Determination of the effects of rosemary (Rosmarinus officinalis L.) plant, solvent extract and essential oil on the oxidative stability of hazelnut oil during the deep fat frying procedure

In this study, the effects of rosemary (Rosmarinus officinalis L.) plant, its solvent extract and essential oil on the oxidative stability of hazelnut oil during deep frying was investigated. In addition, 2,2?- diphenyl -1-picrylhydrazyl (DPPH) radical scavenging activity, reducing power and the antioxidant activities with conjugated diene method and ß-carotene bleaching method of essential oil, ethanol and methanol extracts of rosemary were determined, and thus they were compared with the values of butylated hydroxytoluene (BHT) and ?-tocopherol. In general, extracts showed similar values to BHT and ?-tocopherol, while the essential oil of rosemary had lower values. The induction periods of hazelnut oils containing 0.25-2.0 mg/g concentrations of solvent extracts and 1-20 % (w/w) rosemary plant at 150 oC were found higher than the induction periods of control. The induction period of triglycerides prepared from hazelnut oil was determined as 3.93 min., while the induction periods of triglycerides containing rosemary additives changed between 3.67 and 27.19 min.During the deep frying procedure made at 180 ± 5 °C for 10 times a day for 6 days, the changes in some physical and chemical characteristics of oils taken at the end of the days were investigated. Hazelnut oils containing 1 mg/g concentration of rosemary, ethanol/methanol extracts and essential oils and 1-5 % (w/w) of rosemary plant had lower amounts of conjugated diene content, p-anisidine value and polar material content compared to control. In addition, during frying procedure, changes in L*, a* ve b* color values and viscosity were lower compared to control. At the end of 6 days, the induction periods of hazelnut oils containing rosemary plant, essential oil and extracts were between 9.43 and 35.01 min, which were much higher than the induction period of control (4.28 min). The study results indicated that hazelnut oil containing 5 % of rosemary plant had the best frying performance. It was concluded that rosemary additivies had no statistically significant effect on the texture, color and sensorial properties of the fried potatoes (crispiness, taste, smell and total acceptance) (p>0.05). However, it was determined that the additives increased the amount of the oil absorbed by potatoes to some extent.Key Words: Deep frying, hazelnut oil, rosemary plant, essential oil, solvent extract, induction period, antioxidant activity