Hydrophobic antioxidant

Aldini et al. proposed a method for measuring TAC fractions due to hydrophilic and hydrophobic antioxidants (A6). The hydrophilic system used a water-soluble free radical initiator (ABAP) and a hydrophilic fluorogenic probe (2, 7 -dichloro-dihydrofluorescein). The hydrophobic system was based on a hydrophobic initiator, 2,2/-azobis(4-methoxy-2,4-dimethylvaleronitrile) (MeO-AMVN), and a lipophilic fluorescence probe, 4,4-difluoro-5(4-phenyl-l,3-butadienyl)-4-bora-3a, 4a-diaza-s-indacene-3-undecanoic acid (Cl 1-BODIPY581/591). The red fluorescence of the probe decreased and green fluorescence increased upon oxidation (A6). 

ABTS,+ also can be dissolved in hydrophobic media and used for estimation of antioxidants by decolorization assay (R3). In principle, various organic media can be used, but ethanol is preferred with respect to methanol or acetone due to the higher stability of ABTS,+ (C4). The DPPH reduction assay is well-suited for assay of hydrophobic antioxidants due to the insolubility of DPPH in aqueous media (A 15, B15). 

Figure 7. A schematic of probable distribution of hydrophilic and hydrophobic antioxidants in bulk oil (oil-air interface) and oil-in-water emulsion interface [adapted from (46)].

Other Phenolic Antioxidative Compounds from Plants Higher plants are rich in a myriad of phenolic compounds in their secondary metabolite pool. Among these, phenolic acids and polyphenolic derivatives are found to be the most important series of hydrophilic-hydrophobic antioxidative compounds naturally present. In foods, these polyphenolic compounds act as radical scavengers... 

Living organisms have a defense system consisting of intracellular and extracellular antioxidants. These include hydrophobic and hydrophiUc substances, as well as intermediate substances that act at interphases and primarily affect cellular membranes (Figure 8.5). Hydrophobic antioxidants include tocopherols, carotenoids, xanthophils, bilirubin, andubiquinol-10 (coenzyme QIO). a-Tocopherol is the most important hydro-... 

It seems apparent from the data in Table 1 that the more hydrophobic antioxidant the stronger aggregation with the micelle and hence slower its diffusion as shown in entries 2-9 6-11 and 13-14. Especially low diffusion coefficient values are observed for AA16 and LG in the micellar SDS solution because in this system these antioxidants are present... 

Christodouleas, D., C. Fotakis, K. Papadopoulos, E. Yannakopoulou, and A. C. Calokerinos. 2009. Development and validation of a chemiluminogenic method for the evaluation of antioxidant activity of hydrophilic and hydrophobic antioxidants. Anal. Chim. Acta 652 295-302. 

Substituted phenols such as cresols, p-fcrf-butylphenol, / -phcnylphenol, resorcinol, and cardanol (derived from cashew nut shells) have also been used as precursors for phenolic resins. Alkylphenols with at least three carbons in the substituent lead to more hydrophobic phenolic resins that are compatible with many oils, natural resins, and rubbers.7 Such alkylphenolic resins are used as modifying and crosslinking agents for oil varnishes, as coatings and printing inks, and as antioxidants and stabilizers. Bisphenol-A (2,2-p-hydroxyphenylpropane),... 

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... 

Acylations of carbohydrate derivatives such as alkyl glucosides and galactosides have also been successfully performed in ionic liquids [63]. Similarly, the flavonoid glycosides naringin and rutin were acylated with vinyl butyrate in ionic liquid media in the presence of a number of lipases, e.g., CaLB (Novozym 435), immobilized TIL, and RmL [119]. The products are of interest for application as strong antioxidants in hydrophobic media. 

The electronic property of the amino acid on the C-terminus also has an effect on antioxidant activity (Li et al., 2011), that is, the larger the electronic property, the higher is the activity. The C-terminus is a polar position that is thus affected by its electrostatic potential, to some extent therefore, the amino acids Trp, Glu, Leu, lie, Met, Val, Tyr, etc. are suitable at the C-terminus. Some researchers have speculated that the identity of the amino acid on the C-terminus would play an important role in its activity. Suetsuna (2000) separated and identified a radical scavenging peptide, Tyr-Phe-Tyr-Pro-Glu-Leu, from casein hydrolysate, and it was confirmed that the Glu-Leu on the C-terminus mainly contributed to its antioxidant activity. Kim et al. (2009) speculated that the hydrophobic property of the amino acid on the C-terminus, for example, Val and Leu, had a distinct effect on the activity, as determined from the analysis of antioxidative peptides derived from venison hydrolysate. 

Chen et al. (1996) investigated 28 synthetic peptides that were based on the antioxidative peptide Leu-Leu-Pro-His-His. They found that the deletion of the C-terminus His decreased the activity, whereas the deletion of the N-terminus Leu had no effect therefore, it seemed that the C-terminus was related to the antioxidative activity of the peptide, while the N-terminus had no effect. Saito et al. (2003) pointed out that two Tyr-containing tripeptides (Tyr-X-Tyr) showed higher activity than did two His-containing tripeptides (His-X-His). According to the structural characteristics, the hydrophobicity of an amino acid on the N-terminus is the most important property for activity with respect to the same amino acid in the central position in addition, Tyr on the N-terminus has stronger hydrophobicity than His. Therefore, it can be predicted that Tyr-X-Tyr has higher activity than His-X-His. 

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. 

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