| Abstract
| - Proteins isolated from blue-green algae Spirulinaplatensis strain Pacifica were characterized byvisible absorption, differential scanning calorimetry (DSC), viscometry, and dynamic oscillatoryrheological measurements. Unique thermal unfolding, denaturation, aggregation, and gelation ofthe algal protein isolate are presented. DSC analysis showed that thermal transitions occur at about67 and 109 °C at neutral pH. Calcium chloride stabilized the quaternary structure againstdenaturation and shifted the transitions at higher temperatures. Viscometric studies of Spirulinaprotein isolate as a function of temperature showed that the onset of the viscosity increase is closelyrelated to the dissociation−denaturation process. Lower viscosities were observed for the proteinsolutions dissolved at pH 9 due to an increased protein solubility. Solutions of Spirulina proteinisolate form elastic gels during heating to 90 °C. Subsequent cooling at ambient temperatures causeda further pronounced increase in the elastic moduli and network elasticity. Spirulina protein isolatehas good gelling properties with fairly low minimum critical gelling concentrations of about 1.5 and2.5 wt % in 0.1 M Tris buffer, pH 7, and with 0.02 M CaCl2 in the same buffer, respectively. It issuggested that mainly the interactions of exposed hydrophobic regions generate the molecularassociation, initial aggregation, and gelation of the protein isolate during the thermal treatment.Hydrogen bonds reinforce the network rigidity of the protein on cooling and further stabilize thestructure of Spirulina protein gels but alone are not sufficient to form a network structure.Intermolecular sulfhydryl and disulfide bonds were found to play a minor role for the networkstrength of Spirulina protein gels but affect the elasticity of the structures formed. Both time andtemperature at isothermal heat-induced gelation within 40−80 °C affect substantially the networkformation and the development of elastic modulus of Spirulina protein gels. This is also attributedto the strong temperature dependence of hydrophobic interactions. The aggregation, denaturation,and gelation properties of Spirulina algal protein isolate are likely to be controlled from protein−protein complexes rather than individual protein molecules. Keywords: Spirulina platensis; algae protein; thermal transitions; denaturation; aggregation;gelation; molecular forces; heating rate
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