Physical and chemical changes of silver carp sausages during fermentation with Pediococcus pentosaceus

Improvement mechanism of volatile flavor in fermented tilapia surimi by cooperative fermentation of Pediococcus acidilactici and Latilactobacillus sakei: Quantization of microbial contribution through influence of genus

Single starter can hardly improve the volatile flavor of fermented fish surimi. In this study, the changes of volatile compounds (VCs) and microbial composition during cooperative fermentation of Latilactobacillus sakei and Pediococcus acidilactici were studied by headspace solid-phase microextraction gas chromatography-mass spectrometry and 16S rRNA gene high-throughput sequencing. During cooperative fermentation, most VCs and the abundance of Latilactobacillus and Lactococcus significantly increased, while Pediococcus, Acinetobacter, and Macrococcus obviously decreased. After evaluation of correlation and abundance of each genus, Latilactobacillus and Lactococcus possessed the highest influence on the formation of volatile flavor during cooperative fermentation. Compared with the natural fermentation, cooperative fermentation with starters significantly enhanced most of pleasant core VCs (odor activity value≥1), but inhibited the production of trimethylamine and methanethiol, mainly resulting from the absolutely highest influence of Latilactobacillus. Cooperative fermentation of starters is an effective method to improve the volatile flavor in the fermented tilapia surimi.

Novel insight into the formation and improvement mechanism of physical property in fermented tilapia sausage by cooperative fermentation of newly isolated lactic acid bacteria based on microbial contribution

Single starter can hardly elevate the gel property of fermented freshwater fish sausage. In this work, in order to improve the physical properties of tilapia sausage, two newly isolated strains of lactic acid bacteria (LAB), Latilactobacillus sakei and Pediococcus acidilactici were used for cooperative fermentation of tilapia sausage, followed by the revelation of their formation mechanisms during cooperative fermentation and their improvement mechanisms after comparison with natural fermentation. Both strains, especially L. sakei possessed good growth, acidification ability, and salt tolerance. The gel strength, hardness, springiness, chewiness, whiteness, acidification, and total plate count significantly elevated during cooperative fermentation with starters. Pediococcus, Acinetobacter, and Macrococcus were abundant before fermentation, while Latilactobacillus quickly occupied the dominant position after fermentation for 18-45 h with the relative abundance over 51.5 %. The influence of each genus on the physical properties was calculated through the time-dimension and group-dimension correlation networks. The results suggested that the increase of Latilactobacillus due to the good growth and metabolism of L. sakei contributed the most to the formation and improvement of gel strength, texture properties, color, acidification, and food safety of tilapia sausage after cooperative fermentation. This study provides a novel analysis method to quantitatively evaluate the microbial contribution on the changes of various properties. The cooperative fermentation of LAB can be used for tilapia sausage fermentation to improve its physical properties.

Red Yeast Rice and Optimal Fermentation Periods Improve the Quality of Esan Fermented Fish Sausage

Esan fermented fish sausage (EFFS) has an unappealing off-white color. The incorporation of an appropriate amount of red yeast rice (RYR) and the selection of an optimal fermentation period may yield visually appealing, high-quality sausages. This study is aimed at investigating the effects of different RYR levels (0, 0.35, and 0.7%) and fermentation periods (0, 2, 4, and 6 days) on the quality parameters of EFFS. The following parameters were examined for raw EFFS: CIE color values (L∗, a∗, and b∗), microbial analyses (total viable count, lactic acid bacteria, and yeast and mold counts), titratable acidity (TA), pH, weight loss, cooking loss, texture profile analysis (TPA), and sensory evaluation (color, odor, hand-feel texture, overall acceptability, and overall preference ranking). The quality parameters of the cooked EFFS were CIE color values and sensory evaluation (color, odor, mouthfeel, texture, flavor, overall acceptability, and overall preference ranking). The results showed that 0.35 and 0.7% RYR increased the a∗ (red/green) values of raw and cooked EFFS but decreased the L∗ (lightness) and b∗ (yellow/blue) values. These RYR levels significantly improved the sensory color, overall acceptability, and overall preference ranking of the raw and cooked EFFSs. However, no statistical differences were observed between the effects of 0.35 and 0.7% RYR. RYR levels did not affect the microbial analyses, TA, pH, weight loss, cooking loss, or TPA. Moreover, they had no effect on the odor and hand-feel texture of raw EFFS, or the odor, mouthfeel texture, or flavor of cooked EFFS. Therefore, RYR supplementation improved the color quality of the EFFSs without altering the other quality parameters, with 0.35% RYR deemed optimal. Moreover, the fermentation period significantly influenced most quality parameters, except CIE color values and sensory color perception of raw and cooked EFFSs. Most sensory parameters improved by day 2, remained unchanged until day 4, and then deteriorated on day 6.

Characterization of the physicochemical Properties, bacterial community and non-volatile profiles of fermented Yu jiangsuan by Weissella cibaria and Lactobacillus plantarum

Yu jiangsuan (YJS) is a unique traditional fermented condiment in China. Physicochemical, bacterial communities, and non-volatile properties were examined in inoculation Autochthonous Weissella cibaria and Lactobacillus plantarum. The results indicated that inoculation samples did well in shortening fermentation time; amino acid nitrogen (AN) and TCA-soluble peptide contents of fermented YJS were 10.8% and 17.4% higher than those of naturally fermented YJS, respectively. However, its total volatile base nitrogen (TVB-N), thiobarbituric acid (TBARS), and nitrite were only 74.3%, 87.2% and 83.6% of those of naturally fermented YJS. In addition, the dominant bacterial genera were Lactobacillus, Weissella and Pectobacterium, whose contributions were 41.2%, 20.3% and 5.5%, respectively. Moreover, 26 significantly differential metabolites were identified, and involved in 10 metabolic pathways. The decomposition of substrates and the formation of differential metabolites in YJS were primarily centered on the TCA cycle and the metabolism of carbohydrates. Therefore, this study is conducive to discovering the bacterial community structure and metabolite composition of probiotic inoculated YJS fermentation, as well as the potential value of core functional bacteria genera in controlling YJS production in industry.

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.

The effect of heating method on the gel structures and properties of surimi prepared from Bombay duck (Harpadon nehereus)

This study investigates the effects of heating method, setting time, and setting temperature on the gel properties, water holding capacity (WHC), molecular forces, protein composition, protein conformation, and water transition of Bombay duck (BD) surimi gel. The obtained results demonstrate that the best gel properties are obtained by two-step heating at 30°C for 120 min while the hardness was 10.418 N and the breaking force was 4.52 N. Gel softening occurs at setting temperatures greater than 40°C due to the effect of endogenous enzymes in destroying the protein structure and increasing the hydrophobic and disulfide interactions. Low-field nuclear magnetic resonance spectra confirm that high two-step setting temperatures induce gel softening and the destruction of the surimi gel structure, as evidenced by the increased water migration at these temperatures. Of all protein conformations in the gel, the β-sheet structure, decreases from 38.40% at 30°C to 11.75% at 60°C when the setting time is 60 min, is the most susceptible to gel softening. Overall, the data reported herein provide a scientific basis for the development of new BD surimi products on an industrial level.

Effect of Pre-Emulsion of Pea-Grass Carp Co-Precipitation Dual Protein on the Gel Quality of Fish Sausage

Currently, the processing method of introducing plant protein into meat products has attracted great attention. However, the direct addition of plant protein often leads to a decline in meat product quality. This paper aims to provide an efficient method for incorporating plant protein into fish sausage. Pea protein isolate (PPI), grass carp protein isolate (CPI) and pea-grass carp coprecipitated dual protein (Co) were derived from pea and grass carp by an isoelectric solubilisation/precipitation method. At the same time, the blended dual protein (BL) was obtained by blending PPI with CPI, and the plant and animal protein content of Co and BL was both controlled to be the same. The four proteins were combined with soybean oil and water to form a three-phase pre-emulsification system of protein-oil-water, which was added to grass carp meat as a replacement for animal fat to prepare fish sausage. The gelation properties of the four fish sausages and those without protein were analysed. The results showed that the gel quality of PPI fish sausage is poor, while the overall quality of Co fish sausage as a whole was significantly superior to that of PPI and BL, which was equivalent to CPI fish sausage. The sensory score of the Co fish sausage was slightly lower than that of CPI, but it had significantly higher water-holding capacity and hardness (p < 0.05). The Co fish sausage showed the synergistic effect of heterologous proteins, while BL had some antagonistic effects. This study shows that Co pre-emulsion is an effective strategy to introduce plant protein, so it has a good application prospect in the meat industry.

Effect of κ-carrageenan on the gelation properties of oyster protein

Proteins and polysaccharides commonly coexist in the food system, forming complexes and coacervates to make tailor-made food. In this study, the effects of κ-carrageenan on the rheological behavior, network structure, textures, and molecular force of oyster protein (OP treated with high-pressure homogenization were investigated. Rheological results showed that κ-carrageenan improved the storage modulus of OP, and the higher concentration of κ-carrageenan accelerated the gelation of OP. The second derivative of infrared spectroscopy revealed that κ-carrageenan contributed to the formation of β-sheet in OP. Molecular force and texture analysis showed that κ-carrageenan might promote the increase of hydrophobic bonds and disulfide bonds, which was helpful to enhance gel strength. The microstructure showed that the OP gel with 1.5% κ-carrageenan had a compact network structure with abundant minor mesh and sheet edge. This study reveals the gelation mechanism of OP/κ-carrageenan and provides the theoretical basis for developing innovative oyster products.

Starter inoculums assisted fermentation of Puntius sp. - role of Lactiplantibacillus plantarum and Staphylococcus piscifermentans to reduce fermentation time while increasing safety

AIMS

To evaluate the role of starter inoculums to reduce total fermentation time as well as improve safety and quality of Sheedal, a fermented fish-product of India.

METHODS AND RESULTS

Lactiplantibacillus plantarum and Staphylococcus piscifermentans were isolated from the Sheedal and used as starter inoculums. To justify fermenting and probiotic properties of the starter inoculums, characteristics like proteolytic and lipolytic activity, cell-surface hydrophobicity, cell auto-aggregation and co-aggregation, antibiotic susceptibility and antimicrobial assay were performed. Changes of the count of lactic acid bacteria, staphylococci and Enterobacteriaceae were studied periodically.

CONCLUSIONS

Higher increase of α-amino nitrogen and TCA-soluble peptides during fermentation was observed in treatment which was inoculated with both L. plantarum and S. piscifermentans. Poor competitiveness of staphylococci in presence of LAB was found. Inoculation of both L. plantarum and S. piscifermentans as starter showed positive effect to reduce significantly the fermentation period from usual 4-5 months to 75 days, whereas, same was achieved after 105^th and 120^th by the use of either L. plantarum or S. piscifermentans, respectively.

SIGNIFICANCE AND IMPACT OF STUDY

Reduction of the total fermentation period is considered as an additional advantage in Sheedal technology in addition to the safety of the product as evidenced by low pH and high titratable acidity.

Effect of Mixed Starters on Proteolysis and Formation of Biogenic Amines in Dry Fermented Mutton Sausages

In this study, by comparing the four groups of sausages, namely, CO (without starter culture), LB (with Lactobacillus sakei), LS (with L. sakei 3X-2B + Staphylococcus xylosus SZ-8), and LSS (with L. sakei 3X-2B + S. xylosus SZ-8 + S. carnosus SZ-2), the effects of mixed starter cultures on physical-chemical quality, proteolysis, and biogenic amines (BAs) during fermentation and ripening were investigated. Inoculation of the mixed starter cultures increased the number of lactic acid bacteria and staphylococci in sausages during fermentation and ripening for 0 to 5 days. The L. sakei 3X-2B + S. xylosus SZ-8 + S. carnosus SZ-2 mixed starter accelerated the rate of acid production and water activity reduction of sausages and improved the redness value. Compared with CO, the mixed starter effectively inhibited Enterobacteriaceae. At the end of ripening, the LSS group was approximately 1.25 CFU/g, which was less than the CO group, thereby reducing the total volatile basic nitrogen (TVB-N) in the LSS group. The free amino acids in the LS and LSS groups (224.97 and 235.53 mg/kg dry sausage, respectively) were significantly (p < 0.001) higher than that in the CO group (170.93 mg/kg dry sausage). The level of histamine, cadaverine, putrescine, and common BAs showed an opposite trend to the increase of the corresponding precursor amino acid content, which were significantly lower (p < 0.001) in the LS and LSS sausages than in CO. This study showed that L. sakei 3X-2B + S. xylosus SZ-8 + S. carnosus SZ-2 is a potential mixed starter for fermented meat products.

Muscle Protein Hydrolysates and Amino Acid Composition in Fish

Fish muscle, which accounts for 15%-25% of the total protein in fish, is a desirable protein source. Their hydrolysate is in high demand nutritionally as a functional food and thus has high potential added value. The hydrolysate contains physiologically active amino acids and various essential nutrients, the contents of which depend on the source of protein, protease, hydrolysis method, hydrolysis conditions, and degree of hydrolysis. Therefore, it can be utilized for various industrial applications including use in nutraceuticals and pharmaceuticals to help improve the health of humans. This review discusses muscle protein hydrolysates generated from the muscles of various fish species, as well as their amino acid composition, and highlights their functional properties and bioactivity. In addition, the role of the amino acid profile in regulating the biological and physiological activities, nutrition, and bitter taste of hydrolysates is discussed.

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.

Effect of Lactobacillus plantarum on antioxidant activity in fermented sausage

This study investigated in vitro antioxidant activity of Lactobacillus plantarum CD101 and its effect on antioxidant peptides formation in fermented sausage. The antioxidant substances of L. plantarum CD101 were mainly distributed on the cell surface and extracellular secretions. L. plantarum CD101 affected the acidification and proteolysis during the fermentation. Combined with electrophoresis and peptide content analysis, these results indicated the effectiveness of the starters in promoting peptide formation, accompanied by a small change in antioxidant activities. Forty-four effective peptides were identified by LC-MS/MS. The masses of the peptides were less than 3 kDa, and their amino acid sequences were between 5 and 27 amino acids in length. Thus, L. plantarum CD101 may be beneficial to inhibit the oxidative rancidity of fermented sausage through its in vitro antioxidant activity, while effectively promoting protein degradation with a weak effect on antioxidant peptides promotion.

Hydrolysis of raw fish proteins extracts by Carnobacterium maltaromaticum strains isolated from Argentinean freshwater fish

•

Carnobacterium and Vagococcus genera were identified from Paraná River freshwater fishes.

•

Low acidifying and antilisterial Carnobacterium strains were selected.

•

Proteolysis of raw fish extract by C. maltaromaticum strains was confirmed.

•

C. maltaromaticum strains may be used as functional cultures to develop novel LPFP.

Lactic acid bacteria (LAB) isolated from freshwater fish (hatcheries and captures) from Paraná river (Argentina) were analyzed by using culture-dependent approaches. The species belonging to Carnobacterium (C.) divergens, C. inhibens, C. maltaromaticum, C. viridans and Vagococcus (V.) salmoninarum were identify as predominant by RAPD-PCR and 16 s rRNA gene sequencing. C. maltaromaticum (H-17, S-30, B-42 and S-44) grew in raw fish extract and slightly reduced the medium pH (5.81–5.91). These strains exhibited moderate fish sarcoplasmic protein degradation (≤ 73 %) releasing small peptides and free amino acids, being alanine, glycine, asparagine and arginine concentrations increased in a higher extent (17.84, 1.47, 1.26 and 0.47 mg/100 mL, respectively) by S-44 strain at 96 h incubation. Interestingly C. maltaromaticum H-17 was able to inhibit Listeria monocytogenes. Results suggest that these strains would contribute to the development of new safe and healthy fishery products with improved nutritional and sensory characteristics.

Pediococcus pentosaceus PP04 Ameliorates High-Fat Diet-Induced Hyperlipidemia by Regulating Lipid Metabolism in C57BL/6N Mice

In this study, Pediococcus pentococcus PP04 isolated from the Northeast pickled cabbage had good gastrointestinal tolerance and can colonize in the intestine stably. C57BL/6N mice were fed a high-fat diet to build animal models and treated with Pediococcus pentosaceus PP04 to evaluate the antihyperlipidemia effect. After 8 weeks, the indicators of hyperlipidemia, liver injury, and inflammation were measured. The treatment of P. pentosaceus PP04 reduced the gain of total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), free fatty acids (FFAs), leptin, alanine aminotransferase (ALT), aspartate aminotransferase (AST), lipopolysaccharides (LPS), and tumor necrosis factor-α (TNF-α) significantly. The western blotting results suggested P. pentosaceus PP04 ameliorated high-fat diet-induced hyperlipidemia by the AMPK signaling pathway, which stimulated lipolysis via upregulation of PPARα and inhibited lipogenesis by downregulation of SREBP-1c, fatty acid synthase (FAS), and stearoyl-CoA desaturase-1 (SCD1) mainly. Furthermore, P. pentosaceus PP04 improved high-fat diet-induced oxidative stress effectively by triggering the Nrf2/CYP2E1 signaling pathway that enhanced the antioxidant activity including superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px).

A study revealing volatile aroma produced by Pediococcus pentosaceus in dough fermentation

Pediococcus pentosaceus is important probiotics in Chinese Laomian. Its role in meat and fermented vegetable has been largely demonstrated, but few studies have investigated the role of P. pentosaceus in Chinese Laomian. For this purpose, we simulated Laomian fermentation using Saccharomyces cerevisiae and P. pentosaceus. Volatile aroma was detected by headspace solid-phase microextraction gas-chromatography-mass spectrometry. Real-time fluorescent quantitative polymerase chain reaction was used to determine dynamic growth of S. cerevisiae and P. pentosaceus in fermentation. Extracellular proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Folin-Ciocalteu method was used to detect extracellular protease activity in different pH values. Owing to addition of P. pentosaceus, the types and contents of esters increase, the relative contents of acetic acid hexyl ester, formic acid octyl ester, and heptanoic acid ethyl ester rise obliviously; especially, the relative content of hexanoic acid ethyl ester was highly correlated with P. pentosaceus by increasing 20.61%. As the gel electrophoresis results display, due to mixed fermentation of S. cerevisiae and P. pentosaceus, the 25k Da and 51k Da proteins expression quantity of P. pentosaceus clearly increased. Under neutral and alkaline culture conditions, the extracellular protease activity of P. pentosaceus is higher. This research benefits to gain insight into the fermentation actions of P. pentosaceus in Chinese Laomian.

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.

Quality evaluation of surimi and fish nuggets from Queen fish (Scomberoides commersonnianus)

The purpose of this study was formulation and evaluation of physicochemical properties of fish and surimi nuggets prepared from Queen fish (Scomberiodes commersonnianus) during 90 days of storage. Chemical analysis showed that surimi nuggets contained less protein, fat, and ash due to washing steps during surimi preparation. The titratable acidity, peroxide, and TBA values for fish nuggets were significantly higher than surimi nuggets during frozen storage (p < .05). Moreover, the textural properties of the products exhibited more firmness of surimi nuggets before cooking compared with fish nuggets (p < .05) and more firmness of fish nuggets after cooking compared with surimi one (p < .05). Furthermore, surimi nuggets were lighter and had lower total bacterial counts rather than fish nuggets during frozen storage (p < .05). SDS-PAGE of the samples during storage exhibited more intensity of the bands related to α-actinin, actin, and β-tropomyosin in surimi nuggets compared with that for fish nuggets. Moreover, the sensory evaluation showed that acceptability of surimi nuggets was more than that for fish nuggets after frozen storage. These results showed that surimi nuggets had higher quality indicators rather than fish nuggets.

Effects of different starter culture combinations on microbial counts and physico-chemical properties in dry fermented mutton sausages

This study was conducted to evaluate the effects of inoculation with different mixed starter culture combinations on microbial counts, physico-chemical properties, and proteolytic and lipolytic properties of dry fermented mutton sausages during fermentation and ripening. Four different batches of mutton sausages were manufactured: CO batch, no starter cultures, used as control; LB batch with Lactobacillus sakei; LS batch with L. sakei + Staphylococcus xylosus; and LSS batch with L. sakei + S. xylosus + Staphylococcus carnosus. The results showed that adding starter culture caused Lactobacillus and Staphylococcus to become dominant bacteria and reduced the Enterobacteriaceae count in the inoculated sausages. The mixed starter cultures (LS & LSS) accelerated acidification and reduced water activity and lipid oxidation. Statistical analysis revealed that the use of mixed starter cultures, especially the combination L. sakei + S. xylosus + S. carnosus, contributed to proteolysis and lipolysis, increasing total free amino acids and polyunsaturated fatty acids. The above results demonstrate that the use of mixed starter cultures contributes to improving the composition of free amino acids and free fatty acids as well as the hygienic quality of dry fermented mutton sausages.

Isolation and identification of hyper-ammonia-producing bacteria from commercial fermented skates (Raja kenojei)

Ammonia-producing bacteria were isolated and identified from five commercial fermented skates (A1, A2, A3, A4, and A5). In addition, the pH, ammonia nitrogen, total volatile nitrogen (TVBN), trimethylamine nitrogen (TMAN), and amino nitrogen contents of skate samples were also determined. A total of 88 strains of ammonia-producing bacteria was isolated and seven hyper-ammonia-producing bacteria isolates (A2-2, A2-3, A2-12, A2-18, A2-20, A3-6 and A3-14) were selected based on ammonia nitrogen producing ability. Those isolates were identified as Proteus hauseri (three strains), Providencia rustigianii (three strains), and Kurthia gibsonii. The pH and ammonia nitrogen content in skate samples were ranged from 8.63 to 9.03, and 4.86 to 7.31 g/kg, respectively. No significant difference of pH values was observed in skate samples A2, A3, A4 and A5. While, skate samples A3, A4 and A5 showed similar level of TVBN and TMAN content. Skate sample A2 showed the highest amino nitrogen content among all samples, which indicated the highest degree of protein degradation of skate muscle during fermentation. Bivariate cluster analysis showed that skate samples A3, A4, and A5 clustered together at a relatively high level, implying a similar microbial environment during fermentation. The cluster analysis allowed different commercial fermented skates to be clearly differentiated based on the characteristics determined in this study. This study can provide important information for investigating the mechanisms underlying ammonia flavor formation in skate muscle during fermentation.

Effects of inoculating autochthonous starter cultures on N-nitrosodimethylamine and its precursors formation during fermentation of Chinese traditional fermented fish

This study investigated the effects of Lactobacillus plantarum 120, Saccharomyces cerevisiae 2018 and Staphylococcus xylosus 135 inoculation on N-nitrosodimethylamine (NDMA) and its precursors formation, and on microbiological characteristics of Chinese traditional fermented fish products (CTFPs). The results indicated that three strains could directly degrade NDMA in culture broth, and the highest degradation rate was observed in L. plantarum 120. The lactic acid bacteria counts in samples inoculated with L. plantarum 120 and mixed starter cultures were significantly (P < 0.05) higher than the others during the initial and middle fermentation stages (≤3 weeks). The final contents of total volatile base nitrogen, trimethylamine, dimethylamine, nitrite and NDMA in inoculated samples were significantly (P < 0.05) lower than those in spontaneous fermentation samples. According to these results, the inoculation with autochthonous starter cultures was a promising method to inhibit the NDMA and its precursors accumulation in CTFPs during fermentation process.

Endogenous proteolytic enzymes--a study of their impact on cod (Gadus morhua) muscle proteins and textural properties in a fermented product

The aim of this study was to investigate endogenous proteolytic activities in a cod product and their impact on muscle proteins and textural properties during fermentation and storage. The result of specific proteolytic activities showed that cathepsins, especially cathepsin B, had the highest activities during fermentation and storage. SDS-PAGE indicated more degradation of myofibrillar proteins by cathepsin L than other proteases and that the hydrolysis by cathepsins was pronounced in the last stage of fermentation. Texture analysis showed that cathepsins had a negative impact on gel strength and this impact increased in the last stage of fermentation. However the product still had a firm texture. During storage (4 °C) for one week, no significant changes were seen in the gel strength. In conclusion, cathepsins had more impact on muscle proteins and textural properties than other proteases during fermentation but had little impact on gel strength during storage at 4 °C.