Reactive oxygen species

Phenolics in Food and Nutraceuticals is the first single-source compendium of essential information concerning food phenolics. This unique book reports the classification and nomenclature of phenolics, their occurrence in food and nutraceuticals, chemistry and applications, and nutritional and health effects. In addition, it describes antioxidant activity of phenolics in food and nutraceuticals as well as methods for analysis and quantification. Each chapter concludes with an extensive bibliography for further reading. Food scientists, nutritionists, chemists, biochemists, and health professionals will find this book valuable.

Phenolics in food and nutraceuticals

Phenolic compounds and their role in oxidative processes in fruits

Phenolic secondary metabolites play an important role in plant-derived food quality, as they affect quality characteristics such as appearance, flavour and health-promoting properties. Their content in foods is affected by many factors that influence phenolic stability, biosynthesis and degradation. In terms of their biosynthesis the key enzyme phenylalanine ammonia-lyase (PAL) is especially relevant, as it can be induced by different stress (environmental) conditions. In addition, polyphenol oxidases (PPO) and peroxidases (POD) are the main enzymes responsible for quality loss due to phenolic degradation. The different factors affecting phenolic-related food quality are reviewed. These include internal (genetic) and environmental (agronomic) factors, technological treatments applied during postharvest storage of fruits and vegetables, as well as processing and storage of the processed products. The different strategies that are required to either maintain or enhance the phenolic-related quality of foods are critically reviewed. Genetic modification designed to decrease polyphenol oxidases or peroxidases is not always a feasible method, owing to side problems related to the growth and defence of the plant. Agronomic treatments can be used to enhance the phenolic content and pigmentation of fruits and vegetables, although the information available on this topic is very scarce and even contradictory. Some postharvest treatments (cold storage, controlled or modified atmospheres, etc) can also improve phenolic-related quality, as well as new processing methods such as irradiation (gamma, UV), high-field electric pulses, high hydrostatic pressures and microwaves. Les composes phenoliques, metabolites secondaires des plantes, jouent un role dans la qualite des fruits, au niveau de l'apparence, de la flaveur et des qualites nutritives. L'enzyme cle de leur biosynthese est la phenylalanine ammonium-lyase, regulee par les facteurs environnementaux. La polyphenol oxydase et la peroxydase sont responsables des degradations donc des pertes de qualite. Les differents facteurs internes (genetiques) et externes (agronomiques) affectant la qualite des produits vegetaux sont etudies. Les differentes mesures envisageables (modification genetique, traitements chimiques ou physiques apres recolte) pour modifier le contenu en compose phenoliques et donc la qualite des produits vegetaux sont etudies.

Phenolic compounds and related enzymes as determinants of quality in fruits and vegetables

Free radicals, reactive oxygen species, oxidative stress and its classification

This review examines the parameters of enzymatic browning in apple and apple products that is, phenolic compounds, polyphenoloxidases, and other factors (ascorbic acid and peroxidases), both qualitatively and quantitatively. Then the relationships between intensity of browning and the browning parameters are discussed, including a paragraph on the methods used for browning evaluation. Finally, the different methods for the control of browning are presented.

Enzymatic browning reactions in apple and apple products

Lactic acid bacteria – Potential for control of mould growth and mycotoxins: A review

To clarify the role of pear peroxidase (POD) in enzymatic browning, oxidation of 4-methylcatechol, chlorogenic acid, and (−)-epicatechin catalyzed by purified polyphenol oxidase (PPO), purified POD, or combinations of the two enzymes was followed by HPLC. It was shown that pear POD had no oxidative (oxygen dependent) activity. However, in presence of PPO, POD enhanced the phenol degradation. Moreover, when PPO was entirely inhibited by NaCl after different oxidation times, addition of POD led to a further consumption of the phenolic compound. Two mechanisms have been proposed to explain this additional consumption. First, our results have demonstrated that, whatever the substrate used, PPO oxidation generated H2O2, the amount of which varies with the phenolic structure. Second, quinonic forms are used by POD as peroxide substrate. These two mechanisms associated with the kinetic properties of pear PPO and POD are consistent with an effective involvement of pear POD in enzymatic browning. Keywords: Enzymat...

Oxidation of Chlorogenic Acid, Catechins, and 4-Methylcatechol in Model Solutions by Combinations of Pear (Pyrus communis Cv. Williams) Polyphenol Oxidase and Peroxidase: A Possible Involvement of Peroxidase in Enzymatic Browning†

The effect of cysteine and cysteine-quinone addition compound (CQAC) on apple polyphenol oxidase (PPO) activity was investigated by HPLC and polarography, using 4-methylcatechol(4MC), chlorogenic acid (CG), and (-)-epicatechin (EC) as substrate. With 2.2 mM 4MC, in the presence of cysteine at thiolto phenol ratios above 1, there was no effect in the degradation rates of 4MC, while CQAC formation was proportional to the 4MC loss but without color formation. For cysteine to phenol ratios below 1, the degradation rate of 4MC was slowed down; the lower the cysteine content, the earlier the decrease in 4MC degradation was observed. In the latter case, the CQAC content increased and then decreased but developed a strong color. Similar results were obtained with CG or EC as substrate. In the presence of CQAC, polarography experiments showed that they were not substrate but competitive inhibitors of apple PPO with a slightly higher affinity than their phenol precursors. HPLC analysis showed that Cys-5-MC (the CQAC derived from 4MC) was rapidly degraded, whereas 4MC degradation was slowed with a strong violet color formation. Nonenzymatic cooxidation reactions between CQAC and o-quinone leading to the regeneration of phenol and the formation of pigments were observed. Cysteine at a higher concentration prevented color development by trapping o-quinones as colorless CQAC, while at low amounts the o-quinones formed in excess can cooxidize CQAC, leading to a phenol regeneration with a deep color formation.

Cysteine as an inhibitor of enzymic browning. 2. Kinetic studies

This review describes the naturally occurring mechanisms in cereals that lead to a reduction of Fusarium trichothecene mycotoxin accumulation in grains. A reduction in mycotoxin contamination in grains could also limit fungal infection, as trichothecenes have been reported to act as virulence factors. The mechanisms explaining the low toxin accumulation trait, generally referred to as type V resistance to Fusarium, can be subdivided into two classes. Class 1 includes mechanisms by which the plants chemically transform the trichothecenes, leading to their degradation or detoxification. Among the detoxification strategies, glycosylation of trichothecenes is a natural process already reported in wheat. According to the structure and the toxicity of trichothecenes, two other detoxification processes, acetylation and de-epoxidation, can be expressed, at least in transgenic plants. Class 2 comprises mechanisms that lead to reduced mycotoxin accumulation by inhibition of their biosynthesis through the action of plant endogenous compounds. These include both grain constitutive compounds and compounds induced in response to pathogen infection. There are already many compounds with antioxidant properties, like phenolic compounds, peptides or carotenoids, and with prooxidant properties, like hydrogen peroxide or linoleic acid-derived hydroperoxides, that have been described as ‘modulators’ of mycotoxin biosynthesis. This review addresses for the first time different studies reporting specific in vitro effects of such compounds on the biosynthesis of Fusarium mycotoxins. A better understanding of the natural processes limiting accumulation of trichothecenes in the plant will open the way to the development of novel breeding varieties with reduced ‘mycotoxin risk’.

Florence Richard-Forget

Papers

Enzymatic browning reactions in apple and apple products

Lactic acid bacteria – Potential for control of mould growth and mycotoxins: A review

Oxidation of Chlorogenic Acid, Catechins, and 4-Methylcatechol in Model Solutions by Combinations of Pear (Pyrus communis Cv. Williams) Polyphenol Oxidase and Peroxidase: A Possible Involvement of Peroxidase in Enzymatic Browning†

Cysteine as an inhibitor of enzymic browning. 2. Kinetic studies

Natural mechanisms for cereal resistance to the accumulation of Fusarium trichothecenes