Studies on the Brown Discoloration of Fish Producta-IV

Nitrogen Content of the Browning Substances

Abstract

It has previously been reported that the brown discoloration of fish products is mainly due to the reaction between carbonyl compounds derived from autoxidized oil and volatile bases such as ammonia, but the mechanism of this reaction has not been solved.
In this paper, in order to make clear the mechanism of the browning reaction, the browning substances derived from several model systems were fractionated and the nitrogen content and other properties were investigated.
Autoxidized methyl esters of cuttle-fish liver oil were incubated with ethanol solution of ammonia at 37°C. Yielded browning substances were fractionated by silicic acid column chromatography. For each fraction, the extent of browning, nitrogen content, mean molecular weight and IR absorption spectrum were measured.
With the progressive degree of polymerization, the nitrogen in the brown substance increased, but the amount of nitrogen was too low to be a product of the Maillard reaction. It also differed from the Maillard reaction in that the nitrogen content of the browning substances was not proportional to the initial amount of nitrogen com-pounds. Consequently, the browning reaction mechanism of the autoxidized oil-ammonia system differs from that of the Maillard reaction.
KOH also caused browning, but the extent of browning was far less than that with the same concentration of ammonia.
The browning substances extracted from defatted saury meat-autoxidized oil system and discolored boiled-dried anchovy closely resembled in nature those of the ammonia-autoxidized oil model system.