Methods for Screening Cloud Point Temperatures
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A novel and simple method for the measurement of cloud point temperatures of solutions is presented. Cloud point determination, which is currently used to establish the phase diagrams of protein solutions, is indicative of proteins interactions and constitutes a useful tool for food products engineering. We describe a novel experimental setup that allows screening of a large number of physical-chemical conditions in one measurement and the determination of cloud point temperatures both above and below ambient temperature. We use a simple method to avoid solvent evaporation and condensation, so that the set-up can be used for solutions prepared with a volatile solvent. We present the operating parameter range and the precision of the measurement. The optical properties of the system are calibrated with solutions of known transmittance, and the determination of cloud point temperatures is validated on a standard non-ionic surfactant solution. Finally, we demonstrate the efficiency of the method by determining the phase diagram of a wheat protein extract, soluble in a water/ethanol mixture. Complemented with differential scanning calorimetry measurements, the liquid-liquid phase transition can be determined up to a protein concentration of 250 g/L, a range inaccessible with conventional methods for this protein extract.
KeywordsPhase diagram Cloud point Liquid-liquid phase separation Triton TX-114 Wheat gluten Microplate
The authors acknowledge the Doctorale School GAIA and the Labex Numev (ANR-10-LAB-20) for the financial support of the PhD grant of J. Pincemaille. We also thank the CEPIA department of INRA and the scientific council of Montpellier SupAgro for financial support. Pascal Martinez, Eric Alibert and Sébastien Gaucel are thanked for their technical support for the set-up configuration.
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