Characterisation of aroma-active compounds in Guilin Huaqiao white sufu and their influence on umami aftertaste and palatability of umami solution

Addition of retronasal milk fat odour during milk consumption increased liking without affecting intake

Reduction of food fat content often comes at the cost of sensory appeal. Given that odours can enhance various fat-related sensory characteristics, their use as fat substitutes seems promising. This cross-over study investigated whether sensory characteristics of a low-fat product (dairy milk) can be enhanced by the addition of a fat-related aroma (cream) and whether this influences subsequent eating behaviour within an ecologically valid scenario. Fifty-six consumers evaluated 0% fat milk without aroma (skim), 0% fat milk infused with cream aroma (skim+) and 3.5% fat milk without aroma (full) on perceived flavour intensity, creamy mouthfeel, aftertaste and liking (ranking rating scale - 100-unit VAS). In three separate subsequent sessions, 54 of the participants consumed the samples above as fixed preloads (300 ml) after which they were provided an ad-libitum breakfast consisting of granola and yogurt. Appetite ratings (hunger, fullness, desire to eat, prospective consumption) were collected pre- and post-preload and post-breakfast. While skim + samples were more liked compared to skim ones, there was no difference in flavour intensity, creamy mouthfeel, or aftertaste. Full fat samples were rated higher than both skim and skim + ones on all attributes. Despite the added aroma (skim+) enhancing liking, it did not influence subsequent intake amounts or eating rate. In fact, there were no differences in intake or appetite between any of the preloads. This demonstrates that odours can be used to enhance liking of reduced-fat food products, yet the broader implication of such an approach on food intake behaviour remains to elucidated.

Dynamic changes in microbial communities during sweet flour sauce fermentation and their correlations with physicochemical properties and volatile compounds

Sweet flour sauce is a traditional fermented condiment in China, known for its distinct sweet and savory flavor profile. During the fermentation process, the dominant bacterial genera were Ralstonia and Bacillus, and the dominant fungal genera were Aspergillus, Issatchenkia, Clavispora, and Zygosaccharomyces. In addition, total acidity (TA) and amino acid nitrogen (AAN) in different fermentation stages were determined by the acidometer titration method, and reducing sugar (RS) was determined by the 3,5-dinitrosalicylic acid method. The correlation network revealed TA, RS, and AAN were closely related to multiple microorganisms. TA showed significant positive correlations with Gluconobacter, Candida, and Clavispora. RS was positively correlated with Geotrichum, and AAN was positively correlated with Methylobacterium-Methylorubrum and Zygosaccharomyces. Correlation network analysis was also conducted to show the significant correlations among 2 bacterial genera, 9 fungal genera, and 16 characteristic volatile compounds. In general, the relationships between fungus and volatiles were more significant, with a wide range of yeasts exerting significant functions in forming flavor compounds, whereas most bacteria were negatively correlated with volatiles. Among fungi, Clavispora and Meyerozyma were positively associated with furfural, methional, 5-methyl-2-phenyl-2-hexenal, 2-isopropyl-5-methylhex-2-enal, and benzeneacetaldehyde. Zygosaccharomyces exhibited strong correlations with acetic acid, 2-furanmethanol, phenylethyl alcohol, and 2-methyl-1-butanol. These findings can be used to better understand and manage the fermentation process, making it possible to improve the quality of sweet flour sauce by enriching key microorganisms. PRACTICAL APPLICATION: During the fermentation of sweet flour sauce, the metabolic activities of microbial communities exerted an important function in forming unique sensory and nutritional properties. These findings revealed significant correlations among microorganisms, vital physicochemical indices, and key volatiles, providing a theoretical foundation for regulating the fermentation process, enhancing product qualities, and developing functional strains.

The rapid fermentation of Euphausia superba sauce and revealing of the relationship between key flavor compounds and core microorganisms

Euphausia superba is a highly stocked biological resource, while its utilization in producing shrimp sauce is rarely reported. Traditional fermentation methods of seafood sauces usually need long fermentation period. This study proposed a rapid fermentation method for Euphausia superba sauce (AKS) and verified the feasibility, then revealed the key flavor substances and functional core microorganisms and established their relationship. Results showed that the rapidly fermented AKS owned the amino acid nitrogen content of 1.10 g/100 mL, the total nitrogen of 15.21 %, the volatile base nitrogen of 63.94 mg N/100 g, and the liquefaction rate of 87 %. Asp, Glu, Thr, GMP, malic acid, acetic acid, lactic acid, methanethiol, pentanal, propanal, etc. were screened out as the key flavor compounds. Peptoniphilus, Halomonas, Paenochrobactrum, Proteus, etc. were picked out as the core microorganisms. Further analysis revealed that Paenochrobactrum, Halomonas, Erysipelothrix, Aquamicrobium and Leucobacter were involved in the generation of free amino acids, organic acids, aldehydes and ketones. This study provided a reference for the rapid fermentation of AKS during industrial production, laying the foundation for effective control fermentation process and ensuring quality stability of prepared AKS.

Ultra-processed plant-based analogs: Addressing the challenging journey toward health and safety

Currently, plant-based analogs are presented as healthier alternatives to the products they are intended to replace. However, the processing to which ultra-processed plant-based analogs are subjected to acquire the characteristics of animal-derived products might result in the opposite effect, producing unhealthy ultra-processed foods. In the present review, a list of strategies widely known and already employed in animal-derived products is suggested to achieve healthier, safer, and tastier ultra-processed plant-based analogs: fermentation, employment of probiotics and postbiotics, NaCl replacement or substitution, addition of antioxidants, and fatty profile enhancement. In general, these strategies are not yet applied to the plant-based products available on the market; thus, this research paper might induce new investigation pathways for researchers and producers to develop actually healthier alternatives.

Revealing the formation mechanisms of key flavor components during the fermentation of bamboo shoots by combining flavoromics and metagenomics

Microbial metabolism plays a critical role in the flavor development of Guangxi fermented bamboo shoots (GFBS). To clarify the role of microorganisms in flavor formation and predict the metabolic pathways of key characteristic flavor compounds, this study employed metabolomics, Odor Activity Value (OAV), and Taste Activity Value (TAV) calculations, integrated with Partial Least Squares Discriminant Analysis (PLS-DA), to investigate changes in GFBS flavors-represented by volatile flavor compounds, organic acids, and free amino acids-across a 30-day fermentation period. Metagenomic datasets were used to identify taxonomic and functional changes in the microbial community. As a result, 26 characteristic flavor compounds (OAV or TAV > 1) were identified in mature GFBS, and 23 differential flavor compounds were identified at different fermentation stages using PLS-DA (VIP > 1.2). The top 10 microbial genera associated with these characteristic flavor compounds were identified, including Acinetobacter, Enterobacter, Raoultella, Enterococcus, Klebsiella, Lactococcus, Leuconostoc, Weissella, Lactiplantibacillus and Limosilactobacillus. Based on these findings, a predictive metabolic network of key flavor compounds in GFBS was constructed, providing a comprehensive understanding of the diverse metabolic roles of microorganisms during fermentation. This work lays a theoretical foundation for the standardized production and quality control of GFBS flavor.

Antifungal Effects and Postharvest Diseases Control Potential of E, E-2, 4-Nonadienal against Rhizopus stolonifer

Pathogenic microorganisms are a significant cause of food spoilage, adversely affecting both product quality and human health. This study evaluated the antifungal activities of 34 aldehydes against foodborne and plant pathogenic fungi, identifying 8 promising lead compounds. Among them, E, E-2, 4-nonadienal exhibited optimal effects against Rhizopus stolonifer with an EC50 of 11.29 μg/mL. In vitro assays demonstrated that E, E-2, 4-nonadienal significantly impact R. stolonifer through both direct contact and fumigation. The preliminary mode of action (MOA) studies indicated that it effectively inhibited spore germination, disrupted ergosterol biosynthesis, and induced oxidative stress, affecting the permeability of the fungal cell membrane and altering mycelial morphology. Additionally, E, E-2, 4-nonadienal significantly reduced soft rot in spore-infected stored cherry tomatoes and showed low toxicity. Thus, aldehydes, exemplified by E, E-2, 4-nonadienal, are potential food and agricultural preservatives, offering efficiency, safety, and cost-effectiveness.

Key aroma compounds associated with umami perception of MSG in fried Takifugu obscurus liver

Monosodium glutamate (MSG) is a basic representative of umami taste, but it exerts adverse effects as reported in several studies. Enhancing umami perception through aroma-taste interactions is a potentially useful approach as a flavor enhancer to reduce future MSG intake. We identified the aroma compounds in fried Takifugu obscurus liver, then studied the effect of aroma compounds on perceived umami taste using the sensomics approach. A total of 117 volatile compounds were identified from the fried liver. Thereinto, 30 volatile compounds related to five basic tastes were detected by gas chromatography/olfactometry-associated taste analysis. Aroma compounds associated umami, sweet and salty perception in the fried Takifugu obscurus liver showed the potential to enhance umami perception of MSG solutions. Three aldehydes, i.e. heptanal, (Z)-4-heptenal and 2-methylbutanal, significantly enhanced the umami intensity perception of an MSG solution (p < 0.05). The use of aroma compounds to enhance umami perception is considered as a promising tool, further broadening the research area of umami science for application as flavor enhancers in the food industry. In addition, this study also provides an insight into revealing aroma-taste interaction.

Dynamic changes and interaction between different aroma types during low-temperature roasting of bud green tea

As an important process for enhancing aroma of Wuyi rock tea, roasting has gradually been applied to the processing of bud green tea (BGT). However, there is a lack of comprehensive research on the impact of roasting on BGT aroma. This research provides a detailed analysis of the changes in aroma perception and compounds during the low-temperature roasting process (105°C, 90 minutes) of BGT. First, the changes in aroma perception were studied using quantitative descriptive analysis (QDA). The aroma perception of BGT transformed from fresh to chestnut like. Next, headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) analysis was conducted to characterize the volatile compounds during roasting. A total of 313 volatile compounds were identified, among which 72 showed significant differences. Compounds such as linalool, benzyl alcohol, ionone, and ethyl salicylate (floral aroma) and 2,6-dimethylpyrazine, 2,3-dimethylpyrazine, 2-acetylpyrrole, and 3-furfural (caramel-like aroma) were confirmed to be involved in the formation of the chestnut-like aroma during roasting process. In addition, representative aroma compounds with different characteristics were selected based on monomolecular olfactory results to simulate sensory-level aroma interactions. The results showed that fresh and tender aromas exhibited mutual enhancement at low concentrations, while sweet and chestnut-like aromas showed mutual enhancement at all concentrations.

Widely targeted metabolomics combined with E-tongue and E-nose reveal dynamic changes of tender coconut water in responses to the infection of Ceratocystis paradoxa

Ceratocystis paradoxa is a major cause of postharvest disease in tender coconuts worldwide. We conducted a comprehensive study using widely targeted metabolomics, electronic tongue (E-tongue), and electronic nose (E-nose) analyses to investigate the impacts of C. paradoxa invasion on the quality of tender coconut water (TCW) from fresh control (FC), uninoculated (UN), skin-inoculated (SI), and deep-inoculated (DI) nuts. DI exhibited significantly higher taste indicators associated with bitterness, saltiness, astringency aftertaste, and bitter aftertaste, as well as odor sensor values related to various compounds such as long-chain alkanes, hydrides, methane, organic sulfides, etc. Invasion of C. paradoxa into the endosperm altered the flavor characteristics of TCW mainly through the modulation of carbohydrate and secondary metabolite pathways. Furthermore, significant correlations were observed between the differentially expressed flavorful metabolites and the sensor indicators of the E-nose and E-tongue. These findings offer valuable insights into understanding the impact of C. paradoxa infection on coconuts.

Microbiology of fermented soy foods in Asia: Can we learn lessons for production of plant cheese analogues?

The food industry is facing the challenge of creating innovative, nutritious, and flavored plant-based products, due to consumer's increasing demand for the health and environmental sustainability. Fermentation as a unique and effective tool plays an important role in the innovation of food products. Traditional fermented soy foods are popular in many Asian and African countries as nutritious, digestible and flavorful daily staples or condiments. They are produced by specific microorganisms with the unique fermentation process in which microorganisms convert the ingredients of whole soybean or soybean curd to flavorful and functional molecules. This review provides an overview on traditional fermented food produced from soy, including douchi, natto, tempeh, and sufu as well as stinky tofu, including the background of these products, the manufacturing process, and the microbial diversity involved in fermentation procedures as well as flavor volatiles that were identified in the final products. The contribution of microbes to the quality of these five fermented soy foods is discussed, with the comparison to the role of cheese ripening microorganisms in cheese flavor formation. This communication aims to summarize the microbiology of fermented soy foods in Asia, evoking innovative ideas for the development of new plant-based fermented foods especially plant-based cheese analogues.

Suanyu fermentation strains screening, process optimization and the effect of thermal processing methods on its flavor

Suanyu is a famous traditional fermented aquatic food in south China. However, the quality of Suanyu is unstable due to natural fermentation based on the environment. This work screened suitable microbial fermenters (Enterococcus rivorum and Enterococcus lactis) from traditional fermented fish and optimized a suitable fermentation process. Effects of different fermentation (natural and mixed starters fermentation) and thermal treatments (microwave, frying and roasting) on the flavor of Suanyu were investigated. Compared to the natural fermentation group, the TVB-N content (31.5 mg/100 g) was lower, the total acidity (5.12 g/kg) and flavor compounds content were richer in the mixed starters fermentation group (P < 0.05). But there was no significant difference in histamine content (P > 0.05). The roasting treatment group contained higher contents of free amino acids, organic acids, nucleotides and richer key aroma components. The electronic nose was able to distinguish between the differently treated samples. The sensory evaluation result showed that roasted and fried samples had a more acceptable flavor and color. This work will provide a theoretical reference for the standardized production of Suanyu and the development of pre-cooked products.

Microbial community succession and their relationship with the flavor formation during the natural fermentation of Mouding sufu

Mouding sufu, a traditional fermented soybean product in China, has been recognized by the public in the southwestern regions of China. To reveal the microbial community succession and their relationship with the flavor formation during the natural fermentation of Mouding sufu, microbial community, non-volatile flavor compounds and volatile flavor compounds were analyzed by high-throughput sequencing, high-performance liquid chromatography, gas chromatography ion migration spectroscopy, respectively. The results showed that Lactobacillus and Klebsiella were the most abundant bacterial genus, whereas the main fungal genera were unclassified-f-Dipodascaeae and Issatchenkia. In addition, Glutamic acid, Aspartic acid, Alanine, Valine, Lysine, Histidine, lactic acid, succinic acid, and acetic acid were the main non-volatile flavor substances. Furthermore, the taste activity values of glutamic acid, aspartic acid and lactic acid reached 132, 68.9, 18.18 at H60, respectively, meaning that umami and sour were the key taste compounds. Simultaneously, ethyl 3-methylbutanoate-M, ethyl propanoate, methyl 2-methylbutanoate, ethyl 2-methylbutanoate, ethyl 3-methylbutanoate-D, ethyl isobutyrate, linalool-M, linalool-D, cis-4-heptenal, 2-methylpropanal were the characteristic volatile flavor of Mouding sufu. Finally, correlation analysis showed that g__Erwinia and g__Acremonium correlated with most of the key aroma compounds. 20 bacteria and 21 fungi were identified as core functional microbe for Mouding sufu production.

Characterization of the key odor-active compounds in different aroma types of Fu brick tea using HS-SPME/GC-MSO combined with sensory-directed flavor analysis

Fu brick tea (FBT) is popular for its unique 'fungal flower' aroma, however, its key odor-active compounds are essentially unknown. In this study, the odor-active compounds of "stale-fungal" aroma (CJX), "fresh-fungal" aroma (QJX), and "fermentation-fungal" aroma (FJX) types FBT were extracted and examined by headspace solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) and gas chromatographyolfactometry (GC-O). A total of 43 volatile and 38 odor-active compounds were identified by these methods. Among them, the content of dihydroactindiolide (4596-13189 µg/L), (E)-linalool oxide (2863-6627 µg/L), and benzyl alcohol (4992-6859 µg/L) were highest. Aroma recombination experiments further verified that these odor-active compounds could be simulated the overall aroma profile of FBT successfully. Furthermore, omission experiments confirmed that 15, 20, and 15 key odor-active compounds in CJX, QJX, and FJX FBT, respectively. This study will provide a theoretical basis for comprehensively understanding the formation of characteristic aromas in FBT.

Egg yolk phospholipids as an ideal precursor of fatty note odorants for chicken meat and fried foods: A review

Egg yolk phospholipids (PLs) have been demonstrated to generate large quantities of lipid-derived odorants, especially the fatty note odorants. Recently, egg yolk PLs have been successfully used in chicken meat and fried foods to improve aroma. This review comprehensively summarizes the properties of egg yolk PLs as precursors of fatty note odorants, including their classes, extraction, identification, oxidation, decomposition and odorant formation, applications, considerations and future prospects in the food industry. Most likely, phosphatidylcholine (PC) is the most abundant class in egg yolk PLs, and PC is more efficient than phosphatidylethanolamine in generating fatty note odorants; moreover, the predominant polyunsaturated fatty acid is linoleic acid, and its corresponding predominant hydroperoxide is 9-hydroperoxy-10,12-octadecadienoic acid during autoxidation, which is the precursor of 2,4-decadienals and 2,4-nonadienals, the key fatty note odorants. Therefore, egg yolk PLs could be an ideal precursor of fatty note odorants for chicken meat and fried foods.

A signal detection reminder methodology to evaluate effects of odor-taste-taste interactions to enhance the perceived saltiness

Currently, numerous attempts are made to increase the perceived saltiness of food without adding more NaCl. In the present study, a method based on a reminder design and signal detection theory was used to evaluate the effects of cheddar cheese odor, meat odor, and monosodium glutamate (MSG) on the perceived saltiness and preference of three intensities of NaCl through the d' and R-Index. A solution of 2 g/L NaCl combined with odorless air was the blind reference product, which was also tested as one of the test products. The reference sample was compared to the target samples. A total of twelve right-handed subjects (19-40 years; body mass index BMI 21-32; 7 females and 5 males) performed sensory difference tasks across six days. Cheddar cheese odor was more effective in increasing the perceived saltiness and preference of NaCl solutions than meat odor. When MSG was added to the NaCl solutions, the perceived saltiness and preference were increased. Overall, the signal detection reminder method could provide a comprehensive psychophysical framework to measure saltiness perception and preference of odor-taste-taste interactions using d' (a distance measure) and R-index (an area measure).

Microbiology, flavor formation, and bioactivity of fermented soybean curd (furu): A review

Soybeans are an important plant-based food but its beany flavor and anti-nutritional factors limit its consumption. Fermentation is an effective way to improve its flavor and nutrition. Furu is a popular fermented soybean curd and mainly manufactured in Asia, which has been consumed for thousands of years as an appetizer because of its attractive flavors. This review first classifies furu products on the basis of various factors; then, the microorganisms involved in its fermentation and their various functions are discussed. The mechanisms for the formation of aroma and taste compounds during fermentation are also discussed; and the microbial metabolites and their bioactivities are analyzed. Finally, future prospects and challenges are introduced and further research is proposed. This information is needed to protect the regional characteristics of furu and to regulate its consistent quality. The current information suggests that more in vivo experiments and further clinical trials are needed to confirm its safety and the microbial community needs to be optimized and standardized for each type of furu to improve the production process.

The Enhancement of the Perception of Saltiness by Odorants Selected from Chinese Douchi in Salt Solution

Douchi is a traditional fermented soya bean product that is popular for its smelled saltiness and unique flavor. In order to look for the relationship between smelled saltiness of volatiles and their saltiness-enhancing properties, gas chromatography-olfactometry/associated taste was used to select odorants associated with saltiness in Yongchuan Douchi. The enhancement effects of saltiness intensity by selected odorants were further verified by sensory evaluation analyses of 2-alternative forced-choice and odor-induced saltiness enhancement in a follow-up study. A total of 14 odorant compounds were selected for their odor-associated saltiness perception. The compounds of 2-ethyl-3,5-dimethyl pyrazine, 2,5-dimethyl pyrazine, dimethyl trisulfide, 3-(methylthio) propanol and 3-(methylthio) propanal could significantly enhance saltiness perception in salt solution. Among them, 2-ethyl-3,5-dimethyl pyrazine was reported for the first time to be able to improve the salty taste. The study suggested that salty food is an ideal material for selecting saltiness-enhancing odorants, which could provide more direct theoretical support for salt reduction in the food industry.

Dynamic correlations between major enzymatic activities, physicochemical properties and targeted volatile compounds in naturally fermented plain sufu during production

Dynamic changes and correlations between physicochemical properties, 14 targeted volatile compounds (TVCs) and six groups of enzyme activities during eight production stages of naturally fermented plain sufu were explored. Multiple factor analysis was used to discriminate between and group the samples into three clusters: cluster I comprised tofu and pehtze; cluster II comprised dried pehtze and salted pehtze; cluster III involved the aging stages. Clusters I and II were characterised by higher enzyme activities, while cluster III was characterised by the presence of diverse TVCs. Protease and esterase were strongly correlated with most of the TVCs. Esterase, in particular, contributed to the formation of three high molecular weight esters, namely, ethyl dodecanoate, ethyl (Z)-9-octadecenoate and ethyl (Z, Z)-9,12-octadecadienoate. The enzymes found contributed to the texture and flavour of naturally fermented sufu and will provide a good guide and control for using the enzymes directly to ripen sufu products.

Fermented meat sausages and the challenge of their plant-based alternatives: A comparative review on aroma-related aspects

Traditional fermented meat sausages are produced around the world due to their convenience and sensory characteristics which are responsible for their high acceptability. They constitute a cultural heritage as shown by the high diversity of products around the world. Recent trends are addressing issues regarding innovation in their formulation by reduction of salt, fat and additives (curing salts). However, the current trend towards a reduction in the consumption of meat has produced an increase in the formulation of meat product analogues. This trend is the main focus of producers to offer new attractive products to consumers even though the aroma profile of traditional fermented meat sausages is not reached. In this manuscript, we review and discuss the chemistry of aroma formation in traditional fermented meat sausages in contrast to the potential of plant-based ingredients used in meat analogues.

Key aroma-active compounds in brown sugar and their influence on sweetness

Brown sugar (non-centrifugal cane sugar) is popular for its pleasant caramel-like aroma and sweetness. Vacuum simultaneous steam distillation and extraction (V-SDE) and gas chromatography-mass spectrometry (GC-MS) was used to study the volatile fraction of brown sugar. To further determine the aroma-active compounds in brown sugar, gas chromatography-mass spectrometry-olfactometry (GC-MS-O) were used in conjunction with aroma extraction dilution analysis (AEDA), odor activity values (OAVs), and sensory evaluation to analyze the effects of the key aroma-active compounds on sweetness. A total of 37 aroma-active compounds were obtained, mainly including ketones, pyrazines, alkanes, phenols and alcohols, which contributed caramel, sweet and fruity notes to brown sugar. Among them, furfural, benzeneacetaldehyde, 2,3-butanedione, β-damascenone, 2-methoxyphenol, dihydro-2-methyl-3(2H)-furanone, 2-furanmethanol and butyrolactone could significantly enhance the sweetness of sugar solution because of the congruency of the aroma attributes and sweetness.

Traditional fermented soybean products: processing, flavor formation, nutritional and biological activities

Traditional fermented soybean food has emerged as an important part of people's dietary structure because of the unique flavors and improved health benefit. During fermentation, the nutrients in soybean undergo a series of biochemical reactions catalyzed naturally by microorganism secreted enzymes. Thereafter, many functional and bioactive substances such as bioactive peptides, unsaturated fatty acids, free soy isoflavones, vitamins and minerals are produced, making fermented soy products more advantageous in nutrition and health. This review comprehensively discusses the historical evolution, distribution, traditional fermentation processing, main sources and characteristics of fermented strains, flavor components, nutritional properties, and biological activities of four traditional fermented soybean foods including douchi, sufu, dajiang, and soy sauce. In the end, we introduce four major challenges encountered by traditional fermented soybean foods including high salt content, formation of biogenic amine, the presence of pathogenic microorganisms and mycotoxins, and quality inconsistency. We conclude that the establishment of scientific quality standard and innovated fermentation processing is the potential solutions to combat the issues and improve the safety of traditional fermented soybean products.