Formation, Nutritional Value, and Safety of D-Amino Acids

Abstract

31The extent of racemization of L-amino acid residues to D-isomers in food proteins increases with pH, time, and temperature. The nutritional utilization of different D-amino acids vary widely, both in animals and humans.In addition, some D-amino acids may be deleterious. For example, although D-phenylalanine is nutritionally available as a source of L-phenylalanine, high concentrations of D-tyrosine inhibit the growth of mice. The antimetabolic effect of D-tyrosine can be minimized by increasing the L-phenylalanine content of the diet. Similarly, L-cysteine has a sparing effect on L-methionine when fed to mice; however, D-cysteine does not. The wide variation in the utilization of D-amino acids is exemplified by the fact that D-lysine is not utilized as a source of L-lysine, whereas the utilization of D-methionine as a source of the L-isomer for growth is dose-dependent, reaching 7&% of the value obtained with L-methionine. Both D-serine and the mixture of L-L and L-D isomers of lysinoalanine induce histological changes in the rat kidneys.D-tyrosine, D-serine, and lysinoalanine are produced in significant amounts under the influence of even short periods of alkaline treatment. Unresolved is whether the biological effects of D-amino acids vary, depending on whether they are consumed in the free state or as part of a food protein. Possible, metabolic interaction, antagonism, or synergism among D-amino acids jn vivo also merits further study. The described results with mice complement related studies with other species and contribute to the understanding of nutritional and toxi col ogi ca 1 consequences of i ngesti ng D-ami no acids.Such an understanding will make it possible to devise food processing conditions to minimize or prevent the formation of undesirable D-amino acids in food proteins and to prepare better and safer foods.

High-risk bio-waste processing by alkaline hydrolysis and isolation of amino acids

“…With alkaline hydrolysis of the studied samples the metionin experienced slight degradation and its concentration, taking into consideration the alkaline medium, is satisfactory. Occurrence of D-iso leucine in the analysed samples indicates the fact that most likely the biggest number of amino acids during alkaline hydrolysis has been racemized [17,19,14]. The content of D-iso leucine as well as Iso leucine in animal protein is found usually in the share of 2,7 %, whereas in soya it is found in a share of 4,5 % [19,22].…”

“…Occurrence of D-iso leucine in the analysed samples indicates the fact that most likely the biggest number of amino acids during alkaline hydrolysis has been racemized [17,19,14]. The content of D-iso leucine as well as Iso leucine in animal protein is found usually in the share of 2,7 %, whereas in soya it is found in a share of 4,5 % [19,22]. With alkaline hydrolysis of high-risk bio-waste relatively high concentrations of iso leucine have been obtained.…”

“…With alkaline hydrolysis of high-risk bio-waste relatively high concentrations of iso leucine have been obtained. Leucine is found in animal protein in an amount of 6,3 % whereas soya as protein source contains 7,8 % [19]. In comparison to other amino acids leucine has shown relative resistance to alkali medium and it is found also in higher concentrations.…”

“…In addition, previous investigations have made it obvious that most amino acids are racemizated during alkaline treatment [14,17,18,19]. Taking all of the above stated into consideration, the aim of this paper was to determine the amino acid content in hydrolysed material following the alkaline hydrolysis of slaughterhouse waste in the form of animal remains.…”

d- and l-amino acids in Antarctic lakes: assessment of a very sensitive HPLC-MS method

“…Most amino acids contain an asymmetric centre, and the analysis of L-or D-enantiomers is very important in several research fields, such as food chemistry [2], geochronology [3] and exploration of other planets [4]. The homochirality of life on Earth occurs because L-amino acids are the only enantiomers used during the biosynthesis of proteins and peptides [5].…”