title: Solubility and viscosity of herring (Clupea harengus) proteins as affected by freezing and frozen storage.
abstract: The aim of this work was to evaluate the effects of freezing and frozen storage at -24 degrees C on the quality of Icelandic herring fillets, focusing on protein solubility and viscosity at pH 2.7 and 11 used for pH-aided protein isolation. The evaluation of quality was based on chemical analyses, protein degradation measurements, and changes in protein solubility and viscosity at pH 2.7 and 11 after up to 6-mo frozen storage of the herring fillets. Lipid oxidation measured as TBARS values increased significantly during the frozen storage (P < 0.05). Protein solubility at pH 2.7 decreased during frozen storage for 6 mo, where the solubility was about 10% lower after 6-mo frozen storage compared to the beginning (P < 0.05). At pH 11, the solubility became approximately 15% lower after 6-mo frozen storage compared to initial solubility (P < 0.05). Viscosity, measured at pH 2.7, increased after 3 mo of frozen storage (P < 0.05). At pH 11, the viscosity increased significantly after 1-wk frozen storage, compared to fresh herring fillets, but did not increase significantly with further storage (P < 0.05). Changes found in solubility and viscosity indicated protein degradation due to freezing and frozen storage. SDS-PAGE analysis did not reveal any protein cross-linking or aggregation formation, either with frozen storage or due to exposure to low pH.
authors.affiliation: Matis-Food Research, Innovation and Safety, Skulagata 4, 101 Reykjavik, Iceland. mg@matis.is
authors.forename: M
authors.initials: M
authors.lastname: Geirsdottir
authors.forename: H
authors.initials: H
authors.lastname: Hlynsdottir
authors.forename: G
authors.initials: G
authors.lastname: Thorkelsson
authors.forename: S
authors.initials: S
authors.lastname: Sigurgisladottir
mesh_terms: D000818:Animals; D029941:Fish Proteins / Q000032:analysis / Q000737:chemistry*; D005399:Fishes; D005511:Food Handling / Q000379:methods*; D005519:Food Preservation / Q000379:methods*; D005615:Freezing; D006863:Hydrogen-Ion Concentration; D015227:Lipid Peroxidation; D017747:Seafood / Q000032:analysis / Q000592:standards*; D012995:Solubility; D017392:Thiobarbituric Acid Reactive Substances / Q000032:analysis; D013997:Time Factors; D014783:Viscosity
chemical_list: D029941:Fish Proteins; D017392:Thiobarbituric Acid Reactive Substances