Suan Yu Research Articles

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.

Effects of Liquid Smoking on the Microbiological and Physicochemical Characteristics of Suan Yu, a Traditional Chinese Fermented Fish Product

ABSTRACT This work studied the changes in microbiological and physiochemical properties during the fermentation of Suan yu by liquid smoking and traditional smoking (batches B, C, and A). Lactobacillus plantarum, Pediococcus pentosaceus, Saccharomyces cerevisiae, and Hansenula polymorpha were the dominant microorganisms in the three samples. Only the acid-resistant Staphylococcus xylosus and Staphylococcus carnosus survived in the acid environment of the final fermented products. The amounts of Enterobacteriaceae, Enterococci, and Pseudomonades in the final fermented products were under the detection limit. Batch B and C samples had higher rate of reduction in pH (4.24 ± 0.17–4.39 ± 0.18 from 6.21 ± 0.24, respectively) and lower acetic acid generation rate (0.06%±0. 00% and 0.05%±0. 00%, respectively) than batch A samples. Large amounts of free amino acids were generated during the fermentation of the samples. Batches B and C had thiobarbituric acid reactive substances (TBARS) value between 0.88 ± 0.03 and 0.89 ± 0.03, total volatile basic nitrogen (TVB-N) value between 18.9 ± 0.34 and 18.8 ± 0.33 mg/kg, and benzo(a)pyrene (BaP) content of 0.1 ± 0.00 μg/kg, which was lower than those of fermented Suan yu prepared by traditional smoking. Sensory analysis indicates that these sample groups have unique smoking and fermentation flavor. Consequently, the fermented Suan yu produced through liquid smoking is a kind of fermented aquatic product with full-bodied smoking flavor, palatable acid flavor, abundant nutrition, and high safety.

Effects of Amino Acid Decarboxylase Genes and pH on the Amine Formation of Enteric Bacteria From Chinese Traditional Fermented Fish (Suan Yu).

The formation of biogenic amines (BAs) is an important potential risk in Suan yu. This study investigated the amine production abilities of 97 strains of enteric bacteria screened from Suan yu. The genotypic diversity of amino acid decarboxylase and the effect of pH were explored on 27 strains of high-yield BAs. Results showed that high levels of putrescine, histamine, and cadaverine were produced by the 97 strains. In addition, 27 strains carried odc, speA, speB, adiA, and ldc genes. Thirteen carried hdc gene. Morganella morganii 42C2 produced the highest putrescine content of 880 mg/L via the ornithine decarboxylase pathway. The highest histamine content was produced by Klebsiella aerogenes 13C2 (1,869 mg/L). The highest cadaverine content was shown by Klebsiella pneumoniae 47C2 (1,821 mg/L). odc, adiA, speB, ldc, and hdc play important roles in the cellular acid stress response. Acid stress caused the growth delay but can increase the contents of putrescine, histamine, and cadaverine. Decarboxylase was strain specific rather than species specific. This study provides a reference for the genotypic diversity of decarboxylase and effect of pH on the types and abilities of BAs produced by enteric bacteria in Suan yu.

Effects of three carp species on texture, color, and aroma properties of Suan yu, a Chinese traditional fermented fish

Effects of three carp species on texture, color, and aroma properties of Chinese traditional fermented freshwater fish (Suan yu) were investigated. Suan yu were produced from Ctenopharyngodon idella (Grass Carp, GC), Hypophthalmichthys molitrix (Silver Carp, SC), and Cyprinus carpio (Common Carp, CC) as the control. GC displayed the highest hardness and resilience, while SC showed the lowest texture except for springiness (p < .05). GC had the greatest L* and ΔE* values but the least a* value (p < .05). Esters (7), alcohols (7), acids (9), aldehydes (8), ketones (1), hydrocarbons (4), and others (5) were identified by GC-MS in all samples. E-nose analysis showed a remarkable difference in the overall aroma profile among all samples. Sensory evaluation and PCA analysis indicated that grass carp could be used as an alternative raw material for Suan yu production, which would improve the utilization of freshwater fish. Practical applications Suan yu is a type of Chinese traditional fermented freshwater fish with a unique flavor, which is popular among consumers. Such products are commonly manufactured from fresh common carp (Cyprinus carpio) with long-term anaerobic fermentation. Grass carp (Ctenopharyngodon idella) and silver carp (Hypophthalmichthys molitrix) are popular among consumers as major domesticated fish in China with higher annual harvests than that of common carp, which show potential as raw materials for Suan yu production. It is the first time to investigate the texture, color, and aroma of Suan yu produced from the three carp species (grass carp, silver carp, and common carp) in the same process and to evaluate their quality differences and acceptability. This will help increase the sources of raw materials for Suan yu production and improve the utilization of freshwater fish.

Aroma profiles of commercial Chinese traditional fermented fish (Suan yu) in Western Hunan: GC-MS, odor activity value and sensory evaluation by partial least squares regression

ABSTRACT In this study, the aroma volatile compounds of commercial Chinese traditional fermented fish (Suan yu) from western Hunan were investigated. A total of 59 volatile compounds were identified and quantified by GC-MS combined with headspace solid-phase microextraction. Esters and alcohols presented over 50 percent of the overall aroma in concentration. With the calculation of odor activity values (OAVs), 20 odorants were recognized as aroma-active compounds due to their OAVs greater than 1, including esters (10), alcohols (5), acids (1), and aldehydes (4). Sensory evaluation revealed higher scores in estery, fruity, and grassy attributes than others. A positive correlation between sensory attributes and aroma-active compounds was clearly elaborated by partial least squares regression analysis (PLSR). PLSR results indicated that ethyl-2-methylbutyrate, ethyl 3-methylbutyrate, and ethyl decanoate were significantly and positively correlated with fruity attribute, while ethyl hexanoate and 1-octen-3-ol had a significant positive impact on estery and grassy attribute, respectively. This study elaborates the aroma profile of Suan yu from western Hunan of China, and implies the availability of PLSR for the flavor evaluation of fish products.

Genetic and Biochemical Evidence That Enterococcus faecalis Gr17 Produces a Novel and Sec-Dependent Bacteriocin, Enterocin Gr17.

Bacteriocins are ribosomally synthesized antibacterial peptides or proteins from microorganisms. We report a novel bacteriocin producing strain, Enterococcus faecalis Gr17, that was isolated from the Chinese traditional low-salt fermented whole fish product Suan yu. E. faecalis Gr17 displayed potent antibacterial activity against foodborne pathogenic and spoilage bacteria. The complete genome of E. faecalis Gr17 contained one circular chromosome and plasmid. The gene cluster of a novel bacteriocin designated enterocin Gr17 was identified. The enterocin Gr17 structural gene encodes a precursor of the bacteriocin. Two other transporter genes and an immunity gene within two divergent operons were identified as being associated with enterocin Gr17 secretion and protection. The novel enterocin Gr17 was purified by ammonium sulfate precipitation, cation exchange, gel filtration, and reverse-phase high-performance liquid chromatography. The molecular weight of enterocin Gr17 was 4,531.01 Da as determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and its mature amino acid sequence of enterocin Gr17 was RSYGNGVYCNNSKCWVNWGEAKENIIGIVISGWATGLAGMGR. Sequence alignment revealed that enterocin Gr17 is a class IIa bacteriocin with similarities to enterocin P. The merits of bactericidal activity, sensitivity to enzymes, and pronounced stability to chemicals, temperature (60°C, 30 min and 121°C, 15 min), and pH (2–10) indicated practicality and safety of enterocin Gr17 in the food industry. The complete genome information of E. faecalis Gr17 will improve the understanding of the biosynthetic mechanism of enterocin Gr17, which has potential value as a food biopreservative.

Technological properties and probiotic potential of yeasts isolated from traditional low‐salt fermented Chinese fish Suan yu

This study aims to investigate the technological properties of yeast strains isolated from traditional low-salt fermented Suan yu fish as starter culture. A step-by-step approach was used to determine the technological properties of the isolated yeast strains. The enzymatic activity (catalase, urease, β-glucosidase, protease, and lipase) under adverse conditions (pH, salt, and temperature) were evaluated. Principal component analysis was used to assess data. Twenty-five strains with desirable technological properties were selected for evaluation of probiotic traits (tolerance at pH 2.5 and 0.3% bile salts, antimicrobial activity, hydrophobic properties, and biofilm production). These isolates were identified by sequencing the D1/D2 region of 26S rDNA. Finally, seven isolates with desirable probiotic traits were analyzed for their ability to survive through gastric transit using a gastrointestinal simulation model. An In vitro test showed that isolates 3, 12, 19, 24, and 43 exhibited high survival levels (60%-70%), similar to those of the indicator strain (Saccharomyces cerevisiae). The results suggest that five isolates (S. cerevisiae strains 3, 12, 19, 24, and 43) showed desirable technological properties and probiotic traits and therefore can be used as functional starter cultures to produce fermented fish products. PRACTICAL APPLICATIONS: Researchers have investigated the activity of LAB as functional and probiotic microorganisms; however, information on the probiotic potential of yeasts remains limited. Yeasts are microorganisms that present and induce biochemical changes in several fermented meat and fish products. In the present study, the technological and probiotic properties of 52 isolates from Suan yu were investigated to identify potential probiotic strains for starter cultures. Our results suggest that five isolated S. cerevisiae strains showed desirable technological properties and probiotic traits and therefore can be used as functional starter cultures to produce fermented fish products, and other fermented foods. Functional yeast isolates are used to effectively improve the quality of fermented fish products for consumer acceptance.This study has focused on the possibility to produce a functional Suan yu using a potential probiotic S. cerevisiae as starter culture to enhance health benefits.

Lipid fraction and fatty acid profile changes in low-salt fermented fish as affected by processing stage and inoculation of autochthonous starter cultures

Effects of processing stage and inoculation of autochthonous starter cultures on the lipid fraction and fatty acid profile in low-salt fermented fish were investigated. Drying had less influence on lipid composition. After 4 weeks of fermentation, there were slight changes in neutral lipid (NL) contents, while the proportion of phospholipids (PL) decreased significantly with a concomitant increase in free fatty acids (FFA). Comparing with the CO batch, addition of starter cultures resulted in increase in FFA contents to different extents, and the sample with Staphylococcus xylosus 135 had the highest FFA contents. Inoculation with Saccharomyces cerevisiae 31 caused minimum PL loss. Fatty acid profile analysis showed that higher proportions of monounsaturated fatty acids and polyunsaturated fatty acids were liberated than saturated fatty acids after fermentation regardless of starter cultures. Addition of starter cultures could retard the loss of the polyunsaturated fatty acids (PUFA) during fermentation. Furthermore, results indicated that the increased FFA especially free PUFA in fermented Suan yu mainly resulted from lipolysis of PL.

Dynamics and diversity of microbial community succession during fermentation of Suan yu, a Chinese traditional fermented fish, determined by high throughput sequencing

The main goal of this study was to investigate the dynamics, diversity and succession of microbial community present during the preparation of Suan yu (fermented fish), with and without starter cultures by high-throughput sequencing of 16S rRNA and ITS1 genes. Firmicutes and Ascomycota were the predominant phyla of bacteria and fungi, respectively, in all samples. At the genus level, Lactobacillus, Macrococcus and Staphylococcus were the predominating bacteria throughout the fermentation process, regardless of the inclusion of starter cultures. Saccharomyces was the predominating fungal genus in the early-fermentation stage of samples that inoculated starter cultures (MS), while the final product was dominated by Candida and Wickerhamomyces. Compared with naturally-fermented samples (NS; no starter cultures), Lactococcus, Leuconostoc, Enterococcus, Vibrio, Fusicolla and Torulaspora were inhibited and Aureobasidium emerged in samples inoculated with starter cultures (P < .05). Unweighted pair-group and principal component analyses of bacterial and fungal compositions revealed that microbiota structures differed between NS and MS samples. Redundancy analysis indicated that water content and pH might be important factors influencing the dominant bacterial and fungal community. Results indicated that microbial community were dynamic during fermentation process and the inoculation of mixed starter culture inhibited the growth of many organisms associated with food spoilage and contributed to the improvement of the quality of Suan yu products.

Phospholipid molecular species composition of Chinese traditional low-salt fermented fish inoculated with different starter cultures

Phospholipid molecular species composition of Chinese traditional low-salt fermented fish (Suan yu) inoculated with different starter cultures was investigated. Fifty-six molecular species of phospholipid including 20 species of phosphatidylcholine (PC), 15 species of phosphatidylethanolamine (PE), 6 species of phosphatidylserine (PS), 9 species of lysophosphatidylcholine (LPC), and 6 species of lysophosphatidylethanolamine (LPE) were identified using ultra-performance liquid chromatography with quadrupole-time-of-flight mass spectrometry (UPLC-Q-TOF-MS). PC (C16:0–C18:1), PE (C16:0–C22:6), PS (C15:0–C22:6), LPC (C22:6) and LPE (C22:5) were the predominant species. Bioactive polyene phospholipids mainly existed in PE. Furthermore, starter cultures exhibited different influence on phospholipid molecular species. Compared to naturally fermented Suan yu, more molecular species of PE and PS as well as polyene phospholipids were detected in the samples inoculated with Saccharomyces cerevisiae 31 and mixed starter cultures.

Biosynthesis of acetate esters by dominate strains, isolated from Chinese traditional fermented fish (Suan yu)

Biosynthesis of acetate esters by Lactobacillus plantarum 120, Staphylococcus xylosus 135 and Saccharomyces cerevisiae 31, isolated from Chinese traditional fermented fish (Suan yu) were studied. A buffer system containing acyl donors (acetic acid/glyceryl triacetate/acetyl-CoA) and aliphatic alcohols (C2-C6) was established, inoculated with intracellular and extracellular extracts of the three strains. The results showed that the biosynthesis pathway of L. plantarum 120 was esterification and alcoholysis, while the biosynthesis pathway of S. xylosus 135 and S. cerevisiae 31 was hydrolysis and esterification, rather than alcoholysis. The ester-synthesizing activity of L. plantarum 120 via alcoholysis was higher than that via esterification at high pH value, while an opposite result for each strain was observed at low pH value. Moreover, the ester-synthesis activity of L. plantarum 120 was higher than that of S. xylosus 135 and S. cerevisiae 31. In addition, microbial ester-synthesis activity increased with the increase of aliphatic alcohol carbon number.

Esterase activities of autochthonous starter cultures to increase volatile flavour compounds in Chinese traditional fermented fish (Suan yu)

ABSTRACTSuan yu, a type of Chinese traditional fermented freshwater fish in solid form, is cheered among consumers due to its characteristic sensory flavour, primarily taste and smell. The purpose of this study was to investigate the presence of esterase activity of Lactobacillus plantarum 120, Staphylococcus xylosus 135, and Saccharomyces cerevisiae 31, in selecting appropriate processing means to accelerate the formation of the desired flavour in Suan yu. The results showed that all strains exhibited esterase activities in both intracellular and extracellular fractions against p-nitrophenyl (p-NP)-acetate, p-NP-butyrate, and p-NP-octanoate, and also that the maximum activity was observed in the intracellular fraction with p-NP-octanoate. Esterase activities of all strains were inhibited by low pH and low water activity (Aw), with the exception of L. plantarum 120 exhibiting an increase in intracellular activity with decreasing Aw. Moreover, L. plantarum 120 and S. xylosus 135 esterase were negatively affected by decreasing temperature, while a positive influence was observed on the intracellular esterase of S. cerevisiae 31. The results suggested that a low pH, a low Aw and a high temperature would be more appropriate for Suan yu processing to produce more flavour compounds which are acceptable by consumers.

Predominant processing adaptability of Staphylococcus xylosus strains isolated from Chinese traditional low-salt fermented whole fish

This study aimed to determine the predominant processing adaptability of 27 selected isolates of Staphylococcus xylosus in ‘Suan yu’, a traditional Chinese low-salt fermented whole-fish product. The isolates were screened for proteolytic, lipolytic, and enzymatic profiles; amino-acid decarboxylase content; antimicrobial activities; and tolerance to low temperatures, pH5.0, and salt. Two S. xylosus strains grew at 10°C in the presence of 10% NaCl and at pH5.0. Agar-plate assays and sodium dodecyl sulphate–polyacrylamide gel electrophoresis revealed that 21 and 8 of the strains exhibited appropriate proteolytic activities against myofibrillar and sarcoplasmic proteins, respectively. All S. xylosus strains also displayed different enzymatic profiles, and most strains showed negative decarboxylase activities. The results of this step were used as input data for a Principal Component Analysis; therefore, the most technologically relevant strain 3 and 8 were combined with L. plantarum 120 as MS1 and MS2, respectively, were further selected for the fermented fish surimi, and the fish surimi inoculated with mixed starter cultures (MS1, MS2) scored high for overall acceptability. Free amino acid contents of 1757 and 1765mg/100g sample were found in fish surimi inoculated with MS1 and MS2, respectively, after 72h of fermentation. Therefore, Sx-3 and Sx-8, which presented the best predominant processing adaptability, is an eligible starter culture for fermented fish production.

Effect of starter cultures on the quality of Suan yu, a Chinese traditional fermented freshwater fish

SummaryThe generation of volatile compounds of four starter cultures composed of isolated microorganisms from traditional Suan yu was investigated. The cultures included two pure starters (PS1: Lactobacillus plantarum 120 and PS2: Pediococcus pentosaceus 220) and two mixed starters (MS1: L. plantarum 120, Staphylococcus xylosus 135 and Saccharomyces cerevisiae 31 at 1:1:1; MS2: P. pentosaceus 220, S. xylosus 135 and S. cerevisiae 31 at 1:1:1). Naturally fermented Suan yu was used as control. The volatile compounds were collected from the headspace of the samples by Solid‐phase microextraction and analysed by gas chromatography–mass spectrometry. The type and total content of volatile compounds in the mixed‐starter‐fermented fish were higher than those of the pure‐starter‐fermented samples and control. A total of seventy nine and eighty volatile compounds were detected in Suan yu fermented with MS1 and MS2, respectively, with ethanol as the predominant compound and hexanal, ethyl acetate, 3‐methylbutanol, 3‐hydroxy‐2‐butanone, hexanoic acid ethyl ester and 2,3‐butanedione as the other compounds. Furthermore, the sensorial acceptance of the different products with mixed starter cultures seemed to improve the quality of Suan yu products.

Effect of autochthonous starter cultures on the volatile flavour compounds of Chinese traditional fermented fish (Suan yu)

SummaryEffect of autochthonous starter cultures on the volatile flavour compounds of Chinese traditional fermented fish was studied. Lactobacillus plantarum 120, Staphylococcus xylosus 135 and Saccharomyces cerevisiae 31, isolated from Suan yu, were selected as starter cultures. Volatiles were extracted by headspace solid‐phase microextraction (SPME) and analysed by gas chromatography–mass spectrometry technology (GC‐MS). Esters and alcohols were the main components of volatiles, accounting for over 50 percentage points in all samples. The highest content of esters (3034.54 μg kg−1) was observed in S1 inoculated with L. plantarum 120, while the highest content of alcohols (2164.53 μg kg−1) and ketones (379.98 μg kg−1) was detected in S3 inoculated with S. cerevisiae 31. The content of acids and aldehydes was lower in inoculated samples. Principal component analysis revealed that the volatile composition was primarily influenced by the nature of the starter cultures. L. plantarum 120 and S. xylosus 135 could accelerate fermentation.

Characterization of the Microbial Flora from Suan Yu, a Chinese Traditional Low-Salt Fermented Fish

The microbial flora of naturally fermented Suan yu was investigated by phenotype combined with gene analysis at different stages of fermentation. Results shows that lactic acid bacteria (LAB) and yeast were gradually increased during fermentation and the counts were ripening to 7.93–8.56 and 5.14–5.75 log cfu/g, respectively, at the end of the fermentation. Staphylococci gradually increased during the first fermentation stage and then slowly decreased until the end of ripening (4.13–4.92 log cfu/g). Majority of the LAB isolated from Suan yu were Lactobacillus plantarum and Pediococcus pentosaceus, followed by Leuconostoc and Lactobacillus paralimentarius species. The yeast mainly consisted of Saccharomyces cerevisiae and Hansenula anomala. The predominant Staphylococcus isolated from Suan yu comprised Staphylococcus saprophyticus and Staphylococcus xylosus. The main microorganism in early fermentation included Leuconostoc mesenteroides, Pseudomonas and Enterobacteriaceae and the followed subsequent stage included L. plantarum, P. pentosaceus, S. xylosus, S. saprophyticus, S. cerevisiae and H. anomala. Practical Applications In this study, the specific microorganisms and their microbial dynamics were investigated during Suan yu fermentation. Results showed that lactic acid bacteria, coagulase-negative Staphylococci and yeat were predominant microorganisms during the ripening fermentation. Therefore, these predominant organisms are responsible for the Suan yu unique flavor, taste, color and ensure their safety. Furthermore, selecting the most appropriate autochthonous microflora as starter formulation can effectively preserve the typical characteristics of the Suan yu.

Lipolysis and lipid oxidation caused by Staphylococcus xylosus 135 and Saccharomyces cerevisiae 31 isolated from Suan yu, a traditional Chinese low‐salt fermented fish

SummaryThe aim of this study was to investigate the lipolysis and lipid oxidation of Staphylococcus xylosus 135 and Saccharomyces cerevisiae 31 in Suan yu. Suan yu were made inoculated with and without two strains at different stages, and model systems of emulsions were also established. Lipolysis and lipid oxidation were evaluated by determining the changes in free fatty acid (FFA) content and composition, conjugated diene (CD) value and thiobarbituric acid reactive substances (TBARS) value. The total FFA of the sample without cultures increased from 476.61 mg/100 g fat to 1413.89 mg/100 g fat after 5 weeks fermentation, while those of samples with cultures declined to 258.98 and 452.89 mg/100 g fat, respectively. On the other hand, CD and TBARS values of samples with inoculation markedly increased. In the model system, higher FFA, CD and TBARS values for the samples added with CFE were observed. This study showed that Staphylococcus xylosus 135 and Saccharomyces cerevisiae 31 made a significant contribution to lipolysis and lipid oxidation during the processing of Suan yu.

Technological properties of Lactobacillus plantarum strains isolated from Chinese traditional low salt fermented whole fish

A total of 21 Lactobacillus plantarum were isolated from a Chinese traditional low salt fermented whole fish product “Suan yu” and identified by biochemical and molecular methods. The isolates were screened for acidifying and amino-biogenic ability for proteolysis, lipolysis, antimicrobial activity, and sensory in order to select the most suitable candidates as the starter cultures. All the strains had high acidifying activities and were able to reduce the pH to lower than 4.5 in 36, 24 and 16 h at 15, 25 and 37 °C respectively. Major strains showed antimicrobial activities against Listeria monocytogenes, Staphylococcus aureus and Escherichia coli, and ten L. plantarum strains could produce bacteriocins. Five L. plantarum strains exhibited weak proteolytic activities against myofibrillar proteins, as evidenced by the agar plate assay and sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS-PAGE). None of the strains showed lipolytic activity. Major L. plantarum strains displayed different enzymatic profiles. Besides, the isolates mostly showed negative-decarboxylase activities, but Lp-10 had a decarboxylase activity against l-tyrosine. Furthermore, the fermented fish surimi inoculated with Lp-15 and Lp-21 strains respectively scored high for overall acceptability. Therefore, Lp-15 and Lp-21 presented the best technological properties, which should be given first priority as the starter culture for manufacturing fermented fish products.

Effect of autochthonous starter cultures on microbiological and physico-chemical characteristics of Suan yu, a traditional Chinese low salt fermented fish

In this study, three groups of mixed starter cultures (S1: Lactobacillus plantarum 120, Staphylococcus xylosus 135 and Saccharomyces cerevisiae 31; S2: L. plantarum 145, S. xylosus 135 and S. cerevisiae 22; S3: Pediococcus pentosaceus 220; S. xylosus 135 and S. cerevisiae 22), isolated from Suan yu, were inoculated to produce the traditional fermented fish. After 42 days fermentation at 24 °C, Suan yu inoculated with different mixed starter cultures underwent rapid growth of lactic acid bacteria (LAB), declined pH, suppressed increase of thiobarbituric acid (TBARS) and total volatile base nitrogen (TVB-N) as well as growth of spoilage bacteria and pathogens. Besides, Suan yu had higher contents of non-protein nitrogen (NPN) and total free amino acids (FAA) compared to the control (P < 0.05). The muscle proteins were severely hydrolyzed during fermentation (SDS-PAGE). Moreover, the sensory evaluation indicates the fermented fish was more widely accepted than the control. The results suggest that the inoculation with S1, S2 and S3 reduced the lag time that fermentation began and improved the quality of Suan yu.

Changes of biogenic amines in Chinese low‐salt fermented fish pieces (Suan yu) inoculated with mixed starter cultures

SummaryIn this study, two groups of mixed starter cultures (S1, S2), which were isolated from Suan yu, were inoculated for this experimental product, and a batch without starters was used as the control. The effect of the mixed starter cultures on the suppression of biogenic amine (BA) produced during the ripening of Suan yu was investigated. Changes in BA, pH, total volatile base nitrogen (TVB‐N), microbial counts and free amino acids (FAA) contents were detected during ripening. The results show that the mixed starter cultures rapidly decreased pH, inhibited the growth of contaminant microorganisms emerged in the sample and drastically reduced the accumulations of tyramine, putrescine and cadaverine. However, histamine and spermine were not produced in any batch. Besides, pH, FAA and BA production were not directly correlated. The study suggests that inoculation with S1 and S2 inhibited BA, thereby improving the product safety.