Investigation of Using Beijing Grass Extract as a Natural Antioxidant in Edible Oil
Beijing grass [Murdannia loriformis (Hassk) Rolla Rao et Kammathy] has been widely used as a Thai medicinal plant. In this study, the antioxidant activity of the ethanolic extract of Beijing grass was evaluated using the DPPH assay. Furthermore, the extract was added into soybean oil and pork lard, which were incubated at 75°C for 14 days. Peroxide value and color of the oil were determined during the storage in order to screen suitability of the extract as a natural antioxidant in edible oil. The antioxidant activity of the Beijing grass extract at 200, 400, 600 and 800 ppm were 60.38, 70.13, 85.38 and 87.29%, respectively according to the DPPH assay. Protection factor was calculated to show a relative increase of the induction period of lipid oxidation due to the addition of antioxidant. The protection factors of the Beijing grass extract in pork lard at 200, 400, 600 and 800 ppm were 1.4, 1.6, 1.6, and 1.6, respectively. This suggested that the extract helped increase oxidative stability of the oil compared to the control without antioxidant. However, antioxidant efficiency of the Beijing grass extract was relatively low compared to synthetic antioxidant BHT which possessed the protection factor of 3.3. The same trend was observed in soybean oil in the way that Beijing grass extract at 200, 400, 600 and 800 ppm showed protection factor of 1.2, 1.2, 1.2, and 1.3, respectively. TBHQ, a synthetic antioxidant, again exhibited significantly higher antioxidant activity compared to the Beijing extract in soybean oil. Measuring the Hunter L, a, b values of the oil suggested that the Beijing extract caused the oil lightness to decrease, while the greenness and blueness increased. In conclusion, the Beijing grass extract showed great potential as an effective natural antioxidant to protect edible oil from lipid oxidation. However, the impact of the extract on the color of the oil is still a great concern that needs to be further investigated.
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