Oxidative Stability and Its Effects on the Quality of Oil Extracted from E. tirucalli trees in Different Agro-Ecological Zones of Tanzania

Abstract

Plant oils are prone to oxidation during long-term storage or through autoxidation. Oils may undergo conversion and degradation due to oxidation and polymerization reactions which can affect their quality. The present research studied oxidative stability and its effects on the quality of oil extracts from E. tirucalli trees found in Dodoma, Mbeya and Dar es Salaam agro-ecological zones in Tanzania. Oxidative stability (Mean induction time) was used as a parameter to evaluate the quality of oil. Oils were extracted from E. tirucalli stem bark samples with different diameters using Soxhlet extraction method. A 873 Biodiesel Rancimat Instrument was used to determine mean induction time of oils. Obtained oxidative stabilities were compared with the standards EN 14214-03 (6 hours) for biofuels suitable for running engines. Analysis of Variance (ANOVA) performed using Minitab software tested the differences in quality of oil. Results showed that oxidative stabilities which ranged from 3 to 5 hours from 3.12h + 0.23 - 5.08h + 0.23, 3.5h + 0.13 – 4.56h + 0.13 and 3.06h + 0.17 – 4.48h + 0.17 for Dodoma, Dar es Salaam and Mbeya respectively, were different from each other (p < 0.05). However, there were no clear trends of differences in oil oxidative stabilities among stem diameters and ecological zones. Also oxidative stabilities were lower than recommended biofuel standard EN 14214-03 (6h). The study concluded that the quality of oil was low and Dodoma offered higher quality of oil than Mbeya, and Dar es Salaam zones.