RHEOLOGICAL PROPERTIES OF CLOUDY AND CLARIFIED JUICE OF MALUS FLORIBUNDA AS A FUNCTION OF CONCENTRATION AND TEMPERATURE

The rheological behaviour of cloudy and clarified juice of Malus floribunda was studied as a function of solid concentration, in a range of 45–70 Brix, at nine temperatures (5–50C). Cloudy and clarified juices are slightly thixotropic at 65–70 Brix and 5–10C. At lower concentrations and higher temperatures the thixotropy is low and can easily be eliminated by shearing. The power law model was applied to fit the pseudoplastic behaviour depending on the concentration level. Cloudy juice has pseudoplastic behaviour for concentrations higher than 45 Brix. Clarified juice is pseudoplastic at 65 Brix for temperatures lower than 25C and Newtonian at higher temperatures and for solid concentrations lower than 60 Brix. The activation energy for flow evaluated with the Arrhenius-Guzman equation, increases with solid concentration and ranged from 10.8 to 3.45 kcal gmol⁻¹ for cloudy juice and 15.3 to 7.9 kcal gmol⁻¹ for clarified juice. A nonlinear correlation accounting for temperature and concentration effects on the consistency coefficient was identified.