A Diffuse Reflectance Measuring Instrument to Determine Peanut Pod Brightness

Abstract

For Valencia peanuts, pod brightness is determined by inspectors during the peanut grading process when peanuts are sold by the grower. Presently, inspectors make visual observation of each peanut pod, from a sample drawn from a bigger lot, and determine the percentage of discolored pods present in the sample. The percent discolored pods is one of ten grade factors that determines the price at which the Valencia peanuts are sold. The visual method seems to be reliable, but it may not be consistent among inspectors nor over time due to the human element involved. An instrument may be more consistent and objective. The design and operation of an optical system for this purpose is described here. A narrow beam of white light was collimated onto the surface of a peanut pod at four consecutive positions spaced at 90 intervals around the circumference of the peanut pod. Diffuse reflectance from the peanut surface was measured at each position using a silicon detector with UV enhanced response. The average of these four values was a good indicator of the pod brightness and was used to detect discolored peanuts. Percent discolored pods determined using this instrument was highly correlated (r2 = 0.98) with the visual evaluations made by inspectors.