Polyphenol oxidase activity in white tan-plant-type sorghums : an important determinant of the relatively dark colour of their porridges

Abstract

The relatively dark colour of food products from white tan-plant (food-grade) sorghums can compromise their acceptability. The relationship between white tan-plant sorghum polyphenol oxidase activity (PPO) and porridge colour was investigated, primarily using lines grown in the same locality over two seasons. Sorghum was intermediate in PPO between wheat and maize. White tan-plant sorghum and white maize whole grain flours were similar in colour. However, with white tan-plant sorghum, the transition from flour to porridge caused a much larger reduction in L* value. Further, the correlation between white tan-plant sorghum PPO activity and porridge L* values was highly significantly negative (P < 0.001), the relationship accounting for 40–50% of variation. PPO in white tan-plant-type sorghums is therefore an important determinant of the relatively dark colour of porridges. Breeding to reduce PPO activity could improve consumer appeal. Cultivar Sima (IS 23520) that had low PPO activity and produced light-coloured porridge could be useful for breeding.