State diagrams of green peas (Pisum sativum L.) powders with different maltodextrin additions.

The purpose of this study was to examine the effect of maltodextrin addition on the physical stability of powdered green peas. The evaluation of the physical state of the material was based on the equilibrium water content of the monolayer (Xm ) and the glass transition temperatures of the powders at room temperature (Tg ) and in the frozen state (Tg' ). Graphical sorption characteristic at 25°C was determined using static-gravimetric method while capacity of the monolayer values was calculated from the mathematical GAB model. Differential scanning calorimetry was carried out in order to determine glass transition lines and freezing curves which combine together were used to plot state diagrams. Relationship between Tg and solid content were shown by using Gordon-Taylor model. Freezing data were modeled employing the Clausius-Clapeyron equation and its development-Chen model. Sorption isotherms showed sigmoidal shape characteristic for high-molecular weight materials. Monolayer moisture content varied between 0.047 and 0.106 g water/g solids. The glass transition temperature of anhydrous green peas increased in from 89.9 to 175.6°C while Tg' value changed from -43.4 to -26.6°C to as a result of 75% polysaccharide addition. The ultimate maximum-freeze-concentration conditions of the powders were observed in range from 0.783 to 0.814 g solids/g sample. Monolayer capacity, Tg and Tg' values increased with increasing maltodextrin amount in the sample which indicates that the addition of starch hydrolysate has a beneficial effect on the stability of powders stored frozen and at room temperature.