Effects of salt extraction and heating conditions on protein characteristics and antioxidant activity of salmon (Salmo salar) bone extract

Abstract

The salmon fillet industry in Thailand contributes a large amount of salmon bone (approximately 443 t/yr) as a by-product from final production. The salmon bone contains 16.65% protein and could be utilized to prepare human food. This study evaluated the effects of various salt concentrations and extraction conditions on the protein characteristics of salmon bone extract. The salmon bone extract was prepared by combining two levels (0.5%, 3.5%) of salt solution (1:6, weight per volume) at various temperatures (55–95°C) for 0.5–8 hr prior to centrifugation. The properties were determined of color, light transmission, total solids, protein content, protein pattern and radical scavenging activity. Lower lightness and light transmission were found in the extract with 3.5% salt addition compared to 0.5% salt at 55°C. At 95°C for 8 hr, extracting the salmon bone with 3.5% salt produced the highest values of 1.62% protein and 4.20% total solids, while extraction with 0.5% salt produced 0.76% protein and 1.31% total solids. Proteins with a molecular weight above 250 kDa, myosin heavy chains, collagen and tropomyosin were found in the extracts at 85°C and 95°C. The extracts with 0.5% salt addition at 55°C and 95°C had greater radical scavenging activity than extraction with 3.5% salt. Based on the protein content and the value of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activity, extraction with 0.5% salt at 95°C for 8 hr showed potential for use as a commercial soup product.