Process Optimization for Extraction of Millet Small Bran Oil by Aqueous Ethanol

Abstract

Millet small bran is a kind of byproduct of the millet processing. It is a cost-effective resource for healthy nutritious oil, which contains 23% oil, with 72% essential fatty acid, tocopherol, phytosterol and oryzanol. In recent years, aqueous enzymatic extraction of millet bran oil has been researched widely. However, this method has the disadvantages of high production costs, low extraction efficiency and great loss of nutrition. In order to reduce the production cost and improve nutritive value of the products, the ethanol extraction method was developed and response surface method (RSM) was used to optimize extraction conditions. The research investigated the influence of extraction temperature, extraction time, solid-liquid ratio and ethanol concentration. The result showed that extraction time, solid-liquid ratio and ethanol concentration made the most contribution to enhancing free oil yield. According to the principle of box–behnken design, response surface analysis of 3 factors and 3 levels was used to optimize the extraction process. The optimal conditions of this aqueous extraction method were: extraction time (120min), solid-liquid ratio (1:5) and ethanol concentration (30%). Under the optimal conditions, the oil yield reached 89.216%. Through determining the quality indices such as acidity, peroxide value and water content of millet small bran oil extracted by aqueous ethanol solution, it could be concluded that the quality of extracted oil was superior to the national standard of crude millet bran oil and similar to the first grade pressed bran oil under the national standard. The contents of tocopherol and phospholipid in millet small bran oil were 131.32mg/100g and 1.12g/100g, respectively. Aqueous ethanol extraction method is not only an efficient and suitable method of extracting millet small bran oil, but also preserve the nutrients like phospholipid and tocopherol to the greatest extent. Hence, it can be concluded that aqueous ethanol technology has a good applying prospect in oil production industry.