Investigation and prediction of the extensional viscosity of okra mucilage using the Giesekus model

Article type: Research Article

Authors: Minh, Nguyen Ngoc^a;

Affiliations: [a] Department of Mechanical Engineering, Thuyloi University, Dong Da, Ha Noi, Vietnam

Correspondence: [*] Address for correspondence: Nguyen Ngoc Minh, Thuyloi University, 175 Tay Son, Dong Da, Ha Noi, Vietnam. Tel.: + 84 0243 563 66 46; Fax: +84 0243 563 33 51; E-mail: [email protected]

Abstract: BACKGROUND:Okra is a vegetable that is widely grown around the world. Okra mucilage contains a high mucus concentration that can be useful for supporting the swallowing process. Although the extensional rheology of okra mucilage is essential to its flow, its extensional viscosity has not received much attention. OBJECTIVE:Using a filament stretching rheometer, the extensional viscosity of the mucilage in okra was examined. The Giesekus model was used to predict this parameter. METHODS:The okra mucilage with different concentrations was extracted from fresh okra. The extensional viscosity was measured using a filament breakup apparatus. The diameter of the liquid bridge was measured by a laser micrometer and it was also observed by a high-speed camera. A rotational rheometer was used to measure the shear viscosity. In addition, the master curves for the shear viscosity were plotted to eliminate the influence of solvent and shear rate and evaluate the influence of concentration on the elasticity of okra mucilage. The okra mucilage shear and extensional viscosity were predicted using the Giesekus model. RESULTS:Every sample of okra mucilage exhibited shear thinning behavior. In addition to having a high extensional viscosity that is hundreds of times higher than its shear viscosity, okra mucilage also exhibited stretching phenomena. The master curves demonstrated that the pseudoplasticity of the okra mucilage increased along with the concentration. The rheological behavior of the mucilage in okra can be explained by the Giesekus model. CONCLUSIONS:Okra mucilage’s shear viscosity exhibited shear thinning behavior and a strong extensional viscosity that was significantly higher than its shear viscosity. The shear and extensional viscosity of okra mucilage can be described and predicted using the Giesekus model.

Keywords: Okra, extensional viscosity, shear viscosity, Giesekus model

DOI: 10.3233/BIR-220006

Journal: Biorheology, vol. 59, no. 1-2, pp. 29-42, 2023