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.