Increasing protein demand has led to growing attention being given to the full utilization of proteins from side streams in industrial fish processing. In this study, proteins were recovered from three protein-rich side streams during Tra catfish (Pangasius hypophthalamus) processing (dark muscle; head-backbone; and abdominal cut-offs) by an optimized pH-shift process. Physicochemical characteristics of the resulting fish protein isolates (FPIs) were compared to industrial surimi from the same raw material batch. The pH had a significant influence on protein extraction, while extraction time and the ratio of the extraction solution to raw material had little effect on the protein and dry matter recoveries. Optimal protein extraction conditions were obtained at pH 12, a solvent to raw material ratio of 8, and an extraction duration of 150 min. The resulting FPI contained <10% of the fat and <15% of the ash of the raw material, while the FPI protein recovery was 83.0−88.9%, including a good amino acid profile. All FPIs had significantly higher protein content and lower lipid content than the surimi, indicating the high efficiency of using the pH-shift method to recover proteins from industrial Tra catfish side streams. The FPI made from abdominal cut-offs had high whiteness, increasing its potential for the development of a high-value product.
Chemical composition and properties of saithe isolate
Iceprotein ehf produces protein from raw fish wood with acid and alkali treatment. This process results in two layers: the upper layer is a protein isolate and the lower layer is a liquid phase. The liquid phase contains proteins that have not been used so far but have potential as food ingredients and as dietary supplements. Saithe proteins have a good chance of being a substance in health food if they are treated correctly. This could increase the value of saithe as it is a cheap and underutilized fish species. The purpose of this experiment was to investigate the possibility of utilization of the lower layer from acid and alkali treatment from saithe. The composition and properties of this substance were identified and its potential as a health food ingredient was concluded. Saithe was treated with acid and alkali and the lower layer was collected. The liquid phase was microfiltered and the protein mass was washed. Analysis of the chemical composition of the raw material, electrophoresis (SDS-PAGE), lyophilization, examination of the relationship between protein solubility and acidity and measurement of ACE inhibitory activity were performed. The results show that the material was about 95% water, 4% protein, 0.16% fat and 0.5% minerals. The proteins were insoluble in water, mostly myosin and actin and were not measured by ACE inhibitory activity. Future plans are to hydrolyze the proteins with enzyme technology to make them soluble and bioactive. Experiments will also be made with the addition of antioxidants to the material before and after enzyme treatment to prevent the oxidation of fats that otherwise degrade the taste quality.
Iceprotein ehf processes proteins from fish raw material with a pH-shift method. The pH-shift method results in two phases: the upper layer being the protein isolate and the lower layer a liquid phase containing insoluble proteins. These insoluble proteins have not been utilized so far but are potential food ingredients or nutritional supplements. If handled in the right manner, saithe proteins have good potential as ingredients in health foods. This way it would be possible to increase the commercial value of saithe which is an underutilized and inexpensive fish species. The purpose of this investigation was to explore the possibilities of utilizing the lower layer from saithe processed with the pH-shift method. The chemical composition and functional properties of the proteins in the lower layer were analyzed and their potential as health food ingredients explored. Saithe was processed with the pH-shift method and the lower layer was collected. The liquid phase was filtered and the protein mass was washed. The chemical composition was determined, the samples were subjected to electrophoresis (SDS-PAGE), freeze-dried, the relationship between solubility of the protein and pH was investigated, and the ACE-inhibiting function was measured. The results demonstrated that the material was 95% water, 4% protein, 0.16% fat and 0.5% minerals. The proteins were insoluble in water and consisted mostly of myosin and actin and did not show ACE-inhibiting activity. The future plan is to hydrolyze the material using enzyme technology to make them soluble and bioactive. Experiments in which antioxidants are added to the material will also be performed before and after enzyme treatment to prevent lipid oxidation which can have a negative effect on the product.