Effect of Temperature on Dynamic Rheology and Colour Degradation Kinetics of Date Paste

Date paste is an intermediate food product and used in various food formulations. The viscoelastic properties and visual colour degradation kinetics of date paste (Lulu cultivar) were investigated at selected temperatures. Small amplitude dynamic oscillation measurements exhibited viscoelasticity of date paste. The elastic modulus (G′) values were consistently higher compared to viscous modulus (G′′) at frequency (ω) range of 0.1 to 10 Hz. Both G′ and G′′ showed slight dependence on frequency however, the dependency decreased with temperature especially for elastic modulus. Complex viscosity (η*) of paste decreased with temperature and followed a power type relationship with frequency. Date paste was classified as weak gel based on the overall mechanical spectra. Fractional conversion technique was used to represent thermal colour degradation kinetics of date paste at selected temperature range (70-120°C). The combination of tristimulus Hunter colour values (L × a × b) adequately represented thermal colour degradation and followed the first order reaction kinetics. Dependence of rate constant during thermal processing followed the Arrhenius relationship with an activation energy value of 65.17 kJ mol.