Oxidative stability of enriched walnut oil with phenolic extracts from walnut press-cake under accelerated oxidation conditions and the effect of ultrasound treatment

In this study, the effect of phenolic extract obtained from walnut press-cake on oxidative stability of walnut oil was evaluated. Besides this, the oxidative stability of ultrasound applied walnut oil with added press-cake, as a valuable source of phenolic compounds, was determined. Oxidative stability of walnut oils upon addition of phenolic extracts (50, 100 and 200mg/kg oil) and -tocopherol (100mg/kg oil) was monitored under accelerated oxidation conditions at 65 degrees C for 20day. Total phenolic content (TPC) of walnut press-cake and phenolic extract from walnut press-cake were 58207.3 and 332679.8mgGAE/kg, respectively. All concentrations of phenolic extracts significantly reduced the formation of oxidation products compared to control. Especially, the walnut oils enriched with 200mg/kg phenolic extract showed the highest oxidative stability. While direct enrichment using ultrasonic maceration (1:100) (walnut press-cake:walnut oil) caused a significant increase in TPC of walnut oil (from 9.76 to 78.80mg GAE/kg), ultrasonic macerated walnut oil had low oxidative stability. Results showed that 200mg/kg oil phenolic extracts from walnut press-cake can be successfully used as a natural antioxidant preparate to improve the oxidative stability of walnut oil.