Antioxidative role of lutein esters extracted from Indian marigold flower on soybean oil during heating

Soybean oil is rich in linoleic acid, a polyunsaturated fatty acid (PUFA) which is susceptible to oxidation during heating/frying. The present study attempts to protect the oil during heating by adding a natural anti-oxidant, lutein-ester, isolated from Indian marigold flower by solvent extraction. Two sets of experiment have been carried out by taking 1 L of soybean oil. In one set, 500 mL of soybean oil is heated for 24 h (8 h daily for 3 consecutive days) and in the second set, lutein ester of 0.01g/kg is added to the remaining 500 mL of soybean oil and the oil is heated for 24 h in the similar manner. Heated oil samples are collected in every 4 h and the protective effects of lutein-ester have been assessed by monitoring the color, viscosity, acid value, peroxide value,p-anisidine value and 4-hydroxy-2-trans-nonenal (HNE) content of the heated oil samples. The content of HNE, which can be used as an index to monitor the overall progression of PUFA towards oxidation, show a value of 10.09+ or -0.1 [mu]M/g in case of control soybean oil and value of 1.11+ or -0.02 [mu]M/g in experimental soybean oil, after 24 h of heating. All the other parameters also confirm that lutein-ester can act as effective antioxidant to protect the oil during frying/heating.