Antioxidants alternatives

The problems of antioxidant loss from polsrmers in contact media, especially in human-contact applications, have generally been associated with the use of traditional low molecular mass antioxidants. Alternative types of antioxidants have been developed to address both questions of safety and efficiency. Three different approaches are highhghted here. 

Beyond globaF antioxidation alternate biological activities for polyphenols with impact on human health... 

In certain brilliantine compositions, vegetable and animal oils are used as substitutes for mineral oil. In these systems, because of their potential for rancidity, antioxidants must be included. Other alternatives to mineral oils that have found utiHty in brilliantines are the polyethylene glycols which come in a variety of solubiHties and spreading properties. Use of these materials offers the advantage of chemical stabiHty to rancidity. Other additives found in brilliantines to improve their aesthetics include colorants, fragrance, medicated additives, lanolin, and fatty acid esters. 

Other Acids. Ascorbic acid (3) is used primarily as an antioxidant and to a lesser extent as an added nutrient ia beverages. It oxidizes readily, preventing the oxidation of certain flavoting compounds. Tartaric (4) and adipic acids are used to a lesser extent ia grape flavored beverages. Malic acid can be used as an alternative to citric acid ia some fmit flavored beverages. 

Polypropylene differs from polyethylene in its chemical reactivity because of the presence of tertiary carbon atoms occurring alternately on the chain backbone. Of particular significance is the susceptibility of the polymer to oxidation at elevated temperatures. Some estimate of the difference between the two polymers can be obtained from Figure 1J.7, which compares- the rates of oxygen uptake of eaeh polymer at 93°C. Substantial improvements can be made by the inclusion of antioxidants and such additives are used in all commercial compounds. Whereas polyethylene cross-links on oxidation, polypropylene degrades to form lower molecular weight products. Similar effects are noted... 

Erythorbic acid and sodium erythorbate are very safe products, widely used in the food industry as antioxidants and alternatives to vitamin C. In the water treatment industry, they are strong reducing agents that reduce metal oxides and hydroxides to their more soluble ferrous forms and promote the passivation of boiler waterside surfaces (magnetite formation). 

An alternative mechanism by which additives may protect polymers from photo-oxidation is radical trapping. Additives which operate by this mechanism are strictly light stabilizers rather than antioxidants. The most common materials in this class are the hindered amines, which are the usual additives for the protection of poly (ethylene) and poly (propylene). The action of these stabilisers is outlined in Reactions 8.3-8.5. 

The final possible mode of action for an antioxidant is as a peroxide decomposer. In the sequences that lead to photodegradation of a polymer the ready fragmentation of the hydroperoxide groups to free radicals is the important step. If this step is interfered with because the peroxide has undergone an alternative decomposition this major source of initiation is removed. The additives which act by decomposing hydroperoxide groups include compounds containing either divalent sulfur or trivalent phosphorus. The mechanism involves... 

Natural pigment production for food coloration includes the entire spectrum of biotechnologies. For example, biological production of carotenoid pigments has medical implications because carotenoids are nutritive (pro-vitamin A), antioxidant, and photoprotective. Carotenoids are produced alternately in agricultural systems (plants), industrial bioreactors (bacterial and fungi), and marine systems (cyanobacteria and algae). 

The food technologist may be especially interested in the fate of the carotenoids in the seed oil. Like red palm oil, the resulting carotenoid-pigmented canola oil may be more stable due to the antioxidant properties of carotenoids and may be more attractive to consumers. Alternatively, for food security concerns, transgenic soybean or canola oils and seed meals that are genetically modified for more efficient bio-diesel production may be bio-safety marked with lipid-soluble carotenoids and water-soluble anthocyanins, respectively. Potatoes are excellent potential sources of dietary carotenoids, and over-expression of CrtB in tubers led to the accumulation of P-carotene. Potatoes normally have low levels of leaf-type carotenoids, like canola cotyledons. 

French researchers provided an alternative to the tartrazine synthetic colorant (E 102), valorizing a phloridzine oxidation product (POP) generated as a by-product of the cider industry. Phloridzine is a polyphenol specific to apples and shows good antioxidant capacity. When apples are pressed to yield juice, phloridzine, oxygen, and polyphenoloxidase enzyme combine to form POP. This brilliant yellow natural colorant with nuances dependent on pH level can be incorporated easily into water-based foods such as beverages (juices, syrups) and confectionery creams because it is stable during production processes. Details about the specific formulations of these colorants are presented in Section 5.1. 

It should be remembered that some of the established antioxidants have other metabolic roles apart from free-radical scavenging. The finding of reduced antioxidant defences in diabetes, for example, may not be prima fascie evidence of increased oxidative stress, since alternative explanations may operate. For example, this may reflect a response to reduced free-radical activity as su ested by the results of a previous study (Collier et al., 1988). In the case of ascorbate, an alternative explanation has been proposed by Davis etal. (1983), who demonstrated competitive inhibition of ascorbate uptake by glucose into human lymphocytes. This view is supported by the similar molecular structure of glucose and ascorbic acid (see Fig. 12.4) and by a report of an inverse relationship between glycaemic control and ascorbate concentrations in experimental diabetes in rats. Other investigators, however, have not demonstrated this relationship (Som etal., 1981 Sinclair etal., 1991). 

Lussier [71] has given an overview of Uniroyal Chemical s approach to the analysis of compounded elastomers (Scheme 2.2). Uncured compounds are first extracted with ethanol to remove oils for subsequent analysis, whereas cured compounds are best extracted with ETA (ethanol/toluene azeotrope). Uncured compounds are then dissolved in a low-boiling solvent (chloroform, toluene), and filler and CB are removed by filtration. When the compound is cured, extended treatment in o-dichlorobenzene (ODCB) (b.p. 180 °C) will usually suffice to dissolve enough polymer to allow its separation from filler and CB via hot filtration. Polymer identification was based on IR spectroscopy (key role), CB analysis followed ASTM D 297, filler analysis (after direct ashing at 550-600 °C in air) by means of IR, AAS and XRD. Antioxidant analysis proceeded by IR examination of the nonpolymer ethanol or ETA organic extracts. For unknown AO systems (preparative) TLC was used with IR, NMR or MS identification. Alternatively GC-MS was applied directly to the preparative TLC eluent. 

A multiwavelength approach might have been considered as an alternative to chemical derivatisation. Ruddle and Wilson [62] reported UV characterisation of PE extracts of three antioxidants (Topanol OC, Ionox 330 and Binox M), all with identical UV spectra and 7max = 277 nm, after reaction with nickel peroxide in alkaline ethanolic solutions, to induce marked differentiation in different solvents and allow positive identification. Nonionic surfactants of the type R0(CH2CH20) H were determined by UV spectrophotometry after derivatisation with tetrabromophenolphthalein ethyl ester potassium salt [34]. Magill and Becker [63] have described a rapid and sensitive spectrophotometric method to quantitate the peroxides present in the surfactants sorbitan monooleate and monostearate. The method, which relies on the peroxide conversion of iodide to iodine, works also for Polysorbate 60 and other surfactants and is more accurate than a titrimetric assay. 

Many reagent grade solvents contain levels of impurities that make them unsuitable for long term use in hplc. Sometimes the impurities are added deliberately as antioxidants, stabilisers, or for denaturing. Wherever possible, hplc grade solvents should be used to prepare mobile phases, or alternatively the solvents should be adequately purified before use. 

DCFH-DA assay was first developed by Valkonen and Kuusi (1997) as an alternative to measure the total peroxyl radical-trapping antioxidant potential of plasma. This assay uses AAPH to generate peroxyl radicals and DCFH-DA as the oxidizable substrate for the generated radicals. The oxidation of DCFH-DA by peroxyl radicals converts DCFH-DA to dichlorofluorescein. DCF is highly fluorescent (excitation 480 nm, emission 526 nm) and also shows absorbance at 504 nm. Therefore, the produced DCF can be monitored either fluorometrically or spectrophotometrically. 

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