The inhibition mechanism of PostbioYDFF-3 on quality deterioration of refrigerated grass carp fillets from the perspective of endogenous enzyme and microorganisms changes.

The protective mode of PostbioYDFF-3 (referred to as postbiotics) on the quality stability of refrigerated fillets was explored from the aspects of endogenous enzyme activity and the abundance of spoilage microorganisms. Compared to the control group, the samples soaked in postbiotics showed significant reductions in TVC, TVB-N and TBARS values by 39.6%, 58.6% and 25.5% on day 5, respectively. In addition, the color changes, biogenic amine accumulation and texture softening of the fish fillets soaked in postbiotics were effectively suppressed. Furthermore, the activity of endogenous enzyme activities was detected. The calpain activities were significantly inhibited (p < 0.05) after soaking in postbiotics, which declined by 23%. Meanwhile, high throughput sequencing analysis further indicated that the growth of spoilage microorganism such as Acinetobacter and Pseudomonas were suppressed. Overall, the PostbioYDFF-3 was suitable for preserving fish meat.

The protective pattern of chitosan-based active coating on texture stabilization of refrigerated carp fillets from the perspective of proteolysis.

Herein, the protective pattern of chitosan coating enriched with green tea extract on texture stabilization of refrigerated grass carp fillets was explored. In general, higher shear force and lower endogenous enzyme activities were observed in coated fillets, with the max. level of cathepsins and calpain decreasing by 30.2 âˆ¼ 39.6 % when compared to the control during storage. Meanwhile, the coating reduced protein composition changes and accumulation of protein degradation products. According to label-free proteomic analysis, the proteome closer to fresh sample was observed in coated fillets than that of the control, as supported by PCA and hierarchical cluster analysis. Meanwhile, 33 differential proteins involved in tissue structure, protein phosphorylation and protein turnover were further screened out, and most DAPs showed up-regulation in coated fillets compared to the control on day 12. Presumably, the coating modulated endogenous enzyme-induced myofibrillar protein degradation and protein phosphorylation level, thereby stabilizing the texture properties of refrigerated fillets.

Identification of characteristic flavor and microorganisms related to flavor formation in fermented common carp (Cyprinus carpio L.).

Microbial metabolism is crucial for the flavor development of traditional Suanyu. A total of 21 characteristic volatile compounds of Suanyu were identified according to GC-MS combined with GC-O analysis. HCA results indicated that the whole fermentation process could be divided into three stages: raw material (fresh), initial fermentation (0-2 week) and the late fermentation (2-4 week). Moreover, nine flavor markers in different fermentation stages were revealed using the OPLS-DA model and VIP values. Furthermore, metagenomic sequencing was used to analyze the possible formation pathways of the characteristic flavor compounds and identify the key microorganisms related to flavor formation at the gene level. The top 10 bacterial genera associated with flavor formation were Staphylococcus, Enterococcus, Vibrio, Kocuria, Lactobacillus, Macrococcus, Streptococcus, Enterobacter, Lactococcus and Pediococcus, accounting for large parts of flavor formation of fermented Suanyu. This study is helpful to elucidate the different metabolic roles of microorganisms in flavor formation during fermentation.

Multifunctional bioactive coatings based on water-soluble chitosan with pomegranate peel extract for fish flesh preservation.

This study aimed to reveal the effects of vacuum-impregnated carboxymethyl chitosan (CMCS) coating with pomegranate peel extract (PPE) on quality retention of fish flesh during refrigeration. Herein, CMCS-PPE coating was effective in attenuating quality loss of grass carp fillets. Compared to Control, the levels of drip loss, total volatile base nitrogen, and K value in coated samples were sharply decreased (p < 0.05) by 24.5%, 35.3% and 25.2% on day 9, respectively. Meanwhile, the coating also helped inhibit oxidation, bioamine accumulation, and texture softening in fillets. Moreover, the microbial enumeration was reduced by >1.4 lg cfu/g as compared to Control on day 6 afterward, and high throughput sequencing analysis further showed the active coating contributed to the notable growth suppression of spoilage bacteria like Shewanella. Additionally, the positive effect of the coating scheme was also verified in longsnout catfish and snakehead, further confirming its good applicability for fish flesh preservation.

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.

Correlations between microbiota succession and flavor formation during fermentation of Chinese low-salt fermented common carp (Cyprinus carpio L.) inoculated with mixed starter cultures.

The correlation between microbiota succession and flavor development in Chinese traditional fermented fish (Suanyu) inoculated with mixed starter cultures was studied. The results showed that 17 free amino acids, 22 free fatty acids and 9 organic acids were present. A total of 81 aroma compounds were detected during Suanyu fermentation. Aldehydes were the most abundant aroma compounds in the early stage of fermentation and esters contributed most to the aroma in the later stage of fermentation. The correlation analysis of microbial succession and flavor dynamics based on bidirectional orthogonal partial least squares (O2PLS) suggested that in addition to starter cultures, other microorganisms including 2 bacteria genera and 11 fungi genera were also responsible for the formation of flavor compounds. These results may help focus further research to improve the flavor quality of traditional fermented fish.

Quality, functionality, and microbiology of fermented fish: a review.

Fermentation is a traditional food preservation method and is widely used for improving food safety, shelf life, and organoleptic and nutritional attributes. Fermented fish are produced and consumed in different parts of the world and are an integral part of many food cultures. Furthermore, fermented fish are a source of interesting microbes and are an important industry in many countries. This review tries to update the types and manufacturing processes for fermented fish around the world. The emphasis is on this work related to fermented fish and their health benefits, as well as the contribution of microorganisms to their fermentation. A variety of different approaches have been used to determine and understand microbial composition and functionality. Moreover, some challenges and future research directions regarding fermented fish are also discussed in this review. Further research into fermented fish products is of crucial importance not only for the food industry but also for human health. However, extensive in vivo and toxicological studies are essential before the application of bioactive-rich fermented fish products for human health benefits.

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.

Inhibition of microbial spoilage of grass carp (Ctenopharyngodon idellus) fillets with a chitosan-based coating during refrigerated storage.

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.

Inhibitory effects of chitosan-based coatings on endogenous enzyme activities, proteolytic degradation and texture softening of grass carp (Ctenopharyngodon idellus) fillets stored at 4 °C.

The study evaluated the inhibitory effects of chitosan-based coatings on endogenous enzyme activities, proteolytic degradation and texture softening of grass carp (Ctenopharyngodon idellus) fillets stored at 4 °C for 15 days. In general, the inhibitory effects of chitosan coating were worse than that of chitosan composite coatings, which significantly inhibited cathepsin B, B + L and calpain activities of fillets, with the most reductions of 58%, 65% and 41%, respectively when compared to the corresponding values of control fillets. Besides, the treatments also retarded the proteolytic degradation through quantifiable indicators including salt-soluble proteins (SSP), TCA-soluble peptides and SDS-PAGE pattern. After storage of 15 days, the shear forces of coated fillets were 28-53% higher than that of control samples. These results indicated that chitosan composite coating combined with glycerol monolaurate and clove essential oil improved the quality of refrigerated grass carp fillets by alleviating endogenous enzyme induced proteolysis and softening.

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

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 NaN3 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.