Compression-relaxation test was used to measure mechanical properties of dried onion and to identify their changes during storage. It was shown that variety of the onion and storage conditions applied in this work had no influence on the mechanical properties of dried onion. Pre-drying treatment affected strongly rheological properties of dried onion. Soaking in water, dipping in starch solution and osmotic dewatering were the pre-drying treatments affected rheological properties of dried onion the most. Rheological properties of dried onion were dynamic, and changed during storage. The kinetics of these changes depended on pre-drying treatment applied.Shrinkage stresses and moisture gradients resulted during drying were responsible for the variation of mechanical properties of dried onion. Relocation of water and relaxation of the shrinkage stresses were reflected in changes of rheological properties of dried onion during storage.

Film-forming solutions based on four types of biopolymers were prepared and their rheological properties were determined. High methylated apple pectin and sodium alginate were used at the concentrations 1%, 1.5%, and 2%, whereas soy protein isolate and pork gelatin were obtained at 4%, 8%, and 12%. The parameters determining the production of the appropriate type of packaging film or edible coating are the setting time on the substrate, regardless of its type, and the gelation temperature, which were analyzed in the study by determination of flow curves and rheological parameters of prepared dispersions. The Newtonian model was used to describe the flow curves of the gelatin and sodium alginate solutions, while the Ostwald–de Waele model was used to describe the flow curves of the soy protein isolate and high methylated apple pectin solutions. The apparent viscosity of all solutions increased with increasing biopolymer concentrations, from 0.0042 to 0.0061 Pa·s and from 0.0187 to 0.0884 Pa·s for high-methylated apple pectin and sodium alginate, respectively; whereas, for a protein-based solution the viscosity increase was from 0.024 to 0.100 Pa·s and from 0.0018 to 0.0056 Pa·s for soy and gelatin, respectively. Modulus of elasticity curves appeared only at the highest concentrations, which means that the formation of the continuous structure of film or coating occurs by different mechanisms depending on the biopolymer type and its amount dispersed in aqueous solutions.