Effects of some natural antioxidants on frying quality of the peanut oil

In this research, the phenolic extracts of fresh tea leaves, grape seeds, tomatoes and pure ?-oryzanol were enriched into peanut oil as antioxidant additives and frying were carried out (180 oC, 7 d, 5 h/d). The activities of the materials were compared with butylated hydroxy anisol (BHA) and butylated hydroxy toluen (BHT), and the effects on usage life were estimated by analytical techniques. The oxidation prevention activities of the extracts and their compatibility with frying oils were determined. The sensory properties of the dough were measured to estimate their appropciatiness to the consumption.In general, all the tested natural antioxidant extracts led to an increase in the use life and stability of oil significantly. Also, there was no sensory difference between the dough samples.The ranges of measurements in the treatment groups were; total polar material-chromatography (10,72-73,80%), total polar material-probe (14,52-88,50%), free acidity (0,090-2,903%), smoke point (233,50-168,35°C), conjugated diens (0,01-0,40%), L (52,68-41,42), a* (3,41-5,26), b* values (-5,30-10,46), turbidity (0,70-10,40 NTU), viscosity (69,57-442,00 cP), total phenolics (0,36-4,20 mg GA/100g oil), antioxidant capacity (0,53-11,00 mmol Trolox/100g oil) and the oil absorbed by dough (3,62-14,22%). The fatty acid and sterol composition of seventh day oil samples showed that the additions can prevent the oxidative degradation of unsatutared fatty acids, especially oleic acid. Frying oil enriched with green tea extracts had higher sterol levels than that of other frying oils.In conclusion, it was found that thermal stability of groundnut oil during frying was enhanced by the lycopene and green tea extracts, and the nutritional value at the end of frying process were better with the ?-oryzanol added sample. Accordingly, it was determined that natural antioxidants were both preventing the oxidative deterioration of the frying oil and developing better sensory properties in the fried food. Hence, it was recommended that, natural antioxidant extract can easily be enriched into the frying oils without any safety problem and even with better sensory quality in the products.Keywords: Deep-fat frying, fresh tea leaf, grape seed, tomatoes, ?-oryzanol, extract, oxidation, antioxidant capacity.