72 CEREAL CHEMISTRY Variability of Reaction Efficiencies and Pasting Properties of Acetylated Dent Corn Starch from Various Commercial Hybrids M. R. Wilkins, 1 P. Wang, 1 L. Xu, 1 Y. Niu, 1 M. E. Tumbleson, 2 and K. D. Rausch 1,3 ABSTRACT Cereal Chem. 80(1):72–75 Genetic diversity in corn (maize) has contributed to variability in corn processing characteristics. Differences in acetylated dent corn starch pasting properties and reaction efficiencies due to hybrid were assessed. Ten dent corn hybrids grown during 1998 and nine dent corn hybrids grown during 1999 were wet-milled in the laboratory. Starch from each hybrid was modified using a laboratory-scale acetylation procedure. NaOH consumed and reaction time were recorded for each reaction. A Rapid Visco Analyser (RVA) was used to measure starch pasting properties. Acetyl content was measured by a spectrophotometric method, from which reaction efficiency was calculated. Reaction efficiencies were observed at 35–56%. Overall reaction efficiencies for starch samples from 1998 hybrids were lower than samples from 1999 hybrids. Differences in peak viscosity, trough viscosity, final viscosity, setback, and pasting temperature were found among 1998 hybrids. Differences in trough viscosity, final viscosity, and breakdown were found among 1999 hybrids. Genetic diversity of the world corn (maize) supply has increased over the past several years. Through use of hybridization and genetic engineering, scientists have developed hybrids yielding more than 200 bushels per acre with resistance to a variety of diseases and pests. Currently, hybrids with benefits to corn processors are also being developed. For years, corn dry millers have used hybrids with large amounts of hard endosperm, often called food-grade hybrids, because of their ability to yield more flaking grits. Recently, hybrids with high amounts of extractable starch have been introduced to benefit the wet- milling industry. Corn hybrids containing starch that exhibits prop- erties of modified starches, beneficial nutritional components, and high-value pharmaceuticals have been discussed as future uses of genetic modification in corn. Hybrid effect on various corn-processing characteristics has been established in both corn wet milling and dry milling. Peplinski et al (1989) observed dry-milling fraction yields were hybrid-dependent. Zehr et al (1995) wet-milled several hybrids in the laboratory and found starch and coproduct yields were hybrid-dependent. Singh et al (1997) observed a hybrid effect on the starch yield increase of wet- milled hybrids due to lactic acid addition during steeping. Singh et al (1998) observed a hybrid effect on starch yield for hybrids subjected to a variety of postharvest handling procedures. Mathew et al (1999) found that both corn hybrid and growth environment affected corn curl properties and pet food extrudates processed from whole corn meal. Wilkins et al (2003) found a hybrid effect on several pasting properties of acetylated waxy corn starches as measured by rapid viscosity analysis. No previous studies have been published on the hybrid effect on the acetylation and properties of dent corn starch acetates. Dent hybrids exhibit more genetic diversity than waxy hybrids, particularly in amylose content. Amylose content has an effect on native starch pasting temperature and other pasting properties (Jane et al 1999). Wilkins et al (2003) observed that differences in pasting properties among native waxy starches were observed after these starches were acetylated with a constant amount of acetic anhydride. An increased understanding of genetic effects on this aspect of corn processing should lead to more efficient processing of starch and related coproducts. In this study, we sought to determine how starch isolated from individual dent corn hybrids affected acetylation efficiency and pasting properties. MATERIALS AND METHODS Wet Milling Ten dent corn hybrids (samples 1–10) grown during the 1998 crop year and nine dent corn hybrids (samples 1–8 and 11) grown during the 1999 crop year were provided by a commercial seed company. Eight hybrids (1–8) were grown during both seasons. All hybrids were grown on the same research plots of a major agricultural products company. Each hybrid was available commercially during the two crop years. Three 1,000-g samples of each hybrid (except 1999 samples of hybrid 3 and 1998 samples of hybrid 8, which had only two samples due to seed availability) were milled according to the procedure of Eckhoff et al (1993) to extract starch. Starch samples were organized into replicate blocks. Blocks a–c contained 1998 samples and blocks d–f contained 1999 samples. Each replicate block contained one replicate from each hybrid grown during that season (except block c, which did not contain hybrid 8, and block f, which did not contain hybrid 3). Hybrids were milled randomly within each block. Acetylation Each hybrid starch sample was acetylated once using conditions described by Jarowenko (1986). Five samples of a commercial dent starch (C*Gel 03420, Lot J1463-15, Cerestar USA, Hammond, IN) were laboratory-acetylated to assess reliability of the acetylation procedure. For each reaction, 180 g (db) of starch was combined with 514 g of water to obtain a solid-to-water ratio of 0.35. Starch slurry was mixed for 1 hr to fully suspend starch granules. At 30°C, slurry was adjusted to pH 8.2 with 1.5% (w/v) NaOH. Reaction temperature was controlled by placing the reaction vessel in a temperature- controlled water bath. By using a peristaltic pump (model 77200-60, Cole-Parmer, Vernon Hills, IL) with 0.8-mm diameter tubing (Master- flex L/S 13, Cole-Parmer), 10.4 g (6% of solids) of acetic anhydride were added into the agitated slurry at a rate of 0.24 mL/min while maintaining pH 8.0–8.4 with 1.5% NaOH. The amount of NaOH used and pH were measured for each reaction. The reaction was allowed to continue after acetic anhydride addition was completed and until slurry pH stabilized. A small amount (1.2–1.8 mL) of 6M HCl was added to the slurry with a pipette to lower to pH 6.0 to halt the reaction. The reaction time for each reaction was nearly constant. The slurry was vacuum-filtered through Whatman #3 filter paper. The cake was mixed with 500 mL of distilled water and refiltered to remove salts. The refiltered cake was dried at 49°C overnight. Starch Analyses Each acetylated starch sample was analyzed using a Rapid Visco Analyser (RVA) (model RVA-4, Newport Scientific Pty. Ltd., Warrie- wood, Australia) to determine sample pasting properties. In addition, 1 Graduate fellow, academic professional, research specialist, academic professional, and assistant professor, respectively; Agricultural Engineering, University of Illinois, Urbana, IL 61801. 2 Professor, Veterinary Biosciences, University of Illinois, Urbana, IL 61801. 3 Corresponding author. E-mail: krausch@uiuc.edu. Phone: 217-265-0697. Fax: 217-244-0323. Publication no. C-2002-1204-01R. © 2003 American Association of Cereal Chemists, Inc.