8342937115

EFFECTS OF GAMMA-IRRADIATION ON PEROXIDE FORMATU)N IN PALM OI.EIN

to radiaiion among the commonly used antioxi-dantsin Food (Wilis 1980a). Therefore.theinhib-itingeffectsofantioxidantson radiation-induced peroxidalion in palm olein ismost probablydue to the action ol BI 1T. At present, the mechanism of destruction isnotexactly known. Presumably, the destruction occurred due to direct interactions with gamma-radiation or, due to reactions with radicalsof minorcomponentsin palm olein orwith free radicalsfrom unsaturated fattyacids produced duringirradiation.

In measuring the extent of peroxidation in deteriorated oils and fats, oneshould bearin mind the suitability and accuracy of the methods used. Conjugated dieneand peroxidevaluesare used to measttre primary oxidation. A Iow PV or conju-gated diene valtie does not always indicate agood oil. In fart, the oil cotdd already have a high secondary oxidation value due to degradation of hydroperoxides. ('.onjugated diene indices may also give erroneous results at high doses because not all fattyacid radicalsproduced during irradia-tion form conjugated dienes. Under high irradia-tion doses, given at a high dose ratę (65Gy/min), free radical formation is likely to be veryextensive, and due to high viscosity of palm oil. the oxygen cannot diffuse rapidly enough to form conjugated dienes. But instead, ilu* radicals may react with each other orwith compoundsother than oxygen to form polymer (Howton 1963) or non-conju-gated systems (Swern 1961). These reactions will give Iow conjugated diene values and thus lead to errorsin theanalysis. On the other hand, theTBA value measures the rancid flavoursor odours hut does not indicate the State ofoxidation. Therefore, no single test is adecjuate to fully describe the extent of peroxidation. A combination of PV, conjugated diene and TBA values would indeed give the best indication of thedegreeofoxidation of oils or fats. In addition, most irradiated foods used for human orani mai eon sumpt i on are likelv tobestored fordifferent periodsoftimeand under different conditions after irradiation. In view of t his the naturę of the radicals which promote per-oxidation during storage should be imestigated and identifled in order toovercome the problem.

CONCLUSION

Irradiation of palm olein within the rangę of doses recommended for food preservation and in the presenceofoxvgen, formed hydroperoxide, readily measured by con jugated diene, peroxide value and thiobarbituric acid value. Peroxide formation inereased with inereasing irradiation doses and changed rapidly during post-irradiation storage. Peroxidation occurred at 0°C but the extent was less that that at room temperaturę. Concentration of antioxidant (BUT) at acceptable level (200 ppm) significantly inhibits peroxidation despite its partial destruction during irradiation.

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Hor(;an, V.)., J.I.. Phii pot, B.W. Porter and D.B. R(X)l>YN. 1957. Toxicity of Autoxidi/.ed Squalene and Linoleic Acid and of Simple Peroxides in Relation to Toxicity of Radiation. Biochem, J. 65: 551-558.

Howton, D.R. 1963. Naturę of the Products Formed by /Irradiation of Deaerated Aqueous Potassium Óleate. Hadiat. Res. 20: 161-186.

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