Received for publication 6 Sept. 1983. Journal Paper No. 9614 of the Purdue University Agricultural Experiment Station. We acknowledge the technical assistance of Marcos Paiva. Anna Whipkey, and Marlaya Wyncott. The differential scanning calorimetry analysis was performed by D.R. Cox, Mars Incorporated, England. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.