THE INFLUENCE OF PARTICLE SIZE DISTRIBUTION ON SUNFLOWER TAHINI RHEOLOGY AND STRUCTURE

Different particle size sunflower tahini prototypes were obtained by controlling the milling process of roasted sunflower kernels. Not only the physicochemical properties of these samples but also of an industrial reference were compared and discussed in order to understand tahini behavior and structure. Granulometry was determined by a laser-scattering analyzer and revealed for all studied samples, trimodal particle size distributions. Histogram modes, as well as cumulative volume percentages (CVPs) of small- and middle-class populations, increased with the number of passes through colloidal mill, while for large particle size population, both the modes and CVPs decreased. Pseudoplastic behavior was observed for all sunflower tahini prototypes and reference, irrespective of studied temperature and particle size. However, the value of consistency coefficient ranged from 3,049 to 6.6 Pa sn being strong dependent on particle size and temperature while flow behavior indexes between 0.53 and 0.87. Time-dependent rheological analysis revealed higher thixotropic degree of coarser sunflower tahini samples. Studied samples had rheological properties characteristic for a viscoelastic material, the response in the dynamic frequency sweep being typical for weak gels. The finest sunflower tahini prototype showed the lowest Krieger-Dougherty estimated volume fraction (0.48), while the coarsest sample the highest (0.69), sunflower tahini reference being placed in a median position with a volume fraction of 0.56. By combining all those data, a schematic structure of sunflower tahini was proposed for the first time.