Effect of heat treatment on polyphenolic compounds and antioxidant activity of lentils (Lens culinaris)

The current research involves the study of the effect of thermal treatment in boiling water (cooking) on the nutrient components and phytochemical contents of lentils. The changes of phenolic compounds and antioxidant activity of lentils before and after cooking; as well as the recovered water are investigated. Total polyphenol, flavonoid and tannin content were determined spectrophotometrically using standards methods and LC-MS/MS. Antioxidant activity of methanolic extracts was evaluated using DPPH (2,2-diphenyl-lpicrylhydrazyl) and ABTS (2,2’-azinobis-(3-ethyl benzo thiazoline-6-sulfonic acid)) assays. As compared to the raw lentils, cooking caused significant (p<0.05) decreases in total phenolic content (TPC), total flavonoid content (TFC), DPPH and ABTS free radicals scavenging activity. The obtained results indicated that the polyphenol content of cooking water was significantly higher than that of cooked and raw lentils; however the most important antioxidant activity was recorded for raw lentils. Several phenolic compounds were identified in fresh, cooked lentils and cooking water. The major compound for the three samples is tannic acid with a very remarkable value in the cooking water; while the minor compounds are naringenin for cooked lentils, apigenin for raw lentils and cooking water. Neoformed compounds have been also detected in the cooking water such as: quercetin, hespritin, tr-caffeic acid and chlorogenous acid in the cooking water.