Fish soup versus fish mince: a rapid autoclave method for preparing fish flesh for chemical analysis

Compared to the labour-intensive mincing method, autoclaving (pressurised steam cooking) is a fast way of preparing samples for chemical analysis. In addition, autoclaving dissolves fish scales and so enables more homogenous samples to be prepared. Initial method development work has shown that autoclaving at 150 kPa for 4 h is suitable for preparing samples for proximate and fatty acid analyses. However, the effect of autoclaving period and pressure on amino acid recovery has not been measured. A comparative study was made between autoclaving and mincing. The proximate chemical, fatty acid and amino acid composition of silver perch (Bidyanus bidyanus) was measured. The control samples (n = 3) were minced but not autoclaved. Each autoclaved sample (n = 36) was subjected to one of four autoclave periods (1, 2, 3 or 4 h) and one of three pressures (103, 155 or 207 kPa). Compared with mincing, autoclaving decreased nitrogen, increased energy and fat but had a variable effect on fatty acid recovery. Compared with mincing, autoclaving either had no effect on or increased the recovery of all amino acids, except cystine which was marginally reduced. Thus autoclaving appears to offer a superior method for preparing fish samples for amino acid analysis compared with mincing alone. Increasing autoclave pressure from 103 to 207 kPa had no measured effect on flesh composition. Sample processing time in the autoclave can be reduced from 4 to 1 h with silver perch flesh. © 2000 Society of Chemical Industry