Flavonoids: Hemisynthesis, Reactivity, Characterization and Free Radical Scavenging Activity

Abstract

Phenolic compounds form one of the main classes of secondary metabolites. They display a large range of structures and they are responsible for the major organoleptic characteristics of plant-derived-foods and beverages, particularly color and taste properties and they also contribute to the nutritional qualities of fruits and vegetables. Phenolic compounds are also highly unstable compounds which undergo numerous enzymatic and chemical reactions during postharvest food storage and processing thus adding to the complexity of plant polyphenol composition. Among these compounds flavonoids constitute one of the most ubiquitous groups of all plant phenolics. Owing to their importance in food organoleptic properties and in human health, a better understanding of their structures, their reactivity and chemical properties in addition to the mechanisms generating them appears essential to predict and control food quality. The purpose of this work is an overview of our findings concerning the hemisynthesis, the reactivity and the enzymatic oxidation of some flavonoids and shed light on the mechanisms involved in some of these processes and the structures of the resulting products. The free radical scavenging activity of some of the synthesized compounds is also presented and a structure-activity relationship is discussed. The first part of this review concerns the synthesis and structural characterization of modified monomeric flavanols. The use of these compounds as precursor for the preparation of natural and modified dimeric Molecules 2007, 12 2229 procyanidin derivatives was then explored through different coupling reactions. The full characterization of the synthesized compounds was achieved by concerted use of NMR and ESI-MS techniques. The free radical scavenging activity of some of the synthesized compounds was investigated. The second part of this review concerns the enzymatic oxidation of several flavonols by Trametes versicolor laccase. Most of the major oxidation products have been isolated as pure compounds and their structures unambiguously established through spectroscopic methods. Correlation between the structure of the oxidation product and the substitution pattern of the starting materials allows mechanistic features of this transformation to be elucidated.

Comparison of three drying processes to obtain an apple peel food ingredient

“…Phenolics are produced as secondary metabolites in plants and exert various protective roles; they are responsible for major organoleptic characteristics of plant food, such as visual appearance (color), flavor, bitterness, astringency, and aroma (Es-Safi, Ghidouche, & Ducrot, 2007;Toma´s-Barbera´n & Espı´n, 2001). Phenolics are effective antioxidants and they can exert anti-microbial, anti-inflammatory, anti-carcinogenic, anti-allergic, anti-platelet, vasodilatory, and neuroprotective effects (Es-Safi et al, 2007;Scalbert et al, 2005;Stevenson & Hurst, 2007).…”

Antioxidant Activity in Honeys of Various Floral Origins: Isolation and Identification of Antioxidants in Peppermint Honey

“…Foods containing phenolic compounds have been used not only as nourishment but also in the prevention of cancer, cardiovascular diseases and diabetes. Oxidative stress is thought to contribute to the development of such chronic diseases, and is defined by the imbalance between free radical production and the antioxidant defense system (Es-Safi et al, 2007;Kundu and Surh, 2008;Singh et al, 2008). Many studies have focused on the beneficial effects of natural antioxidant compounds.…”

Effect of Adding Granul Basil (Ocimum americanum) as Antioxidants in Fried Foods

“…Suppression of free radicals by antioxidant occur when unpaired electrons become paired with a hydrogen donor, thus forming a more stable DPPH. 16 Reduction of free radical activity is usually expressed as percent inhibition of DPPH, but can also be expressed as the concentration that causes a loss of 50% DPPH activity (IC5 0 ). IC 50 values are deemed to be good measure of the efficiency of antioxidant compounds or pure extract.…”

“…BHA can induce tumors in stomach of test animal while BHT can induce liver tumors in test animals. 16 Many studies have showed the benefits of plants nutritious as antioxidants, such as to reduce the risk of heart disease, cancer, cataracts and other degenerative diseases due process. It makes nature antioxidants, much in demand in the world.…”