Uncommonly high levels of 3-deoxyanthocyanidins and antioxidant capacity in the leaf sheaths of dye sorghum

Extracts from leaf sheaths of farmers' varieties of dye sorghum cultivated and used in Benin as a source of biocolorings were analyzed for their anthocyanidin and phenolic contents, as well as their antioxidant capacity. The aim was to identify and quantify the types of anthocyanin and phenolic acids. The total anthocyanin content of the leaf sheaths ranged from 13.7 to 35.5 mg of cyanidin 3-glucoside equivalent/g of dry matter (DM), with an average of 27.0 mg/g. The total anthocyanin content is 90 times higher than levels usually reported in fruits and vegetables. Anthocyanin consisted essentially of apigeninidin and luteolinidin, two 3-deoxyanthocyanidins with many applications in food, beverage, and pharmaceutical industries. The apigeninidin content of the leaf sheaths was 30 times higher than that in cereal bran and ranged from 14.7 to 45.8 mg/g, with an average of 31.3 mg/g. The amount of luteolinidin ranged from 0.4 to 2.4 mg/g, with a mean of 1.2 mg/g. The total phenolic content expressed as gallic acid equivalent averaged 95.5 mg/g. The free phenolic acids identified were benzoic acid, p-coumaric acid, and o-coumaric acid at amounts of 801.4, 681.6, and 67.9 μg/g, respectively. The leaf sheaths of dye sorghum have an antioxidant capacity [3.8-5.6 mmol of Trolox equivalent (TE)/g of DM] much higher than that reported for cereal bran and fruits and vegetables.