04758nam a2200265 a 450000100080000000500110000800800410001910000190006024501270007926000160020630000110022250000690023352040310030265000240433365000100435765000140436765000140438165000130439565300130440865300140442165300100443565300230444565300120446865300120448014807962015-09-21       1998    bl uuuu  m   00u1 u    #d1 aPAES, M. C. D.  aPhysical properties and essential amino acid profiles of Brazilian quality protein maize cultivars processed by extrusion.  a1998.c1998  a144 p.  aThesis (Master) - Colorado State University, Fort Collins, 1998.  aIn Brazil, the production of Quality Protein Maize (QPM), a specialty corn with enhanced protein quality due to high lysine and tryptophan contents, is expected to increase in the near future resulting in replacement of ordinary corn in both feed and food markets. However, no information is available on the processing behavior of the Brazilian QPM cultivars  with regard to extrusion, a process used extensively to procedure corn-based products and whose effect on protein quality has been extensively reported in the scientific literature. This study was designed to determine optimum extrusion conditions for QPM whole-grain corn flours, to compare QPM and ordinary corn and products obtained under optimized conditions, and to evaluate the effect of the optimezed extrusion process on essential amino acid profiles of \tQPM and ordinary corn. Whole-grain flours of three Brazilian QPM cultivares (BR 451, BR 473 and BR 2121) and  one yellow dent corn (Pioneer 3779) were prepared at three different moisture levels (15%, 20% and 25%) and extruseded in a single-screw extruder using a 3:1 compression ratio, 80 RPM screw speed, threee die  head temperature (70oC, 100oC and 130oC), and two die diameters (3mm and 5mm). The cultivar/temperature/die diameter/feed moisture combinations represented 72 individual process conditions, which were replicate for a  total of 144 individual runs. Raw material was evaluated for proximate composition, color (L, a,  b Hunter values), particles size distribution, water absorption index (WAI) and essential amino acids. The extrudates physical properties evaluated were expansion ratio, bulk density, breaking strength, color (L. a, b Hunter values) and water absorption index (WAI). Essential amino acids were analyzed in selected extruded samples. Response surface regression analysis for each cultivar was conducted to determine optimum process conditions for extrudate physical properties. QPM extrudates as a result of optimized extrusion conditions were statistically compared to yellow dent corn extrudates with regard to physical properties and essential amino acid profiles. Cultivar and process variables individually or combined were shown to significantly influence extrudates physical properties. The combination of 15% moisture/130oC extrusion temperature, regardless of die diameter, was defined as the optimum extrusion condition for expansion ratio, bulk density and breaking strength for all QPM samples. The ordinary corn presented optimum expansion, density and breaking strength when the conditions were set either at 15% moisture/13oC/5mm die or at 25% moisture/130oC/3mm die. die. Under optimum extrusion conditions, BR 2121 extrudates had a similar expansion ratio, bulk density, breaking strength and better color as those obtained with yellow dent corn. BR 451 extrudates were white in color but were similar in physical properties when compared to ordinary corn extrudates. On the other hand, BR 473 processed through a large die resulted in denser extrudates than the extruded yellow dent corn. Extrusion caused loss of isoleucine, leucine, lysine, threonine and valine content of QPM and ordinary whole-grain corn flours but did not significantly affect histidine, methionine, tryptophan, and phenylalanine contents. Flours extruded through a small die diameter (3mm) had a lower leucine content than those extruded using a large die (5mm). QPM extrudates as a result of optimum extrusion conditions for physical properties, defined in the range used in this study, had a superior essential amino acid profile compared to yellow dent corn. The results suggested that Brazilian QPM cultivars can be used to replace ordinary corn in the production of expanded products, rendering extrudates with superior essential amino acid profiles. Although composition of flours appeared to control the amino acid profiles of the extrudates, processing conditions were more important than feed source to define physical properties of whole-grain corn flour extrudates.  aphysical properties  aMilho  aProteína  aQualidade  aZea Mays  aExtensao  aExtension  aMaize  aPropriedade fisica  aProtein  aQuality