1. Postdoctoral research associate and professor, respectively, Department of Food Science and Technology, University of Nebraska, Lincoln, NE 68583-0919.
2. Corresponding author. E-mail: djackson1@unl.edu. Fax: 402-472-1693.
3. USDA-ARS, 362C Plant Science Hall, University of Nebraska, Lincoln, NE 68583-0915.
4. Professor, Department of Biometry, University of Nebraska, Lincoln, NE 68583-0712.