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    Comparison of True Ileal Amino Acid Digestibility between Adult Humans and Growing Pigs
    (Oxford University Press on behalf of the American Society for Nutrition, 2022-07) Hodgkinson SM; Stroebinger N; van der Wielen N; Mensink M; Montoya C; Hendriks WH; de Vries S; Stein HH; Moughan PJ
    BACKGROUND: It is not feasible to determine the true ileal amino acid (AA) digestibility of protein sources in humans on a routine basis, and the growing pig has been recommended as an animal model for this purpose but requires further validation. OBJECTIVES: To determine and compare true ileal AA digestibility between adult human ileostomates and growing cannulated pigs for a range of food proteins. METHODS: Seven protein sources (black beans, bread, collagen, pigeon peas, wheat bran, whey protein isolate, and zein) that spanned the range of digestibilities typically seen in foods were evaluated. Six female growing pigs received each of the protein sources, as well as a protein-free diet, and digesta were collected via ileal T-cannula. Adult human ileostomates consumed the same protein sources (5-8 ileostomates, depending on the protein source), as well as a protein-free diet, and digesta were collected. Titanium dioxide and celite were included in the diets as indigestible markers. True ileal AA digestibility coefficients were determined. RESULTS: There was a significant effect of protein source (P ≤ 0.001) for all AAs. The effect of species was not significant (P > 0.05) except for total lysine (but not for available lysine). When analyzed within diets, the statistically significant species effect for true lysine digestibility was found for black beans only. Pig and human digestibility values were generally highly and significantly (P ≤ 0.05) correlated. A linear regression equation derived for true ileal AA digestibility (given as coefficients) determined in the human and pig for the overall mean of all AAs was (y = human, x = pig) y = 1.00x - 0.010, with the slope not statistically significant (P > 0.05) from unity and the intercept not different (P > 0.05) from zero. CONCLUSIONS: True ileal AA digestibility values determined in the growing pig can be directly used for predicting digestibility in adult humans.
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    The effect of heat treatment on lysine availability and dye binding capacity of skim milk : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology at Massey University
    (Massey University, 1976) Reeves, Malcolm John
    The reported work on changes in lysine content in milk and dried milk is examined. The cause of these losses, the Maillard reaction, and the methods of lysine determination are discussed. All methods have recognised faults. Little information is available to the food processor regarding the kinetics of these losses, and the methods of their determination are not simple enough for routine quality control application. Although the lysine content of milk products determined after acid hydrolysis is known to be higher than nutritional studies indicate the causes of this are being established. Therefore acid hydrolysis in conjunction with a GLC method of amino acid analysis was adopted after some modification. (It was found that dialysis of the milk prior to hydrolysis resulted in cleaner chromatograms and that as the recovery of several amino acids, such a proline, leucine, and isoleucine, was not affected by heat treatment then these were used as internal 'internal standard'.) No simple rate expression could be found to fit the kinetics of the loss of acid released lysine. A first order model requiring the losses to be increased by a factor of 3.43 was devised and this could be used to satisfactorily predict values for acid available lysine in the heat treated milk. The possibility of the 3.43 factor being due to the regeneration of lysine by acid from Maillard intermediates, although requiring assumptions, was found to be not unreasonable. The energy of activation of the reaction leading to a loss in acid released lysine at 31.5 Kcal/mole is similar to literature values while the model value of 37.2 Kcal/mole is rather higher. The literature findings of little or no loss of lysine during pasteruization, evaporation, and sterilization of milk are supported. The technique of protein determination by dye binding was examined and applied to following changes in lysine in heat treated milk. The inconsistencies in reported work on dye binding is of little consequence as relative changes only are required. Changes in dye binding using amido black did not follow simple order kinetics, even when allowance was made for the constant binding by arginine and histidine. A first order model requiring the changes to be increased by a factor of 3.68 was developed. About 46% of this factor can be explained by assuming constant binding by arginine and histidine, the remainder of the factor possibly being due to Maillard intermediates binding dye, and/or a change in binding stoichiometry occurring. From the model it is possible to predict the observed changes in dye binding. Literature findings were supported. The energy of activation for the dye binding changes is 28.6 Kcal/mole, and for the model, 30.8 Kcal/mole. Ancillary investigations showed that the concurrent colour changes due to heat treatment have an energy of activation of about 30 Kcal/mole, and that there is a relationship between colour and dye binding capacity in heat treated milk. The relationship between the Pro-Milk and a typical absorbance spectrophotometer was determined, and an expression found which would enable a spectrophotometer to be used for protein determination.
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    Nitrogen metabolism in Haemonchus contortus and Teladorsagia circumcincta : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand
    (Massey University, 2012) Umair, Sallah
    This is the first study to characterise proline, arginine and lysine metabolism in homogenates of L3 and adult Haemonchus contortus and Teladorsagia circumcincta. The properties of glutamate dehydrogenase (GDH), glutamate synthase and the GABA shunt were also compared in the two species. The kinetic properties of 26 enzymes were determined. The gene encoding T. circumcincta GDH was sequenced and recombinant TcGDH expressed and biochemically characterised. The ornithine-glutamate-proline pathway was fully functional. The mammalian α-AAA (saccharopine) and pipecolate pathways of lysine catabolism, but not the bacterial enzymes lysine dehydrogenase and decarboxylase, were present in adult worms. The pipecolate pathway was incomplete in L3 of both species, as Pip2CR activity was undetectable. Unusually, lysine ketoglutarate reductase and saccharopine dehydrogenase, Δ1-pyrroline-5-carboxylate synthase and reductase were able to use both cofactors. The glutamine synthetase-glutamate synthase pathway of ammonia incorporation into glutamate was present, except in L3 H. contortus. T. circumcincta GDH was cloned, purified and characterised and the predicted protein sequence was very similar to H. contortus GDH. T. circumcincta recombinant and H. contortus homogenate GDH were both dual co-factor specific, although the latter had 50% greater activity with NAD+/H as cofactor. GDH activity was inhibited by GTP and stimulated by ADP whereas ATP either inhibited or stimulated depending on the concentration and direction of the reaction. The GABA shunt enzymes glutamate decarboxylase and succinic semialdehyde dehydrogenase was not detected in homogenates of whole L3 or adult H. contortus or T. circumcincta. Neither parasite had a full functional ornithine urea cycle, nor appeared to use bacterial pathways to covert arginine to ornithine. NOS were demonstrated histochemically in nerves of adult H. contortus, but was undetectable in homogenates of both species. There was species variation in polyamine metabolism: T. circumcincta used arginase to form ornithine, followed by decarboxylation by ODC, while in H. contortus there was the additional pathway of first decarboxylation by ADC to form agmatine, then hydrolysis by agmatinase to putrescine. The present study helped in the better understanding of nitrogen metabolism and these enzymes can be useful targets if they differ antigenically from the host, provided the enzyme is accessible to blockage by immune effectors.