Progress 12/15/00 to 12/31/03
Outputs
Among three corn mutants (Normal, Waxy and High-amylose), high-amylose corn had the greatest amount of hexane-extractable lipids in the whole kernel. A short-flow dry-milling procedure produced milled corn that was further fractionated by using five sets of Tyler sieves (mesh sizes 3.5, 5, 7, 14, and 30). The "greater than 7 fraction" had the least lipid content among the five fractions (greater than 5, greater than 7, greater than 14, greater than 30 and flour) for all corn types. High-amylose corn had the greatest amount of lipids in the dry milled fractions. The fatty acid composition of whole grain, endosperm, "greater than 7 fraction" and extruded product was characteristic of its corn type. Extruded products from the control corn samples had lower bulk densities than did those from the mutants (waxy and high-amylose). High-amylose corn produced extrudates with a lower expansion ratio and high bulk density. The textural parameter of force or resistance to fracture
was greatest and least in extrudates from waxy and high-amylose corn, respectively. Lipid content, bulk density, expansion ratio, and force were not highly correlated. Storage time affected (P is less than 0.0001) the quality of the extruded products produced from corn stored at both temperatures. Drying temperature did not affect bulk density, expansion ratio, and texture at P is less than 0.05; however, a three-way interaction of drying temperature, storage period, and corn type significantly affected the quality parameters of the extruded products. Thus, postharvest factors affected the extrusion quality of corn through complex relationships. Milling yields, pasting and thermal properties were significantly influenced by corn drying temperature. For all three corn types, the highest yield was from the "greater than 7 fraction", although normal corn had greater yields than did either waxy or high-amylose corn. Changes in milling yields with increased drying temperature indicated
changes in fracturability of corn, which resulted in increased yields of smaller fraction sizes and decreased yields of larger fraction sizes. The enthalpy change of gelatinization of the various endosperm fractions was measured by using a Differential Scanning Calorimeter. The enthalpy values for normal corn decreased from 9.6 J/g for the "greater than 5" fraction to 7.5 J/g for the flour fraction. Waxy corn had greater enthalpy values than did normal and high-amylose corn. The enthalpy change in high-amylose corn increased from 3.5 J/g to 10 J/g as the size of the fraction decreased from the "greater than 5" fraction through flour, respectively. Pasting properties of the various fractions, measured with a Rapid Visco-Analyzer (8% solids basis), revealed that all fractions of normal corn had greater peak and final viscosities than did similar fractions of waxy and high-amylose corn. The "greater than 7" fraction had greater peak and final viscosities than did all other fractions for
all three corn types. The differences in the pasting properties may be a result of structural differences in the starch polymers and the influence of minor components (such as lipids) in the different fractions.
Impacts
Clearly, postharvest factors, especially corn drying temperature, affected the extrusion quality of corn through complex relationships. Determining the changes in endosperm starch and lipids with drying and extended storage of corn will lead to better understanding of their functional impact during processing. These findings will enable processors to optimize handling practices prior to milling and extrusion of corn.
Publications
- Ji, Y., K. Seetharaman, and P.J. White. Optimizing a small-scale corn-starch extraction method for use in the laboratory. Cereal Chemistry. In press for early 2004.
- Vidal-Quintanar, Reyna-Luz, M. H. Love, J. A. Love, P. J. White, and L. A. Johnson. 2003. Lipid-Autooxidation-Limited Shelf-life of Nixtamalized Instant Corn Masa. J. Food Lipids 10:153-163.
- Seetharaman, K., N. Chinnapha, R.D. Waniska, P. White. 2002. Changes in textural, pasting and thermal properties of wheat buns and tortillas during storage. J. Cereal Sci. 35:215-223.
- Johnson, L.A., C.L. Hardy, C.P. Baumel, and P.J. White. 2001. Identifying valuable corn quality traits for starch production. Cereal Foods World 46:417-423.
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Progress 01/01/02 to 12/31/02
Outputs
To determine the effects of postharvest treatment on the quality [bulk density (BD), expansion ratio (ER), and texture] of extruded products, four corn types [two controls, waxy, and high-amylose] were harvested, and dried at three temperatures (27, 65 and 93C) prior to storage at 10 and 25C for up to 12 months. Corn samples were removed and processed every 4 months. A short-flow dry-milling procedure gave milled corn that was further fractionated by using a set of Tyler sieves (mesh sizes 3.5, 5, 7, 14, 30). The fraction collected in sieve 7 was extruded by using a twin-screw extruder. The F-tests (analysis of variance) showed that extrusion quality was affected significantly (P<0.0001) by corn type. Extruded products from the control corn types had lower BD than did those from the waxy and high-amylose types. High-amylose corn gave extrudates that were the least expanded and firmest in texture. Storage time affected (P<0.0001) the quality of the extruded products
produced from corn stored at both temperatures. Lipid content, BD, ER, and force were not highly correlated. Drying temperature did not affect BD, ER, and texture at P<0.05; however, a three-way interaction of drying temperature, storage period, and corn type affected the quality parameters of the extruded products. Changes were also observed in extrudate pasting properties, measured by rapid viscoanalysis (RVA). Cold paste and final viscosities decreased with increased storage time for extrudates from all three corn types. Functionality of the extrudates changed with post-harvest treatments and age of corn prior to milling. Differences were observed in the thermal properties of the extrudates from different corn types with increased storage time. Gelatinization onset temperature, by differential scanning calorimetry, increased from 48 to 70 C, 50 to 70 C and 50 to 105 C for normal, waxy and high-amylose corn extrudates, respectively, with increased storage time. A corresponding
decrease in enthalpy values was observed. The stored corn endosperms also were analyzed for thermal and pasting properties. Significant differences were observed in the DSC onset temperatures (oT) and enthalpies of endosperms, showing two general trends. Waxy corn fractions showed the least variability in oT between the two storage times, except in waxy corn dried at 93 C. Secondly, waxy and high-amylose corn fractions showed greater variability in enthalpies of gelatinization over storage than did normal corn. Also, peak and final viscosities, measured by RVA, were greater at 8 months than at 4 months in most fractions, with some exceptions. Most notable was the final viscosity of waxy corn fractions dried at 93 C, which showed the opposite trend. The peak, trough and final viscosities increased with decreased fraction size for all corn types dried at all temperatures upon storage. Final work in progress includes the measurement of bound and free lipids in the corn endosperm
fractions. Gas chromatography and high-performance liquid chromatography methods have been established to measure and quantify these lipids.
Impacts
Determining the changes in endosperm starches and lipids with drying and extended storage of corn will lead to better understanding of their functional impact during processing. These findings will enable processors to optimize handling practices prior to milling and extrusion of corn.
Publications
- Seetharaman K, N Yao, T Beta, CJ Bern and PJ White. 2002. Changes in thermal and functional properties of dry-milled corn fractions during storage following different post-harvest treatments, American Association of Cereal Chemists Annual Meeting, Proceedings, Oct. 2002 #355, p.147-148. http://www.aaccnet.org/meetings/2002/abstracts/a02ma355.asp
- Beta T, K Seetharaman, K Rezaei, CJ Bern and PJ White. 2002. Extrusion quality as affected by endosperm lipids and postharvest treatment. Corn Utilization and Technology Conference. Abstracts, June 2002.
- Beta T, K Seetharaman, CJ Bern and PJ White. 2002. Effects of postharvest drying and storage parameters on extrusion of corn grits, American Association of Cereal Chemists Annual Meeting, Proceedings, Oct. 2002, #334, p.142-143. http://www.aaccnet.org/meetings/2002/abstracts/a02ma334.asp
- Patel BK, K Seetharaman, T Beta, CJ Bern and PJ White. 2002. Effects of postharvest storage on the functional properties of corn grit extrudates, American Association of Cereal Chemists Annual Meeting, Proceedings, Oct. 2002, #345, p. 145. http://www.aaccnet.org/meetings/2002/abstracts/a02ma345.asp
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Progress 01/01/01 to 12/31/01
Outputs
Among three corn mutants (Normal, Waxy and High-amylose), high-amylose corn had the greatest amount of hexane-extractable lipids in the whole kernel. A short-flow dry-milling procedure produced milled corn that was further fractionated by using five sets of Tyler sieves (mesh sizes 3.5, 5, 7, 14, and 30). The "greater than 7 fraction" had the least lipid content among the five fractions (>5, >7, >14, >30 and flour) for all corn types. High-amylose corn had the greatest amount of lipids in the dry milled fractions. The fatty acid composition of whole grain, endosperm, "greater than 7 fraction" and extruded product was characteristic of its corn type. The relationship of hexane-extractable lipids to characteristics of extruded products made from the corn was determined. Extruded products from the control corn samples had lower bulk densities than did those from the mutants (waxy and high-amylose). High-amylose corn produced extrudates with a lower expansion ratio and
high bulk density. The textural parameter of force or resistance to fracture was greatest and least in extrudates from waxy and high-amylose corn, respectively. Lipid content, bulk density, expansion ratio, and force were not highly correlated. Milling yields, pasting and thermal properties were significantly influenced by corn drying temperature. For all three corn types, the highest yield was from the "greater than 7 fraction", although normal corn had greater yields than did either waxy or high-amylose corn. Changes in milling yields with increased drying temperature indicated changes in fracturability of corn, which resulted in increased yields of smaller fraction sizes and decreased yields of larger fraction sizes. The enthalpy change of gelatinization of the various endosperm fractions was measured by using a Differential Scanning Calorimeter. The enthalpy values for normal corn decreased from 9.6 J/g for the "greater than 5" fraction to 7.5 J/g for the flour fraction. Waxy corn
had greater enthalpy values than did normal and high-amylose corn. The enthalpy change in high-amylose corn increased from 3.5 J/g to 10 J/g as the size of the fraction decreased from the "greater than 5" fraction through flour, respectively. Pasting properties of the various fractions, measured with a Rapid Visco-Analyzer (8% solids basis), revealed that all fractions of normal corn had greater peak and final viscosities than did similar fractions of waxy and high-amylose corn. The "greater than 7" fraction had greater peak and final viscosities than did all other fractions for all three corn types. The differences in the pasting properties may be a result of structural differences in the starch polymers and the influence of minor components (such as lipids) in the different fractions.
Impacts
Determining the changes in endosperm lipids with drying and extended storage of corn will lead to better understanding of their functional impact during processing. These findings will enable processors to optimize handling practices prior to milling and extrusion of corn.
Publications
- No publications reported this period
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