OPTIMIZATION OF KREIS TEST FOR EDIBLE OILS

The Kreis test is a chemical method for quality evaluation of edible oils enabling early detection of rancidity. In previous studies, quantities of test oil and phloroglucinol, and incubation period were optimized for groundnut, rice bran and palm oils and efficiency of the test was improved. In this study, optimized conditions for sunflower and mustard seed oils are reported. Through central composite rotatable design, response surface was fit as a function of oil quantity (0.3-3.3 ml) with 1% phloroglucinol (0.08 mol) in acetic acid (0.3-3.3 ml) for an incubation period of 10-90 min. Absorbance readings at 545 nm gave excellent fit to quadratic polynomials with multiple correlations of >0.90. Using the flexible polyhedron search method, optimal conditions (which are applicable to routine tests of all edible oils) for the 2 oils were determined as follows: 1 ml of test oil; 1 ml of 1% phloroglucinol; and 20 min incubation time. It is recommended that reagent concn. should be reduced considerably for analysis of sunflower oils.