptor can detect a limited number of odorant substances. Odorant substances are typically volatile or semi-volatile in nature, exhibit low relative molecular weight, and represent a wide variety of chemical families. These molecules may be released from foods, constituting clouds surrounding them, and are responsible for their aroma properties. A single natural aroma may contain a huge number of volatile components, and some of them are present in trace amounts, which make their study especially difficult. Understanding the components of food aromas has become more important than ever with the transformation of food systems and the increased innovation in the food industry. Two-dimensional gas chromatography and time-of-flight mass spectrometry (GC × GC-ToFMS) seems to be a powerful technique for the analytical coverage of the food aromas. Thus, the main purpose of this review is to critically discuss the potential of the GC × GC–based methodologies, combined with a headspace solvent-free microextraction technique, in tandem with data processing and data analysis, as a useful tool to the analysis of the chemical aroma clouds of foods. Due to the broad and complex nature of the aroma chemistry subject, some concepts and challenges related to the characterization of volatile molecules and the perception of aromas will be presented in advance. All topics covered in this review will be elucidated, as much as possible, with examples reported in recent publications, to make the interpretation of the fascinating world of food aroma chemistry more attractive and perceptive.

Characterization of Six Lactones in Cheddar Cheese and Their Sensory Interactions Studied by Odor Activity Values and Feller's Additive Model

To evaluate the perceptual interactions among important lactone compounds in cheddar cheese, a molecular-level flavoromic approach, in combination with perceptual interaction analysis, was applied. Six aroma-active lactones with flavor dilution factors ranging from 4 to 128 were identified in three cheddar samples by gas chromatography-olfactometry-mass spectrometry. Odor thresholds of these six aroma-active lactones were determined with values from 7.16 to 30.03 μg/kg using a deodorized cheddar matrix. The odor activity value approach demonstrated complicated interactions among the 15 binary mixtures of six important lactones, including additive, synergistic, or masking effects. Based on partial differential odor intensities, each lactone with similar degrees of perceptual interactions in binary mixtures tends to present synergistic or masking effects. Owing to the difference in the chemical structure and mixture composition, δ-dodecalactone and γ-dodecalactone caused promotive and inhibitory effects on the expression of lactone fruity aroma, respectively.

Flavoromic determination of lactones in cheddar cheese by GC-MS-olfactometry, aroma extract dilution analysis, aroma recombination and omission analysis

To systematically identify and quantify the γ- and δ-lactones in Cheddar cheeses, 20 samples from three sources (Ireland, the UK and the USA) were analysed by gas chromatography-mass spectrometry (GC-MS), gas chromatography-olfactometry (GC-O), aroma extract dilution analysis, aroma recombination analysis, and aroma addition/omission analysis. Nine lactones were detected in these samples, and one of these lactones, γ-undecalactone, was identified in Cheddar cheese for the first time. The quantitative results showed that the concentration of lactones in these cheeses usually increased as the length of their maturity period increased. γ-Octalactone, γ-undecalactone, γ-dodecalactone, δ-octalactone, δ-decalactone and δ-dodecalactone were identified as aroma-active substances based on their odour activity values and aroma extract dilution analysis, with flavour dilution factors ranging from 2 to 128. Aroma recombination and omission experiments based on a newly developed deodorised Cheddar matrix further validated the important contributions of these lactones to the overall aroma of Cheddar cheeses. The addition of each lactone to aroma recombination models reduced the aroma intensity of sour and rancid properties to various extents and improved the acceptability of the overall flavour.

The key aroma compounds and sensory characteristics of commercial Cheddar cheeses

To study the key aroma components and flavor profile differences of Cheddar cheese with different maturity and from different countries, the flavor components of 25 imported commercial Cheddar cheese samples in the China market were determined by gas chromatography-mass spectrometry. The quality and quantity of 40 flavor compounds were analyzed by gas chromatography-olfactometry among 71 aroma compounds determined by gas chromatography-mass spectrometry. Combined with odor activity value calculation, principal component analysis (PCA) was conducted to analyze the relationship among 26 flavor compounds with odor activity values >1 and the maturity of Cheddar cheese. The PCA results showed significant differences between the group of mild Cheddar cheese and the groups of medium Cheddar cheese and mature Cheddar cheese, and no significant differences were observed between medium Cheddar cheese and mature Cheddar cheese. According to the results of PCA and consumers' preference test, representative Cheddar cheese samples with different ripening times were selected for the flavor profile analysis. Partial least squares regression analysis was conducted to obtain the relationship between sensory properties and flavor compounds of different Cheddar cheeses. Based on partial least squares regression analysis, 1-octen-3-one, hexanal, acetic acid, 3-methylindole, and acetoin were positively correlated with milky, sour, and yogurt of mild Cheddar cheese. Dimethyl trisulfide, phenylacetaldehyde, ethyl caproate, octanoic acid, and furaneol and other compounds were positively correlated with fruity, caramel, rancid, and nutty notes of the medium and mature Cheddar cheeses.