Effect of low and high pH treatment on the functional properties of cod muscle proteins

The functional properties of cod myosin and washed cod mince (myofibrillar protein fraction) treated at high (11) and low (2.5) pH were investigated after pH readjustment to 7.5. The solubility of refolded myosin was essentially the same as the native myosin. The pH-treated myofibrillar proteins had increased solubility over the whole ionic strength range studied. Acid and alkali treatment gave myosin and myofibrillar proteins improved emulsification properties, which were correlated with an increase in surface hydrophobicity and surface/interfacial activity. Enhanced gel strength was observed with acid- and alkali-treated myosin compared to native myosin, while the same treatment did not significantly improve the gel strength of acid- and alkali-treated myofibrillar proteins. The acid- and alkali-treated protein samples unfolded and gelled at a lower temperature than did the native proteins, suggesting a less conformationally stable structure of the refolded proteins. Functional studies show that acid and alkali treatment, which leads to partial unfolding of myosin may improve functional properties of cod myosin and myofibrillar proteins, with the greatest improvement being from the alkali treatment. The results also show that improvements in functionality were directly linked to the extent of partial unfolding of myosin on acid and alkali unfolding and refolding.