Color and health: identification and antioxidant activity of polyphenols in legumes and their correlation with seed color.

Legumes, are one of the most important basic staple food for human worldwide that provide a broad range of healthy micro- and macro-nutrients such as proteins, carbohydrates (dietary fiber), minerals, vitamins and phytochemicals like phenolics. Phenolics compounds have been ascribed as antioxidants able to delay or inhibit oxidative damage, thus preventing the onset of oxidative stress related deseases in humans [1]. Many epidemiological and interventional studies indicated that the daily consuption of food rich in polyphenols is inversely associated with coronary heart desease, type II diabetes mellitus onset, obesity, a lower incidence of breast cancer and results in lower LDL cholesterol and higher HDL cholesterol [2]. Flavonoids represent one of the group of major interest among phenolics exibiting a very strong antioxidant activity. Legumes are a source of flavonoids, namely flavonols, flavan-3-ols and anthocyanins [3]. Those compounds aside from their healthy activity on humans, affect the phisical and morphological features of the plant, as the colour of the seeds [4]. With this study we aim to optimize and validate an analytical method to identify and quantify simultaneously 14 polyphenols in 36 legumes varieties through HPLC-DAD. Polyphenols under survey were: caffeic acid, chlorogeninc acid, ferulic acid, gallic acid, p-coumaric acid, syringic acid, kaempferol-3-glucoside, quercetin, rutin, catechin, epicatechin, cyanidin-3-glucoside, and delphinidin-3-d-glucoside. The method has been validated through linearity, interday and intraday repeatability, limit of detection (LOD), limit of quantification (LOQ) and recoveries. The aforesaid phenolics have been quantified in all the legumes samples and results showed that total content of the analyzed polyphenols was ranged from 3 mg/kg to 1630.5 mg/kg in red dehulled lentils and ruviotto beans respectively. Additionally total phenolic content (TPC) has been evalued by means of the Folin Cioacalteau assay and the antioxidant power of extracts was evaluate by their ability to scavenge the 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical. The higher antioxidant activity was shown by the dark testa samples (black lentils and diavoli beans) in respect to the pale ones and a positive correlation was found between total phenolic content (TPC) and IC50 for dark coloured varieties. In conclusion this study shows that legumes can be ascribed as a good source of polyphenols and that the colour of the seed coat can be predictive of the presence of bioactive compounds such as polyphenols.