Quantitative assessment of antioxidant properties of natural colorants and phytochemicals: carotenoids, flavonoids, phenols and indigoids. The role of β‐carotene in antioxidant functions

Abstract

Reactive oxygen species are potentially damaging molecules. An important function of antioxidants is to intercept harmful triplet states, in order to prevent the formation of singlet oxygen, or to quench singlet oxygen directly. However, antioxidants are also reactive towards other active oxygen species such as the hydroxyl radical, the superoxide anion and the non-excited oxygen ground state in the presence of radical initiators. It is well known that¯avonoids and carotenoids show strong antioxidant properties. Polyenes and carotenoids are the best known among the compounds that quench singlet oxygen by ef®cient energy transfer. A large number of modi®ed, synthetic analogues and derivatives have been synthesised to prepare even better quenchers than the natural carotenoids. Phenols are also excellent chain-breaking antioxidants. Recently, many indigoid dyes (including bacterial indigoids) were studied, with the remarkable result that most, but not all, members of this class of chromophores quench singlet oxygen at the diffusion limit and some of them are excellent radical traps. It has been shown in this study that a quantitative assessment of antioxidant properties of avonoids, carotenoids, phenols and natural indigoids can be achieved using the following three assays: (1) oxygen pressure dependence; (2) peroxide formation; (3) singlet oxygen quenching. Reactivities towards both excited states and ground state radicals can be properly described by these assays. The remarkable role of b-carotene as an`unusual antioxidant' (Burton GW and Ingold KU, Science 224: 569±573 (1984)) in reactions using various oxygen pressures becomes clearer. The socalled`pro-oxidant effects' concern primarily the antioxidant itself and its degradation, since no or very little damage to the substrate occurs in this type of experiment. Three main categories of antioxidants may be classi®ed: (1) excellent antioxidants that perfectly quench excited states as well as ground state radicals (eg actinioerythrol, astaxanthin); (2) good antioxidants that strongly inhibit peroxide formation but are less ef®cient in quenching excited states (eg¯avonols, tocopherols) or lead to considerable degradation of the antioxidant itself (eg b-carotene, lycopene); (3) moderate antioxidants that fail to excel in both reactivities (eg z-carotene,¯avone).

Quality Parameters and Bioactive Compounds of Red Tomatoes (Solanum lycopersicum L.) cv Roma VF at Different Postharvest Conditions

“…In tomatoes, the principal antioxidants compounds are carotenoids (lycopene), phenolic compounds, flavonoids, and vitamins like C and E (Beutner et al, 2001;Sahlin, Savage, & Lister, 2004;Toor, Lister, & Savage, 2005). In this study, the antioxidant activity was 126.9 ± 0.2 μM TEAC/100 g of tomato pulp.…”

The Influence of Drying Process Conditions on the Physical Properties, Bioactive Compounds and Stability of Encapsulated Pumpkin Seed Oil

“…In contrast to chlorophylls, carotenoids act as antioxidants in stored oils. They are considered the most effective compounds in inhibiting photosensibilized oxidation (Beutner et al 2001). The content of carotenoids in pumpkin seed oils reaches 19-23 mg/kg (Procida et al 2013).…”

Determination of the carotenoid profile in peach fruits, juice and jam

“…Carotenoids have been described as possessing several important functional properties and health benefits [1], mainly antioxidant activity [2,3], as well as prevention of cardiovascular diseases [4,5], cancer [6] and macular degeneration [7,8] and, in some cases, provitamin A activity. These properties make these compounds ideal for the always increasing functional food industry as well as promoting the consumption of the natural products in which they are contained.…”