Milk protein concentrate controls lipid oxidation, fishy odors in frozen herring mince.

Owing to its abundance and underutilization, minced Atlantic herring is a potential raw material for use in omega-3 seafood products. However, mechanically mincing the fish, combined with its high level of polyunsaturated fatty acids (PUFAs), causes lipid oxidation and fishy odors to develop when the product is in frozen storage.

Researchers at the University of Alaska and colleagues elsewhere initially showed that milk protein concentrate (MPC) was able to retard the development of lipid oxidation and fishy odors, while synthetic antioxidants caused off-odors to develop in pelagic fish mince. More recently, the scientists decided to closely examine the antioxidation properties and fish odor binding capability of MPC in frozen herring mince. They found that MPC is a promising alternative to synthetic antioxidants for minimizing rancidity and the onset of fishy odors in frozen pelagic fish mince containing large amounts of polyunsaturated lipids, which could be used in seafood products containing high levels of omega-3 fatty acids.

Fresh Atlantic herring fillets were mechanically deboned to produce a refined mince. The mince was then mixed with MPC at up to 6% levels, packed loosely and stored frozen at -18 C for four months. One mince sample was vacuum-packed and stored at -80 C. Investigators assessed the progress of lipid oxidation by monitoring changes in thiobarbituric acid reactive substances (TBARS), fatty acids, headspace volatiles and fishy odor.

Adding 4% and 6% MPC in samples resulted in 33% and 50% less TBARS and less fishy odor intensity. Moreover, there was greater retention of PUFAs in these samples than in the control at four months of storage. But MPC did not protect fatty acids from degrading, much of which may have already occurred during the mechanical mincing of the mince.

MPC was able to reduce headspace volatiles associated with fishy odors. The concentrate was most effective in binding dimethyltrisulfide, 4-heptenal, 3-methyl-1-butanol and 2-hexenal, which are potent odorants associated with lipid oxidation. MPC inhibited the formation of TBARS and other oxidation products and has the ability to bind volatiles.

Further information. Alexandra Oliveira, Fishery Industrial Technology Center, University of Alaska, 118 Trident Way, Kodiak, AK 99615; phone: [phone]; email: [e-mail].