Protein quality of feeding-stuffs

I. A study was made of the assay of available lysine and available methionine using Tetrahymena pyriformis W, as applied to a variety of protein-rich feedstuffs.2. Results were strongly influenced by the conditions under which the analyses were done. With most of the test samples predigestion with papain caused a large increase in the values obtained.3. An improved assay procedure was developed which included enzymic predigestion of the test samples, 'all-in' sterilization of the medium constituents, and measurement of growth from extinction values. It gave results for available lysine that were broadly similar to those obtained in growth tests with rats, and in chemical tests by the method of Carpenter (1960). Values for available methionine agreed closely with those obtained in microbiological tests with Streptococcus zymogenes.

Section: Discussionmentioning

confidence: 83%

An improved procedure for the assay of available lysine and methionine in feedstuffs using Tetrahymena pyriformis W

Shorrock¹

1976

“…Amino acids in food proteins may suffer nutritional damage during heat-processing or storage; the digestibility of the protein and the biological availability of the constituent amino acids may be reduced, although the amino acid composition as determined by chromatographic analysis of an acid-hydrolysate of the protein may indicate little change. Peptide-bound methionine may undergo oxidation in situ, and it has been suggested that these oxidized residues are of low biological availability, being slow to digest in vivo (Ellinger & Palmer, 1969). In the present study, methionine in all the test proteins was determined by ion-exchange chromatography.…”

mentioning

confidence: 85%

“…Microbiological methods. Total and 'available' methionine were measured microbiologically with Strep, zymogenes NCDO 592 by the method of Ford (1962), modified as described by Boyne et al (1975). Methionine content was also determined using P. cerevisiae ATCC 8042 as described by Hannah, Rhodes & Evans (unpublished results): the test samples were hydrolysed either by treatment with 6 M -H C I , or by digestion with pronase.…”

Section: Total Nitrogen Determinationsmentioning

confidence: 99%

Comparison of chemical and microbiological methods in the estimation of methionine in cowpea (Vigna unguiculata) seeds

Evans

Ford²,

Hannah

et al. 1976

Self Cite

1. Meals were prepared from the seeds of fifteen varieties of cowpea (Vigna unguiculata), one of lima bean (Phaseolus lunatus) and one of yam bean (Sphenostylis stenocarpa), and their methionine content was determined by six different methods.2. Total methionine content was determined by two chemical methods (ion-exchange chromatography and a colorimetric procedure) and by two microbiological methods. The ‘available’ methionine content was determined by microbiological assay with Streptococcus zymogenes.3. All the different methods for total methionine determination gave similar results, with much the same high extent of precision.4. The values for ‘available’ methionine content were similar to or marginally higher than the corresponding microbiological assay values for total methionine content. There was no indication that the methionine in any of the test samples was not completely available.

“…Assay of total and available methionine, leucine, isoleucine, and valine in enzymic digests with Streptococcus zymogenes was performed by the procedure of Ford (1962 modified as described by Boyne, Ford, Hewitt & Shrimpton (1975); (b) assay of available lysine with Tetrahymena pyriformis was done using the procedure of Shorrock (1976); (c) assay of total lysine with Pediocuccus cerevisiae P60 was done using the procedure of Barton-Wright (1963) modified as described by Shorrock Preparation of everted sacs of rat small intestine. Everted intestinal sacs were prepared by the method described by Wilson & Wiseman (1954).…”

Section: Microbiological Assay Procedures (A)mentioning

confidence: 99%

Metabolism of heat-damaged proteins in the rat

Shorrock¹,

Ford²

1978

Self Cite

I . An extract containing 'unavailable' small peptides was isolated from an enzymic digest of heatdamaged cod fillet and examined for its influence on uptake of leucine in the rat small intestine, using the everted-sac technique.2. The extract strongly inhibited the uptake of leucine. It had no effect on uptake of glucose or its metabolism to lactate.3. The findings are discussed in relation to the concept (Buraczewski, Buraczewska & Ford, 1967) that the accumulation of 'unavailable peptide' material in the intestine, found in rats given heat-damaged protein, might hinder the absorption of amino acids by blocking a mechanism involved in their transport across the mucosal barrier.In studies of the influence of heating cod fillet on the course of its digestion in the rat, Buraczewski et al. (1967) found that there were very much higher concentrations of free amino acids and small peptides in the intestinal contents of animals that had been given severely-heated protein than in control abimals given undamaged protein and yet, conversely, the concentrations of free amino acids in the portal blood were much lower. To explain this anomaly they postulated that the accumulation of 'unavailable peptide' material in the intestine, characteristic for heat-damaged proteins, might hinder the absorption of amino acids by saturating the sites involved in their transport across the mucosal barrier.The present paper reports experiments on the influence of 'unavailable peptides ' isolated from enzymic digests of heat-damaged cod fillet on the uptake of leucine from everted sacs of rat small intestine. MATERIALS A N D METHODS Codjillet.A 3 kg block of frozen cod fillets was freeze-dried and milled to form a light flocculent powder. A portion of this preparation was then heated for 20 h in an air oven at 135", as described by Ford & Shorrock (1971).Preparation of enzymic digests. The test proteins were digested successively with pepsin, pancreatin and erepsin, as described by Ford & Salter (1966). The enzymic digests were clarified by centrifugation, and diluted with water to contain 5 mg nitrogenlml.Gel filtration. The enzymic digest was resolved into extracts containing 'undigested protein', 'peptides' and 'free amino acids' by filtration in a calibrated column of Sephadex gel G 25 (Pharmacia (GB) Ltd, London), essentially as described by Ford (1965). The settled height of the gel column was 600 mm and its diameter 42 mm. Portions (10 ml) of the digests were applied to the column which was then eluted with buffer solution, pH 7-6, containing 0.02 M-sodium phosphate and 0.1 M-sodium chloride, and eighty 10 ml fractions were collected. Fraction nos. 32-41 from the digest of the heat-damaged protein were combined to obtain the 'unavailable peptides' preparation and this was freeze-dried.* P60 was done using the procedure of Barton-Wright (1963) modified as described by Shorrock Preparation of everted sacs of rat small intestine. Everted intestinal sacs were prepared by the method described by Wilson & Wiseman (1954). Male hoode...