Non‐protein‐nitrogen in wheat flour

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Abstract
Non‐protein‐nitrogen (NPN) fractions obtained from a water extract of wheat flour by dialysis, heat or trichloroacetic acid (TCA) precipitation were compared. Dialysis was found to give a smaller and more reproducible fraction (about 25 mg. of NPN per 100 g. of flour), containing a higher proportion of amino‐nitrogen than the other two methods. A polysaccharide‐protein complex comprising about 30% of the non‐heat‐coagulable nitrogen, which is non‐dialysable but may be precipitated with TCA after incubation with poly‐saccharases, was studied in relation to the observed differences in NPN fractions.Free glutamic acid, aspartic acid, lysine, glycine, serine, alanine, proline, γ‐amino‐butyric acid, threonine, tyrosine, valine, iscleucine, leucine, glutamine, asparagine and tryptophan were found in the diffusible NPN fraction, and hydrolysis of peptides shown to be present, resulted in the release of no other amino‐acids.The formation of NPN on storage of water or dilute acid extracts of flour is attributed to the combined action of indigenous flour enzymes and microbial contaminants, as it was found to be partially inhibited by boiling and by a selection of antimicrobial agents.