Annatto‐Derived Carotenoids (Bixin and Norbixin) As Biodiesel Antioxidants: Characterization and Effects on Oxidative Stability ( Rancimat and PetroOXY )

ABSTRACT The increasing use of eco‐friendly fuels is increasing the production of biodiesel but soybean biodiesel is also characterized by poor oxidative stability because of its high content of unsaturated fatty acid methyl esters (FAMEs), which restricts the quality of fuels in storage. In the present work, annatto‐derived apocarotenoids (bixin and norbixin) were isolated and characterized as bio‐based antioxidant additives for soybean biodiesel. HPLC–UV/Vis, FTIR, thermogravimetric analysis (TG/DTG), differential scanning calorimetry (DSC), and SEM/EDX analysis demonstrated high purity and cis isomers predominance, demonstrating the effects of molecular structure on oxidative activity. The antioxidant activity was first assessed employing the DPPH radical scavenging method. Then, bixin and norbixin were added to soybean biodiesel at concentrations of 1000–3000 ppm; oxidative stability was analyzed using both the Rancimat method (EN 14112, 110°C) and PetroOXY method (ASTM D7545). Both carotenoids promoted the oxidation induction time in a concentration‐dependent manner, and bixin reached superior antioxidant activity than norbixin in all analyses. Although no compound allowed the biodiesel to fulfill the current Brazilian regulatory requirement of 13 h at 110°C, the beneficial effect showed that these compounds have a good potential as a component of the antioxidant systems. They suggest that annatto carotenoids are a candidate for increasing biodiesel stability when used combined with other antioxidants, and the data provides directions for future development of formulations in accordance with regulations and the goal of more sustainable biodiesel production.