Effect of pulse electric field assisted extraction on anthocyanin content and antioxidant activity of purple rice

Abstract

Purple rice (Oryza sativa L.) is popular for planting and consuming in North and Northeast Thailand. The important pigment on the purple rice grain is anthocyanin which has high antioxidant activity. This research studied the effect of applying a pulse electric field (PEF) technique on the extraction of the total anthocyanin content, and the antioxidant activity of purple rice. The extraction treatment was divided into two levels of PEF [low and high PEF]. The low PEF treatment condition used low pulse numbers (0, 100, 300, and 500) at three levels of electric field intensity (2, 3, and 4 kilovolts / centimetres (kV cm–1) in 1 Hz). The high treatment condition used an electric field intensity of 6 kV cm–1 in 1 Hz with the pulse numbers of 1,000, 3,000, 4,000, and 5,000. The results indicated that a sample extracted with low PEF showed low anthocyanin content but high % of DPPH inhibition. In contrast, a high level of anthocyanin content and low % of DPPH inhibition were found in the high PEF extraction treatment. The result demonstrated that PEF technology did not cause a chemical change to anthocyanin but affected antioxidant activity. This effect was due to high energy and temperature generated in the high PEF treatment. The PEF technique has a benefit in decreasing the time required for the extraction process and does not negatively affect the anthocyanin extracted. The appropriate PEF extraction condition for purple rice was obtained at 6 kV cm–1 with 3,000 pulses, which provided an acceptable total anthocyanin content (2.50 ± 0.09 mg l–1) and was consistent with a percent inhibition of DPPH (60.97 ± 0.64). The results of this study have implications for the ongoing development and use of food-based products.