THE REACTIVITY OF PORCINE PANCREATIC ALPHA-AMYLASE TOWARDS NATIVE, DEFATTED AND HEAT-MOISTURE TREATED POTATO STARCHES BEFORE AND AFTER HYDROXYPROPYLATION

Potato starch was defatted (hot 75% n-propanol) and heat-moisture trea ted (100 degrees C, 30 % moisture) for various time intervals. The res ults showed that the above treatments increased the susceptibility of potato starch granules (heat-moisture treated > defatted) towards hydr olysis by porcine pancreatic alpha-amylase. These differences can be a ccounted for by the structural changes that occur within the amorphous and crystalline regions of the starch granule during defatting and he at-moisture treatment. Native, defatted (7h) and heat-moisture treated ( 100 degrees C, 30 % moisture, 16h) potato starches were hydroxyprop ylated (ia different levels of molar substitution [MS]) with propylene oxide (2 --> 20 %). The results showed that the alkaline reagents (Na OH and Na2SO4) used during hydroxypropylation increased the susceptibi lity of the above starches (native > defatted > heat-moisture treated) towards hydrolysis by alpha-amylase. Addition of propylene oxide to a lkali treated starches, further enhanced their susceptibility, towards alpha-amylase. However, granule susceptibility towards cl-amylase did not increase exponentially with increase in MS. The extent of hydroly sis began to decrease at MS levels of 0.29 (native), 0.28 (heat-moistu re treated) and 0.26 (defatted).