Quantitative quality tests for fish meal. II. An investigation of the quality of south African fish meals and the validity of a number of chemical quality indices

This report indicates that the quality of fish meal can conveniently be expressed by two independent indices: a pre-processing spoilage index and a heat abuse index. It is shown that indices of spoilage such as total volatile basic nitrogen (TVBN) or free fatty acid (FFA) can be misleading. As an additional quality index the phospholipid (PL) content is suggested. This index measures the PL content of the residual lipids in the meal and allows the quality of the dried presscake to be assessed separately from the added stickwater. The polyunsaturated fatty acid (PUFA) content of the meal lipids is also an excellent guide for detecting heat abuse during drying of the meal. Using this measurement no evidence was found to conclude that steam (indirect) dryers cause more heat damage to meals than flame (direct) dryers.