Comparison of direct addition and using of antioxidant active film containing nettle leaves extract in oxidative stability of soybean oil

Using of natural antioxidants instead of synthetic compounds is a novel approach in food processing and preservation. The aim of this work was to compare the antioxidant activities of ethanol extracts of nettle (Urtica dioica L.) in stabilizing soybean oil in two forms of direct addition to oil and using of extract loaded starch based active film. At first, the phenolic composition and antioxidant capacity of nettle extract (NE) were measured. Afterward, protective effects of NE and active film in stabilizing soybean oil were compared to synthetic antioxidant (tert-butyl hydroquinone, TBHQ), by measuring their peroxide values, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and oxidative stability index (OSI) during 60 days storage at 25°C. DPPH radical scavenging activity and OSI of oils enriched with 800 ppm of NE at day 60 had not significant difference with those of sample containing 100 ppm TBHQ. Results of these experiments in the oils contacted with active films revealed that the increasing of migrated antioxidant during storage time, caused to increase of antioxidant activity and OSI. Peroxide value (PV) of soybean oil increased by increasing storage time, but the both of direct addition and using of active film were able to control the increasing rate of PV in oil and in the long storage periods, the effect of active film was more than direct addition of NE. Nevertheless, NE exhibited negative effects on color properties of soybean oil and green color of oil was increased by increasing of loaded NE and also increasing of migration rate from active films. The results of this research indicated that the using of active film containing nettle extract is able to preserve the oxidative stability of soybean oil during storage.