Protein-bound D-amino acids, and to a lesser extent lysinoalanine, decrease true ileal protein digestibility in minipigs as determined with (15)N-labeling.
Heat and alkali treatment of food may increase the concentrations of protein-bound D-amino acids and cross-links such as lysinoalanine (LAL). To examine how protein treatment affects digestibility, purified test meals [total protein 150 g/kg dry matter (DM), 0.44 MJ/(kg BW(0.75). d)] were prepared, containing (g/kg DM) casein, 75; beta-lactoglobulin, 50; or wheat protein, 40. Each was (15)N-labeled. Test proteins were used either in their native form or after treatment for 6 or 24 h at 65 degrees C, pH 10.5-11.5. Each meal was fed to nine adult miniature pigs (twofold complete cross-classification). Chyme was collected continuously over 33 h postprandially via T-fistulas in the terminal ileum, and digestibilities of test proteins and individual L- and D-amino acids were calculated on the basis of recovery of (15)N and the respective amino acids in the chyme. Treatment of casein, beta-lactoglobulin or wheat protein for 24 h increased levels of D-amino acid residues. L-Asparagine and aspartate (L-Asx) were particularly susceptible; 14. 7 +/- 0.4, 11.7 +/- 0.2 and 11.0 +/- 0.9%, respectively, underwent racemization. LAL levels increased in parallel; 11.7 +/- 0.3, 13.6 +/- 0 and 14.8 +/- 0.0%, respectively, of total lysine was converted to LAL. At the same time, prececal protein digestibility was decreased by 13.4 +/- 2.3, 15.3 +/- 1.4 and 17.8 +/- 1.2% units, respectively (P < 0.05; mean +/- SEM, n = 9). Digestibility of individual L-amino acids decreased by 10-15%, but L-amino acids prone to peptic cleavage, such as L-phenylalanine and L-tyrosine, were not affected. Digestibilities of D-amino acids and LAL were approximately 35%. It seems that mainly D-amino acids, and to a lesser extent LAL, were responsible for lower digestibility by interfering with peptic cleavage.
de Vrese
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M
Federal Dairy Research Centre, Department of Physiology and Biochemistry of Nutrition, D-24103 Kiel, Germany.
Frik
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R
Roos
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N
Hagemeister
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H
D000596:Amino Acids / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D004044:Dietary Proteins / Q000378:metabolism / Q000494:pharmacology*; D004063:Digestion; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007082:Ileum / Q000378:metabolism*; D007536:Isomerism; D007553:Isotope Labeling; D008241:Lysinoalanine / Q000494:pharmacology*; D008297:Male; D008894:Milk Proteins / Q000378:metabolism; D009587:Nitrogen Isotopes; D010940:Plant Proteins / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D013552:Swine; D013556:Swine, Miniature / Q000378:metabolism*; D014908:Triticum
D000596:Amino Acids; D004044:Dietary Proteins; D008894:Milk Proteins; D009587:Nitrogen Isotopes; D010940:Plant Proteins; D011506:Proteins; D008241:Lysinoalanine