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New Evidences of Glass Transitions and Microstructures of Soy Protein Plasticized with Glycerol
Author(s) -
Chen Pu,
Zhang Lina
Publication year - 2005
Publication title -
macromolecular bioscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.924
H-Index - 105
eISSN - 1616-5195
pISSN - 1616-5187
DOI - 10.1002/mabi.200400179
Subject(s) - glycerol , glass transition , differential scanning calorimetry , amorphous solid , microstructure , chemistry , soy protein , small angle x ray scattering , materials science , crystallography , chemical engineering , polymer chemistry , polymer , scattering , organic chemistry , food science , thermodynamics , optics , physics , engineering
Summary: Soy protein isolate (SPI) and glycerol were mixed under mild (L series) and severe (H series) mixing conditions, respectively, and then were compression‐molded at 140 °C and 20 MPa to prepare the sheets (SL and SH series). The glass transition behaviors and microstructures of the soy protein plasticized with glycerol were investigated carefully by using differential scanning calorimetry and small‐angle X‐ray scattering. The results revealed that there were two glass transitions in the SPI/glycerol systems. When the glycerol contents ranged from 25 to 40 wt.‐%, all of the SL‐ and SH‐series sheets showed two glass transition temperatures ( T g1 and T g2 ) corresponding to glycerol‐rich and protein‐rich domains, respectively. The T g1 values of the sheets decreased from −28.5 to −65.2 °C with an increase of glycerol content from 25 to 50 wt.‐%, whereas the T g2 values were almost invariable at about 44 °C. The results from wide‐angle X‐ray diffraction and small‐angle X‐ray scattering indicated that both protein‐rich and glycerol‐rich domains existed as amorphous morphologies, and the radii of gyration ( R g ) of the protein‐rich domains were around 60 nm, a result suggesting the existence of stable protein domains. The results above suggest that protein‐rich domains were composed of the compact chains of protein with relatively low compatibility to glycerol and glycerol‐rich domains consisted of relative loose chains that possessed good compatibility with glycerol. The significant microphase separation occurred in the SPI sheets containing more than 25 wt.‐% glycerol, with a rapid decrease of the tensile strength and Young's modulus.Schematic of the microstructures of glycerol‐plasticized soy protein with glycerol‐rich and protein‐rich domains.