Antioxidants colour stability

Sumitomo Chemical and some other companies have developed products that contain both phosphorus and phenolic groups in the same molecule. The idea is that a single additive will serve both the functions of a phenolic antioxidant (colour stability) and of a secondary antioxidant (resistance to odour generation and to hydrolysis). One of the first targets is low-density polyethylene film. 

The change in colour of a 20% solution of povidone K 17 (Kollidon 17 PF) in water was from a slight yellow tint (Yellow 7 according to Ph.Eur.) to stronger yellow (Yellow 4) after thermal sterilization at 120-121 °C for 20 min. The addition of 0.2% of sodium bisulfite provided excellent colour stabilization. Ascorbic acid cannot be used as an antioxidant as it undergoes hydrolysis itself, giving rise to an even darker yellow-brown colour. 

An antioxidant to stabilize the colour of solution could be added (0.02% sodium bisulfite or 0.5% cysteine). 

It appears from Figs. 9.5 and 9.6 that there is a huge variation in colour stability between meat from different sources. A range of intrinsic factors influence the oxidative balance in raw meat and thereby the colour stability of the meat (Bertelsen et al., 2000). Thus the oxidative stability of muscles is dependent on the composition, concentrations, and reactivity of (i) oxidation substrates (lipids, protein and pigments), (ii) oxidation catalysts (prooxidants such as transition metals and various enzymes) and (iii) antioxidants, e.g., vitamin E and various enzymes. For review see Bertelsen et al. (2000). 

Specifications for identity and purity and toxicological evaluation of food colours. FAO Nutrition Meetings Report Series, No. 38B, 1966 WHO/Food Add/66.25. Specifications for the identity and purity of food additives and their toxicological evaluation some antimicrobials, antioxidants, emulsifiers, stabilizers, flour treatment agents, acids, and bases (Ninth report of the Joint FAO/WHO Expert Committee on Food Additives). FAO Nutrition Meetings Series, No. 40,1966 WHO Technical Report Series, No. 339,1966 (out of print). 

The only vitamins likely to be found in unfortified soft drinks are vitamin C (either added as an antioxidant or deriving from fruit materials) and vitamin A precursor (beta-carotene, added as a colour). However, soft drinks provide a good medium for vitamin fortification, the limitations being solubility (for fat-soluble vitamins), flavour impairment (for example the meaty notes of thiamine) and stability. 

Some undesirable impurities deteriorate the material properties of recycled plastics by reducing their stability. These contaminants consist not only of residues of polymerisation catalysts, but also of salts of metals introduced during polymer processing and exploitation [34, 35]. Metallic impurities arise from contaminated filler as well. Ions of copper and iron belong to the most dangerous species. They catalyse homolysis of hydroperoxides and increase the consumption of phenolic antioxidants or phenolic moieties of UV absorbers by their oxidation into dienoide compounds [36, 37, 38]. Residues of titanium and aluminium polymerisation catalysts can form coloured salts with phenolic antioxidants. 

Inhibition of development of rancidity Strong antioxidative effect, Arg and xylose giving much less colour On heating, antioxidant capacity of 5 g Trolox equiv. per 100 g dried extract develops Improved oxidative stability... 

Details are given of ways of improving the gamma irradiation stability of flexible PVC. The variables of interest were resin molecular weight, plasticiser loading, stabiliser type, and choice of antioxidant. The criterion for improvement was colour change after irradiation. 2 refs. 

For the stability of solutions in water the only parameter sensitive during the storage is the colour. If an antioxidant like 0.5% cysteine is added also the colour can be stabilized as can be seen in Table 159. 

Some ingredients such as sugar and protein have a tendency to stabilise most natural colours, whereas others, i.e., salts, some colloids, ethanol and sometimes flavours, may have a negative influence on the stability of the added colonr. High amonnts of ascorbic acid, sulphur dioxide and other antioxidants may... 

Most efforts have been put into developing natural colours with improved stability towards low pH, light and heat and with increased brightness of the different pigments. The technologies that have been applied are microencapsulation, addition of antioxidants, emulsions and oil snspensions. 

With the use of antioxidants it is consequently possible to increase the stability of paprika, carotenes and lutein colours considerably and thereby match... 

The main weak point in the polyester chain is the j3-methylene group. When diethylene glycol links are formed, the stability of polyesters in oxidation is lowered even more. Phosphites and hindered phenols (see Table 1) are currently used in PET to improve thermo-oxidative stability. It was shown that after five melt extrusions the stabilized PET retained its polymer qualities (colour, clarity, viscosity and carboxyl end group content) and that a blend of a hindered aryl phosphite and a hindered phenolic antioxidant (4 1) was more effective than each one of the components [2]. 

The choice of stabilizers for PET (antioxidant and/or metal deactivator) is based mainly on the method of additive incorporation into the polymer and the end use/application of the polymer. For example, if it is preferable for the additive to be added in the polymerization reactor, then the volatility and the thermal stability of the stabilizer need consideration because of the high temperatures and vacuum prevailing in the reactor. PET thin films require maximum colour improvement... 

Bemrah, N., J. C. Leblanc, and J. L. Volatier. 2008. Assessment of dietary exposure in the French population to 13 selected food colours, preservatives, antioxidants, stabilizers, emulsifiers and sweeteners. Food Addit. Contam. Part B Surveill. 1(1) 2-14. 

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