CHARACTERIZATION OF THE PORE STRUCTURE OF STARCH BASED FOOD MATERIALS

Macroscopic pore structure parameters (bulk density, true density and porosity) and microscopic pore structure parameters (percentage closed pore volume and pore size distribution) for a highly expanded type (Wonder White Sandwich Bread) and a relatively compact type (Chessmen Butter Cookies) starch based food material were determined and their pore structures were compared. Bulk density determined by solid displacement and true density determined by pycnometry yielded porosity measurements of 0.9 for bread and 0.6 for cookies. Percentage closed pore volume calculated by comparing the true density of porous samples of bread and cookies with the true density of their compacted pellets showed that both bread and cookies contained closed pores. Pore size distributions representative of the mercury porosimetry range (pores less than 200 mum in diameter) indicated that the smallest pore diameter was 6 Am for both bread and cookies. Pore size distributions obtained corresponded to about 16% and 65% of the total pore volume in bread and cookies, respectively. Both bread and cookie samples were found to undergo capillary hysteresis. Unidimensional mercury intrusion studies revealed a highly interconnected pore structure both in bread and cookies. Scanning electron microscopy (SEM) photomicrographs used to evaluate the pore structure qualitatively showed no directional orientation of the pore structure