Roll and extrusion-cooking of grain sorghum grits

Abstract

Sorghum grits were processed by roll-cooking using a Buflovak double drum drier or on a pilot-plant GF double drum drier and by extrusion cooking in a Killion K-100 standard plastics extruder. (i) Water-absorption index, (ii) water-solubility index and (iii) Brabender amylograph viscosity patterns were determined for sorghum grits roll-cooked over the grit moisture range 15-30% and with roll surface temp. ~255, 285 and 300°F (300 to ~550°F on GF drier) and for grits extrusion cooked at moisture levels from 15 to 35% and with the barrel held at various temp. between 230 and 450°F. With both roll- and extrusion-cooking at a given moisture level, (i) passed through a max. as cooking temp. increased, dropping off as temp. sufficient to produce degradation were reached. (ii) increased progressively with increase in cooking temp. With roll-cooking, (i) at a given cooking temp. up to 425°F increased with increasing moisture levels; at any cooking temp. (ii) increased with increase in moisture level. With extrusion-cooking, (i) at a given cooking temp. was higher at high moisture levels, but (ii) was higher at low moisture levels. This is believed to be caused by greater shear degradation of starch during extrusion at low moisture levels. Gelatinization of sorghum grits by roll- or extrusion-cooking to similar (i) levels, gave a higher amylograph cooked paste viscosity with the roll-gelatinized products. Sorghum grits can be processed either by roll- or extrusion-cooking to materials having (i) and (iii) similar to those of processed corn meal satisfactory for use in corn soya milk. Control of processing conditions permits