Evaluation of Physicochemical Properties, Fatty Acid Composition and Antioxidant Activity of Engkabang (Shorea spp.) Seed Oils

Sahlinah, Abdul Rakman (2022) Evaluation of Physicochemical Properties, Fatty Acid Composition and Antioxidant Activity of Engkabang (Shorea spp.) Seed Oils. Masters thesis, Faculty of Resource Science and Technology.

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Abstract

The seeds from the Shorea genus are popular among Sarawak locals and known as ‘Buah Engkabang’. However, the information on Shorea seed and oil is still scarce. Thus, the objectives of this study were to collect the Shorea oilseeds (Shorea macrophylla, Shorea palembanica, Shorea stenoptera and Shorea pinanga) and then to gather their proximate, minerals and anti-nutritive factors data, as well as the effects of extraction methods and oil refining on the physical and chemical properties, fatty acid composition, antioxidant activity and total phenolic content (TPC).The proximate composition are significantly different (p<0.05) between the seeds of S. macrophylla (moisture: 21.47%; ash: 0.67%; total lipid: 41.37%; total fibre: 15.67%; total carbohydrate: 79.44%), S. palembanica (moisture: 27.25%; ash: 1.98%; total lipid: 49.06%; total fibre: 7.72%; total carbohydrate: 82.37%), S. stenoptera (moisture: 16.06%; ash: 4.42%; total lipid: 38.80%; total fibre: 30.687%; total carbohydrate: 66.45%) and S. pinanga (moisture: 35.56%; ash: 2.23%; total lipid: 46.91%; total fibre: 8.09%; total carbohydrate: 79.64%). K and Zn are the predominant macro and microminerals, respectively. The evaluation of antinutrients disclosed low phytate but high oxalate content in S. macrophylla (0.29% and 1.91%), S. palembanica (0.29% and 2.43%), S. stenoptera (0.09% and 2.65%) and S. pinanga (0.06% and 3.61%). The mechanical extraction method is the choice of Shorea seed oil extraction because the mechanically extracted S. palembanica oil (cis-MUFAs: 34.49%; acid value: 3.47 mg NaOH/kg; peroxide value: 10.62 meq O2/kg; TPC: 2.49 mg GAE/kg) is of higher quality than the Soxhlet extracted oil (cis-MUFAs: 34.23%; acid value: 8.00 mg NaOH/kg; peroxide value: 14.58 meq O2/kg; TPC: 0.68 mg GAE/kg) (p<0.05). The fatty acid composition in Shorea oils dominantly consists of stearic, oleic and palmitic acids similar to the fatty acid profile of cocoa butter, indicating the potential of Shorea seed oils to be utilised in the chocolate industry. Point-Biserial Correlation (rpb) was used to investigate the impact of oil refining on physical and chemical characteristics, fatty acid composition, antioxidant activity and TPC. A significant negative correlation between oil refining and acid and peroxide values (rpb= -1.00, p<0.05) demonstrates that oil refining effectively reduces acid and peroxide values, resulting in improved oil quality. The refining process has no significant impact on the fatty acid content according to oil analysis using Gas Chromatography-Mass Spectrometer (GC-MS) and Attenuated Total Reflectance-Fourier Transform Infrared Spectrometer (ATR-FTIR) (p>0.05). However, there is an increase in essential fatty acid of linoleic acid in S. macrophylla oil from undetected to 1.01% and S. pinanga oil from 0.34% to 0.41% with the elimination of harmful fatty acids such as elaidic and erucic acids in S. macrophylla oil. Refining increased the antioxidant activity of S. palembanica (crude: 813.02 μg/mL; refined: 239.88 μg/mL) and S. pinanga (crude: 214.11 μg/mL; refined: 56.77 μg/mL) oils, whilst refining S. macrophylla (crude: 244.55 μg/m; refined: 471.36 μg/mL) and S. stenoptera (crude: 152.22 μg/mL; refined: 249.49 μg/mL) oils reduced their antioxidant activity.

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