Evaporation antioxidants

To obtain maximum lifetime, the oxidants must not be lost during service. A major potential source of loss is the evaporation of the antioxidant. Evaporation is often observed with BHT (butylated hydroxytoluene), a monomeric phenol, and to avoid evaporation less volatile, higher molecular weight antioxidants are used (i.e. bisphenols). 

Additives such as antioxidants and photostabilizers of low-molecular weight face two major problems (1) they may evaporate during high temperature moulding and extrusion process or (2) they may migrate to the surface of the plastic and get extracted. There are, in general, three ways of overcoming these problems. 

Evaporation is the oldest process for the concentration of liquid foods. Temperatures are higher compared to those of the more modern membrane filtration or freeze concentration processes. Tocopherols, carotenes, ascorbic acid, flavonoids and other phenolic antioxidants are partially destroyed by heating. Therefore, it is necessary to minimise the time needed for evaporation, and heating to the evaporation temperature should be carried out very rapidly. The temperature may be decreased if the pressure is reduced. The process is then more expensive, but losses of antioxidants become substantially lower. 

It is not only lipids but also essential oils which are sensitive to oxidative changes on storage. Sometimes stabilised by synthetic or natural antioxidants, they usually contain substances showing moderate antioxidant activity, but these may be lost by evaporation or oxidised by air oxygen unless more powerful phenolic antioxidants are added. 

The pressurised dissolution/cooling procedure of Macko el al. [490], which uses a UV-transparent low-boiling point solvent, is fast and simple as no additional evaporation of the solvent, preconcentration or redissolution of the additive is necessary. Macko el al. [491] have given an extensive listing of HPLC analyses of aromatic antioxidants and UVAs which can be separated with n-heptane and n-hexane as the main component of the mobile phase. The method was also used for HPLC quantification of thioether antioxidants (Santonox R, Chimox 14 and Irganox PS 802) in MDPE [612],... 

Polymer extracts are frequently examined using GC-MS. Pierre and van Bree [257] have identified nonylphenol from the antioxidant TNPP, a hindered bisphenol antioxidant, the plasticiser DOP, and two peroxide catalyst residues (cumol and 2-phenyl-2-propanol) from an ABS terpolymer extract. Tetramethylsuccino-dinitrile (TMSDN) has been determined quantitatively using specific-ion GC-MS in extracts of polymers prepared using azobisisobutyronitrile TMSDN is highly volatile. Peroxides (e.g. benzoyl or lauroylperoxide) produce acids as residues which may be detected by MS by methylation of the evaporated extract prior to GC-MS examination [258]. GC-MS techniques are... 

The effectiveness of the antioxidant depends not only on its reactivity, but also on its molecular weight that affects the rate of the antioxidant loss due to evaporation. The following example illustrates this dependence. Antioxidants of the structure 2,6-bis (1, l-dimethylethyl)phenols with para-substituents of the general structure ROCOCH2CH2 were introduced into decalin and polypropylene films that were oxidized by dioxygen at... 

The general rules that should therefore be observed include the use of a blanket of nitrogen whenever possible and evaporation of solvents at the lowest feasible temperatures, which must not exceed 50°C. The addition of an antioxidant such as butylated hydroxytoluene (2,6-di-/-butyl-4-methylphenol) to the extraction solvents (0.1 g 1 ) might be necessary to prevent deterioration of unsaturated lipids but it is essential for storage of lipid extracts at about 0.1% of the weight of lipid. Inactivation of lipolytic enzymes may usually be achieved by addition of an alcohol such as methanol or, in some cases, isopropanol. The latter is recommended for some more stable enzymes sometimes found in plant tissues. Alternatively the plant may be briefly immersed in boiling water. 

The antioxidant activity of rosemary and sage (leaves and extracts) were most effectively investigated [96,97], Traditional extracts of spices and herbs are obtained by steam distillation (essential oil) or by extracting the botanical with solvents such as alcohol, hexane, or acetone, and removing the solvents by evaporation. The SFE process for production of the inherent natural antioxidants is now the most gentle and effective method [70],... 

Encapsulated Flavors. Modified procedures during the past decade have permitted the preparation of encapsulated flavors with flavor levels over twice that of prior available products. Spray drying has been the principal key to this success. First, an oil flavnr is emulsified into an aqueous solution or is dispersed in an edible carrier material, after which the emulsion is pumped through an atomizer into a high-temperature chamber. The water evaporates rapidly, and particles of carrier material are formed around the flavor. However, some of the flavor component reaches the surface of the product. This requires the addition uf antioxidants to suppress oxidative changes in the flavor ingredient. 

Ethoxyquin, a synthetic antioxidant, is not generally allowed for human consumption in foods, but it is being added to animal feed and to fruits as an antiscald agent (94,143). Ethoxyquin is also used in the spice industry to prevent carotenoid loss during postharvest handling. However, ethoxyquin-treated paprika is unacceptable for some markets and some consumers (129). Perfetti et al. (130) described a method for determination of ethoxyquin in paprika and chili powder. Ethoxyquin was extracted from the spice with hexane and partitioned into 0.3 N HC1. After adjusting the solution to pH 13-14, ethoxyquin was extracted into hexane, and the hexane layer was evaporated to dryness. An acetonitrile solution of the residue was then analyzed by reversed-phase HPLC, with detection at 254 nm. The mobile phase was water/acetonitrile with ammonium acetate buffer. Recoveries from samples fortified at 50, 100, and 200 ppm averaged 92%, with a coefficient of variation of 2.3%. The method was applied to a number of commercial samples of paprika and chili powder. Ethoxyquin was found in paprika samples at levels up to 63 ppm and in chili powder samples at levels up to 20 ppm. 

The tocopherol content of midseason orange oils followed the order Brown peel shaver (216 ppm), FMC in-line extractor (126 ppm) and screw press (104 ppm). The method of extraction influenced both the evaporation residue and the tocopherol content of orange oil, the higher the evaporation residue, the higher the tocopherol content. Since tocopherol is a good antioxidant,... 

The extracting liquor containing the oily low molecular weight extractable fraction and some antioxidant (2,6-di-tcrt-butyl-p-cresol) was concentrated by evaporation of the volatile solvents and dried in vacuum at 50 °C. for further analysis by GLC, NMR, and low voltage mass spectrometry, or used in other experiments as previously described. 

---