Structural Changes and Functional Properties of Threadfin Bream Sarcoplasmic Proteins Subjected to pH-Shifting Treatments and Lyophilization

Authors

  • Jirawat Yongsawatdigul,

    1. Author Yongsawatdigul is with School of Food Technology, Inst. of Agricultural Technology, Suranaree Univ. of Technology, Nakhon Ratchasima 30000, Thailand. Author Hemung is with School of Science and Technology, Nong Khai Campus, Khon Kaen Univ., Nong Khai 43000, Thailand. Direct inquiries to author Yongsawatdigul (E-mail: jirawat@sut.ac.th).
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  • Bung-Orn Hemung

    1. Author Yongsawatdigul is with School of Food Technology, Inst. of Agricultural Technology, Suranaree Univ. of Technology, Nakhon Ratchasima 30000, Thailand. Author Hemung is with School of Science and Technology, Nong Khai Campus, Khon Kaen Univ., Nong Khai 43000, Thailand. Direct inquiries to author Yongsawatdigul (E-mail: jirawat@sut.ac.th).
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Abstract

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 α-helical and β-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.

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