Preparation of raw and cooked fish extracts
Frozen salmon (Salmo salar ) and fresh grass carp (Ctenopharyngodon idella ) were purchased from local supermarket. Two milligrams of raw fish meat were manually homogenized in 8mL ice-cold phosphate-buffered saline (PBS) until a smooth paste was achieved. Protein was then extracted overnight at 4°C with constant stirring. The protein extract was centrifuged and supernatant was filter-sterilized through a 0.22 µm polyethersulfone membrane. The fish protein extracts were stored at -20°C until use.
Several cooking methods including steaming (at 100°C), boiling (at 100°C), baking (at 150°C), lightwave cooking (at 180°C), frying (at 180°C) and air-frying (at 200°C) were used to prepare cooked salmon and grass carp for comparison of its protein profile. Raw salmon meat, weighed 20 g per pack, was cooked until the core temperature of salmon meat reached 80°C as measured using digital thermometer. After cooking, all samples were weighed and 1/10 of the raw and cooked fish samples were extracted in 8mL PBS as described above. All protein extracts were stored at -20°C until use.