Grains, leaves, sheaths, glumes and stalks of sorghum varieties were analyzed for total phenols, condensed tannins, flavan-4-ols, anthocyanins and in vitro antioxidant activity. Black sorghum bran was used to evaluate the effectiveness of organic acids and enzymes on extractability of phenols. Flavonoid profiles of grains and non-grain tissues were determined and characterized using HPLC-PDA and HPLC-ESI-MSn. The presence of a pigmented testa and spreader genes (B1B2S) is a predictor for polymeric flavonoids (tannins) but not for simple phenols such as flavan-4-ols, 3-deoxyanthocyanins, flavones and flavanones. Simple flavonoids increased antioxidant capacity of sorghum, and were present in all sorghum except for the white pericarp sorghums that did not have flavanones. The "red turning into black" gene increased phenols in Type I sorghum. The leaves, sheath and glumes of sorghum had higher levels of phenols (78-600 times more), with in vitro antioxidant properties than commonly seen in grains. Pigmentation of plant components increased levels of 3- deoxyanthocyanins but not flavones nor flavanones. The leaves of biomass sorghum, Collier variety, had 3.4 times more 3-deoxyanthocyanins than the leaves of Tx430 Black x Sumac which had the highest levels (1810 ?g/g) of 3- deoxyanthocyanins among the leaves. The use of 1% HCl/ethanol provides a possible food grade substitute solvent for 1%HCl/methanol in the extraction of phenolic compounds from sorghum. All enzymes evaluated broke down bran particles forming a gel-like material which had increased phenols and antioxidant activities but not 3- deoxyanthocyanins as revealed by HPLC analysis. Microscopy examination showed the gel matrix rich in fiber and can possibly be used for nutraceutical applications. Careful understanding of enzyme activities is necessary for effective extraction of 3-deoxyanthocyanins from sorghum. Sorghum leaves, sheaths and glumes are excellent sources of bioactive compounds, up to 600 times more than the grains of some varieties. Sorghum with the "red turning to black genes" is a potential source of 3- deoxyanthocyanins and flavan-4-ols. With the trend towards sorghum as biomass for ethanol production, plant breeders must select special traits aimed at developing enhanced desired functionality such as antioxidant potential and other healthy attributes with application in food, pharmaceutical/nutraceutical and cosmetic industries.

Ce travail porte sur la synthèse chimique d’analogues simples d’anthocyanes, une classe majeure de pigments naturels solubles dans l’eau. Onze ions flavylium substitués par des groupements hydroxyl,méthoxyl et beta-D-glucopyranosyloxyl en positions 4’, 5 et 7 ont été préparés en utilisant des procédures simples. De plus, les deux principales 3-désoxyanthocyanidines du sorgho rouge, l’apigéninidine (APN) et la lutéolinidine (LTN), ont été synthétisées en une seule étape. Les propriétés physico-chimiques ainsi que l’activité antioxydante ont été étudiées pour le chlorure de 3’,4’,7-trihydroxyflavylium (P1), son 7-O-beta-D-glucoside (P2) et le chlorure de 3’,4’,5,7-tétrahydroxyflavylium (LTN). Grâce à leur noyau catéchol, ces pigments complexent rapidement FeIII, AlIII and CuI et ne se lient que faiblement à FeII tout en stimulant son autoxydation en FeIII. Suite à la complexation de CuII, les pigments subissent une oxydation. Les aglycones P1 et LTN sont des ligands modérés de l’albumine de sérum humain (HSA) et leurs chalcones ont montré une plus grande affinité pour la HSA que leurs formes colorées. Leur capacité antioxydante a été démontrée par le test de réduction du radical stable DPPH et par l’inhibition de la peroxydation lipidique induite par le fer héminique, un modèle de stress oxydant postprandial dans l’estomac. Les aglycones P1 et LTN (particulièrement, dans leur forme incolore chalcone) sont plus efficaces que le glucoside P2. / This work deals with the chemical synthesis of simple analogs of anthocyanins, the main class of watersolublenatural pigments. Eleven flavylium ions with hydroxyl, methoxyl and beta-D-glucopyranosyloxylsubstituents at positions 4’, 5 and 7 have been prepared by straightforward chemical procedures.Moreover, the two main 3-deoxyanthocyanidins of red sorghum, apigeninidin (APN) and luteolinidin(LTN), have been synthesized in a one-step protocol. The physicochemical properties and antioxidantactivity are investigated for 3’,4’,7-trihydroxyflavylium chloride (P1), its 7-O-beta-D-glucoside (P2) and3’,4’,5,7-tetrahydroxyflavylium chloride (LTN). Owing to their catechol B-ring, they rapidly bind FeIII,AlIII and CuI, more weakly interact with FeII while promoting its autoxidation to FeIII. Following CuIIbinding, the pigments undergo oxidation. Aglycones P1 and LTN are moderate ligands of human serumalbumin (HSA) with chalcones having a higher affinity for HSA than the corresponding colored forms.The antioxidant activity of P1, P2 and LTN is investigated via two tests: reduction of the stable DPPHradical and inhibition of heme-induced lipid peroxidation (a model of postprandial oxidative stress inthe stomach). Aglycones P1 and LTN (especially in their colorless chalcone form) are more potent thanglucoside P2.