374 FOOD SCIENCE APPLICATIONS 



measured, permit estimation of the induction period — the period of time 

 when relatively little oxidation is taking place but after which rapid oxi- 

 dation and rancidity develop. Measurement of the induction period is 

 generally more desirable and useful than is the determination of a single 

 value on the curve. 



None of the methods based on a single test are at all reliably correlated 

 with the organoleptic flavor of the oil. Depending upon such factors as 

 the storage temperature of the oil during oxidation or whether or not an 

 antioxidant was present, the values for a given test corresponding to a 

 certain degree of rancidity may be quite different. If all these possible 

 sources of discrepancy are kept in mind, it is possible to use successfully 

 any of the tests by closely calibrating results from time to time with 

 organoleptic rancidity. Of the tests mentioned, the procedure for peroxide 

 number (which is very simple to execute) and the test forT.B.A.^^ are 

 perhaps most widely used. The limitations of these tests must be con- 

 stantly kept in mind if their use is not to result in misleading conclusions. 



P^ish oils are more unsaturated than any other common oils and are, 

 therefore, highly susceptible to oxidation. Special precautions are needed 

 during their analysis to prevent changes from occurring during the analy- 

 sis itself. It is advisable whenever possible to keep them under an atmos- 

 phere of nitrogen at all times during analysis. For this purpose, nitrogen 

 of a high degree of purity (99.99 per cent or better) should be used. 

 Oxygen, contained as an impurity in some commercial nitrogen, may 

 cause oxidation. The nitrogen, when applied to fish oils, should be bub- 

 bled through the oil to displace oxygen dissolved in the oil as well as any 

 in the headspace. 



LITERATURE CITED 



1. Almy, L. H., /. Atn. Chem. Soc, 47, 1381(1925). 



2. Assoc. Offic. Agr. Chemists, "Official and Tentative Methods of Analysis," 9th 



Ed., Washington, Assoc. Offic. Agr. Chemists, 1960. 



3. Beatty, S. A., and Gibbons, N. E., /. Fisheries Research Board Can., 3, 77(1936). 



4. Bligh, C. C, and Dyer, W. J., Can. J. Biochem. and Physiol., 37, 91 1(1959). 



5. Clark, E. T., and Hillig, F., J. Assoc. Ofic. Agr. Chemists, 21, 684(1938). 



6. Geiger, E., Food Research, 9, 1(1944). 



7. Groninger, Herman, Food Technol. 15, 10(1961). 



8. Jones, N. R., Biochem. J. 58, XLVII(1954). 



9. Lang, O. W., Farber, L., Beck, C, and Yerman, F., Ind. Eng. Chem., Anal. Ed., 



16, 490(1944). 



10. Olcott, H. S., and Einsct, E., J. Am.. Oil Chemists' Soc. 35, 161(1958). 



11. Stansby, M. E., /. Assoc. Offic. Agr. Chemist, 34, 549(1951). 



12. Stansby, M. E., Food Technol., 12, 260(1958). 



13. Stansby, M. E., Harrison, R. W., Dassow, J., and Sater, M., Ind. Eng. Chem., 

 Anal. Ed., 16, 593(1944). 



14. Wheeler, D. H., Oil and Soap, 9, 89(1932). 



15. Yu, T. C, and Sinnhuber, R. O., Food Technol., 11, 104(1957). 



