Retention of natural antioxidants of blends of groundnut and sunflower oils with minor oils during storage and frying

Unrefined groundnut oil (GNO) and refined sunflower oil (SFO) were blended with four minor oils including laboratory refined red palmolein (RRPO), physically refined rice bran oil (RBO), unrefined sesame oil (SESO), and unrefined coconut oil (CNO) containing natural antioxidants viz., β-carotene, tocopherols, oryzanol and lignans. The five blends prepared were GNO + RRPO (80:20), GNO + RBO (80:20), GNO + SESO (80:20), SFO + RRPO (50:50) and SFO + CNO (60:40). Prepared blends contained saturated fatty acids (SFA) (16.7–53.3 %); monounsaturated fatty acids (MUFA) (16.0–45.5 %) and polyunsaturated fatty acids (PUFA) (29.2–37.8 %). GNO blends viz., GNO + RRPO, GNO + RBO and GNO + SESO contained β-carotene (10.7 mg/100 g), oryzanol (0.12 g/100 g) and lignans (0.35 g/100 g) respectively as natural antioxidants. SFO was enriched with β-carotene (28.7 mg/100 g) and medium chain fatty acids (34.2 %) by blending with RRPO and CNO respectively. The oil blends (200 ml) were packed and stored at 38 °C/90 % relative humidity (RH) and 27 °C/65 % RH and samples were withdrawn at fixed intervals for analysis. Freshly prepared blends were also investigated for their frying performance. During storage, GNO + RBO blend showed highest oxidative stability probably due to the presence of oryzanol in the order GNO + RBO > GNO + SESO > GNO + RRPO. During frying, the peroxide value of GNO blends with RBO (rich in oryzanol) and SESO (rich in lignans) was less while the free fatty acid value was less in SFO blends with RRPO and CNO. Hence, blending of natural antioxidants rich minor oils (RRPO, RBO and SESO) with the major vegetable oils (GNO and SFO) may preserve them by lowering their rate of oxidation during storage and frying.