Chemical and biological assay procedures for lysine in fish meals.

Abstract

AbstractSixteen laboratories from different countries undertook chemical tests to determine the lysine content of 8 samples of fish meal. The chemical tests were total lysine (gas liquid chromatography or ion exchange chromatography), dye binding capacity (DBC), dye binding lysine (DBL), and reactive lysine (FDNB). The same samples of fish meal were analysed for biologically‐available lysine in four laboratories by chick feeding experiments. Estimates of lysine by all methods except DBC differed significantly between laboratories, but generally meals were ranked similarly by each laboratory. The largest estimate of between laboratory variance, and also the poorest concordance of ranking of the meals by the different laboratories was shown by DBL. The chemical methods for measuring lysine gave means which were significantly different from the bioassay results. However, all the chemical methods gave values which correlated with the bioassay values. The DBC, DBL and FDNB methods gave similarly high correlation coefficients while total lysine was less well correlated. Use of the chemical methods to predict values for biologically‐available lysine gave wide confidence limits which are likely to encompass the variability in the majority of commercial fish meal samples. Consequently none of the chemical methods can be regarded as satisfactory for the purpose of distinguishing between normal commercial samples of fish meals in terms of an absolute content of biologically‐available lysine. The chemical methods may, however, be used in a more limited sense to detect differences in quality between meals of known history without indicating any absolute values for biologically‐available lysine. The dye binding methods appear suitable for process control within a fish meal factory where the analyses are carried out in a single laboratory and the nature of the raw material is known.