Study On The Fermented Freshwater Fishes Surimi And Its Gel Formation Mechinism

Surimi, a high protein content, low fat content, and taste tender, are very popular in the world. But the raw materials of surimi are mainly used marine fish and freshwater fish is seldom used for difficult to form gel, and has lower gel strength and easy gel deterioration. Application of bio-fermentation method to maintain and improve the quality of products or inhibit the growth of bacteria is a good food processing and preservation method which has been widely used in the livestock meat processing, such as fermented ham and sausage. This study, according to the microbial fermentation performance and surimi production of the basic technology and combined with modern food and fermentation technology, will develop fermented surimi with a unique flavor, high-nutrition, high-security, long-term storage. This study has an academic significance for understanding structural changes of fish protein in the context of fermentation and the formation mechnisms of gelation, and establishs a new bio-fermentation processing technology system to provide a solid theoretical and a scientific basis for the aquatic processing industries.Determination of the seven Lactobacillus (LC, LS, Lp-1, LP-5, Lp-8, Lp-10. Lp-15), two Pediococcus pentosaceus (PP and Pp-8) and a Staphylococcus xylosus (Sx-12) growth, acid, salt, protein and fat production capacity of decomposition, antagonism, such as antibacterial physiology. The results showed that these strains have good fermentation and growth properties. The acid production for 9 Lactobacillus species in 24 hours was significantly different compared with the 0 h. During 24 h fermentation, the pH of samples with Lp-8 decreased rapidly from around 6.12 to 3.95; pH for Sx-12 decline slowly, and at 48 h pH was 5.0. LS and Lp-1 had more poor salt tolerance than the other bacterial. Performances of a preliminary indication for Lp-5, Lc, Sx, Pp, Lp-8, Lp-15 showed good fermentation characteristics and used them as the starter cultures to make fermented surimi. As fermentation time increased, silver carp sausages inoculated with starter (Lp-5, Lc, Sx-12, PP, Lp-8, Lp-15) showed a lower pH than the control Non-protein nitrogen and aminopeptide nitrogen content increased with fermentation time, Staphylococcus xylosus showed the largest contend during 60 h fermentation. TVBN value of the samples inoculated starter is still fresh standard (15-25 mg/100 g) after 60 h fermentation. In contrast, the control has been corruption after 48 h. Starter cultures exhibited higher texture profiles (hardness, gumminess, springiness and chewiness) and whiteness than the control (P < 0.05), and inhibit the growth and reproduction of Pseudomonas and Enterobacteriaceae(p <0.05). Apart from Sx-12, adding starter effectively suppressed the accumulation of histamine, cadaverine, putrescine, tryptamine and tyramine during fermentation. Sensory evaluation (flavor, texture, appearance and overall acceptability) showed that adding starter significantly improve the quality of surimi,especially strains LC, PP, Lp-8 showed higher sensory characteristics.On the basis of the of a single starter, the mixed starter cultures were used in the manufacture of fermented surimi. During the 72 h fermentation at 30°C, silver carp surimi inoculated with mixed starter cultures resulted in a rapid pH decrease, suppression in the growth of Enterobacteriaceae, Pseudomonas, yeasts and molds, and exhibited higher texture profiles (hardness, gumminess, springiness and chewiness) and whiteness than the control (P < 0.05). The changes in non-protein nitrogen (NPN), free amino acid and SDS-PAGE indicated severe hydrolysis of muscle protein occurred during fermentation. Polyunsaturated fatty acids were higher in quantity in sausages with cultures compare to the control. No significant differences for taste, texture, and appearance were found among batches with mixed starters. The sausage inoculated with the combination of lactobacillus plantarum-15, Staphylococcus xylosus-12 and Lactobacillus casei subsp casei-1.001 (S-PXC) gained highest scores for flavor and overall acceptability. Application headspace solid-phase microextraction and gas chromatography-mass spectrometry (HS-SPME-GC-MS) and olfactory monitors was identified for the determination of flavor-contributing volatiles for silver carp sausages fermented with mixed starter cultures. Fourty-two and fourty-four compounds were identified from the silver carp sausages fermented at 24 h and 48 h, respectively. Acetic acid, hecanal, hexanol, ethyl acetate and 2,3-pentanedione, 2-pentene-1-ol were the main flavor compounds of fermented silver carp sausages inoculated S-PXC. The gel strength of silver carp surimi inoculated with mixed starter cultures increased with the time. To reveal the gel formation mechanism, the changes of the structure of myofibrillar proteins was determined by using fourier transform infrared (FT-IR), laser Raman and circular dichroism spectroscopy methods. During the process of fermentation, activity sulfhydryl decreased with the time, and the content of disulfide bonds and hydrophobic surface protein with fermentation time increased. FT-IR and Raman spectroscopy showed the formation of hydrogen bonds between the molecular-folded structure of the protein-protein interaction formation played an important role. Disulfide conformation samples from the control of the whole next-next-trans conformation (gauche-gauche-tran s) adjacent to (the gauche) and anti-next-trans conformations coexist. With the fermentation time, the original buried tyrosine residues gradually exposed to the surface. the two structures of the myofibrillar proteins further analysis showed that fermentation resulted in a decreased proportion of coil structures and increased the proportion ofβ-sheet structures. The thermal denaturation temperature and enthalpy of myosin gradually increased with the fermentation time. During fermentation 48 h, thermal denaturation temperature and enthalpy increased 3.28°C and 0.176J/g than the fresh muscle, respectively. In contrast, the actin decreased 1.43°C for heat denaturation temperature and 0.015J/g for enthalpy. The lower pH significantly affects the muscle fiber protein denaturation temperature and enthalpy. Microstructural study revealed that fermented silver carp sausage had a three-dimensional network. A more void and open structure correlated well with fermentation time and was associated with higher acids. The gel strength of silver carp surimi during fermentation increased with the time mainly was the interactions of S-S bond, hydrogen bonding and hydrophobic bond.Surimi during the fermentation accompanied by an extremely complex physico-chemical and microbiological changes. Fermentation, using different methods and fermentation conditions, accompanied by a different biochemical process, which resulted in fermented end-products varying quality. Therefore, on the basis of single factors study, a three-level Central Composite Design (CCD) factorial design was employed combining with response surface methodology (RSM) to optimize the fermentation condition for the production of fermented silver carp surimi. Response surface analysis showed that and the interaction of the factors of response values gel strength and overall acceptability were significantly correlated. The greatest strength gel is 1192.8 g.cm at the optimizing conditions.Comparative analysis at room temperature and refrigerated (4℃), vacuum and vacuum-packed meat fermentation characteristics of fermented surimi biochemical changes. The results showed pH, TBA, and the non-protein nitrogen increased with storage time, and the whiteness, moisture content, and the gel strength decrease during storage. Cold storage can effectively inhibit the growth of Enterobacteriaceae and Pseudomonas, but the samples storage at room temperature, these microorganisms increased. The changes of TVBN and TBA of fermented silver carp surimi at different storage temperature of 20℃,25℃,30℃were studied. The kinetics models of TVBN and TBA with respect to storage time and temperature was established so as to predict the quality change and shelf life of fermented silver carp surimi during storage. The changes of TVBN and TBA value with time and temperature showed precision of the first order chemical reaction and Arrhenius equation. EA and K0 of TVBN and TBA change reaction were obtained. These were 52.433 kJ/mol, 1.344×1011 and 32.6239 kJ/mol, 4.785×108, respectively. The kinetics model could provide an important reference for the predication the changes of fermented silver carp surimi during storage. The shelf life of fermented silver carp surimi at different storage temperature was calculated based on the kinetics models.