Sorghum–cowpea composite porridge as a functional food, Part II: Antioxidant properties as affected by simulated in vitro gastrointestinal digestion

• Digested sorghum–cowpea composite porridge has radical scavenging properties.
• Composite porridges and their digests inhibit LDL oxidation and oxidative DNA damage.
• Compositing cereals with legumes increases nitric oxide radical scavenging activity.

The effect of compositing red non-tannin sorghum with brownish-cream cowpea and in vitro gastrointestinal digestion on total phenolic and flavonoid contents and antioxidant properties of a sorghum–cowpea composite porridge was studied. Maize–soybean composite porridge was used as a reference sample. Antioxidant properties were studied using radical scavenging activities against the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid), peroxyl and NO radicals as well as inhibition of low density lipoprotein (LDL) oxidation and oxidative damage of vector DNA. Hydroperoxide content of the samples was also measured. All the samples demonstrated radical scavenging activity. Simulated duodenal digests of the porridges had hydroperoxides and therefore caused LDL oxidation. The undigested porridges and simulated gastric digests inhibited LDL oxidation. Compositing the cereals with legumes increased total phenolic and flavonoid contents and NO scavenging activity of their porridges. In vitro gastrointestinal digestion of the porridges increased their total phenolic and flavonoid contents, radical scavenging activities and LDL oxidation inhibitory activity.