Rheological modeling and activation energy of Persian grape molasses

摘要

Study the rheological behavior, modeling and activation energy (E-a) of Persian grape molasses (PGM) at different conditions. The shear rate and shear stress of PGM were measured at 25, 45, and 65 degrees C and Brix concentrations (BC) of 35, 50, and 76%. Next different statistical parameters and Sigma plot software were used to test the obtained data on six different rheological models. Then the E-a and consistency coefficient of PGM were calculated at different BC using exponential and power equations. PGM exhibited a shear-thickening behavior (n 1) at BC's of 35-76% between 25 and 65 degrees C. It showed the best fitness (R-2 = 1.00) with power law (Ostwald-de-Waele) model. The exponential relationship for computing E-a had higher R-2 (0.937) than those in power law relationship (0.876). When the BC in PGM increased from 35 to 50% and then from 50 to 76% both at 25 degrees C, the E-a raised similar to 10 and 100%. Exponential relationships were more trustable to calculate the effects of BC on consistency coefficient andE(a)of PGM than power law equations. There is a high potential to raise the empiricalE(a)by increasing the BC of PGM to 76% at low temperature and retard its degradation process significantly.Practical ApplicationsPersian grape molasses (PGM) has high content of glucose and fructose, mineral, organic acid and bioactive compounds. The PGM with good nutritional components can be substituted instead of sugar in different food, and its rheological parameters will enhance the organoleptic (texture, color and flavor) properties of resulting products, considerably. On the other hand, rheological values of PGM will help us to solve numerous engineering calculations involved with this product when is produced in an industrial scale. Additionally, identifying rheological properties will help us to select and control processing equipment (such as mixing, dispersing, refining, spinning, concentration, and packaging), predict energy requirements, and evaluate sensory assessment of this product properly. Additionally, calculation of empirical activation energy could assist us to evaluate the degradation process of PGM and possibly predict its storage time at different brix concentrations and storage temperatures.