Rasa Slizyte

Quality changes of salmon by-products during storage: Assessment and quantification by NMR

Safe utilization of fish by-products is an important task due to increasing fish consumption. It can provide new valuable food/feed and will increase the economical profit and sustainability of the fishery industry. NMR spectroscopy is a reliable tool able to monitor qualitative and quantitative changes in by-products. In this work the trichloroacetic acid extracts of salmon backbones, heads and viscera stored at industrially relevant temperatures (4 and 10°C) were studied using NMR. Twenty-five metabolites were detected and the possibility of salmon by-products utilization as a source of anserine, phosphocreatine and taurine was discussed. Statistical data elaboration allowed determining the main processes occurring during by-products storage: formation of trimethylamine and biogenic amines, proteolysis and different types of fermentations. By-products freshness was evaluated using a multi-parameter approach: the trimethylamine and biogenic amines concentration changes were compared with Ki and H-values and safe temperatures and times for storage of salmon by-products were proposed.

Dietary fish protein hydrolysates containing bioactive motifs affect serum and adipose tissue fatty acid compositions, serum lipids, postprandial glucose regulation and growth in obese Zucker fa/fa rats.

The worlds fisheries and aquaculture industries produce vast amounts of protein-containing by-products that can be enzymatically hydrolysed to smaller peptides and possibly be used as additives to functional foods and nutraceuticals targeted for patients with obesity-related metabolic disorders. To investigate the effects of fish protein hydrolysates on markers of metabolic disorders, obese Zucker fa/fa rats consumed diets with 75 % of protein from casein/whey (CAS) and 25 % from herring (HER) or salmon (SAL) protein hydrolysate from rest raw material, or 100 % protein from CAS for 4 weeks. The fatty acid compositions were similar in the experimental diets, and none of them contained any long-chain n-3 PUFA. Ratios of lysine:arginine and methionine:glycine were lower in HER and SAL diets when compared with CAS, and taurine was detected only in fish protein hydrolysate diets. Motifs with reported hypocholesterolemic or antidiabetic activities were identified in both fish protein hydrolysates. Rats fed HER diet had lower serum HDL-cholesterol and LDL-cholesterol, and higher serum TAG, MUFA and n-3:n-6 PUFA ratio compared with CAS-fed rats. SAL rats gained more weight and had better postprandial glucose regulation compared with CAS rats. Serum lipids and fatty acids were only marginally affected by SAL, but adipose tissue contained less total SFA and more total n-3 PUFA when compared with CAS. To conclude, diets containing hydrolysed rest raw material from herring or salmon proteins may affect growth, lipid metabolism, postprandial glucose regulation and fatty acid composition in serum and adipose tissue in obese Zucker rats.

Bioactivities of fish protein hydrolysates from defatted salmon backbones

Graphical abstract

Production of High Quality Fish Oil by Thermal Treatment and Enzymatic Protein Hydrolysis from Fresh Norwegian Spring Spawning Herring By-Products

There is an increasing demand for omega-3 containing fish oils. By-products from fish fillet production can be utilized for the production of fish oils and be a valuable source of omega-3 for human consumption. The aim of this work was to evaluate industrial processes for production of quality oil for human consumption made from Norwegian spring spawning herring by-products. A mobile production plant was used to compare two industrial processes, thermal treatment (wet rendering) and enzymatic protein hydrolysis, for production of oil from herring by-products immediately after filleting. Results show that high quality herring oil can be produced from fresh by-products. The use of by-products immediately after filleting resulted in a low amount of free fatty acids for all the produced oils (below 0.4%). Thermal treatment at 70°C resulted in an oil with lower oxidation status and higher stability compared to the oils produced by enzymatic protein hydrolysis. Nevertheless, both processing methods gave a crude oil of high quality compared to crude oils on the market.

Hydrolyzed proteins from herring and salmon rest raw material contain peptide motifs with angiotensin-I converting enzyme inhibitors and resulted in lower urine concentrations of protein, cystatin C and glucose when fed to obese Zucker fa/fa rats

The use of angiotensin-I converting enzyme (ACE) inhibitors is a common strategy for treating kidney disease. Several amino acid sequences with ACE inhibiting activity are identified in filet and rest raw material from various species of fish, and fish protein hydrolysates could be of interest for possible treatment or prevention of kidney disease. Therefore, we hypothesized that protein hydrolysates from rest raw material from herring and salmon contained ACE inhibiting motifs, and could beneficially affect typical markers for kidney function in an obesity rat model prone to developing renal failure. We identified 81 and 49 peptide sequences with known ACE inhibiting activity in herring and salmon protein hydrolysates from rest raw material, respectively. To investigate the effects of fish protein hydrolysates on markers of kidney function, obese Zucker fa/fa rats consumed diets with 25% of protein from herring (HER) or salmon (SAL) protein hydrolysate from rest raw material and 75% of protein from casein/whey, or 100% protein from casein/whey (CAS) for 4 weeks. Rats fed HER or SAL diets had lower urine concentrations (relative to creatinine) of protein, cystatin C and glucose when compared to rats fed CAS diets, with no differences between groups for serum concentrations of protein, creatinine and cystatin C. To conclude, protein hydrolysates from herring and salmon rest raw material contained several peptide sequences with known ACE inhibiting activities, and resulted in lower urine concentrations of proteins, cystatin C and glucose when fed to obese Zucker rats.

In vitro pepsin digestibility and amino acid composition in soluble and residual fractions of hydrolyzed chicken feathers

ABSTRACT Beta‐keratin in poultry feathers is a structural protein that is resistant to degradation due to disulfide and hydrogen bonds. Feather meal can be a valuable feed compound if the digestibility can be increased. The objective of the present study was to analyze the effects of chemical, enzymatic, and pressure‐thermic treatments for chicken feathers on solubility, in vitro protein digestibility (IVPD), and amino acid composition of solubilized and residual fractions. Two experiments were conducted. In experiment 1, models for solubility and IVPD were developed including the above factors applying a central composite face‐centered design. Addition of sodium hydroxide (NaOH) and sodium sulfite (Na2SO3), and autoclaving time affected solubility and IVPD of the feather hydrolysates, but not addition of keratinolytic enzyme. In experiment 2, 7 combinations of the hydrolysis factors NaOH, Na2SO3, and autoclaving time with a predicted IVPD of 900 g/kg of DM, calculated for the sum of solubilized and residual feather fractions, were included to measure effects on IVPD and amino acid composition in each fraction. The IVPD values were higher for solubilized than residual fractions when treated with NaOH and autoclaving, but no differences were found when treated with Na2SO3 and autoclaving. Losses of cystine were substantial for all treatments, but lower for Na2SO3 than for NaOH. Furthermore, use of lower Na2SO3 concentration and longer autoclaving time reduced losses of cystine. Compared with NaOH treatments, Na2SO3 gave lower losses of threonine, arginine, serine, and tyrosine. With reference to the ideal protein profile for Atlantic salmon (Salmo salar L.), the treatments with 60 or 90 min autoclaving and 0.36 or 0.21% Na2SO3 had the highest chemical scores. The scores were generally higher for amino acids in residual than solubilized fractions, but with 90 min autoclaving and 0.21% Na2SO3 differences were small. In conclusion, hydrolysis of chicken feathers with low concentrations of Na2SO3 combined with autoclaving results in feather meal with high nutritional value for Atlantic salmon; separation of solubilized and residual fractions is not necessary.

Palmaria palmata as an alternative protein source: enzymatic protein extraction, amino acid composition, and nitrogen-to-protein conversion factor

The red seaweed Palmaria palmata has previously been reported to have high protein content high in essential amino acids. To extract the proteins a rigid cell wall consisting mainly of β-(1→4)/β-(1→3)-D-xylans must be disrupted. Different methods have been used to overcome this problem along with various methods used for protein evaluation. In this study, the effect of enzymatic pre-treatment on protein extraction was examined. Both enzymatic hydrolysis with xylanase and protease were tested. The amino acid content of the fractions was examined after extraction. The amino acid composition was similar to what has previously been reported; P. palmata was high in essential amino acids. Accordingly, a nitrogen-to-protein conversion factor was calculated for each fraction individually and protein results were compared with calculation using the proximate 6.25 conversion factor. The nitrogen-to-protein conversion factor varied between fractions but all factors were significantly lower than the popularly used 6.25 indicating that this conversion factor for processed P. palmata is effectively and considerably overestimating the protein content. Enzymatic pre-treatment with xylanase resulted in enhanced amino acid content and successful protein extraction. Enzymatic hydrolysis using protease resulted in higher protein content in the liquid extract compared to hydrolysis with xylanase, due to the release of proteins, peptides, and amino acids. Therefore, hydrolysis with protease is not suitable to extract proteins from P. palmata with the method described within this study but might be an optimal method to examine the bioactivity by extracting the protein hydrolysates. However, the result from this study confirm that hydrolysis with xylanase is a feasible choice to extract proteins of good quality from P. palmata.

Two-stage processing of salmon backbones to obtain high-quality oil and proteins

Traditional processing technologies for fish by-products containing significant amounts of oils usually either give high amounts of oil or maximised solubilisation of proteins. Due to lower yields and insufficient quality, the proteins or the oil is considered as secondary products. The proposed concept combines a gentle thermal separation of oil followed by enzymatic hydrolysis of the remaining protein-rich fraction. The first stage, thermal treatment (40 °C) of fresh salmon backbones, separated up to 85% of the oil from the raw material and gave high-quality oil (PV = 0.2 0.0 meq kg , 0.16 0.05% free fatty acids). Separation of a significant part of the oil gave reduced mass flow into the enzymatic stage, which then requires less enzymes and reduced energy consumption. Among the tested enzymes: Trypsin, Corolase PP and Mixture of Papain and Bromelain gave the highest yield of fish protein hydrolysates (FPH), while use of Protamex and Corolase PP resulted in FPH with the best sensory properties leading to the lowest bitterness.