Prospects of rapeseed oil by-products with respect to antioxidative potential

Abstract

The current project focuses on the extraction of antioxidants from the by-product of rapeseed (canola) oil processing using an optimised method. Press cakes of the oil processing are normally referred to as meals. Commercial rapeseed and mustard meals (taken from different German and Indian companies) were investigated for their phenolic content. Sinapic acid, the main phenolic compound of rapeseed constitutes over 73% of free phenolic acids and about 99% of the main phenolic acids bound as esters and glucosides. Sinapin, the cholin ester of sinapic acid is the major phenolic ester in rapeseed. Different solvent systems were used to obtain antioxidative extracts from rapeseed meal. The extracts were investigated for their content of phenolic compounds. In addition, meal extracts were fractionated as free, bound, released and insoluble phenolic compounds. Individual phenolic compounds and a solvent extract (70% methanol as extraction solvent) were further investigated in oxidation experiments using stripped rapeseed oil. The oxidation at 40 °C was monitored by the formation of hydroperoxides (indicating primary oxidation products) and hexanal (secondary oxidation products). The experiments indicate that the addition of sinapic acid (concentration-dependent) causes inhibition of peroxide formation higher than alpha-tocopherol in oils. The 70% methanolic extract of rapeseed meal added as an equivalent of 500 μmol kg oil –1 (based on the total phenol content) showed good antioxidative activity compared to the addition of 500 μmol kg oil –1 sinapic acid. By-products of rapeseed oil processing have the potential of being a millennium renewable raw material. Rapeseed ranks currently the third source of vegetable oil (after soy and palm) and the third leading source of oil meal (after soy and cotton). Thus, any significant contribution related to extraction of valuable compounds from rape meal will have overall a large contribution to the meal industry. To cite this article: U. Thiyam et al., C. R. Chimie 7 (2004) .