Odour-active volatiles in lupin kernel fibre preparations (Lupinus angustifolius L.): effects of thermal lipoxygenase inactivation

Kernel fibre from narrow-leafed lupin (Lupinus angustifolius L.), exhibiting multiple health benefits as a food ingredient, suffers from undesirable formation of off-odours during storage at 20 °C. To study the impact of lipoxygenase (LOX), involved in quality changes during processing and storage in many legumes, an aliquot of the raw material was hydrothermally treated in order to inactivate LOX. By means of aroma extract dilution analyses, 25 odorants were detected to be impact compounds in both fibre preparations. Seven of them being associated with lipid oxidation were quantified during storage for one year using stable isotope dilution assay. The concentration of most odorants increased significantly (p < 0.05) during storage, and their formation was even promoted by the previous heating step. The quantitative aroma analyses were supported by sensory analyses. Principal component analysis of the odour profile revealed clear differences in overall perception between untreated and heat-treated samples. As shown by sensory evaluation, there is a relationship between ageing and the formation of deleterious odour attributes such as fatty or rancid appearance. Most likely, non-enzymatic oxidation plays a predominant role in the evolution of lipid oxidation, implying that previous heat treatment as recommended for soybeans needs to be reconsidered for lupins.