ESTIMATING POTATO CRISP COLOR VARIABILITY USING IMAGE-ANALYSIS AND A QUICK VISUAL METHOD

Image analysis gave better precision than colorimetry in measuring the darkening caused by excess free sugar during crisping of potatoes. The image analyser was used to measure individual crisp Average Optical Density (AOD) values in order to examine the variability of AOD within and between tubers. It is unnecessary to measure more than one crisp per tuber when assessing breeding lines, although two crisps per tuber are recommended for quality control. Crisps from at least ten tubers should be measured. A 'Quick Crisp' method, in which single crisps from each of four tubers are judged against standard samples, is reported. Regression of results from this method on crisp reflectance percentage (Agtron score) gave R2 of 0.967. However, the observer tended to overestimate at low values and underestimate at high values. Over several trials, the crossover point varied from 15 to 50 Agtron score units. Measurement of crisp colour variability for improving selection, management and purchasing decisions is discussed.