A method was developed for preparing flat potato chips suitable for colorimetric measurement and visual evaluation. Flat potato chips were evaluated by three techniques: (1) colorimetric, including and excluding ultraviolet (UV) light in measuring beam to determine fluorescence effects; (2) spectrophotometric (380 to 740 nm), alternately backing chips with black or white reflector to permit calculation of light scattering; (3) visual, under controlled illumination by an experienced panel using a simple color-scoring system.
Excluding UV light increased Hunter aL and bL values. Although visual color scores under two luminaires (UV included and UV somewhat attenuated) were similar, greater attenuation of the UV light might affect visual impressions. Visual scores were highly correlated with Hunter L and aL, indicating that these instrumental measurements could be used to predict visual impressions of chip color. Munsell notations of chip color derived from spectrophotometric measurements backed with white reflector matched Munsell papers better than notations derived from data corrected for light scattering.
Color photographs were made of a series of flat potato chips with a Munsell gray scale in the frame register, permitting precise reproduction of a new visual color guide. The method of flat chip preparation for instrumental measurement and the visual color guide are offered as improved optional procedures in U.S. Standards for Grades of Potatoes for Processing.