Contribution of Mixed Starter Cultures to Flavor Profile of Suanyu - A Traditional Chinese Low-Salt Fermented Whole Fish

Comprehensive insights into the mechanism of flavor formation in mandarin fish (Siniperca chuatsi) with inoculated fermentation

The inoculated fermentation is an effective way to shorten fermentation time and improve the flavor quality in fermented food. Therefore, this work aims to analyze the difference between traditional and inoculated fermentation, and explore the mechanism of flavor formation in mandarin fish during fermentation. Results showed that a total of 67 volatile compounds were detected, and 13 key flavor compounds were identified in fermented mandarin fish. Inoculation promotes the oxidation and hydrolysis of fatty acids, thus forming more aldehydes and alcohols. Moreover, inoculated fermentation inhibited the growth of Enterococcus, Carnobacterium and Morganella, thereby reducing indole content. In addition, inoculation increased the taste activity values of Glu, Gly and Ala, which improved umami taste and sweet taste of fermented mandarin fish. In short, the mixed inoculation shortened the fermentation time from 12d to 8d, which improved the flavor quality of fermented mandarin fish.

Changes in microbial composition during flue-cured tobacco aging and their effects on chemical composition: a review

The aging is a crucial stage in tobacco processing, which contributes to the reduction of impurities and irritation, and the stabilization of the internal chemical composition of the leaves. However, it usually takes a long time (2-3 years) for the nature aging process of tobacco (20 °C-30 °C, relative humidity of 65-75%), which seriously affects the processing efficiency of tobacco. Microorganisms play an important role in the change of chemical composition and characteristic aromatic substances of tobacco. Acinetobacter, Sphingomonas Aspergillus, Bacilli, and Pseudonocardia is the main microorganism in the aging process of tobacco, which increasing the aromatic substances (such as alcohols, ketones, and esters) by the action of the enzymes and metabolites, and degrade the harmful components (such as alkaloid, nicotine and nitrosamines in tobacco). This review systematically summarizes recent advancements in understanding the primary microbial composition and the changes in chemical composition during tobacco aging. This knowledge is helpful for screening functional strains, and control the process of tobacco aging by the inoculation of these strains.

The Formation and Change of Volatile Flavor Compounds During the Cooking of Sheep Bone Soup

To investigate the formation of flavor compounds in sheep bone soup, E-nose, gas chromatograph (GC), and gas chromatography-mass spectrometry (GC-MS) were used to determine the changes in lipid oxidation, Maillard reaction, and volatile flavor compounds during the slow cooking process of 4 h. The thiobarbituric acid reactive substances (TBARS) value began to increase significantly (p < 0.05) after 2 h of cooking, reaching its peak in the third hour before significantly decreasing. The intensity of the Maillard reaction significantly increased after 2 h of cooking and subsequently stabilized. Thirty-nine flavor compounds were identified, primarily comprising aldehydes, ketones, alcohols, esters, aromatic compounds, and heterocyclic compounds. The formation of volatile flavor compounds in sheep bone soup was associated with lipid oxidation, particularly the oxidation of unsaturated fatty acids, and the Maillard reaction. Lipid oxidation produced a large number of volatile flavor compounds, such as aldehydes and ketones. The Maillard reaction gave sheep bone soup a certain flavor. Aldehydes were mostly influenced by cooking time, becoming the main flavor compounds in the bone soup after 2.5 h of cooking, accounting for more than half of the total volatile flavor compounds. The highest content and richest profile of volatile flavor compounds were obtained in the soup cooked for 2.5 h and 3 h. This study provides a theoretical basis for the flavor regulation of sheep bone soup.

The effects of fermented sausage quality driven by reduction of NaCl: Investigation into the microbial community and flavor profiles

The primary objective of this study was to evaluate the impact of NaCl reduction (2.50 %, 2.25 %, 2.00 %, 1.75 %, and 1.50 %) on the physicochemical characteristics, microbial communities, flavor profile, and sensory characteristics of fermented sausage. The water activity increased with the reduction of the NaCl content from 2.50 % to 1.50 %, while the pH value, chewiness, and hardness decreased. High-throughput sequencing results showed that Staphylococcus saprophyticus, Staphylococcus kloosii, Latilactobacillus sakei, and Enterococcus pseudoavium were the dominant bacteria at the end of fermentation, and the 2.00 % NaCl treatment exhibits the highest bacterial diversity. A total of 32 volatile compounds were identified, of which there were 16 main volatile compounds. Sensory evaluation showed lower scores for chewiness, color, and flavor in sausages with less than 1.75 % NaCl. Furthermore, the correlation analysis showed that four bacterial species (Lb. sakei, S. saprophyticus, S. kloosii, and E. pseudoavium) were positively correlated with the major volatile compounds such as nonanal, ethyl propionate, ethyl hexanoate, and 1-hepten-3-one. Overall, it can be concluded that when NaCl content is reduced to less than 1.75 %, compensatory measures are needed to achieve better quality and flavor in fermented sausage. This study offers a thorough understanding of the association between bacterial communities and volatile flavors in low-salt fermented sausage.

Formation of volatile compounds in salt-mediated naturally fermented cassava

Cassava is a starchy staple typically consumed in tropical countries; however, its high moisture content renders it susceptible to post-harvest deterioration. Fermentation has been used to improve shelf-life, functional properties, nutrient bioavailability, minimize toxic compounds, and alter aroma. In this study, the effect of added salt (5-25 %) on the pH, titratable acidity (TTA), and volatile compounds (VOCs) in cassava fermented was investigated. A sharp reduction in pH from 6.98 to 6.20 to 4.81-4.00 and concomitant increase in TTA (0.027-0.297 %) was observed in all the samples on day 2 except the 25 % added salt ferments. The 32 VOCs quantitated on day 50 by headspace solid-phase microextraction (HS-SPME) arrow coupled with gas chromatography-mass spectrometry (GC-MS) and classified as: alcohol (9), aldehydes (6), ketones (5), carboxylic acids (5), esters (3), nitriles (2), phenol (1) and hydrocarbon (1) were affected by the amount of added salt. PCA explained 68.50 % of the variance and cluster samples based on the similarities between the identified VOCs and showed that fermentation mediated by 15 % added salt presented a VOCs profile comparable to using 20 % of salt, with the former representing a lower cost. The addition of salt can be used to control acidification, adopted as an effective preservation technique, and mediate VOCs production during cassava fermentation.

Dynamic changes in the gel properties, microbial community, and volatile flavor profile of Spanish mackerel (Scomberomorus niphonius) sausages inoculated with Lactiplantibacillus plantarum CY1-2

Spanish mackerel is an important economic fish species in China, but corruption undermines its overall economic value. Fermentation serves as a crucial technique for preserving perishable fish in developing countries. This study aimed to examine the dynamic changes in the gel properties, physicochemical properties, microbial diversity, and volatile flavor compounds (VFCs) of Spanish mackerel sausages inoculated with Lactiplantibacillus plantarum CY1-2 during fermentation. The correlation between key microorganisms and VFCs was explored using a two-way orthogonal partial least squares analysis. The results showed that the group inoculated with strain CY1-2 exhibited significant improvements compared with the control group after 40 h of fermentation. Specifically, gel strength increased by 207.7%, total free amino acids increased by 37.49%, DPPH and ABTS radical scavenging rates increased by 34.12% and 58.73%, and TVB-N levels decreased by 54.2%, respectively. In addition, using gas chromatography-mass spectrometry, 36 VFCs were detected in fermented sausages, including 9 aldehydes, 9 hydrocarbons, 7 alcohols, 4 acids, 2 ketones, and 5 esters. High-throughput sequencing demonstrated that the bacterial profiles were altered in sausages inoculated with strain CY1-2 during fermentation. Enhydrobacter dominated initially but was quickly replaced by Macrococcus after 8 h of fermentation, while Lactobacillus became the dominant genus after 40 h. Correlation analysis revealed that Lactobacillus and Staphylococcus played important roles in the production of VFCs in the fermented sausages. Notably, Lactobacillus was positively associated with 2-undecanone, pentadecane, and hexanal. This study confirmed that strain CY1-2 inoculation could enable the production of high-quality fermented fish sausages.

Saccharomyces cerevisiae strains L7 contribute to flavor and deacidification in Suanyu, a Chinese traditional fermented fish

Saccharomyces cerevisiae L7 was found to be an excellent starter and biological deacidification strain for Suanyu, however, the underlying mechanisms remain poorly understood. This study aimed to investigate the acid inhibition mechanism of S. cerevisiae L7. The strain enhances the sensory and flavor characteristics of Suanyu. The growth of Lactiplantibacillus plantarum is inhibited due to competition for carbon sources, resulting in a decrease in cell count from 9.00 Lg CFU/mL at 48 h to 7.70 Lg CFU/mL in co-culture. The addition of yeast reduces acidity, decreasing it from 5.83 g/kg to 0.82 g/kg at 48 h, while increasing sugar utilization to 94.52%. We found that cell contact was the main method of inhibition between the two microbials. Transcriptome analysis revealed that multiple pathways were affected under co-culture, ultimately leading to a decrease in lactic acid production. These findings provide valuable insights into the microbial interactions involved in biological deacidification.

Dynamic changes in volatile profiles and bacterial communities during natural fermentation of Mei yu, traditional Chinese fermented fish pieces

Microbial metabolism is important for the unique flavor formation of Mei yu, a kind of traditional Chinese fermented fish pieces. However, the interactive relationship between microorganisms and flavor components during fermentation is still unclear. In this study, electronic nose and headspace-solid-phase microextraction-gas chromatography-mass spectrometry analysis were performed to identify flavor components in Mei yu during the fermentation, and the absolute microbial quantification was conducted to identify the diversity and succession of microbial communities. During fermentation, there was an increase in the types of volatile compounds. Alcohols, aldehydes, aromatics and esters were the main flavor compounds and significantly increased in Mei yu, while hydrocarbon and aldehydes significantly decreased. The absolute abundances of Lactobacillus, Lactococcus and Weissella increased significantly after 3 days' fermentation, which were closely associated with the productions of 1-nonanol, 2-methoxy-4-vinylphenol, guaiacol, ethyl palmitate and ethyl caprylate that might though pathways related to fatty acid biosynthesis and amino acid metabolism. However, these genera were negatively correlated with the production of indole. Additionally, the total volatile basic nitrogen (TVB-N) levels of Mei yu fermented during 3 days were within the limits of 25 mg TVB-N/100 g fish, with the contents of free amino acids and lipoxygenase activities were significant lower than that of 4 days' fermentation. In view of food safety and flavor, it suggested that the natural fermented Mei yu at room temperature should be controlled within 3 days. This study highlights the application of absolute quantification to microbiome analysis in traditional fermented Mei yu and provides new insights into the roles of microorganisms in flavor formation during fermentation.

Lipidomics profile and volatile compounds of squids (Illex argentinus, Ommastrephes Bartram and Dosidicus gigas) in the Argentine, North Pacific Ocean, Equator and Peru by UPLC-triple TOF-MS and HS-SPME-GC-O-MS

Comprehensive lipid and volatile compound analyses were performed with squids collected from four varied geographical locations to discriminate the regional characteristics. A total of 1442 lipid molecules and 110 volatiles were detected in the squid muscle samples. There were significant differences in the lipid profiles between Argentine squid (Illex argentinus, AGT), North Pacific Ocean squid (Ommastrephes Bartram, NPO), Equatorial squid (Dosidicus gigas, EQ), and Peruvian squid (Dosidicus gigas, PR) muscle. Phosphatidylcholines (14.64%), triacylglycerols (12.42%), and ceramides (10.97%) were the main lipid components. The contents of polyunsaturated fatty acid in phospholipids and in glycerolipids were 30.35-52.05% and 18.11-25.15%, respectively. The volatiles in squids exhibited significant regional variation; 1-pentanol and 1-octanol, 2-ethyl-1-hexanol and terpinen-4-ol, 2,7-ethyl-1-hexanol, 3-methy-1-butanol and 2-propyl-1-pentanol were identified as characteristic flavor compounds in AGT, NPO, EQ, and PR, respectively. Sphingomyelin, phosphatidylserine, phosphatidylethanolamine, and ceramide were strongly correlated with volatiles in squid muscle. Our study is a reference for the lipid nutritional value and flavor compounds of squids.

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.

Multi-omics analysis reveals the microbial interactions of S. cerevisiae and L. plantarum on Suanyu, Chinese traditional fermented fish

S. cerevisiae and L. plantarum play important roles in Suanyu fermentation. This study investigated the interaction between S. cerevisiae and L. plantarum during fermentation and its impact on metabolic pathways. Co-culturing S. cerevisiae and L. plantarum increased pH to 5.72, reduced TVB-N to 9.47 mg/mL, and achieved high utilization rates of sugars (98.9%) and proteins (73.7%). During microbial interactions, S. cerevisiae and L. plantarum produced antibiotics, including phenyllactate and Gentamicin C1a, inhibiting the growth of each other. S. cerevisiae used S-adenosyl-l-methionine to counteract acid production of L. plantarum, establishing dominance in Suanyu fermentation. Microbial interactions influenced carbohydrate and energy metabolism pathways, such as nicotinate and nicotinamide metabolism and purine metabolism. S. cerevisiae significantly impacted gene expression in protein synthesis and cell growth pathways, including ribosome, SNARE interactions, basal transcription factors, and MAPK signaling. These findings offer insights into microbial interactions and metabolic processes during Suanyu fermentation.

The Effect of Lactiplantibacillus plantarum x3-2b Bacterial Powder on the Physicochemical Quality and Biogenic Amines of Fermented Lamb Jerky

In this study, a protective agent was added to prepare a high-activity Lactiplantibacillus plantarum x3-2b bacterial powder as a fermentation agent and explore its effect on the physicochemical quality, biogenic amines, and flavor of fermented lamb jerky. A composite protective agent, composed of 15% skim milk powder and 10% trehalose, was used, and bacterial mud was mixed with the protective agent at a 1:1.2 mass ratio. The resulting freeze-dried bacterial powder achieved a viable count of 5.1 lg CFU/g with a lyophilization survival rate of 87.58%. Scanning electron microscopy revealed enhanced cell coverage by the composite protective agent, maintaining the cell membrane's integrity. Inoculation with x3-2b bacterial powder increased the pH and the reduction in aw, enhanced the appearance and texture of fermented lamb jerky, increased the variety and quantity of flavor compounds, and reduced the accumulation of biogenic amines (phenethylamine, histamine, and putrescine). This research provides a theoretical basis for improving and regulating the quality of lamb jerky and establishes a foundation for the development of bacterial powder for the commercial fermentation of meat products.

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.

Physiochemical Quality, Microbial Diversity, and Volatile Components of Monascus-Fermented Hairtail Surimi

In order to study the effects and mechanism of Monascus on the quality of hairtail surimi, high-throughput sequencing technology, headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC/MS), and electronic nose techniques were used to investigate the changes in the quality, microbial diversity, and volatile flavor compounds of Monascus-fermented hairtail surimi (MFHS) during fermentation. The results showed that the total volatile basic nitrogen (TVB-N) index of hairtail surimi fermented by Monascus for 0-5 h met the requirements of the national standard. Among them, the 1 h group showed the best gel quality, which detected a total of 138 volatile substances, including 20 alcohols, 7 aldehydes, 12 olefins, 4 phenols, 12 alkanes, 8 ketones, 15 esters, 6 acids, 16 benzenes, 4 ethers, and 8 amines, as well as 26 other compounds. In addition, the dominant fungal microorganisms in the fermentation process of MFHS were identified, and a Spearman correlation analysis showed that 16 fungal microorganisms were significantly correlated with the decrease in fishy odor substances in the fermented fish and that 8 fungal microorganisms were significantly correlated with the increase in aromatic substances after fermentation. In short, Monascus fermentation can eliminate and reduce the fishy odor substances in hairtail fish, increase and improve the aromatic flavor, and improve the quality of hairtail surimi gel. These findings are helpful for revealing the mechanism of the quality formation of fermented surimi and provide guidance for the screening of starter culture in the future.

Evaluation of Autochthonous Coagulase-Negative Staphylococci as Starter Cultures for the Production of Pastırma

The aim of the study was to investigate the effects of Staphylococcus xylosus 39, S. equorum 53, or S. vitulinus 75, previously isolated from pastırma, on the quality characteristics of pastırma, a Turkish dry-cured meat product, and to evaluate their potential use as starter cultures. The pastırma production was carried out with a traditional method. The control pastırma groups were manufactured without adding any starter culture. At the end of production, the groups were subjected to microbiological and physico-chemical analyses. The pH was above 5.5, and the aw value was below 0.90 in all groups. The strains used exhibited good adaptation to the pastırma. The S. equorum 53 decreased the thiobarbituric acid reactive substances (TBARS) value in pastırma, while the S. xylosus 39 increased the redness (a*) color value. The autochthonous strains caused a decrease in the palmitic acid (C16:0). However, they had no significant effect on the stearic acid (C18:0) and the oleic acid (C18:1n-9c). A total of 41 volatile compounds were identified in the groups. S. vitulinus 75 increased both benzaldehyde and 2-methyl-3-phenylpropanal levels. In addition, the principal component analysis (PCA) of volatile compounds provided a good separation, and PC1 separated S. xylosus 39 from other groups.

Volatile compounds comparison and mechanism exploration of non-smoked traditional Chinese bacon in Southwestern China and Eastern China

Non-smoked traditional Chinese bacon is popular in China. However, the aromas of the non-smoked bacon from Eastern China (EC bacon) and Southwestern China (SW bacon) differed significantly. This study investigated these differences and the key volatile compound formation mechanisms. A total of 175 volatile compounds were detected in the bacon samples, while 32 key aroma compounds were screened based on odor activity values (OAVs). Multivariate statistical analysis showed that ten odorants could be considered discriminative compounds, including hexanal, octanal, and 1-octen-3-ol, etc. The fatty aroma of EC bacon was mainly attributed to a higher aldehydes content, which is due to more oxidation of fatty acids. Meanwhile, the SW bacon smelled sweeter since there was more ester in the sample. The correlation analysis between the fatty acid profiles and key aroma compounds indicated that the discriminative aldehyde formation in the EC bacon was primarily attributed to oleic and linoleic acid oxidation, which were both potential biomarkers.

Simultaneous Preparation of Chitin and Flavor Protein Hydrolysates from the By-Products of Shrimp Processing by One-Step Fermentation with Lactobacillus fermuntum

One-step fermentation, inoculated with Lactobacillus fermentum (L. fermentum) in shrimp by-products, was carried out to obtain chitin and flavor protein hydrolysates at the same time. The fermentation conditions were optimized using response surface methodology, resulting in chitin with a demineralization rate of 89.48%, a deproteinization rate of 85.11%, and a chitin yield of 16.3%. The surface of chitin after fermentation was shown to be not dense, and there were a lot of pores. According to Fourier transform infrared spectroscopy and X-ray diffraction patterns, the fermented chitin belonged to α-chitin. More than 60 volatiles were identified from the fermentation broth after chitin extraction using gas chromatography-ion transfer spectrometry analysis. L. fermentum fermentation decreased the intensities of volatile compounds related to unsaturated fatty acid oxidation or amino acid deamination. By contrast, much more pleasant flavors related to fruity and roasted aroma were all enhanced in the fermentation broth. Our results suggest an efficient one-step fermentation technique to recover chitin and to increase aroma and flavor constituents from shrimp by-products.

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.

Investigation of volatile flavor compounds and characterization of aroma-active compounds of water-boiled salted duck using GC-MS-O, GC-IMS, and E-nose

To clarify the characteristic aroma substances of water-boiled salted duck (WSD), headspace-gas chromatography-mass spectrometry-olfactometry (HS-GC-MS-O), gas chromatography-ion mobility spectrometry (GC-IMS) combined with an electronic nose (E-nose) were used to analyze the volatile flavor profile of three types of WSD (containing four samples). Thirty-one and fifty volatile flavor components were identified by GC-MS and GC-IMS, including aldehydes, alcohols, esters, ketones, hydrocarbons, and others. The characteristic aroma compounds of WSD, including pentanal, hexanal, heptanal, octanal, nonanal, (E)-2-octenal, benzaldehyde, (E)-2-nonenal, decanal, 1-octen-3-ol, 1-octanol, 1-pentanol, ethyl acetate, d-limonene, and 2-pentylfuran, were confirmed by GC-O, odor activity values (OAVs), and aroma-recombination and omission experiments. The aroma description of these aroma-active compounds can be divided into 6 categories, namely, "fruity", "mushroom", "fat", "sweet", "faint scent" and "potato, scorch" aromas. The difference between samples was mainly caused by the differential volatile compounds, followed by the identification method.

Effect of Biogenic Amine-Degrading Lactobacillus on the Biogenic Amines and Quality in Fermented Lamb Jerky

This study compares five types of lamb jerky, namely, CO (without starter culture), PL-4 (with producing putrescine, cadaverine, histamine, and tyramine), BL4-8 (degrading putrescine, cadaverine, histamine, and tyramine), CL4-3 (degrading putrescine and tyramine), and X3-2B (degrading histamine and tyramine). A study was performed to examine the effects of starter culture on the physical−chemical quality, flavor, and biogenic amines (BAs) during fermentation and ripening. At the end of fermentation, the pH value of the BL4-8 group (4.75) was significantly lower than that of other groups (p < 0.05). After high-temperature roasting, the water activity (0.55), water content (22.6%), nitrite residue (0.41 mg/kg), and TBARS value (0.27 mg/100 g) of the X3-2B group were significantly lower than those of other groups (p < 0.05). The findings show that adding starter BL4-8, CL4-3, and X3-2B can increase the variety and content of flavor in the product. The levels of histamine, putrescine, and tyramine were significantly lower in the BL4-8, CL4-3, and X3-2B groups than in CO and PL-4 groups. This study shows that BL4-8, CL4-3, and X3-2B are potential starters for fermented 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.

Exploring the Fungal Community and Its Correlation with the Physicochemical Properties of Chinese Traditional Fermented Fish (Suanyu)

Suanyu is a traditional natural fermented fish product from Southwest China that contains very complex microflora. The main purpose of this study was to explore the fungal community and its relationship with the physicochemical properties of Suanyu. The fungal community structure of Suanyu from the main provinces (Guizhou and Hunan) was studied via high-throughput sequencing. The correlation between dominant fungi and physicochemical characteristics was analyzed via Spearman's correlation coefficient. The results showed that the pH value, total volatile base nitrogen content, and thiobarbituric acid reactive substance content ranges of Suanyu samples were 4.30-5.50, 17.11-94.70 mg/100 g, and 0.61 to 3.62 mg/kg, respectively. The average contents of total volatile base nitrogen, thiobarbituric acid reactive substance, and total BAs in Suanyu from Guizhou were lower than those from Hunan. The main BAs were phenethylamine, putrescine, cadaverine, histamine, and tyramine. Ascomycota was the dominant fungal phylum, and Kodamaea, Debaryomyces, Wallemia, Zygosaccharomyces, and unclassified Dipodascaceae were the dominant fungal genera in different samples. Moreover, high abundance levels of Kodamaea and Zygosaccharomyces were found in Suanyu from Guizhou. According to the correlation analysis, Kodamaea and Zygosaccharomyces were negatively correlated with TBARS (R² = -0.43, -0.51) and TVBN (R² = -0.37, -0.29), and unclassified Dipodascaceae was significant negatively correlated with tyramine (R² = -0.56). This study expands the understanding of the fungal community and the fermentation characteristics of the dominant fungi in Suanyu.

Investigation of fermentation-induced changes in the volatile compounds of Trachinotus ovatus (meixiangyu) based on molecular sensory and interpretable machine-learning techniques: Comparison of different fermentation stages

Fermented golden pomfret (Trachinotus ovatus) is appreciated by local consumers owing to its distinct flavor. Electronic nose (E-nose) and gas chromatography-ion mobility spectrometry (GC-IMS) technologies were used to analyze the changes in volatile compounds responsible for evolution of the golden pomfret odor profile during fermentation. Forty-five ion peaks were detected using GC-IMS. Although aldehydes represented the major initial volatile compound group, their levels decreased as fermentation proceeded. Between 3 and 15 days, increased levels of esters contributed to a stable volatile organic compounds profile. After 18 days, high levels of indole and pyrazines were detected. Eleven key volatile compounds were screened based on partial least squares discriminant analysis (PLS-DA). Back propagation artificial neural network (BP-ANN) predicted the fermentation stage enabling the development of better strategies to regulate golden pomfret fermentation. This study provided a theoretical basis for real-time monitoring and quality control of Chinese fermented golden pomfet.

Sodium Reduction in Traditional Fermented Foods: Challenges, Strategies, and Perspectives

Sodium salt is a pivotal ingredient in traditional fermented foods, but its excessive consumption adversely affects human health, product quality, and production efficiency. Therefore, reducing sodium salt content in traditional fermented foods and developing low-sodium fermented foods have attracted increasing attention. Given the essential role of sodium salt in the safety and quality of fermented foods, appropriate approaches should be applied in the production of low-sodium fermented foods. In this review, the challenges of sodium reduction in traditional fermented foods are presented, including the possible growth of pathogenic bacteria, the formation of hazardous chemicals, flavor deficiency, and texture deterioration. Physical, chemical, and biological strategies are also discussed. This review provides references for improving the quality and safety of low-sodium fermented foods.

Exploring the bacterial community for starters in traditional high-salt fermented Chinese fish (Suanyu)

Traditional high-salt fermented Suanyu is an ethnic fermented fish product in southwest China. Lactic acid bacteria (LAB) are the most appropriate strains because of their technological properties during ripening fermentation. The diversity of LAB in high-salt fermented Chinese Suanyu was examined through high-throughput sequencing (HTS), and the most suitable LAB strain was acquired through strain isolation and characterization, surimi simulation fermentation system, and principal component analysis (PCA). The processing adaptability of the strain was examined via Suanyu fermentation. Results showed that Lactobacillus, Tetragenococcus, and Weissella were the dominant bacteria in Suanyu, and their contributions were 53.99%, 35.60%, and 4.10%, respectively. The most suitable strain (Lactobacillus plantarum B7) rapidly produced acid, exhibited a strong antibacterial activity, showed salt tolerance, and had no amino acid decarboxylase activity. pH decreased to about 3.6. Eventually, the ability to tolerate 20% salt was observed, and the activity of amino acid decarboxylase was negative. Fermented Suanyu with B7 rapidly produced acid (11.7% d^-1). The non-protein nitrogen (NPN) and total free amino acid (FAA) contents of fermented Suanyu were higher and its total volatile base nitrogen (TVB-N), thiobarbituric acid (TBARS), and biogenic amines (BAs) levels were lower than those of naturally fermented Suanyu. Therefore, B7 is a potential microbial starter for Suanyu industrial production.

Fish sauce fermentation using Marinococcus halotolerans SPQ isolate as a starter culture

A total of 344 halophilic bacteria were isolated from fish fermentation broths, solar salt crystals, seawater, and muds from ponds of salt pans in Vietnam and subjected to aroma evaluation using fish broth containing 29 ~ 30% (w/v) NaCl. One isolate from a salt crystal with the highest aroma score was selected, identified by using 16S rDNA sequence, and named Marinococcus halotolerans SPQ. The GC-MS results of the fish broth fermented by M. halotolerans SPQ revealed elevated concentrations of several aroma compounds such as ethyl alcohol, 1-propanol, 1-butyl alcohol, 1-amyl alcohol, and methionol. During the validation tests for M. halotolerans SPQ, using 2 kg of anchovy fish in 30% (w/v) NaCl at pH 5.78, the total and amino nitrogen values in the broth increased over time from 15.2 g/L at the beginning to 26.3 g/L at 6th month, with these values being comparable to those of the control. The ammoniacal nitrogen value (2.52 g/L) in the inoculated broth at 6th month was slightly higher than that (2.21 g/L) of control. The histamine content of the fish broth inoculated with M. halotolerans SPQ after 6 months was 110.12 mg/L, less than the maximum permitted safety limit of 200 mg/L, indicating it to be safe. Physical parameters, such as the total, amino, ammoniacal nitrogens, and histamine content of fish broth fermented by M. halotolerans MPQ met the standards for Vietnamese fish sauces. Two important umami amino acids, aspartic and glutamic acid, were seen to significantly increase, by 23.5% and 35.1%, respectively, even in the extremely harsh fermentation conditions posed by 30% (w/v) NaCl. The color, odor, and taste of the fish sauce fermented by M. halotolerans SPQ elicited the highest preference score accorded by the panelists. Taken together, M. halotolerans SPQ is a promising starter culture strain for fish sauce fermentation.

Use of Autochthonous Lactiplantibacillus plantarum Strains to Produce Fermented Fish Products

The present research was aimed to the optimization of the production of a fish fermented salami-like product using autochthonous Lactiplantibacillus plantarum starters. The activity was performed through two phases: (1) Optimization of fermented fish product composition by using a 2^k-p Fractional Factorial Design: the variables tested were nitrites (0–150 ppm), salt (2.5–7.5%), sucrose (0–4%), white pepper (0–0.10%), and fermentation temperature (10–30°C); (2) Product realization and evaluation of its microbiological profile [aerobic microbiota (APC), Pseudomonadaceae (PSE), Enterobacteriaceae (E), and lactic acid bacteria (LAB) populations], chemico-physical parameters (pH and a_w), and sensorial quality (odor, texture, color, and overall acceptability) during its storage at 4°C for 21 days. In the first step, the fish pulp was mixed with the appropriate amounts of ingredients, according to the experimental design; each batch was individually inoculated with the studied starter (L. plantarum 11, L. plantarum 69, and L. plantarum DSM1055) at 10⁷ cfu/g and incubated at 10, 20, or 30°C for 7 days. The lowest fermentation time (time to reach pH 4.4) was obtained with 4% sucrose, 100 ppm nitrite and a process temperature of 30°C. In the second step, salami-like were produced according to the individuated formulation and inoculated with the studied starters (10⁷ cfu/g); the fish mixture was stuffed into a natural casing and left to ferment at 30°C for 7 days. The use of the selected strains not only assured a correct fermentation but reduced the process time at only 2 days; during refrigerated storage, a good microbiological, chemico-physical and sensorial quality of the final product was recorded for at least 21 days.

Effects of flavourzyme addition on physicochemical properties, volatile compound components and microbial community succession of Suanzhayu

Flavourzyme is known to promote protein decomposition, resulting in more peptides and amino acids which can improve the quality of fermented foods. In this study, the effects of flavourzyme addition on the fermentation of Suanzhayu fish were investigated. The results showed that the addition of 50 U/g flavourzyme reduced the water activity (a_w) of products and promoted the release of trichloroacetic acid (TCA)-soluble peptides and free amino acids (FAAs). Thus, the stability of the product was improved and its nutritional value was increased. In addition, with the addition of flavourzyme, Lactobacillus and Saccharomyces more quickly became the dominant genera in the fermentation. Furthermore, the formation of alcohols, aldehydes, and esters was promoted in flavourzyme addition group. Redundant analysis (RDA) indicated that Lactobacillus and Lactococcus play important roles in the formation of flavors, especially for the characteristic flavors of Suanzhayu. Flavourzyme addition may be a novel method to greatly improve the properties of Suanzhayu and shorten the fermentation time.

The volatile flavor compounds of Shanghai smoked fish as a special delicacy

In this work, the effects of substrates on volatile flavor compounds of Shanghai smoked fish (SSF) from grass carp was investigated by head space-solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) by changing the ratios of soy sauce (15%-25%) to white sugar (10%-20%) and replacing white sugar with reducing sugar (glucose, fructose, and ribose). The results showed the key volatile flavor compounds (ROAV ≥ 1) of SSF were 2,4-decadienal, p-xylene, nonanal, and 1-octen-3-ol with the relative contents of 10.33, 1.14, 4.84, and 1.76%, respectively. Furthermore, the existence of soy sauce had an enhancing role in the production of pyrazines, but no significant difference in white sugar. The contents of isovaleraldehyde and benzeneacetaldehyde were increased when white sugar was replaced with glucose, octanol, and 2-pentyl furan for fructose, no obvious difference in ribose. Moreover, the optimal ratios of soaking solutions were 20% soy sauce and 15% white sugar based on the scoring method of sensory evaluation. This study will provide a theoretical basis for the formation of volatile flavor compounds of SSF. PRACTICAL APPLICATIONS: Grass carp usually grows in freshwater such as pond or lake, but bacteria with earthy smell are easily attached to plankton such as diatom and cyanobacteria leading to the accumulation of bad odor substances through the food chain. Shanghai smoked fish (SSF) deeply loved by public is a traditional special dish with crispy crust and delicious taste. The attractive flavor of grass carp could be increased with the help of the Maillard reaction (MR) and seasonings. Therefore, the effect of the MR on the volatile flavor compounds of SSF was investigated by HS-SPME-GC/MS in this work. A detailed study on the volatile flavor compounds of Shanghai smoked fish could not only enrich the theoretical knowledge of flavor chemistry of freshwater fish, but have a profound contribution to the development of freshwater fish processing techniques.

Technological roles of microorganisms in fish fermentation: a review

Fermentation is an important way to process and preserve fish. It not only gives the product a unique flavor and texture, but it also contributes to increased nutritional value and better functional properties. The production of fermented fish relies on naturally occurring enzymes (in the muscle or the intestinal tract) as well as microbial metabolic activity. This review focuses on the role of microorganisms on texture change, flavor formation, and biogenic amines accumulation in fermented fish. In addition, the production conditions and the major biochemical changes in fermented fish products are also introduced to help understand the factors influencing the quality of fermented fish. Moreover, prospects for further research of fermented fish are discussed.

Shortening Fermentation Period and Quality Improvement of Fermented Fish, Chouguiyu, by Co-inoculation of Lactococcus lactis M10 and Weissella cibaria M3

Chouguiyu, a Chinese traditional fermented fish, is famous for its uniquely strong odor and desirable taste. However, traditional spontaneous fermentation often resulted in contamination and unstable quality of products. In this study, individual or conjunctive inoculation of two indigenous lactic acid bacteria (LAB), Lactococcus lactis M10 and Weissella cibaria M3, was tested for their effect on improving Chouguiyu's quality. It was shown that inoculation would not affect the system's pH, while increased the total bacteria count and lactic acid bacteria amounts. Matrix-assisted laser desorption/ionization time-of-flight mass (MALDI-TOF) analysis results revealed that Lactoc. lactis M10 and W. cibaria M3 could quickly occupy a dominant position in the ecosystem, and Lactoc. lactis M10 played an important role in the control of spoilage bacteria. Volatile basic nitrogen (TVB-N), thiobarbituric acid reactive substances (TBARS), and biogenic amines results also showed that Lactoc. lactis M10 had a positive effect on improving the product's quality. Co-inoculation of Lactoc. lactis M10 and W. cibaria M3 could promote the formation of flavor according to the E-nose and gas chromatography-mass spectrometer (GC-MS) analyses, especially for the aroma-active and key volatile compounds. PCA plots of E-nose and hierarchical clustering analysis of GC-MS profiles revealed that the co-inoculation sample at the fifth day (LW5) was the most similar to the natural fermentation sample at the seventh day (C7). The overall acceptance of LW5 was also the closest to that of C7 in sensory evaluation. In conclusion, mixed starter culture was shown to have a good effect on improving product quality and enhancing flavor with fermentation time shortened by 29%.