Moisture Sorption Behavior of Deproteinized Sunflower Meal and Patterned Food Extrudate

Abstract

This research was undertaken to evaluate the influence of the extrusion process on the sorption behavior of deproteinized sunflower meal (DSM). A patterned food extrudate (PFE), prepared from a mixture of DSM and corn grits (1:1), was obtained, and the equilibrium isotherms of both products (DSM and PFE) were determined at three temperatures (20 °C, 30 °C, and 40 °C) by the static gravimetric method. The comparison of the sorption behavior of the products showed that extrusion decreased the equilibrium moisture content and the monolayer moisture, while the hysteresis effect was significantly raised in size and span. The experimental sorption isotherms were fitted by five modified models including the temperature effect: Chung–Pfost, Halsey, Oswin, Henderson, and GAB. The modified models of Oswin were established to be suitable to describe the equilibrium sorption isotherms in the temperature range from 20 °C to 40 °C. The net isosteric heat of sorption of DSM and PFE decreases consistently with the increase in moisture content. Extrusion reduces the bond energy between the solid matrix and the water molecules. The ranges of moisture content and relative humidities in the temperature interval studied, appropriate for long-term storage of DSM and PFE, were predicted.