Effect of roasting processes on some properties of sesame and sesame paste: Rheological, color, textural and moisture adsorption

Sesame seeds were roasted using conventional method at 120, 150, and 180ºC for120 min. The changes occurred in the moisture content, color values and texturalproperties (hardness and fracturability) of sesame seeds were simulated usingexponential, kinetic and polynomial models for conventional roasting. Responsesurface methodology was applied to develop predictive models and optimize the hotair, electrical oven and vacuum oven roasting processes. As considering desirabilityfunction of each color and texture parameters, the optimum roasting temperature andtime ranges for production of sesame paste were determined as 155-170ºC and 40-60min at hot air roaster, respectively. The effects of dehulling and roasting process onthe moisture adsorption isotherms and thermodynamic properties of sesame seedwere investigated. Though the trend of sorption isotherms of the samples weresimilar, equilibrium moisture content was decreased with dehulling and roastingprocess at a certain water activity. The Guggenheim-Anderson-de Boer (GAB) andHalsey models were found to adequately describe the sorption characteristics. Thevalues of differential enthalpy and differential entropy decreased with application ofdehulling and roasting process. The effects of gum type and temperature on thethixotropic behavior of sesame paste were determined. The different mathematicalmodels were used for description of structural breakdown of paste. The first-ordershear stress decay with non-zero equilibrium was determined as the most successfulmodel.