Hydrophilic antioxidants

Nowadays, consumers would like those antioxidants present in food products not only to stabilise food lipids, but also to be absorbed through the intestinal wall and protect the lipids of blood plasma against oxidation. This effect is relatively evident in the case of tocopherols (which are liposoluble) or ascorbic acid (which is hydrophilic), but much less evidence is available on antioxidants of medium polarity, such as flavonoids, rosemary oleoresins or green or black tea catechins. 

Natural antioxidants may be classified according to their nutritive value or according to their solubility. The hydrophobic vitamin E and the hydrophilic vitamin C are thus important both as nutrients and as antioxidants. The nonnutritive antioxidants may similarly be divided into lipid-soluble and water-soluble antioxidants, as shown in Fig. 16.3, which will also form the basis for a discussion of exploitation of combinations of anhoxidants in order to improve protective effects. 

Such a plethora of radicals produced as a result of normal cellular metabolism needs to be rapidly scavenged by cytoprotective enzymes and antioxidants present in the cell and cellular membranes, both hydrophobic and hydrophilic compartments. The... 

The photochemiluminiscence (PCL) assay was initially used by Popov and others (1987). Popov and Lewin (1994 1996) have extensively studied this technique to determine water-soluble and lipid-soluble antioxidants. The PCL assay measures the antioxidant capacity, toward the 02 radical, in lipidic and water phase. This method allows the quantification of both the antioxidant capacity of hydrophilic and/or lipophilic substances, either as pure compounds or complex matrices from different origin synthetic, vegetable, animal, human, etc. The PCL method is based on an approximately 1,000-fold acceleration of the oxidative reactions in vitro by the presence of an appropriate photosensitizer. The PCL is a very quick and sensitive method. Chua and others (2008) used this assay to determine the antioxidant potential of Cin-namomum osmophloeum, whereas Kaneh and Wang and others (2006) determined the antioxidant capacity of marigold flowers. The antioxidant activity of tree nut oil extracts was also assessed by this method (Miraliakbari and Shahidi 2008). 

An improved method has been developed and validated using fluorescein as the fluorescent probe (Ou and others 2001). This modification provides a direct measure of hydrophilic chain-breaking antioxidant capacity against peroxyl radical. This method has been applied in vegetables of many kinds (Ou and others 2002 Cho and others 2007) and in tropical fruits (Talcott and others 2003 Mahattanatawee and others 2006). 

The ORAC assay proposed by Ou and others (2001) is limited to hydrophilic antioxidants because of the aqueous environment of the assay. However, lipophilic antioxidants play a critical role in biological defense systems. Huang and others (2002) expanded the assay to the lipidic fraction by introducing a randomly methylated 13-cyclodextrin (RMCD) as a water-solubility enhancer for lipophilic antioxidants. Various kinds of foods, including fruit juices and drinks, fruits, vegetables, nuts, and dried fruits, have been evaluated with this method (Zhou and Yu 2006 Wu and others 2004 Kevers and others 2007 Wang and Ballington 2007 Almeida and others 2008 Mullen and others 2007). 

In 2003, Prior and others described methods for the extraction and analysis of hydrophilic and lipophilic antioxidants, using modifications of the ORAC procedure. These methods provide, for the first time, the ability to obtain a measure of total antioxidant capacity in the protein free plasma, using the same peroxyl radical generator for both lipophilic and hydrophilic antioxidants. This assay was also used to measure the total antioxidant capacity of guava fruit extracts (Thaipong and others 2006). 

Another assay that is very similar to the ABTS assay is the AGV-dimethyl-p-phenylenediamine (DMPD assay). In the presence of a suitable oxidant solution at an acidic pH, DMPD is converted to a stable and colored DMPD radical cation (DMPD +). Antioxidants capable of transferring a hydrogen atom to the radical cause the decol-orization of the solution, which is spectrophotometrically measured at 505 nm. The reaction is stable, and the endpoint is taken to be the measure of antioxidant efficiency. Antioxidant ability is expressed as Trolox equivalents using a calibration curve plotted with different amounts of Trolox (Fogliano and others 1999). This method is used to measure hydrophilic compounds. The presence of organic acids, especially citric acid, in some extracts may interfere with the DMPD assay, and so this assay should be used with caution in those extracts rich in organic acids (Gil and others 2000). 

Alcolea JF, Cano A, Acosta M and Arnao MB. 2002. Hydrophilic and lipophilic antioxidant activities of grapes. Nahrung/Food 46(5) 353-356. 

Amao MB, Cano A and Acosta, M. 2001a. The hydrophilic and lipophilic contribution to total antioxidant activity. Food Chem 73(2) 239—244. 

Cano A and Arnao MB. 2005. Hydrophilic and lipophilic antioxidant activity in different leaves of three lettuce varieties. In J Food Prop 8(3) 521—528. 

Cho YS, Yeum KJ, Chen CY, Beretta G, Tang G, Krinsky NI, Yoon S, Lee-Kim YC, Blumberg JB and Russell RM. 2007. Phytonutrients affecting hydrophilic and lipophilic antioxidant activities in fruits, vegetables and legumes. J Sci Food Agric 87(6) 1096-1107. 

Prior RL, Hoang H, Gu L, Wu X, Bacchiocca M, Howard L, Hampsch-Woodill M, Huang D, Ou B and Jacob R. 2003. Assays for hydrophilic and lipophilic antioxidant capacity (oxygen radical absorbance capacity (ORACfl)) of plasma and other biological and food samples. J Agric Food Chem 51(ll) 3273-3279. 

Wu X, Beecher GR, Holden JM, Haytowitz DB, Gebhardt SE and Prior RL. 2004. Lipophilic and hydrophilic antioxidant capacities of common foods in the United States. J Agric Food Chem 52(12) 4026-4037. 

Under normal reaction conditions, phenolic compounds are the predominant antioxidants in hydrophilic extracts of samples that easily transfer one hydrogen to the peroxy radical (ROO ). 

Boldyrev, A. A., Koldo, A., Kurella, E., Maltseva, V., and Stvolinski, S. (1993). Natural histidine-containing dipeptide carnosine as a potent hydrophilic antioxidant with membrane stabilizing function. A biomedical report. Mol. Chem. Neuropathol. 19,185-192. 

In summary, the structural characteristics of peptides with high antioxidant activity are as follows a hydrogen bonding and hydrophilic amino acid residue in the position next to the C-terminus, a hydrophobic amino acid residue at the N-terminus, and an electronic amino acid residue at the C-terminus. 

There are other desirable properties for the powder, such as exhibiting a hydrophilic surface, but these are related to tablet performance, to product stability (antioxidant), or to esthetic characteristics (e.g., colors, flavors). 

Similar to hydrophilic flavonoids, hydrophobic flavonoids can affect membrane permeability. Alterations in this biophysical property of liposome bilayers lead to the release of bulky molecules entrapped into the inner aqueous space. As mentioned in the previous section, a strong correlation was found between flavonoid retention to a hydrophobic matrix and their capacity to induce membrane leakage [Ollila et al., 2002]. Interestingly, hydrophilic flavonoids, such as (—)-epicatechin and related procyanidins (dimer to hex-amer) prevented Fe2 + -mediated liposome permeabilization, although in this case the beneficial effect could be related to both their antioxidant and metal chelating capacities and their membrane stabilizing properties [Verstraeten et al., 2004],... 

The second system involves numerous hydrophilic or lipophilic molecules like ascorbic acid (AH-) (vitamin C) and a-tocopherol (aT-OH) (vitamin E). These low-molecular-weight antioxidants (LMWA) reduce ROS by oxido-reduction reactions ... 

The new cyclosporine formulation (Sandimmun Neoral, Novartis Pharmaceuticals Corporation, East Hanover, NJ) is a self-microemulsifying drug delivery system, which consists of the drug in a lipophilic solvent (corn oil), hydrophilic cosolvent (propylene glycol) surfactant and an antioxidant [37]. Upon contact with GI fluids, Sandimmun Neoral readily forms a homogenous, monophasic microemulsion, which allows the absorption of the drug molecules. Unlike Sandimmun, the formation of this microemulsion is independent of bile salt activity, and indeed, studies have shown that the absorption of cyclosporine from the new formulation is much less dependent on bile flow [38] and is unaffected by food intake [39],... 

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