Rheological characteristics of reconstituted freeze‐dried dragon fruit pulp powder: Effect of concentration and temperature

Abstract

The rheological properties of reconstituted freeze-dried dragon fruit pulp powder (RFD) were studied at different combinations of concentration (25, 35, 45, and 55 °Brix) and temperature (15, 25, 35, and 45°C) using a rheometer. The RFD samples exhibited non-Newtonian fluid behavior. The behavior index ( n ) of the power law was less than one in all the experimental runs, revealing the shear-thinning nature of the RFD sample. The activation energy calculated from the Arrhenius equation at different concentrations was found to be in the range of 5.207 − 19.726 kJ/mol. The effect of concentration on viscosity at different shear rates was found to correlate with the power law type model with higher efficacy than the exponential type model. The combined effect of concentration and temperature was developed using multiple linear regression analyses. The storage modulus (G′) and loss modulus (G″) were estimated for RFD samples for different concentrations at a temperature of 45°C. The experimental data showed that both G′ and G″ increased with the increase of frequency. The RFD sample showed viscoelastic nature, which was revealed by the greater values of G′ than G″ at a specific frequency. This study on rheological behavior would assist with equipment design, consumer acceptability, and engineering calculations during dragon fruit pulp powder processing. Practical applications Dragon fruit is very perishable in nature. The freeze-dried fruit powder can be used as an ingredient in the preparation of food products by reconstituting with water. The addition of water alters the total soluble solids content as well as the intermolecular linkages, affecting the rheological characteristics of the reconstituted sample. Temperature and pressure are two processing factors that might have an impact on the rheological characteristics of a sample. Food rheology explains the flow properties of a liquid or semi-liquid food and contributes to heat and mass transfer during heating, pumping, and mixing. Thus, the rheological study provides information regarding selecting proper unit operation during processing.