The amino acid and mineral composition of white fish meal containing enzyme-digested or untreated stickwater solids

Abstract Two representative commercial white fish meal samples were used to study the effect of added enzyme-digested (FMED) or untreated (FMR) stickwater solids on their protein quality. They contained the same amino acids in approximately similar proportions. The main advantage of the enzymatic digestion of stickwater solids is that the product becomes more soluble and less viscous, thus reducing build up on the interior of the evaporators and dryers and that it improves the recovery of fish proteins from the press liquor. The crude protein content of FMED (64.2%) was comparable to that of FMR (61.6%), estimated by the Kjeldahl nitrogen method, but these figures were higher than their true protein contents as determined by quantitative amino acid analysis. Although the total lipid content (6.0%) of FMED differs from FMR (3.41%), their apparent metabolizable energies were similar. Determination of 5-hydroxylysine as an index of collagen indicated that FMED and FMR contained 33.5 and 33.3% collagen, respectively.