Evaluation of the displacement value as a method to detect reduced corn wet-milling quality

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 degrees C in batch dryers. Additional samples, obtained from commercial elevators in 1992, had been dried with air temperatures ranging from 52 to 136 degrees 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 degrees 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 degrees C for batch-dried samples. While DV correlated with drying temperature in batch-dried samples (r = 0.66), it did not correlate with starch yield or recovery of commercial samples (r less than of equal to 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 greater than or equal to 70 degrees C. All samples dried at 115-136 degrees C had significantly lower starch recoveries.