Rates of free fatty acid formation from phospholipids and neutral lipids in frozen cape hake (Merluccius spp) mince at various temperatures

Hake mince was stored in frozen condition at −5°C, −18°C and −40°C. Samples were withdrawn periodically, and the lipids were extracted and analysed for free fatty acid and phosphorus (P) content. The free fatty acid contents were corrected for the presence of acidic phospholipids and converted into genuine free fatty acid contents. The results at −5°C and −18°C showed an initial rapid surge of free fatty acid formation with a concomitant decrease in P content, followed by a second phase of slower free fatty acid generation and loss of lipid‐P. At −40°C only one phase of free fatty acid generation and loss of lipid‐P was observed. The rates of the enzymic hydrolyses of the phospholipids and the neutral lipids were calculated at the three temperatures. An Arrhenius plot showed that the decrease in rate of free fatty acid formation with decreasing temperature was greater for the phospholipids than for the neutral lipids. In the rapid and more important phase, the two rates were identical at about −12°C while above this temperature the phospholipids hydrolysed faster and below it the neutral lipids. Activation energies for the enzymic hydrolyses were calculated.