2.4.5. Formaldehyde content
Formaldehyde content in crab muscle was determined according
to the method of Nash (1953). Fish muscle (5 g) was placed in
50 ml beaker and 20 ml of 5% trichloroacetic acid (TCA) was added.
The mixture was homogenized (IKA Labortechnik, Selangor,
Malaysia) at a speed of 13,000 rpm for 2 min. The homogenate was
then filtered using Whatman paper No. 41 (Whatman International
Ltd, Maidstone, England). The extraction was repeated by homogenizing
the residue with 10 ml of 5% TCA, followed by filtering. The
filtrate was combined and neutralized to pH 6.0–6.5 with 1 or 2 N
NaOH. The final volumewas made up to 50 ml using distilled water.
To neutralized filtrate (3 ml), 3 ml of acetylacetone reagent was
added and mixed thoroughly. The reaction mixture was kept at
60 C for 15 min and cooled in running water. The absorbance was
measured at 412 nm. The blank was prepared by using 5% trichloroacetic
acid instead of filtrate. Formaldehyde content was
calculated from a standard curve (0–24 mg formaldehyde) and
expressed as mg/g sample.