title: Structural changes and functional properties of threadfin bream sarcoplasmic proteins subjected to pH-shifting treatments and lyophilization.
abstract: Structural changes and functional properties of threadfin bream (Nemipterus sp.) sarcoplasmic proteins (TB-SP) subjected to various pH conditions (pH 3, 5, 6.3, 9, and 12) after subsequent pH readjustment to pH 7 were investigated. Fourier transform infrared spectroscopy revealed the loss of alpha-helical and beta-sheet structures of TB-SP after being subjected to pH 3 or pH 12 treatments. The extent of structural and conformational changes of TB-SP subjected to pH 3 was greater than alkaline pHs (pH 9, 12) and pH 5, respectively. The water holding capacity of lyophilized TB-SP treated at pH 3 and pH 12 increased about 6.5- and 5.4-fold, respectively, as compared to the crude counterpart. Both acid and alkaline pH treatments increased fat absorption capacity of lyophilized sample about 2-fold, but drastically decreased its solubility. The water soluble fraction of extremely acidic (pH 3-->7) and alkaline (pH 12-->7) samples exhibited higher oil binding capacity as measured by diphenylhexatriene fluorescence and emulsifying activity. A gel-like structure was formed when water-soluble fraction of crude TB-SP and those subjected to moderate pHs (pH 5, 9) at 2 mg/mL was prepared for the emulsion containing 50% oil (v/v). Functional properties of TB-SP varied, depending on the pH-adjustment process applied.
authors.affiliation: School of Food Technology, Inst. of Agricultural Technology, Suranaree Univ. of Technology, Nakhon Ratchasima 30000, Thailand. jirawat@sut.ac.th
authors.forename: Jirawat
authors.initials: J
authors.lastname: Yongsawatdigul
authors.forename: Bung-Orn
authors.initials: BO
authors.lastname: Hemung
mesh_terms: D000327:Adsorption; D000818:Animals; D045703:Emulsifying Agents / Q000737:chemistry; D004655:Emulsions / Q000737:chemistry; D005229:Fatty Acids, Monounsaturated / Q000737:chemistry; D029941:Fish Proteins / Q000737:chemistry* / Q000302:isolation & purification; D005525:Food-Processing Industry / Q000191:economics; D005612:Freeze Drying; D005782:Gels / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007220:Industrial Waste / Q000032:analysis*; D010473:Perciformes; D017433:Protein Structure, Secondary; D000074262:Rapeseed Oil; D012037:Refuse Disposal / Q000379:methods; D012519:Sarcoplasmic Reticulum / Q000737:chemistry*; D012995:Solubility; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D014867:Water / Q000032:analysis
chemical_list: D045703:Emulsifying Agents; D004655:Emulsions; D005229:Fatty Acids, Monounsaturated; D029941:Fish Proteins; D005782:Gels; D007220:Industrial Waste; D000074262:Rapeseed Oil; D014867:Water