The contribution of autochthonous microflora on free fatty acids release and flavor development in low-salt fermented fish

The impacts of cold plasma on the taste and odor formation of dried silver carp products

This study investigated non-thermal pretreatment (cold plasma, CP) on the flavor (taste and odor) profiles of dried fish products. CP treatment of 5 min contributed to accumulation of umami nucleotides adenosine 5'-monophosphate (AMP) from 30.96 to 40.82 μg/g and inosine 5'-monophosphate (IMP) from 2009.29 to 2132.23 μg/g, and significant reduction of bitter hypoxanthine ribonucleoside (HxR) and hypoxanthine (Hx), respectively (P < 0.05) in the dried fish products. A noticeable enhancement in sweet glycine (from 429.41 to 490.03 mg/100 g) and umami glutamic acid (from 55.68 to 67.76 mg/100 g) accompanied with the CP treatment (P < 0.05) based on taste activity value (TAV > 1). And the characteristic odor volatiles (nonanal, hexanal and 1-octen-3-ol) were strengthened 2.13-, 2.16- and 2.17- folds, respectively (P < 0.05). The results of equivalent umami concentration and Gibbs free energy calculation, combining with the correlation analysis, indicate that nucleotides and free amino acids synergically enhanced the taste improvement of dried fish products. Moderate lipids oxidation favored the formation of characteristic volatiles. The CP pretreatment offered new strategies for enhancing flavor of dried fish products.

Effects of different curing concentrations and drying times on the microbial community structure and metabolites of dried Spanish mackerel

Cured Spanish mackerel has a promising market owing to its nutritious nature as well as ease of transportation and preservation. However, the nutritional and flavor formation mechanism of Spanish mackerel after curing and drying is unclear. To overcome this problem, the effects of different processing conditions on the free amino acid, microbial community, and flavor of Spanish mackerel were explored. Staphylococcus and Cobetia are the main microorganisms in cured mackerel and are closely associated with the formation of their quality. Compared with fresh mackerel, cured mackerel contains increased levels of protein, fat, and chloride, contributing to its distinctive flavor. The contents of free amino acids in the BA64 group were substantially higher than those in other groups, particularly the contents of threonine, glycine, and tyrosine. These findings will contribute to the development of high-quality cured Spanish mackerel products and cured aquatic products.

Lipid Hydrolysis, Oxidation, and Fatty Acid Formation Pathway Mapping of Synergistically Fermented Sausage and Characterization of Lipid Mediating Genes

Starter cultures play a significant role in lipid hydrolysis, prevention of lipid oxidation, and synthesis of fatty acid in fermented sausage, enhancing product quality. In this study, five synergistic bacterial strains were used, including Pediococcus pentosaceus (B-3), Latilactobacillus sakei DLS-24 (D-24), Latilactobacillus acidophilus DLS-29 (D-29), Lactiplantibacillus pentosus (B-1), and Lactiplantibacillus plantarum (B-2). Sausage B1B3D24 gave the highest free fatty acid with 39.45 g/100 g at 45-Day. Based on 2-thiobarbituric acid reactive substance, B2B3 contains 112.68 MDA/kg. Lipoxygenase activity displays the lowest in B1B3D24 with 0.095 μmol/min·mg followed by B2B3 with 0.145 μmol/min·mg. B1B3D24 contains 11.35 g/kg of monounsaturated fatty acid with the highest content in eicosenoic acid (C20:1) and palmitoleic acid (C16:1). The fatty acid synthesis pathway in B1B3D24 contains an active positive interaction with PUFA to increase the isotopomers of ω-3 and ω-6 fatty acids. In addition, lipid mediating genes in B1B3D24 show the highest counts in fatty-acid synthase, carbonyl reductase 4, 3-oxoacyl-[acyl-carrier-protein] synthase III, hydroxysteroid 17-beta dehydrogenase 8, and acetyl-CoA carboxylase.

Insight into the role of lipids in odor changes of frozen grass carp (Ctenopharyngodon idella) based on lipidomics and GC-MS analysis: Impact of freeze-thaw cycles and heat treatment

The role of lipids in changes of volatile organic compounds (VOCs) in grass carp during 1 month of frozen storage with different freeze-thaw cycles and subsequent heat treatment was investigated. Sixty VOCs were identified in all groups by SPME-GC-MS. Odor contents fluctuated along with the freeze-thaw cycles and heat treatment, and the highest odor content was observed in frozen sample without freeze-thaw cycles. Freeze-thaw and heat treatment significantly promoted the lipid oxidation and hydrolysis for all the groups(p<0.05). Lipid metabolites were analyzed using non-targeted lipidomics and could be well distinguished among different freeze-thaw groups and heat-treatment groups. A total of 10 key differential lipid molecules were annotated, involving 4 metabolic pathways related to lipid degradation and odor formation. Spearman correlation analysis showed that these key differential lipids were significantly related to the formation of key VOCs (p<0.05).

Fluctuation of flavor quality in roasted duck: The consequences of raw duck preform's repetitive freeze-thawing

This study aimed to investigate the changes in flavor quality of roasted duck during repetitive freeze-thawing (FT, -20 ℃ for 24 h, then at 4 ℃ for 24 h for five cycles) of raw duck preforms. HS-SPME/GC-MS analysis showed that more than thirty volatile flavor compounds identified in roasted ducks fluctuated with freeze-thawing of raw duck preforms, while hexanal, nonanal, 1-octen-3-ol, and acetone could as potential flavor markers. Compared with the unfrozen raw duck preforms (FT-0), repetitive freeze-thawing increased the protein/lipid oxidation and cross-linking of raw duck preforms by maintaining the higher carbonyl contents (1.40 ∼ 3.30 nmol/mg), 2-thiobarbituric acid reactive substances (0.25 ∼ 0.51 mg/kg), schiff bases and disulfide bond (19.65 ∼ 30.65 μmol/g), but lower total sulfhydryl (73.37 ∼ 88.94 μmol/g) and tryptophan fluorescence intensity. Moreover, A lower protein band intensity and a transformation from α-helixes to β-sheets and random coils were observed in FT-3 ∼ FT-5. The obtained results indicated that multiple freeze-thawing (more than two cycles) of raw duck preforms could be detrimental to the flavor quality of the roasted duck due to excessive oxidation and degradation.

Influence of acid-reducing Saccharomyces cerevisiae on the microbial communities and metabolites of Suanyu

The inoculation of S. cerevisiae can address the excessive acidity in Suanyu, but its influence on the microbial community structure has not been documented. In this study, the microbiota succession, and metabolites of Suanyu with the inoculation of acid-reducing S. cerevisiae L7 were explored. The findings revealed that the addition of S. cerevisiae L7 elevated the pH, and decreased the microbial α-diversity. In Suanyu, the dominant bacterial genera were Lactiplantibacillus and Bacillus, while the dominant fungal genera were Meyerozyma and Saccharomyces. Following the inoculation of S. cerevisiae L7, the relative abundance of Lactiplantibacillus decreased from 21 % to 13 %. Meanwhile, the growth of fungi such as Meyerozyma and Candida was suppressed. The rise in Saccharomyces had a significant impact on various pathways related to amino acid and carbohydrate metabolism, causing the accumulation of flavor compounds. This study sheds more lights on the methods for manipulating microbial community structure in fermented food.

Discrimination and characterization of volatile organic compounds and nutritional values of three varieties of chopped pepper seeds

Fermented-chopped pepper is a widely consumed condiment in China due to its attractive flavor. Chopped pepper seed (CPS) is the byproduct generated during the production of chopped pepper and is generally discarded as waste. In this study, the volatile organic compounds (VOCs) and nutritional value of three varieties of CPS were investigated. Results indicated that the nutritional compositions of the three CPS varieties exhibited significant differences. All CPS samples contained 17 amino acids and were rich in fatty acids, with unsaturated fatty acids being predominant and accounting for 79 % of the total fatty acids. A total of 53 VOCs were identified by gas chromatography-ion mobility spectrometry, which could be classified into 9 groups, with aldehydes, esters, and alcohols comprising the three largest groups. The three varieties of CPS had remarkably varied aromas whereas there are five key VOCs (i.e., 2-pentylfuran, methional, ethyl 3-methylbutanoate, dimethyl disulfide, and nonanal) in all CPS samples. Network correlation analysis revealed that VOCs are closely correlated with amino and fatty acids. Thus, this study provides a useful basis for understanding the nutritional values and flavor characteristics of different CPS varieties, which could be used as an ingredient and might have great potential in the food industry.

Formation mechanism of lipid-derived volatile flavor compounds metabolized by inoculated probiotics and their improving effect on the flavor of low-salt dry-cured mackerel

This study aimed to evaluate the contribution and mechanisms of Lactobacillus plantarum and Zygosaccharomyces mellis inoculation to the enhancement of aroma in low-salt dry-cured mackerel (LDCM). Inoculating probiotics significantly improved the LDCM's aroma, with mixed probiotics showing a superior effect. The contents of lipid-derived volatile flavor compounds (LVFCs), free fatty acid contents, and key enzyme activities significantly increased (p < 0.05) in probiotic-treated groups. The dominant species in the probiotics-treated groups were the inoculated Lactobacillus plantarum and Zygosaccharomyces mellis, which were the main producer of metabolic enzymes for the generation of LVFCs. Lactobacillus plantarum performed well in lipid hydrolysis and aldehydes reduction, while Zygosaccharomyces mellis played a main role in aldehyde production.

Effect of Lactobacillus helveticus IMAUJBH1 on fat and volatile flavor substances in fermented mutton sausages

The decomposition and oxidation of fat is essential for the formation and quality of the unique flavor of sausage. To explore the effect of lactic acid bacteria on fat decomposition and oxidation in fermented sausage, free fatty acids and volatile flavor compounds were determined by gas chromatography (GC) and headspace solid-phase microextraction (HS-SPME)-GC-MS, respectively. The results showed that the addition of Lactobacillus helveticus IMAUJBH1 inhibited fat peroxidation and relatively increased the proportion of monounsaturated fatty acids. A total of 47 volatile flavor compounds were detected, including aldehydes, esters, alcohols, and ketones. The content of substances such as hexanal, heptanal, nonanal and 1-octene-3-ol related to lipid oxidation was significantly reduced. The results obtained in this study show that the strain can further affect the flavor of the product by inhibiting the formation of lipid oxidation or peroxide flavor substances to a certain extent.

Effect of L. Plantarum Y279 and W. Cibaria Y113 on microorganism, lipid oxidation and fatty acid metabolites in Yu jiaosuan, A Chinese tradition fermented snack

Fatty acids are one of the main sources of flavour in fermented Yu jiaosuan (YJS) in southwest China. Bacilli (50.18 %) and Oxyphotobacteria (32.70 %) were the dominant class. Lactiplantibacillus (40.51 %) and Weissella (20.43 %) were the dominant species in the inoculated fermented group (HY). The peroxide value (ZY: 0.025 g/100 g, HY: 0.016 g/100 g) and lipoxygenase (LOX) (ZY: 5.7654 U/min·g, HY: 3.3856 U/min·g) in the HY group were significantly lower compared with the natural fermentation group (ZY), while acid lipase activity (ZY: 0.3184 U/h·g, HY: 0.7075 U/h·g) and neutral lipase activity (ZY: 12.65443 U/h·g, HY: 20.25142 U/h·g) were significantly higher than the control sample. Totally 40 differential fatty acid metabolites were screened. Arachidonic acid metabolism, unsaturated fatty acid biosynthesis and linoleic acid metabolism were potential metabolic pathways. Seven major bacterial species were closely associated with 15 differential fatty acid. This study contributes to the targeted production of fatty acid functional active substances of YJS.

Mechanism of salt effect on flavor formation in lightly-salted large yellow croaker by integrated multiple intelligent sensory and untargeted lipidomics analyses

Salt has a great influence on food flavor formation. In this study, electronic tongue and nose, gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry, and lipid oxidation levels were used to investigate the influence of different NaCl concentrations on the flavor formation of lightly salted large yellow croaker. The results showed that salt improves the sensory characteristics of the product. Hexanal, 2,5-octanedione, octanal, 1-octen-3-ol, nonanal, and heptanal were key flavor compounds. Phospholipids containing 18-carbon fatty acids are major flavor precursor substances. The TBARS values in samples increase with the increase of salt levels significantly (p < 0.05). Products marinated in 6% NaCl showed the highest lipase activity. Thus, NaCl promotes the hydrolysis and oxidation of phospholipids by increasing lipase activity to produce key flavor substances. This study provides valuable insights into the effects of NaCl on flavor formation, which may help to regulate the flavor of salt-reduced food.

Flavor formation of tilapia byproduct hydrolysates in Maillard reaction

The Maillard reaction (MR) of tilapia byproduct protein hydrolysates was investigated for the use of byproduct protein as a food ingredient and to mask its fishy odor and bitter flavor. The flavor differences in tilapia byproduct hydrolysates before and after the MR were analyzed to explore the key flavor precursor peptides and amino acids involved in MR. The results suggested that eight key volatile substances, including 2,5-dimethylpyrazine, 2-pentylfuran, hexanal, octanal, nonanal, (E)-2-decenal, decanal, and 1-octen-3-ol contributed most to the MR products group (ROAV > 1). Ten volatile compounds, including 1-octen-3-ol, hexanal, 2-pentylfuran, 2,5-dimethylpyrazine, methyl decanoate, and 2-octylfuran, were the flavor markers that distinguished the different samples (VIP > 1). The four most consumed peptides were VAPEEHPTL, GPIGPRGPAG, KSADDIKKAF, and VWEGQNIVK. Umami peptides and bitter free amino acids (FAAs) were the key flavor precursor peptide and FAAs, respectively. Overall, the hydrolysates of tilapia byproducts with flavor improved by MR are a promising strategy for the production of flavorings.

Comparative analysis of key precursors and metabolites involved in flavor formation of different rapid-fermented Chinese fish sauces based on untargeted metabolomics analysis

Our study aimed to characterize the flavor precursors and metabolite profiles during fermentation of three rapid-fermented fish sauces (koji fermentation (YQ), insulation fermentation with koji (BWQ) and insulation fermentation with enzyme (BWE)) by a comparative metabolomics analysis. The total amount of free amino acids and free fatty acids in BWQ and BWE samples was significantly higher than that in YQ sample during fermentation, and C16:0, C22:6, C18:1, C14:1, C18:0 and C20:5 were deemed as key flavor precursors of three fish sauces. We identified 51, 47 and 45 differential metabolites as crucial components in YQ, BWE and BWQ samples. Specific metabolites in three samples were mainly related to amino acid metabolism, especially histidine, cysteine and methionine metabolism. Furthermore, 5 bacteria genera exhibited positive impacts on the generation of various flavor-related metabolites. This study provides a theoretical basis for targeted control of flavor and quality in the production of rapid-fermented fish sauce.

The contribution of inoculated probiotics to increased protein-derived volatile flavor compounds

This study aimed to evaluate the contribution and mechanisms of Lactobacillus plantarum and Zygosaccharomyces mellis inoculation to the enhancement of protein-derived volatile flavor compounds (PVFCs) in low-salt dry-cured mackerel (LDCM). The contents of PVFCs (3-methylbutanal and phenylacetaldehyde), intermediates (α-ketoisocaproate and phenylpyruvic acid), precursor (α-ketoisocaproate and phenylpyruvic acid), and key enzyme activities (protease and transaminase) significantly increased (p < 0.05) in probiotic-treated groups. The dominant species in the probiotics-treated groups were the inoculated Lactobacillus plantarum and Zygosaccharomyces mellis, which were the main producer of key enzymes for the generation of PVFCs. Lactobacillus plantarum performed well in protein degradation and amino acid transamination, resulting in generating more 3-methylbutanal and phenylacetaldehyde, while Zygosaccharomyces mellis played a main role in phenylethanol production. The synergistic action of Lactobacillus plantarum and Zygosaccharomyces mellis could promote the formation of 3-methyl-1-butanol.

Transforming the fermented fish landscape: Microbiota enable novel, safe, flavorful, and healthy products for modern consumers

Regular consumption of fish promotes sustainable health while reducing negative environmental impacts. Fermentation has long been used for preserving perishable foods, including fish. Fermented fish products are popular consumer foods of historical and cultural significance owing to their abundant essential nutrients and distinct flavor. This review discusses the recent scientific progress on fermented fish, especially the involved flavor formation processes, microbial metabolic activities, and interconnected biochemical pathways (e.g., enzymatic/non-enzymatic reactions associated with lipids, proteins, and their interactions). The multiple roles of fermentation in preservation of fish, development of desirable flavors, and production of health-promoting nutrients and bioactive substances are also discussed. Finally, prospects for further studies on fermented fish are proposed, including the need of monitoring microorganisms, along with the precise control of a fermentation process to transform the traditional fermented fish to novel, flavorful, healthy, and affordable products for modern consumers. Microbial-enabled innovative fermented fish products that consider both flavor and health benefits are expected to become a significant segment in global food markets. The integration of multi-omics technologies, biotechnology-based approaches (including synthetic biology and metabolic engineering) and sensory and consumer sciences, is crucial for technological innovations related to fermented fish. The findings of this review will provide guidance on future development of new or improved fermented fish products through regulating microbial metabolic processes and enzymatic activities.

Flavor Formation in Dry-Cured Fish: Regulation by Microbial Communities and Endogenous Enzymes

Dried salted fish is a traditional dry-cured fish that is sprinkled with salt before the curing process. With a unique flavor as well as diverse varieties, dry-cured fish is popular among consumers worldwide. The presence of various microbial communities during the curing process leads to numerous metabolic reactions, especially lipid oxidation and protein degradation, which influence the formation of flavor substances. However, during industrial curing, the quality of dry-cured fish is difficult to control, leading to the formation of products with diverse flavors. This review describes the curing process of dried salted fish, the key microorganisms involved in the curing process of typical dried salted fish products at home and abroad, and the correlation between biological metabolism and flavor formation and the underlying mechanism. This review also investigates the prospects of dried salted fish products, proposing methods for the analysis of improved curing processes and the mechanisms of dried salted fish. Through a comprehensive understanding of this review, modern production challenges can be addressed to achieve greater control of microbial growth in the system and improved product safety. In addition to advancing our understanding of the processes by which volatile flavor compounds are formed in conventional dry-cured fish products, we expect that this work will also offer a theoretical framework for enhancing their flavor in food processing.

Effects of cold storage time on the quality and active probiotics of yogurt fermented by Bifidobacterium lactis and commercial bacteria Danisco

In this study, the commercial bacteria Danisco and Bifidobacterium lactis were used to ferment soy yogurt, and then the quality of yogurt and the number of active probiotics in yogurt during storage were investigated. The results showed that the total number of viable bacteria in soy yogurt increased first and then decreased, but all of them met the standard for the number of viable bacteria in probiotic foods. The content of protein, lipid, and total sugar in soy yogurt decreased gradually with the extension of storage time. The texture, water holding capacity, and rheological properties of soy yogurt were improved within 0-10 days, and there was no significant change after 15 days. However, brightness and whiteness of yogurt were significantly reduced. Based on realizing the reuse of soy whey, this study provided a theoretical basis for the research of the shelf life of soy yogurt. PRACTICAL APPLICATION: This study developed a soy yogurt with good quality and provided a theoretical basis for the study of the shelf life of soy yogurt. In addition, some technical support was provided for the reuse of soy whey.

Characterization of a fermented dairy, sour cream: Lipolysis and the release profile of flavor compounds

Lipolysis and flavor development during fermentation of sour cream were studied by evaluating the physicochemical changes, sensory differences and volatile components. The fermentation caused significant changes in pH, viable count and sensory evaluation. The peroxide value (POV) decreased after reaching the maximum value of 1.07 meq/kg at 15 h, while thiobarbituric acid reactive substances (TBARS) increased continuously with the accumulation of secondary oxidation products. The Free fatty acids (FFAs) in sour cream were mainly myristic, palmitic and stearic. GC-IMS was used to identify the flavor properties. A total of 31 volatile compounds were identified, among which the contents of characteristic aromatic substances such as ethyl acetate, 1-octen-3-one and hexanoic acid were increased. The results suggest that lipid changes and flavor formation in sour cream are influenced by fermentation time. Furthermore, flavor compounds may be related to lipolysis such as 1-octen-3-one and 2- heptanol were also observed.

Application and Effect of Pediococcus pentosaceus and Lactiplantibacillus plantarum as Starter Cultures on Bacterial Communities and Volatile Flavor Compounds of Zhayu, a Chinese Traditional Fermented Fish Product

Zhayu is a type of traditional fermented fish product in China that is made through the fermentation of salted fish with a mixture of cereals and spices. Inoculation fermentation was performed using Pediococcus pentosaceus P1, Lactiplantibacillus plantarum L1, and a mixture of two strains, which were isolated from cured fish in Hunan Province. Compared with the natural fermentation, inoculation with lactic acid bacteria (LAB) accelerated the degradation of myosin and actin in Zhayu, increased the trichloroacetic acid (TCA)-soluble peptide content by about 1.3-fold, reduced the colony counts of Enterobacteriaceae and Staphylococcus aureus by about 40%, and inhibited their lipid oxidation. In the texture profile analysis performed, higher levels of hardness and chewiness were observed in the inoculation groups. In this study, the bacterial community and volatile flavor compounds were detected through 16S high-throughput sequencing and headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). Inoculation with L. plantarum L1 reduced around 75% abundance of Klebsiella compared with the natural fermentation group, which was positively correlated with 2,3-Butanediol, resulting in a less pungent alcohol odor in Zhayu products. The abundances of 2-pentylfuran and 2-butyl-3-methylpyrazine were increased over threefold in the L1 group, which may give Zhayu its unique flavor and aroma.

Effects of vegetable oil and ethylcellulose on the oleogel properties and its application in Harbin red sausage

The effects of ethylcellulose (EC) concentration (6-12 %) and types of vegetable oil (sunflower, peanut, corn, and flaxseed oils) on the color, hardness, oil loss, lipid oxidation, and rheology property of oleogels were investigated in this study. Peanut oil (PO) oleogel was selected to replace pork fat partially in Harbin red sausage. Meanwhile, the fatty acid profile, texture, and sensory attributes of the reformulated sausages were analyzed. Oleogels formulated with higher EC concentration had higher brightness and hardness, a higher degree of lipid oxidation, and greater storage (G') and loss (G'') moduli. Oleogels formulated with PO had lower oil loss, flaxseed oil oleogel had higher hardness. Corn oil and PO oleogels had a lower level of lipid oxidation. The texture, lipid oxidation, and sensory attributes of the reformulated sausages, in which 10-30 % pork fat was replaced with PO oleogel, did not significantly differ from those without oleogel replacement. Meanwhile, the reformulated sausages had a healthier fatty acids profile and higher nutritional value.

Unraveling the microbial succession during the natural fermentation of grass carp and their correlation with volatile flavor formation

Complex microbial communities contribute significantly to the flavor formation of traditional fermented fish products. However, the relationship between microorganisms and flavor formation in traditional fermented grass carp products is still unclear. In this study, the diversity and succession of microbial communities and the variation of volatile compounds during natural fermentation of grass carp were analyzed using high-throughput sequencing of 16S rRNA and headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS), respectively. The core functional microorganism and key volatile compounds were identified, and their potential relationship was revealed using a correlation network model analysis. The microbial community analysis result showed that the microbial diversity during natural fermentation of grass carp decreased markedly with increasing fermentation time, and Lactiplantibacillus, Staphylococcus, and Enterobacter were the dominant genera in naturally fermented grass carp. HS-SPME-GC-MS analysis result showed that 45 volatile compounds were identified from fermented samples, among which 13 compounds (e.g., hexanal, heptanal, nonanal, decanal, 3-octanone, 3-methyl-1-butanol, 1-hexanol, 1-heptanol, 1-octen-3-ol, 1-octanol, ethyl acetate, 3-methyl-1-butanol acetate, and 2-methoxy-4-vinylphenol) were identified as the key volatile compounds. Additionally, the correlation network model analysis result revealed that Lactiplantibacillus showed significantly positive correlations with most of the key volatile compounds, making an important contribution to the formation of volatile flavor in naturally fermented grass carp. This study may lead to an understanding of the role of core functional microorganisms in the formation of volatile flavor during the natural fermentation of grass carp and provide some theoretical guidance for the industrial production of high-quality fermented grass carp products.

Changes of Physicochemical Characteristics and Flavor during Suanyu Fermentation with Lactiplantibacillus plantarum and Saccharomyces cerevisiae

This study investigates the changes of the physicochemical characteristics and flavor of fermented Suanyu (Chinese fermented fish) during fermentation with Lactiplantibacillus plantarum (L. plantarum) and Saccharomyces cerevisiae (S. cerevisiae). The related indicators, including pH, water activity (Aw), volatile base nitrogen (TVB-N), thiobarbituric acid (TBA), free amino acids (FAAs), microbial community, and volatile compounds were determined. L. plantarum fermentation samples (LP) and natural fermentation samples (NF) were used as controls. The pH and Aw of three groups of Suanyu samples decreased continuously through the entire fermentation process. Meanwhile, the TVB-N of three groups of samples increased gradually, while TBA first increased and then decreased. Notably, the pH, Aw, TVB-N, and TBA of MF group samples (inoculated L. plantarum and S. cerevisiae) were significantly lower than the NF group samples. In addition, both TVB-N and TBA of the MF group samples were lower than those of the LP group samples during fermentation, suggesting that combined fermentation could inhibit the growth of undesirable microorganisms more effectively. Lactobacillus were the main bacterial genus of the three group fermented samples during fermentation, and combined fermentation could promote the growth of Lactobacillus more significantly. In addition, the highest content of umami (145.16 mg/100 g), sweet amino acids (405.75 mg/100 g), and volatile compounds (especially alcohols and esters) were found in MF group samples, followed by the NF and LP group samples, indicating that combined fermentation could give Suanyu a better flavor quality. This study may provide a theoretical basis for the industrial production of fermented fish products and the improvement of fermentation technology.

Effects of Sous Vide Cooking on the Physicochemical and Volatile Flavor Properties of Half-Shell Scallop (Chlamys farreri) during Chilled Storage

This study explored the effects of sous vide (SV) cooking treatments on the physicochemical quality and volatile flavor of half-shell scallop (Chlamys farreri) during 30 d of chilled storage. The vacuum-packed scallop samples were cooked at 70 °C (SV-70) and 75 °C (SV-75) and maintained for 30 min. The samples were compared with the positive control (cooked at 100 °C for 10 min, CK). The results indicate that the total volatile basic nitrogen (TVBN), pH, texture, and malondialdehyde (MDA) content gradually increased, while the myofibrillar protein (MP) extraction rate of the CK, SV-70, and SV-75 samples significantly decreased with increasing chilled storage time. Significantly, the SV cooking treatments maintained a much higher water-holding capacity of scallop muscle, compared with the conventional cooking process at 100 °C. Additionally, the SV-75 cooking treatment maintained relatively stable TVBN, pH, and MDA content, springiness, and shearing force properties of scallop samples, especially during 0-20 d of storage. Volatile flavor analysis showed that a total of 42 volatile organic compounds (VOCs) were detected in the scallop samples, and there were no considerable differences in these VOCs between the CK and SV-75 cooked samples (0 d). Overall, the SV cooking treatments effectively maintained acceptable and stable physicochemical and volatile flavor properties of half-shell scallop samples during chilled storage.

Flavor formation based on lipid in meat and meat products: A review

Meat product is popular throughout the world due to its unique taste. Flavor is one of the most important quality characteristics of meat products and also is a key influencing factor in the overall acceptability of meat products. The flavor of meat products is formed by precursors undergoing a series of complex reactions. During meat product processing, lipids are hydrolyzed by lipase to produce flavor precursors such as free fatty acid, then further oxidized to form volatile flavor compounds. This review summarizes lipolysis, lipid oxidation, and interaction of lipid with Maillard reaction and amino acid during meat products processing and storage as well as influencing factors on lipid degradation including raw meat (source of meat, feeding pattern, and castration), processing methods (thermal processing, nonthermal processing, salting, and fermentation) and additives. Meanwhile, the volatile compounds produced by lipids in meat products including aldehydes, alcohols, ketones, and hydrocarbons are summed up. Analytical methods of volatile compounds and the application of lipidomics analysis in mechanisms of flavor formation of meat products are also reviewed. PRACTICAL APPLICATIONS: Flavor is one of the most important quality characteristics of meat products, which influences the acceptability of meat products for consumption. Lipids play an important role in the flavor formation of meat products. Understanding the relationship between flavor compounds and changes in lipid compositions during the processing and storage of meat products will be helpful to control the quality of meat products.

Effect of High Hydrostatic Pressure on the Metabolite Profile of Striped Prawn (Melicertus kerathurus) during Chilled Storage

A variety of metabolites contribute to the freshness and taste characteristics of seafood. This study investigated the effects of high hydrostatic pressure (HHP; 400, 500, and 600 MPa) for 10 min) on the metabolome of striped prawn during chilled storage, in relation to microorganisms' development. All treated samples showed lower viable counts throughout storage compared to the untreated counterparts. The limit of acceptability from a microbiological point of view was extended from 9 to as many as 35 days by 600 MPa treatment. Metabolites were quantified by ¹H-NMR through a targeted-untargeted metabolomic approach. Molecules linked to nucleotides' degradation and amines' anabolism suggested an overall freshness improvement granted by HHP. Notably, putrescine and cadaverine were detected only in untreated prawn samples, suggesting the inactivation of degradative enzymes by HHP. The concentration of molecules that influence umami perception was significantly elevated by HHP, while in untreated samples, the concentration of molecules contributing to a sour taste gradually increased during storage. As metabolomics was applied in its untargeted form, it allowed us to follow the overall set of metabolites related to HHP processing and storage, thus providing novel insights into the freshness and taste quality of striped prawn as affected by high hydrostatic pressure.

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).

Effect of CO2 on the spoilage potential of Shewanella putrefaciens target to flavour compounds

To investigate the regulation mechanism of CO₂ (0% CO₂, 20% CO₂, 60% CO₂, and 100% CO₂) on the spoilage potential of S. putrefaciens target to flavour compounds, the metabolic activity of S. putrefaciens and the changes in flavour compounds extracted from inoculated large yellow croakers were evaluated. Results showed that CO₂ significantly reduced biofilm formation capacity and suppressed synthesis of intracellular adenosine triphosphate (ATP). The production of unpleasant flavour compounds, such as total volatile basic nitrogen (TVB-N), trimethylamine (TMA), inosine (HxR), hypoxanthine (Hx), histidine, lysine, histamine, putrescine, 1-octen-3-ol, hexanal and benzaldehyde, was inhibited by CO₂. The hydrolysis and oxidation of lipid in CO₂-treated samples were alleviated and unsaturated fatty acids (UFAs) were in a higher percentage. In summary, CO₂ efficiently reduced the spoilage potential of S. putrefaciens and contributed to better flavour quality of samples during 4 °C storage. A more effective inhibition by 100% CO₂ was observed.

Whole-Genome Sequencing of a Potential Ester-Synthesizing Bacterium Isolated from Fermented Golden Pomfret and Identification of Its Lipase Encoding Genes

Microbial ester synthases are regarded as valuable catalysts in the food industry. Here, one strain of Acinetobacter venetianus with ester synthase-production capacity, SCSMX-3, was isolated from traditional fermented golden pomfret. It exhibited good growth in mesophilic, low salt, and slightly alkaline environments. The ester synthase produced by SCSMX-3 displayed maximum activity at pH 8.0 and 35 °C. Genome sequencing revealed that the strain contains one circular chromosome of 336313 bp and two circular plasmids (plasmid A-14424 bp and plasmid B-11249 bp). Six CRISPR structures enhance the genomic stability of SCSMX-3 and provide the opportunity to create new functional strains. Gene function analysis indicated that SCSMX-3 produces the necessary enzymes for survival under different conditions and for flavor substance synthesis. Furthermore, 49 genes encoding enzymes associated with lipid metabolism, including three triacylglycerol lipases and two esterases, were identified through the NCBI Non-Redundant Protein Database. The lipase encoded by gene0302 belongs to the GX group and the abH15.02 (Burkholderia cepacia lipase) homolog of the abH15 superfamily. Our results shed light on the genomic diversity of and lipid metabolism in A. venetianus isolated from fermented golden pomfret, laying a foundation for the exploration of new ester synthases to improve the flavor of fermented fish products.

Paradoxical effects of lipolysis on the lipid oxidation in meat and meat products

Lipolysis in meat and meat products is a phenomenon involving hydrolysis of lipids, notably via enzymatic catalysis that takes place even postmortem. During refrigerated and frozen storage of meat, in particular fish, endogenous lipolytic enzymes actively degrade triacylglycerols and phospholipids resulting in accumulation of free fatty acids and other hydrolytic products. A classical conjecture suggests that lipolysis enhances lipid oxidation which is involved in quality deterioration of fresh meat and, to some degrees, flavor development of certain meat products. Recent studies (<5 years) have shown that under some circumstances, lipolysis of certain lipolytic enzymes can inhibit lipid oxidation in muscle models, which provides more insight in lipid oxidation mechanisms in muscle matrices as well as implies potential strategies for improving meat quality. This review will discuss such paradoxical effects and potential mechanisms of lipolysis on lipid oxidation in meat and meat products.

Screening of Lactiplantibacillus plantarum with High Stress Tolerance and High Esterase Activity and Their Effect on Promoting Protein Metabolism and Flavor Formation in Suanzhayu, a Chinese Fermented Fish

In this study, three Lactiplantibacillus plantarum, namely 3-14-LJ, M22, and MB1, with high acetate esterase activity, acid, salt, and high-temperature tolerance were selected from 708 strains isolated from fermented food. Then, L. plantarum strains MB1, M22, and 3-14-LJ were inoculated at 107 CFU/mL in the model and 107 CFU/g in actual Suanzhayu systems, and the effects during fermentation on the physicochemical properties, amino acid, and volatile substance were investigated. The results showed that the inoculated group had a faster pH decrease, lower protein content, higher TCA-soluble peptides, and total amino acid contents than the control group in both systems (p < 0.05). Inoculation was also found to increase the production of volatile compounds, particularly esters, improve the sour taste, and decrease the bitterness of the product (p < 0.05). L. plantarum M22 was more effective than the other two strains in stimulating the production of isoamyl acetate, ethyl hexanoate, and ethyl octanoate. However, differences were discovered between the strains as well as between the model and the actual systems. Overall, the isolated strains, particularly L. plantarum M22, have good fermentation characteristics and have the potential to become excellent Suanzhayu fermenters in the future.

Improving the Flavor of Fermented Sausage by Increasing Its Bacterial Quality via Inoculation with Lactobacillus plantarum MSZ2 and Staphylococcus xylosus YCC3

This research aims to investigate the effects of Staphylococcus xylosus YCC3 (Sx YCC3) and Lactobacillus plantarum MSZ2 (Lp MSZ2) on lipid hydrolysis and oxidation, the bacterial community’s composition, and the volatile flavor compounds in fermented sausage. The bacterial community was examined by plate counting and high-throughput sequencing. Differential flavor compounds in non-inoculated and inoculated sausages were identified by principal component analysis (PCA) and orthogonal partial least squares discrimination analysis (OPLS-DA). The results showed that the free fatty acid (FFA) content was increased after inoculating with Sx YCC3 or Lp MSZ2. The pH, peroxide value (POV), thiobarbituric acid reactive substances (TBARS) value, lipoxygenase activity, and the counts of Enterobacteriaceae were lower in the inoculated sausage than in the non-inoculated sausage. The bacterial inoculation enhanced the competitiveness of Staphylococcus and Lactobacillus and restricted the growth of unwanted bacteria. The OPLS-DA revealed that (Z)-hept-2-enal, (E)-2-octenal, 1-nonanal, octanal, and 1-octen-3-ol were common differential flavor compounds that were found in the inoculated sausages but were not found in the non-inoculated sausages. A positive correlation was observed between the differential flavor compounds and the relative abundance of Staphylococcus or Lactobacillus, or the FFA content. Our results indicated that inoculation with Sx YCC3 or Lp MSZ2 can improve fermented sausages’ flavor by enhancing their bacterial quality and increasing their FFA content.

Physicochemical properties and adaptability of amine-producing Enterobacteriaceae isolated from traditional Chinese fermented fish (Suan yu)

The formation of biogenic amines (BAs) is an important potential danger in traditional fermented fish (Suan yu), and Enterobacteriaceae play an important role in the formation of BAs. The amine production abilities of 97 strains of Enterobacteriaceae screened from traditional fermented Suan yu were analyzed by reversed-phased high-performance liquid chromatography (HPLC). The genotypic diversity of amino acid decarboxylase on 23 strains of high-yield BAs was verified by PCR. Enterobacteriaceae with the highest production of amines was determined by analysis of the effects of physicochemical factors (pH, NaCl, temperature, and aerobic/anaerobic) on BA production and principal component analysis (PCA). The adaptability of the strains was examined using surimi simulation fermentation system, and the correlations among the indicators were analyzed using Cytoscape. Results showed that 97 strains of Enterobacteriaceae had strong amine-producing ability. Furthermore, 23 strains producing high yields of putrescine, cadaverine, and histamine were identified. All of the strains carried Idc, odc, speA, speB, and adiA, and five strains carried hdc. pH mainly affected the BA production of amine-producing bacteria. Three strains (Enterobacter asburiae 26C3, Klebsiella pneumoniae 47C2, and Morganella morganii 45C3) had the best amine-producing ability and used as the inoculated group. In this group, the values of BA (228.70-290.05 mg/kg) and the total volatile base nitrogen (TVB-N, 173.87-221.87 mg/100 g) exceeded the limit. Moreover, myofibrillar protein degradation was significant as indicated by the sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis and decreased FAA content. Cytoscape software and principal component analysis (PCA) indicated that Enterobacteriaceae and pH were related to BA formation in Suan yu. These results provide a theoretical basis for controlling the BA of fermented fish products.

Analysis of the relationship between microorganisms and flavour development in dry-cured grass carp by high-throughput sequencing, volatile flavour analysis and metabolomics

Complex microbial community plays an important role for flavor formation in traditional dry-cured grass carp. To investigate the correlation between microorganisms and flavour development, the bacterial diversity and flavour quality of dry-cured fish at different stages of fermentation were analysed using high-throughput sequencing, volatile flavour analysis and metabolomics. Cobetia, Staphylococcus and Ralstonia were the dominant genera in dry-cured fish, with relative abundances of 37.78%, 34.46% and 3.2%, respectively. The flavour of dry-cured fish samples varied as the abundance of aldehydes, alcohols, small peptides, FAAs and carboxylic acids showed a great increase during fermentation. Moreover, there were significant correlations (P < 0.05) between specific microorganisms and volatile indicators, as well as flavour metabolites. Staphylococcus, as the dominant bacterial genus, is involved in the mechanism of flavour formation in dry-cured fish during fermentation. This information is useful for elucidating the mechanism of flavour formation in dry-cured fish.

Effects of Lactobacillus plantarum C7 and Staphylococcus warneri S6 on flavor quality and bacterial diversity of fermented meat rice, a traditional Chinese food

Fermented meat rice (FMR) is a traditional Chinese fermented food with special flavor and abundant microorganisms. Lactobacillus and Staphylococcus species have been found to be excellent strains in FMR during fermentation. However, their roles in FMR flavor formation remain yet to be elucidated. Here, we investigated the correlation between physicochemical properties and volatile flavor components, as well as the microbial community during FMR fermentation. First, we determined pH, total titratable acids (TTA), proteins, total lipids, organic acids, free amino acids (FAAs), and volatile flavor compounds (VFCs). With increasing fermentation time, inoculation with Lactobacillus plantarum C7+ Staphylococcus warneri S6 (LP + SW) accelerated the decrease in pH, increased TTA, and reduced protein and total lipid content of FMR. In addition, LP + SW inoculation resulted in significantly (P < 0.05) higher contents of β-eudesmol, nerolidol, ethyl caproate, citronellal, lactic acid, and most FAAs (aspartic acid, glutamic acid, alanine, and lysine) in FMR compared to natural fermentation. Second, inoculated fermentation promoted the growth of Lactobacillus plantarum and/or Staphylococcus warneri and inhibited the growth of some potentially pathogenic microorganisms such as Acinetobacter and Enhydrobacter. Lactobacillus and Staphylococcus were found to be highly correlated with the physicochemical properties and VFCs (P < 0.05) of FMR as indicated by redundancy analysis (RDA) and partial least squares (PLS, VIP > 1.0) analysis. Finally, Spearman's correlation (| r | ≥ 0.7, P < 0.05) analysis of SPSS was visualized by the Cytoscape software. The findings suggest that inoculation with L. plantarum C7 and/or S. warneri S6 can significantly improve the flavor quality of FMR.

Lipase Addition Promoted the Growth of Proteus and the Formation of Volatile Compounds in Suanzhayu, a Traditional Fermented Fish Product

This work investigated the effect of lipase addition on a Chinese traditional fermented fish product, Suanzhayu. The accumulation of lactic acid and the decrease of pH during the fermentation were mainly caused by the metabolism of Lactobacillus. The addition of lipase had little effect on pH and the bacterial community structure but promoted the growth of Proteus. The addition of lipase promotes the formation of volatile compounds, especially aldehydes and esters. The formation of volatile compounds is mainly divided into three stages, and lipase had accelerated the fermentation process. Lactobacillus, Enterococcus and Proteus played an important role not only in inhibition of the growth of Escherichia-Shigella, but also in the formation of flavor. This study provides a rapid fermentation method for the Suanzhayu process.

The relationship between flavor formation, lipid metabolism, and microorganisms in fermented fish products

Traditional fermented fish products are favored due to their unique flavors. The fermentation process of fish is accompanied by the formation of flavor substances through a complex metabolic reaction of microorganisms, especially lipolysis and lipid oxidation. However, it is difficult to precisely control the reaction of microorganisms during the fermentation process in modern industrial production, and fermented fish products have lost their traditional characteristic flavors. The purpose of this review is to summarize the different kinds of fermented fish, core microorganisms in it, and flavor formation mechanisms, providing guidance for industrial cultural starters. Future research on the flavor formation mechanism is necessary to confirm the relationship between flavor formation, lipid metabolism, and microorganisms to ensure stable flavor and safety, and to elucidate the mechanism directly toward industrial application.