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Oxidace proteinů a lipidů u ryb: dráhy, kinetika a produkty
HEMATYAR, Nima
Fish muscle contains omega-3 fatty acids and high quality protein and other valuable nutrients. On the other hand, due to the high content of water, neutral pH, presence of PUFA and sensitive amino acids, fish muscle is a very perishable food. The progress of lipid and protein oxidation as well as interaction between the oxidation products could have a negative role during storage time. Negative effect of oxidation on the fish fillet quality has been reported by several authors, but still the pathways and products of protein oxidation owning to the diversity of the protein oxidation products is not clear. Pathways of lipid and protein interaction, target amino acids, storage conditions and also, final impact on the fish muscle quality have been investigated in this study. We examined the quality of fish muscle in common carp and perch during different storage conditions (+4°C and -20°C). Also, we compared some quality parameters in perch muscle from two different rearing systems to identify the pathways and products of oxidation. The present study investigated the oxidation progress with respect to TBARS and carbonyls as markers of lipid and protein oxidation respectively as well as contribution of PUFA on the lipid oxidation development. Further, the effect of storage conditions and oxidation on the textural and sensorial parameters were examined. Possible changes of pH, rigor index and biogenic amines, during post mortem were studied. Additionally, we performed proteomic analysis in order to investigate more deeply the protein alteration and find a correlation between protein structures and fish muscle quality. Our results showed a good stability in common carp (Cyprinus carpio) fillet during 6 months storage at -20oC. According to our results, we observed a significant decrease in the firmness of common carp muscle after 1 week and then it was constant while liquid loss increased significantly with storage time. Regarding the sensory parameters, we could not find any differences in the examined parameters in both stored raw and cooked fillets compared to the fresh one. Although, both lipid oxidation parameters (TBARS and PV) were increased significantly but it did not reach the critical level for human consumption. On the other hand, protein oxidation which is involved in WHC deterioration was increased significantly. In addition, we investigated the muscle quality of Eurasian perch (Perca fluviatilis L.) from two rearing systems (RAS and pond). During frozen and refrigerated storage, we observed a significant increase in the amount of TBARS and carbonyls in both rearing systems. Comparison between both rearing systems did not show any differences in the amount of TBARS while carbonyl was significantly higher in the RAS fillets rather than pond fillets particularly, until 4 month storage at -20oC. Also, we found a significant increase in liquid loss and considerable decrease in firmness in the fillets from both rearing systems. Our results showed higher firmness and liquid loss in the RAS fillets compared to the pond one. Proteomic analysis on the fillets from both rearing systems during frozen storage showed more stability in the RAS fillet however, western blot revealed more oxidized carbonyls in the RAS fillets rather than pond fillet specially, at time 0 and 4. Probably, formation of ice crystals and accumulation of ROS have key roles on the development of oxidation during frozen storage while enzymatic activity follow by protein degradation are important during refrigerated storage.
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Extending of shelf life of chilled fish products
PFLUG, Róbert
This diploma thesis was focused on the possibilities of extending the shelf-life of fish products by dipping containing seven commercial additives. ANTIBAK, MIC STAB, Bakont, SEA-F75, Misocarine LR, SAFE A Plus and AMX liquid. The effectiveness of these substances on the extending of shelf-life was evaluated on the basis of tests of TVC (total viable count), level of fat and protein oxidation, determination of nutritional parameters of muscle, and finaly sensory analysis. Experimental species were 2 important commodities for the Czech aquaculture rainbow trout (Oncorhynchus mykiss) and common carp (Cyprinus carpio). The project was divided into 6 sub-stages. During testing was the initial number of aditives (7) limited by stepwise selection for 2 preparations. Namely Bakont and AMX liquid, which were tested further on trout (filet with skin and scales) and carp (filets with skin without scales) chilled bulk and chilled packaged under vakuum. For trout was studied antimicrobial effect of dipping on eviscerated fish with the head with- or without gills. Treated trout fillets in bulk and vakuum-packed showed significantly less abundance of muscle mikroflora. In the case of carp fillets chilled bulk we can not say that the bath had influence on the CMP in meat. However, the combination of dipping and vakuum packaging was singnificantly different between the control and product Bakont. AMX liquid was not applied in this case in sufficient dose or in sufficient time to carp muscle. A positive finding is that the application of the aditives to the product "eviscerated trout with head" it does not matter, whether the gills are left in fish or not. However, in all cases the analysis of the presence of pathogens Escherichia coli, Salmonella spp. or Listeria monocytogenes were negative. From the results of sensory analysis can be concluded, that the substances contained in aditives are not reflected in the sensory properties of tested fish.
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