FORMATION OF RESISTANT STARCH BY A TWIN-SCREW EXTRUDER

The objective of this study was to evaluate the potential to increase the level of resistant starch (RS) in extruded products by optimizing extruder conditions. Three experiments were conducted as randomized co mplete block designs with two replicates. In the first experiment, cor n starch, wheat starch, and potato starch were added at a level of 30% (w/w) to degerminated yellow corn meal to investigate the influence o f starch type. In the second experiment, citric acid (CA) monohydrate was added to corn meal at levels of 0, 2.5, 5, and 7.5% (w/w). The thi rd experiment was a full-factorial arrangement to evaluate the effect of high-amylose corn starch (HACS) level (0, 15, 30%, w/w) and CA leve l (0, 5, 7.5%, w/w) at two screw speeds (200 and 300 rpm). In the firs t experiment, the means for RS plus dietary fiber for the different st arch formulations ranged from 1.27 to 2.28%. In experiment 2, adding C A increased RS plus dietary fiber content to a maximum of 5.23% at 7.5 % CA. In the third experiment, the means for RS plus dietary fiber ran ged from a low of 1.75% for 100% corn meal at 300 rpm to 14.38% for 7. 5% CA and 30% HACS at 200 rpm. The results indicated a highly signific ant positive relationship between CA and RS formation and the same for amylose content. The RS formation had a negative relationship with sc rew speed, but the influence of screw speed was small when compared wi th that of CA and HACS.