Improving the quality of used frying niger seed oil with adsorbent treatment

High temperature continuous deep fat frying of foods will result in the frying oil and food quality deterioration. Although the quality can be retained by using fresh oil, this approach will increase the production cost. In this study, quality improvement of used niger seed oil using adsorbent treatment was evaluated. Each adsorbent was mixed with 20 h used niger seed oil (15% w/v) at 150 °C and stirred for 30 min. The oil was recovered through centrifugation at 4200 rpm for 15 min. The tested chemical parameters of the oil increased after 20 h of frying (acid value (AV) (2.24–8.31) mg KOH/gm oil, free fatty acid (FFA) (1.13–4.17) %, and peroxide value (PV) (1.00–13.97 mEq oxygen/Kg of oil). The improvement in free fatty acid, peroxide value and oil recovery upon treatment of the fried oil with ash, bentonite, bleaching earth, silca gel and magnesium oxide (MgO) was (61, 57, 80), (66, 43, 88), (56, 21, 85), (61, 50, 70), and (73, 64, 40) % respectively. Ash and MgO effectively improved the physico-chemical characteristics of the used oil. Thus, the two were selected for further optimization of effective concentration and to evaluate their synergetic effect. Treatments with 2.5, 5.0, 7.5, 10.0, 12.5 and 15.0 % of ash reduced the AV of the fried oil by 26, 39, 46, 53, 53 and 60 % respectively (p < 0.05). Also the combination of ash and MgO (1:1) improved the physico-chemical properties of the frying oil to nearly fresh quality.