EFFECT OF EXTRUSION PROCESS PARAMETERS ON THE QUALITY OF BUCKWHEAT FLOUR MIXES

A response surface analysis using a second-order central composite des ign was used to study the effect of extrusion process parameters on th e extrudate quality of three blends containing buckwheat flour. The ex trudates were prepared as three blends. Blend 1 was a 55:40:5 (w/w) mi x of light buckwheat flour, wheat flour, and nonfat dry milk (NFDM). B lend 2 was a 40:55:5 mix of light buckwheat flour, corn meal, and NFDM . Blend 3 was a 30:60:10 mix of light buckwheat flour, corn meal, and NFDM. The blends were processed in a twin-screw extruder with factoria l combinations of the parameters including: process temperatures of 95 -150 degrees C, dough moisture of 15-22% and screw speeds of 260-390 r pm. The linear components alone significantly explained most of the va riation of expansion index, bulk density, water absorption, and breaki ng strength. The greatest amount of variability was explained by proce ss temperature for blend 1. Dough moisture accounted for the greatest amount of variation for blends 2 and 3. Maximum predicted expansion in dex Values and high water absorption percentages were obtained at low dough moisture levels. Dough moisture and process temperatures were th e most important factors predicting bulk density. Sensory evaluation o f texture, color, flavor, and general acceptability scores of selected samples ranked blend 3 > blend 2 > blend 1. The in vitro protein dige stibility values ranked blend 1 > blend 2 > blend 3. An increase of up to 9.5% units in the protein digestibility values was observed when c ompared to the nonextruded raw blends.