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The technological properties of raw fish are influenced by the changes in protein structure under heating, which determines the texture and quality of the product. The aim of the study was to examine the protein denaturation temperature and the rheological properties of Baltic herring muscle tissue. The thermal properties were determined by the differential scanning calorimetry (DSC) method and the rheological properties were determined using dynamic oscillatory tests. DSC showed four peaks associated with denaturing transformations of myosin (39.59 °C), sarcoplasm (51.67 °C), connective tissue (63.16 °C), and actin (74.40 °C). Analysis showed that not all transformations occurred according to the same kinetic model. The first two and the last peak are described by 1st order kinetics, while peak 3 is described by 2nd order kinetics. Correlating the changes in fish tissue structure during heating with the rheological characteristics provides more information. The obtained kinetics models correlated very strongly with the results of model testing. Rheological changes of the G’ and G” values had two inflexion points and demonstrate a high degree of convergence with the DSC changes of herring muscle tissue from 20 to 85 °C.

The food industry is looking for natural additives to improve acid curd cheese (tvarog), while shrimp by-products are being wasted. The concentrated astaxanthin lipid preparation (ALP) was recovered from shrimp shells and added (0%, 0.25%, 0.5% and 1%) to tvarogs stored up to 4 weeks at 5 ± 1 °C. The addition of ALP increased the lipid content and decreased the moisture in cheese. Water activity, acidity and hardness of tvarogs differed significantly between cheese variants. The cheeses with ALP had more stable and lower pH after 4 weeks of storage, and higher titratable acidity immediately after ALP addition. The 0–0.5% ALP samples had the same level and changes in lipid oxidation, while the 1% ALP cheese had more stable thiobarbituric acid values during storage. This may be due to several times greater antioxidant activity (DPPH assay) in the cheese with the highest ALP addition. The addition of astaxanthin had create popular salmon colour and improved objective colour parameters of the cheeses. The best sensory features had 0.5% ALP sample. A higher addition of astaxanthin preparation caused a foreign aftertaste. The use of astaxanthin from shrimp shells to acid curd cheeses enables the creation of new functional properties that are increasingly popular with consumers.

Cold marinades are produced mainly from the Clupeidae fish, because meat of other fish species does not reach a desired level of ripeness in the acid‐salt environment of fresh brine. Hence, this work presents an innovative idea of reusing brine including cathepsins and peptides for marinating cod, salmon, trout, and carp. The extent of marinades ripening improvement depended on fish resistance to the marinating process. The reused brine proved best in improving the ripening of fatty fish (salmon and trout), which were qualified to the first class of resistance to marinating. In the case of cod, the reuse of brine did not elicit a satisfactory improvement in meat ripening. Therefore cod was qualified to the second class of resistance. The reuse of brine resulted in decreased values of lipid oxidation indices (except for cod) and meat hardness, and in increased scores for overall sensory evaluation and total volatile bases nitrogen value.

Brines after herring marinating pose a serious financial problem to the industry and natural environment. Paradoxically, the brine waste containing biological active compounds like proteases and peptides being responsible for marinade quality is discarded with sewage. Results show that the reuse of brine without filtration is not possible because of increase in the bacterial count and lipid oxidation in marinated herring. The desired parameters of marinades were achieved using brine permeate-50 µm free of the suspension and lipids. The best quality and sensory parameters of marinated herring meat were obtained using permeate-0.22 brine, which not contain microorganisms and lipids, and also a high activity of proteases. Reuse of brine allows reducing by half the losses of protein hydrolysis products (PHP) from meat to brine and for reverse diffusion of PHP and peptidases to meat. The marinades produced with the newly-developed method had up to 25% more PHP, up to 20% lower hardness, 10-20% higher activity of proteases, 40-97% lower indices of lipid oxidation, and 5% higher scores in sensory assessment, compared to the marinades produced with fresh brine. The inexpensive and easy to perform microfiltration of brine affords the possibility of increasing the quality and nutritional value of marinades and minimizing both waste volume and production costs.

This study was conducted on fresh and frozen-thawed sprat of the lowest utility, which is not used for consumption. The peptidase activity was measured (i) against acid- and base-hemoglobin (GPA) a...

Summary In the fish industry, brine left after herring marinating is discarded to waste. This study presents laboratory-scale findings regarding recovery of aspartyl (D + E) and cysteine cathepsins (B + L) from waste brine. Ultrafiltration enabled cathepsin recovery from both the soluble and lysosomal fraction of the marinating brine. Retentate 10 kDa had the highest cathepsin activity 140% compared to crude brine. The amount of recovered cathepsins using membranes 30 and 100 kDa was less than 10 kDa, because part of cathepsins passes to permeate. In turn, the salting-out with ammonium sulphate enabled activity recovery of only 80%, but ensured over twofold higher purity of the enzymes than ultrafiltration. The highest precipitation of D + E cathepsins was noted at salt concentration of 40–60%, whereas that of B + L cathepsins at 50–80%. It is recommended to dissolve the salted-out aspartyl cathepsins at pH 4.0 or 8.0, whereas the cysteine ones at pH 5.0. The appropriate selection of parameters enables controlling the aspartyl to cysteine cathepsins ratio in the preparation in the range from 1:2 to 2:1. The new cathepsin preparations showed high activity in a wide range of pH values and ionic strength and can be used in food production.

Background: This study analyzes the effect of salt and acetic acid concentration, time, temperature and fish freezing on the activity and losses of cathepsins during the marinating of Atlantic and Baltic herrings.; Results: The highest contribution to meat general proteolytic activity was found for cathepsin D-like activity. This contribution decreased during the marinating process as a result of, among other things, cathepsin losses to brine. The methods of marinating had a significant impact on cathepsin activity losses. The average ratio of cathepsin D-like activity to L and B in brine accounted for 15:3.5:1.5, respectively. Depending on the method of calculation, cathepsin activity in brine was similar (per gram of tissue/milliliter of brine) or multiply higher (per gram protein in tissue/brine) than in the marinated herring meat. Statistical analysis demonstrated that the extent and structure of cathepsin losses were significantly correlated with the quantitative and qualitative composition of protein hydrolysis products in marinades.; Conclusion: The presented results depict new phenomena of cathepsin losses and explain their impact on the process of fish marinating. Results allow better optimization of the process of meat ripening. The high activity of aspartyl and cysteine cathepsins in brine indicates the real feasibility of their application in the food industry for novel food design. © 2016 Society of Chemical Industry.; © 2016 Society of Chemical Industry.

This paper is the first ever to describe the phenomenon of bimodal distribution of cathepsin D in the lysosomal and soluble fractions of brine left after herring marinating. Up to 2 times higher cathepsin D activity was observed in the lysosome fraction. Activity of cathepsin D in brine increased according to the logarithmic function during low frequency-high power ultrasounds treatment or according to the linear function after multiple freezing-thawing of brine. Activity enhancement was achieved only in the brine devoid of lipids and suspension. Study results show also that measurement of lysosomal cathepsin D activity in the marinating brine requires also determining cathepsin E activity. Decreasing pore size of microfilter from 2.7 to 0.3 μm significantly reduced the lysosome content in the brine. The presence of lysosomes and the possibility of their separation as well as the likely release of cathepsins shall be considered during industrial application of the marinating brine, as new cathepsins preparations in fish and meat technology.

The production of cold fish marinades is characterized by high seasonality, and therefore producers have problems with providing the sufficient supply of marinades. Besides, after the spawning season, herrings do not ripen properly. Therefore, in the present study, marinated Atlantic and Baltic herring fillets were frozen and stored for 2 days up to 5 months using constant and fluctuating temperatures (recrystallization). The freezing-thawing of marinades improves the hardness, color, and overall sensory evaluation of meat. Temperature fluctuations increase the disintegration of the muscle tissue structure and lysosomal membranes, enhancing the activity of aspartyl endopeptidase responsible for improving the texture of meat and increasing the concentration of protein-hydrolyzing products. The highest thaw drip loss and lipid oxidation were observed after 3 months of frozen storage with temperature fluctuation. Frozen storage had a different effect on fatty and thin herrings. Frozen-thawed marinades stored for up to 5 months were of good microbiology quality. Study results show that the freezing of the semi-marinades may be one of the methods for quality improvement and for extending marinades shelf-life before the seasonally increased demand on the market.

The content of total volatile basic nitrogen (TVB-N) is highly determined by the variety of raw material, freezing, salt, and acetic acid concentrations, and therefore the effect of these factors on marinated herring quality was determined in this study. A higher TVB-N content was determined in marinades from fillets than from carcasses and from frozen than fresh herrings. An increase in salt concentration from 5 to 15% reduced the content of TVB-N to a greater extent than the increase in acid concentration from 3 to 8%. However, the increase in salt concentration above 11–13% or of acid above 5% in brine did not result in any significant decrease of meat TVB-N value. The brine TVB-N content was significantly correlated with meat TVB-N and was higher than in meat. The best freshness indicators were NH3-N and tyrosine in brine, which can be deemed more universal indicators of the freshness of marinated herring meat. The diffusion from meat to brine was found to significantly decrease the meat TVB-N...

Herrings are marinated in a brine consisting of salt and acetic acid. During marinating, various nitrogen fractions diffuse from fish flesh to the brine, causing significant nutritional quality losses of the raw material. In this study, it has been demonstrated for the first time that proteases diffuse from the fish to the marinating brine. Using ammonium sulphate precipitation and affinity chromatography on pepstatin-A agarose bed the aspartyl proteases were purified and concentrated over 2600-fold from a marinating brine. Pepstatin-A completely inhibited the activity of the purified preparation. The preparation was active against fluorogenic substrates specific for cathepsin D and E and inactive against substrates specific for cysteine cathepsins. Depending on incubation time, the preparation showed pH-optimum at 2.0 or 4.5. The 2D SDS–PAGE separation demonstrated the presence of a few proteins with molecular weights and pI values typical of cathepsin D, E and pepsin.