Protein quality of feeding-stuffs

Abstract

1. Twelve commercial samples of high-protein feeding-stuffs, six of them fish meals, were used for a study of the reproducibility of chemical, microbiological and biological assay values for individual amino acids. Comparisons were also made of results obtained by different methods for the same amino acid.2. For lysine there was quite good agreement between the results from the different laboratory tests for ‘available’ lysine. The values for ‘total’ lysine were, on average, 10 % higher than those for ‘available’ lysine.3. For methionine the correlations between the chick assay and each of the laboratory tests were similar.4. The results from the ‘total protein efficiency’ test of over-all protein quality, using chicks, showed a close correlation with the results of lysine or methionine assays according to which of the two amino acids was most deficient.5. The results with tryptophan were difficult to interpret and no recommendations could be made as to procedures suitable for general use.6. Although most of the present samples proved to be of good quality, only screening of a much larger number of samples will reveal to what extent commercial protein concentrates of low availability are still liable to come onto the market.

Protein quality of feeding-stuffs

“…A. W. BOYNE, J. E. FORD, D. HEWITT AND D. H. SHRIMPTON 1975no similar information in the literature for isoleucine and tryptophan, althoughCarpenter & Woodham (1974) concluded that for the tryptophan tests the microbiological assay values were probably far too low, although there was a close correlation with the 'chick' values.…”

“…F M 106, 113 and 118 were 'stabilized' by the addition of antioxidant during manufacture. The remaining fish meals and other test materials were described by Carpenter & Woodham (1974).…”

“…Thus in test I ( Table I ) if FM 104 was taken as the standard and assumed to contain 25'7 g methionine/kg CP (the average of values from the eight participating laboratories), and all results from each laboratory were multiplied by the factor needed to convert the result obtained for FM 104 to 25'7, the adjusted values gave a coefficient of variation between laboratories within fish meals of 8.4, compared with I 2 before adjustment. The significance of the between-laboratories variation ( P < 0.001) was reduced but was still evident (P < 0.05), indicating that differences 6-2 * For more detail, see Carpenter & Woodham (1974). t Each value is an average from two independent assays.…”

“…Comparison with the 'microbiological' values for available methionine content suggests that in the fish meals (excluding fish meal F M 102, which was an atypical material of low protein and high ash content) the availability ranged from 0.74 to 0.90, compared with only 0.51 for the meat meal and about 0.90 for the yeasts. A question arises whether the ' microbiological ' values for total methionine content might tend to be too high (see Carpenter & Woodham, 1974) and thus give an erroneously low estimate of availability. The 'chemical' values for methionine content for the fish meals were on average marginally lower, but from the present results it is not possible to assess the significance of the apparently small differences.…”

“…Certainly it would not be possible, from the evidence of a single test within a laboratory, to differentiate between these samples. The question whether such uniformity is typical of materials in commercial use is discussed by Carpenter & Woodham (1974), and will be the subject of a more extensive study of fish meals, meat meals and soya-bean meals (J. E. Ford, D. Hewitt & K. J. Scott, unpublished results). If we consider the additional fish meals used in the present study (compared with that of Carpenter & Woodham (1974)), it is again apparent that most of the variation would have been included within the limits of error associated with a single assay.…”