Maize grits did not expand fully during extrusion at temperatures below 130 °C and some grits remained intact in the extruded product, whereas the extrudates were overcooked and unacceptably brown in colour at barrel temperatures greater than 160 °C. Hence, the experiments were carried out at temperatures of 130, 140, 150, and 160 °C.This temperature range had little differential effect on the retention of any of the vitamins. Thiamin and pyridoxine, reported earlier to be the most thermo-sensitive, decreased during extrusion along with niacin. However, they decreased by the same amount at all temperatures. In contrast, other studies (Beetner et al., 1974, 1976 [ Beetner et al., 1974, Beetner et al., 1976]; Harper, 1979; Camire et al., 1990; Killeit, 1994) have shown that the percentage of thiamine retained decreased from 40% to 60% to between 50% and 20% as temperatures increased from 140 to 190 °C. These data represent a huge range in variation and suggest that variables other than temperature may play a role. One study ( Björck and Asp, 1983) found that an increase in barrel temperature increases riboflavin retention possibly due to a decrease in shear resulting from decreases in melt viscosity at higher temperatures.
In contrast with the study, other researchers did not use a low residence time extruder. Killeit (1994) noted that increasing throughput, and therefore decreasing residence times, improved the retention of the B vitamins. Our work supports this and suggests that over the useful temperature operating range of this extruder, the loss of B vitamins was independent of temperature
The addition of maize germ material and amylose starch to maize, either separately or together, did not affect vitamin retention in the extrudates nor did the addition of the germ material increase the levels of thiamin in the extrudate. In effect, the results for the additives experiment were similar to those of the temperature experiment and the results for maize only in experiment 1 ( Table 4).3 個解答語言1 0 年前
Commercially available, specification 220 maize (corn) grits were purchased from Corson Grain Ltd (Box 1046, Gisborne, NZ). The maize grits are degermed before manufacture and for this reason contain about 75% starch, about 8% protein and less than 0.5% oil. Dried green peas (variety Rex, Crop and Food Research) were coarsely roller milled and sieved in our laboratory to produce a pea grit product of similar size to the spec. 220 maize. The pea grits contained approximately 43% starch, about 22% protein and 1.3% oil. An unmilled naked oat variety (CRO 59) was used as the whole grain. Whole oats contain approximately 62% starch, about 11% protein and 4% oil. They therefore contain far more oil than the other grain products, and this is likely to alter their processing properties. Because pea grits did not extrude well in the equipment available due to their high protein content, they were blended 50/50 with maize grits. In all cases the ingredients contained about 12% moisture as used.
The food products used in this study were made on a Dorsey, single-screw, short barrel (90 mm) snack food extruder. The extruder was fitted with a 4-start screw and a 2-hole die with 5 mm apertures. The ingredients were fed into the extruder in the form of a dry granular material at the rate of 75 g min−1 using a mass flow feeding device.2 個解答語言1 0 年前