preparation-of-high-quality-fermented-fish-product

Preparation of High-Quality Fermented Fish Product

This protocol provides a method for preparation of industrialized fermented fish product with sturgeon (Aquilaria sinensis) meat product. The procedures ...

Jiangnan University

The structural changes and aggregation properties of silver carp actomyosin acidified with d-gluconic acid-δ-lactone (GDL) were investigated. Results showed that silver carp actomyosin underwent aggregation and formation of precipitate as indicated by turbidity and centrifugation coupled electrophoresis analysis. Circular dichroism indicated that myosin rod unfolded during acidification, resulting in a gradual decrease in α-helical content. The changes in tertiary structure of actomyosin under acidic conditions were demonstrated by second-derivative UV spectra and intrinsic fluorescence. Tyrosine residues were exposed to the surface of proteins when pH was decreased to 5.5, and were buried inside the protein aggregates with further reduction in pH. In contrast, more tryptophan residues were exposed to the polar environment with decreasing pH. 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide crosslinking experiments showed that the intensity of myosin heavy chain (MHC) bands decreased sharply with decreasing pH and the actin bands decreased more slowly, suggesting that MHC is the major protein component involved in the non-covalent cross-linking and formation of aggregates during acidification of silver carp actomyosin.

Aggregation and structural changes of silver carp actomyosin as affected by mild acidification with D-gluconic acid δ-lactone.

The study was aimed to investigate different roles of endogenous and Lactobacillus plantarum proteases during fast fermentation of silver carp. The results show that endogenous proteases could degrade both sarcoplasmic and myofibrillar proteins. In contrast, L. plantarum had low proteinase activities and could only hydrolyze sarcoplasmic peptides. This indicates that gel properties could be mainly affected by endogenous proteolysis while microbial proteolysis contributed to the production of smaller peptides and free amino acids which may be related to flavor and taste. Texture and free amino acid analyses verified these hypotheses. It shows that endogenous lysosomal proteases were the major contributors for the decrease of gel strength while L. plantarum proteolytic activities could lead to the increase of aspartic acid, glutamic acid, and alanine, which may result in umami and sweet taste; and also lead to a rise in some amino acids which were volatile compounds precursors. 

A comparison of endogenous and microbial proteolytic activities during fast fermentation of silver carp inoculated with Lactobacillus plantarum.

To investigate the contribution of autochthonous microflora on free fatty acids (FFA) release and flavor development in low-salt fermented fish, three groups of processed fish, including bacteriostatic-acidification group (BAG), bacteriostatic group (BG), and spontaneous fermented fish (CG) were established. Results showed that addition of NaN reduced microbial load in BAG and BG below 3.5 log CFU/g after 3 weeks of incubation. Activities of lipases and lipoxygenase declined markedly with increasing time, where BG had the highest activities, followed by CG and BAG. There is a 36.3% higher in the total FFA content in CG than that in BAG, indicating both microbial and endogenous lipases contributed to the FFA liberation in fermented fish while endogenous lipases play a major role. However, compared to BAG and BG, largely higher levels of volatile compounds were observed in CG, suggesting that autochthonous microflora dominated the generation of volatile flavor compounds in fermented fish.

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

The objective of this study was to investigate the differential role of cathepsin B, L, D and calpain in degradation and disassembly of myofilament. Myofibrillar protein of grass carp (Ctenopharyngodon idella) was incubated with proteases monotonously, simultaneously or sequentially. Subsequently, protein degradation were detected using SDS-PAGE and myofilament disassembly induced by changes of non-covalent interactions were measured through SDS-PAGE using l-Ethyl-3-(3-Dimethylaminopropyl) Carbodiimide (EDC) as a zero length cross-linker. Additionally, content of heat shock proteins which functioned in stabilizing assembly architecture of myofibrillar protein was determined. Results showed that calpain and cathepsin B, calpain and cathepisn L could act in a stepwise and complimentary manner to synergistically dissociate and degrade myofibrillar protein. In synergistic action, cathepsin B disrupted the thick filament assembly through lowering the UNC45 and HSP90 concentration in myofibrillar protein, facilitating the degradation of dissociated MHC by calpain. Meanwhile, Cathepsin L was shown to preferentially remove the actin from thin filament via lowering the content of HSP27 and αb-crystallin, to create dissociated actin as substrate supply for calpain.

Synergistic action of cathepsin B, L, D and calpain in disassembly and degradation of myofibrillar protein of grass carp.

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.

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

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.

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

The effects of a chitosan-based coating on the inhibition of microbial spoilage of grass carp (Ctenopharyngodon idellus) fillets were studied during refrigerated storage for 15 days in terms of pH, total volatile base nitrogen (TVB-N), trimethylamine (TMA), adenosine triphosphate (ATP)-related compounds, K value, microbial enumeration and high-throughput sequencing. The results indicated that the fillets treated with chitosan-based coating enriched with 0.3% glycerol monolaurate and 0.5% clove essential oil had lower values of TVB-N, TMA, hypoxanthine riboside (HxR), hypoxanthine (Hx) and K value with the significant reductions (P < 0.05) of nearly 34, 73, 32, 74 and 38%, respectively, when compared to the control at day 15 of storage. Using high-throughput sequencing analysis, the major bacteria phyla of Firmicutes, Cyanobacteria and Bacteroidetes and the bacteria family of Lachnospiraceae and Bacteroidaceae were observed in fresh grass carp. As storage time increased, the coated samples retained bacterial diversity. However, Shewanellaceae, Pseudomonadaceae and Flavobacteriaceae increased and became the predominant microbiota in spoiled control samples. The significant difference between the bacteria species in the control and coated samples showed that the coating had the potential to inhibit microbial growth, especially spoilage microorganisms, and reduced quality deterioration caused by bacteria during refrigerated storage of grass carp fillets.

Yan-Shun Xu

Jiangnan University

Preparation of High-Quality Fermented Fish Product