Flavonoids were extracted from Zizyphus spina-christi leaves by Ethyl acetate after acid digested and used as antioxidant. The dried extract was added separately to each sample of fat extracted from hallow cow and sheep bones as follows: T1 cow fat, T2 control for cow fat, T3 sheep fat and T4 control for sheep fat (the control T2 and T4 reffered to samples without added antioxidant).
Samples were stored at -18, 5, 25 and 55 °C for 28 days. The storage trials were conducted at -18, 5 and 25 °C for 28 days for T1, T2, T3 and T4. The chemical indices examined initially and at the end of storage period. PVs was 1.46, 1.46, 1.8 and 1.8 meq/ Kg oil respectively, FFA values were 0.245, 0.245, 0.244 and 0.244% respectively and TBA values were 0.015, 0.015, 0.023 and 0.023 mg malonaldehyde/ Kg oil respectively. The statistical analysis for the obtained results revealed insignificant differences (p< 0.05) among both storage periods and storage temperatures. It was also found that the added antioxidants (Zizyphus leaf) hadn't showed preservative effect on added fat samples.
The storage trial for fat samples were also conducted at 55°C for 28 days. The initial values for PVs were 1.46, 1.46, 1.8 and 1.8 meq/ kg oil respectively and the final values were 3.2, 4.4, 3.6 and 5.4 meq/ kg oil respectively. The FFAs values were initially 0.245, 0.245, 0.244 and 0.244% respectively and the final values were 0.394, 0.507, 0.451 and 0.564% respectively. The TBA values were initially 0.015, 0.015. 0.023 and 0.023 mg malonaldehyde/ kg oil respectively and the final values were 0.02, 0.032, o.o334 and o.o452 mg malonaldehyde/ kg oil respectively. The statistical analysis revealed insignificant differences p< 0.05 among storage periods for both PV and FFA values (except T1 that didn't show significant effect p< 0.05 for FFA) and TBA values. The added antioxidants (Zizyphus leaf) hadn't revealed significant effect on stored oil samples as reflected by obtained results.