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ABSTRACT
Carriers are added with fruit pulp in several drying methods. The flow behavior of the feedstock is an important property in determining equipment design and drying condition. In this study, the effect of carrier type, carrier percentage, and concentration of date pulp feedstock (DPF) on the rheological properties were investigated. The DPF was prepared with Fardh dates cultivar with maltodextrin (MD), gum arabic (GA), and sodium caseinate (SC) carriers at two levels (dates:carrier −70:30 and 60:40, dry weight basis) and three concentrations (20, 30, and 40%). The carriers were found to be effective in reduction of the shear stress for the shear rate range 1–100 s−1. At shear rate 1 s−1, GA-blended DPF and at shear rate 100 s−1, MD-blended DPF offered the lowest shear stresses. Viscosity was decreasing while increasing the shear rate from 1 to 100 s−1, and decreasing the concentration from 20 to 40%. MD- and GA carrier-blended DPFs had exhibited similar viscous behavior. Shear-thinning behavior with GA- and MD-blended DPFs and shear-thickening behavior with SC-blended DPF were observed. Yield stresses of Herschel–Bulkley, Casson and Bingham were increasing with increase in concentration. Temperature dependency of the viscosity was found higher in control than in the carrier-blended DPF. The activation energy was calculated using Arrhenius relationship between temperature and viscosity while heating as well as cooling. The activation energy was increasing while increasing the DPF concentration during heating and reciprocal results were found during cooling. No significant influence of carriers or carrier levels (p < 0.05) was found on activation energy during heating. But while cooling, the activation energy was found higher for the MD-blended DPF than other two DPFs.