Browsing by Author "Nuru, Zehara"

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    Evaluating Quality Deterioration of Used Frying Vegetable Oils and Improving the Quality Using Adsorbent Treatment
    (Addis Ababa University, 2018-03-05) Nuru, Zehara; Getachew, Paulos (PhD)
    Frying is the most commonly used cooking method in food preparation. Continuously frying food items at high temperature will result in frying oil and fried food quality deterioration. in this study as an alternative option the effects of adsorbents (betonite, ash, magnesium oxide, silica gel, and bleaching earth) to improve the quality of used frying vegetable oils (Palm and Niger seed oil) were evaluated. Accordingly, each adsorbent was mixed with 20 hours fried oils (15% w/v) at 150 oC and stirred together for 30 min. The oil was recovered through centrifugation at 4200 rpm for 15 min. Then, the physico-chemical characteristics of the fried and adsorbent treated oils were investigated on both oil types. The chemical quality parameters of palm oil increased after the prolonged frying (i.e. acid value (AV) (0.42 to 1.40) mg KOH/gm oil, free fatty acid (FFA) % (0.20 to 0.64) %, and peroxide value (PV) (1.99 to 11.00 mEq oxygen/gm of oil)). Similarly, in the 20 hrs fried niger seed oil increased values of (AV (2.24 to 8.31) mg KOH/gm, FFA % (1.13 to 4.17), PV (1.00 to 13.97) mEq oxygen/gm of oil) were found. In both fried palm and niger seed oils, magnesium oxide (MgO) treatment gave the highest improvement on the physical quality parameters. Treatment of the fried PO with 15% (w/v) (ash, bentonite, bleaching earth, silca gel and MgO) reduced the FFA% by (55, 45, 35, 65 and 61) % (silca gel > MgO > ash > bentonite > bleaching earth) respectively. Similarly, treatment of the used fried NO with the same adsorbents improved the FFA% by (61, 66, 56, 61 and 73) % respectively. The PV of the fried PO was also reduced by (55, 37, 9, 28 and 64) % respectively (MgO > ash > bentonite > silca gel > bleaching earth). Upon the same treatment the PV of the used NO was improved by (57, 43, 21, 50 and 64) % respectively. The recovery of PO after ash, ii bentonite, bleaching earth, silca gel, MgO treatment was (75, 88, 85, 70, 40) % respectively. Meanwhile with the same treatments of the fried NO, the oil recovery was (80, 88, 85, 70 and 40) % respectively. Based on both physical and chemical quality improvement effectiveness ash and MgO were selected for further objectives of the study (i.e. effect of concentration and synergism by the two adsorbents). To determine the minimum proportion of the selected adsorbents that will improve the quality of the used oil, (2.5, 5.0, 7.5, 12.5) % (w/v) of ash and MgO were used in both fried PO and NO. Treatments with 12.5% and 15.0% of ash improved the AV and FFA% of fried PO to the recommended acceptable range for human consumption. Treatments with (2.5, 5.0, 7.5, 10.0, 12.5 and 15.0) % of ash reduced the AV of fried NO gradient-wise by (26, 39, 46, 53, 53 and 60) % respectively (p < 0.05).