Chemical and nutritional changes in stored herring meal

In Part 2 of this series (Lea, Parr & Carpenter, 1960) it was reported that appreciable losses of available lysine occurred when fresh herring meal in air, or pre-oxidized meal in nitrogen, was heated for 30 h at temperatures below rooo, whereas fresh meal in nitrogen could be subjected to similar heating without loss.It was suggested that this difference in behaviour was due to a 'browning '-type reaction between carbonylic secondary decomposition products of the autoxidizing oil and the €-amino groups of the lysine side-chains, analogous to the well-known reactions between reducing sugars and amino acids or proteins.When the temperature of heating was raised to 115-130' binding of the lysine €-amino groups was greatly increased and occurred in the unoxidized as well as in the oxidized meal, the difference between the two becoming small at the highest temperature.Biely, March & Tarr (1951) had previously made a somewhat similar observation, that heating at 1 4 9 ~ for 2 h appreciably damaged the nutritive value of herring meal containing (presumably oxidized) oil but did not damage defatted meal, whereas heating for 3 h caused more severe and similar damage to both.Apparently, therefore, at least two lysine-binding reactions can occur in heated herring meal, the oxidized fat-dependent type becoming significant under less severe time-temperature conditions than the non-oxidative, fat-independent type.The purpose of the work now reported has been to study the effects of temperature and of moisture content on the high-temperature, non-oxidative lysine-binding reaction, which must be largely responsible for the very low values for available lysine found for some 'scorched' commercial meals.Part of the work has been done with freeze-dried herring press cake and part with bovine plasma albumin 'model' systems, the latter with and without small additions of ribose.A few observations have been recorded also on the binding of methionine, arginine and tryptophan in the heated press cake and on colour changes in both systems.