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 detecti on of corn that had reduced wet-milling quality. In 1991 and 1992, thr ee hybrids were dried at air temperatures between ambient and 115 degr ees C in batch dryers. Additional samples, obtained from commercial el evators in 1992, had been dried with air temperatures ranging from 52 to 136 degrees C. A baseline reference relationship was developed betw een log(10)-resistance and capacitance with data from ambient-dried sa mples. A DV was defined as the horizontal distance along the capacitan ce axis from a sample RC data point to the baseline reference. RC prop erties of samples dried at air temperatures >50 degrees C were compare d to the baseline and the DV determined. Selected drying treatments we re wet-milled by a laboratory-scale procedure to verify milling qualit y and correlation with DV. The effects attributed to hybrid and harves t moisture content on the RC properties of ambient-dried samples were small, allowing the baseline reference to be applied to a wide range o f corn samples. In 1992, the baseline shifted upward from the 1991 bas eline by 0.5 units on the log(10)-resistance axis. DV increased signif icantly at drying air temperatures >50 degrees C for batch-dried sampl es. While DV correlated with drying temperature in batch-dried samples (r = 0.66), it did not correlate with starch yield or recovery of com mercial samples (r less than or equal to 0.10). Although the specific causes could not be determined, the shift in the baseline indicates th e method would be difficult to implement on a practical scale. Althoug h not indicated by DV, starch recovery decreased significantly for sam ples batch-dried at air temperatures greater than or equal to 70 degre es C. All samples dried at 115-136 degrees C had significantly lower s tarch recoveries.