Long-term storage of fish oils frequently leads to deterioration in quality due to enzymatic formation of free fatty acids (FFA). The present investigation has identified a number of chemical characteristics which can serve as indices in predicting which oils arc liable to show FFA escalation on storage. It also outlines measures to be taken to prevent FFA escalation.
I n t r o d u c t i o n
In two previous papers from our Institute it was shown that the quality of the oil and meal produced from anchovy (Engraulis capensis) is mainly determined by the freshness of the starting material and that n o chemical hydrolysis or oxidation takes place during the production process'. ' . Before the oil is converted into margarine and baking fats, however, it is frequently stored for several months in large bulk storage tanks. During this storage period the FFA levels of the oil sometimes increase sharply due t o enzyme activity. This results in deterioration of oil quality which can lead to large financial losses.
This present paper describes an investigation into the factors that are related t o FFA escalation and its probable causes and suggests measures that can be taken to prevent it.
E x p e r i m e n t a l
General
Anchovy oils were obtained from local fish meal factories during production, the sample oils being taken just prior to the oil storage tank. The oils were transported to the Institute in closed jars (1000 ml) where they were analysed for water, FFA, phosphorus (P) and nitrogen (N) contents within 48 h. They were then stored in closed glass bottles (250 ml), filled to capacity and stored at 25°C. The FFA contents of the oils were examined periodically over a period of about 100 days.
Data o n the oil yields of the fish were obtained from the factory managers.
Analytical Determinations
Water
This was determined after addition of toluene to the oil by distillation according t o the Dean and Starke procedure of the American Oil Chemists' Society3.