Effect of BHT and Citric Acid on the Oxidative Stability of Groundnut Oil During Storage

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Date
2015-06-15
Authors
Tagelsir Ahmed Ibrahim Obied, Obied
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uofk
Abstract
Effect of BHT and Citric Acid on Oxidative Stability of Groundnut Oil During Storage Tagelsir Ahmed Ibrahim Obied ABSTRACT: The objective of this study were to (i) evaluate the oxidative stability of groundnut oil in the presence of BHT and citric acid by determining peroxide values at definite storage intervals, (ii) to estimate the inhibition rate of autoxidation due to the application of BHT and citric acid and (iii) to investigate the effect of addition of BHT and citric acid on some physico-chemical characteristics of stored refined groundnut oil. All samples were subjected to physicochemical tests. The physical parameters were refractive index, viscosity and color, and the chemical parameters were peroxide value, acid value, free fatty acid and inhibition ratio of autoxidation. The samples were stored at ambient temperature for 0, 30, 90 and 180 days. The study revealed that citric acid had insignificant effect on the oxidative stability of the refined groundnut oil, while BHT significantly (PX04;0.05) inhibited the formation of hydroperoxides and protected the oil against rancidity up to three months. The inhibition rate of autoxidation by citric acid ranged between 0.024% and 17.66%, whereas that by BHT ranged from 7.33% to 62.68%. The treated oil as well as the control sample retained its original red colour (0.50 Unit) during the first 30 days; the colour was then significantly (PX04;0.05) increased to 0.9-1.0 Unit in the remaining period of storage. All stored samples showed fixed refractive index of 1.471 up to 90 days of storage, thereafter the refractive index was significantly (PX04;0.05) elevated to 1.474 at the last period of storage. Addition of citric acid and BHT slightly increased the viscosity of the refined oil from 31.92 to 32.58 and 32.25 after 30 days and to 32.50 and 32.08 after 90 days, respectively. Citric acid reduced the acid value (AV) of the refined oil from 0.64 mg/g to 0.50 mg/g at the 30th day of storage, whereas BHT reduced it from 0.64 mg/g to 0.51 mg/g at 30th and from 1.45mg/g to 1.34 mg/g at 180th day of storage. The free fatty acids content (FFAs) for the sample treated with citric acid was markedly increased from 0.155% to 0.250%, 0.635% and 0.700% following storage for 30, 90 and 180 days, respectively. Regarding the BHT treated sample, the FFAs percentage remained notably elevated to 0.255%, 0.575 and 0.670% after 30, 90 and 180 days, respectively. However, up to 30 days of storage the FFAs content was below the upper limit (0.3%) stated by the Sudanese Standards for vegetable oils.
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Effect of BHT and Citric Acid on the Oxidative Stability of Groundnut Oil During Storage
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