Factors influencing the relationships between reducing sugars and fry colour of potato tubers of cv. Record

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Abstract
Summary: The influence of sampling and sugar and colour assessment on the correlation between sugar content and fry colour of potatoes was investigated in cv. Record stored at 5 and 10°C (to produce a wide range of reducing sugars), and sampled at the basal, middle and apical region of the tuber.When colour and reducing sugars from adjacent slices were compared excellent correlations were found between these two factors whether the colour was measured objectively, as reflectance density (RD) of the ground paste from fried disks (r = 0.9550) and optical density (OD) of extract from the paste (r = 0.9507), or subjectively against IBVL colour cards (r =−0.9378). Although good correlations were found for individual scorers, using matching colour cards, significantly different regression lines were found between individuals. Reducing sugar levels were generally higher at the basal end than at the apical end. Consequently, the correlations between fry colour and reducing sugars are much poorer if reducing sugar and colour are measured on different tissue in the same tuber and the variation in colour explained by variation in reducing sugar decreased from 90 to 50%.Sampling within tubers thus appears to be a major factor determining the ability to accurately predict fry colour from reducing sugar content. It is suggested that if potatoes for processing are to be rejected on the colour of the darkest part of a tuber then a sample core for sugars should be taken from the basal region of the tuber.