Comparative performance of the L a b colour space and North American colour charts for determining chipping quality in tubers of potato ( Solanum tuberosum L.)

Differences in North American standard charts for the characterization of colour quality of potato chips have contributed to an inability to accurately define the colour of the processed product. Consequently, individual colour standard cards for potato chips from the Snack Food Association (USA) and Agriculture and Agri- Food Canada (AAFC) were analyzed for their reflectance characteristics in the visible spectrum (400 nm-700 nm). In addition, several cultivars were chipped and analyzed for comparison purposes. An objective colour criteria was provided by a visually uniform, three-dimensional colour scale developed by the Commission Internationale de l’Eclairage (International Commission on Illumination) and defined by the L* a* b* colour space. When colour values of the AAFC chipping chart, calculated from L* a* b* values, were plotted against assumed card values, high card variability led to the inability to separate these cards when based on objective analysis by reflectance colorimetry. Although strongly influenced by tuber glucose content, chroma plots (a* vs. b*) revealed that the AAFC colour standards were comparable to processed potato chips from a range of cultivars grown and stored under a range of different conditions. The three colour quality levels of the Snack Food Association were restricted in their colour range and demonstrated unacceptable reflected spectral differences. Plotting L* values (y-axis) against a*/b* values (x-axis) gave a linear relationship regardless of data source, i.e., standard curve origin, cultivar, production area, storage temperature, duration in storage. Based on the above analysis, a standardized and more objective colour standard based upon the L* a* b* colour space is suggested. Key words: Potato, Solanum tuberosum, chip colour, quality standards