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Evaluation of the Displacement Value as a Method to Detect Reduced Corn Wet-Milling Quality

¹Assistant professor, Department of Biological and Agricultural Engineering, Kansas State University, Manhattan, KS66506. Corresponding author. E-mail: krausch@falcon.bae.ksu.edu ²Professors, Department of Agricultural Engineering, University of Illinois, Urbana, IL 61801.

A procedure based on the resistance and capacitance (RC) properties of corn to calculate a displacement value (DV) was evaluated for detection of corn that had reduced wet-milling quality. In 1991 and 1992, three hybrids were dried at air temperatures between ambient and 115°C in batch dryers. Additional samples, obtained from commercial elevators in 1992, had been dried with air temperatures ranging from 52 to 136°C. A baseline reference relationship was developed between log₁₀-resistance and capacitance with data from ambient-dried samples. A DV was defined as the horizontal distance along the capacitance axis from a sample RC data point to the baseline reference. RC properties of samples dried at air temperatures >50°C were compared to the baseline and the DV determined. Selected drying treatments were wet-milled by a laboratory-scale procedure to verify milling quality and correlation with DV. The effects attributed to hybrid and harvest moisture content on the RC properties of ambient-dried samples were small, allowing the baseline reference to be applied to a wide range of corn samples. In 1992, the baseline shifted upward from the 1991 baseline by 0.5 units on the log₁₀-resistance axis. DV increased significantly at drying air temperatures >50°C for batchdried samples. While DV correlated with drying temperature in batchdried samples (r = 0.66), it did not correlate with starch yield or recovery of commercial samples (r ≤0.10). Although the specific causes could not be determined, the shift in the baseline indicates the method would be difficult to implement on a practical scale. Although not indicated by DV, starch recovery decreased significantly for samples batch-dried at air temperatures ≥70°C. All samples dried at 115–136° had significantly lower starch recoveries.