Synergistic study of the antioxidant potential of barley waste for biodiesel

Abstract Recently, use of biodiesel as a diesel substitute has increased significantly. Currently, the biodiesel value added to diesel in Brazil is 10%. To maintain biodiesel quality during storage, antioxidants must be added. The most commonly used antioxidants are synthetic compounds. Due to the diversity of low cost agro-industrial waste with antioxidant activity, including cereal and fruit derivatives, several research studies reported the use of these waste materials as antioxidants. Barley waste (RCV) contains α-tocopherol (vitamin E), which acts as an antioxidant. Thus, this paper aims to investigate the use of RCV and citric acid as antioxidants in biodiesel. The conditions were optimized for the extraction and application of RCV in biodiesel (methyl ester soybean oil) using a 3² factorial design. RCV extracts were added during biodiesel production, which eliminates steps and improves the process. The antioxidant activity was evaluated using an accelerated oxidation method. Addition of RCV (11 g L–1) led to an induction time of 5.76 ± 0.11 h. However, addition of a blend of natural antioxidants [RCV (11 g L–1) and citric acid (0.1% w/v)] led to an increased induction time of 14.67 ± 2.10 h, which was attributed to the synergistic effect of the antioxidants.