Protein value of herring meal and some other protein concentrates of marine origin for the young rat
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Protein concentrates, mainly of marine origin, were tested in nitrogen balance experiments with young rats. Commercial herring meals produced by several methods showed only small differences in protein utilization values. In most cases when differences in nitrogen balance values were found they were mainly due to corresponding differences in the protein digestibility. Press cake meals were slightly better utilized than whole meals, this difference was not accounted for by a corresponding difference in digestibility. Steam drying did not produce meals of better protein value than flame drying. No effect on the protein quality of herring meals was found of the preservatives sodium nitrite or formalin used during the storage of the raw material. Extraction of a whole meal with light petrol did not improve the protein quality wheras extraction of another whole meal with ethyl alcohol, ethyl ether and acetone improved the quality. Four foreign fish meals were of about the same protein value as Norwegian herring meal, whereas one was decidedly better. A sand-eel press cake meal was better than a whole meal produced from this raw material. The whole meal was of about the same protein quality as the herring meals. A flash dried whale meat meal was of about equal protein value as herring meals, but decidedly better than a slowly dried whale meal. A squid meal, a spray dried herring solubles meal and two fish off-fall meals were of decidedly poorer protein quality than the herring meals. Rennet casein was of about the same protein value as the herring meals, whereas the reference protein source, spray dried egg albumin, was better than all the other protein sources tested. Acetone dried samples of herring fillets and whole herring were of moderately better protein value than commercial herring meals. Acetone dried male herring was of poorer protein value than a corresponding sample of female herring. Acetone dried herring roe was of good protein value whereas the corresponding sample of herring milt was of poor protein value.