2421 Research Article Received: 7 May 2009 Revised: 7 July 2009 Accepted: 12 July 2009 Published online in Wiley Interscience: 11 September 2009 (www.interscience.wiley.com) DOI 10.1002/jsfa.3739 Characterisation of odour-active compounds in lupin flour Stephanie Bader, a* Michael Czerny, a Peter Eisner a and Andrea Buettner a,b Abstract BACKGROUND: Lupin ingredients are promising alternatives to soybean products owing to their similarly high protein content. Lupin flour exhibits a green and bean-like off-flavour in higher amounts. The aim of this study was to characterise and identify the main odour-active compounds in lupin flour. RESULTS: The orthonasal aroma of lupin flour was evaluated by means of aroma profile analysis and was found to be characterised by grassy-green, metallic, fatty, fruity, hay-like, cheese-like, and meat-like odour qualities. Volatile compounds of lupin flour of Lupinus angustifolius cv. Boregine were extracted with dichloromethane and isolated by solvent-assisted flavour evaporation. Aroma extract dilution analysis (AEDA) was carried out with the obtained extract. In total, 50 odorants were detected by high-resolution gas chromatography – olfactometry. AEDA revealed 26 odour-active compounds with flavour dilution factors higher or equal to 32. The substances were unequivocally identified by their odour characteristics, their retention indices and their mass spectra using one-dimensional or two-dimensional gas chromatography– mass spectrometry, respectively. CONCLUSION: A series of unsaturated and saturated aldehydes, ketones, carboxylic acids, alkyl-methoxypyrazines and terpenes were identified for the first time as odour-active contributors to the aroma of lupin flour. c  2009 Society of Chemical Industry Keywords: aroma extract dilution analysis (AEDA); high-resolution gas chromatography–olfactometry (HRGC-O); gas chromatogra- phy – mass spectrometry (HRGC-MS); two-dimensional HRGC-MS; Lupinus angustifolius cv. Boregine INTRODUCTION Several hundred species of lupin belong to the genus Lupinus in the legume family (Fabaceae). Lupin seeds of varieties deriving from the Mediterranean region have been used as pickled lupin kernels for food purposes since ancient times. The bitter-tasting kernels of these species contain high amounts of alkaloids (up to 4%), which must be removed before consumption. 1 Today, mainly three types of lupin species containing low levels of alkaloids (normally below 0.02%) are cultivated in Europe, namely white lupins (Lupinus albus L.), blue or narrow-leafed lupins (Lupinus angustifolius L.), and yellow lupins (Lupinus luteus L.), also called ‘sweet lupins’. Lupin ingredients are promising alternatives to soybean products owing to their comparatively high protein content (30 – 38%), the similarly high nutritive value, and the lack of antinutritional factors like trypsin inhibitors that are present in soybeans. Lupin protein ingredients in the form of flour, concentrates, and isolates can be applied in different food groups such as bakery products, salad dressings, lupin pasta, ice cream, and sausages. 2,3 Yet the application of lupin products in food is limited, largely due to their ‘green’ and ‘bean-like’ flavour, as has been shown in previous investigations (Fraunhofer IVV, unpublished data). Among the group of Fabaceae, aroma components of soybean flours have been studied most extensively over three decades. The work started in the late 1960s using different methods of sample preparation and gas chromatographic (GC) analysis combined with mass spectrometry (MS) or flame ionization detection (FID), or gas chromatography–olfactometry (GC-O). 4–7 In further investigations, the volatiles of winged beans and green peas have been studied by several researchers. 8–10 Summarising these studies, many different volatiles from various chemical classes like alcohols, saturated and unsaturated aldehydes or ketones, and terpenes, as well as some others, have been identified in legume flours. Generally, diverse pyrazines and aldehydes were reported as being the most common contributors to the specific aroma profiles of legumes. However, investigations on the odour-active compounds in lupin flour or lupin-derived protein products have not been carried out until now. Furthermore, the identity and origin of flavour compounds have not yet been clarified, nor the contribution to the undesirable green and bean-like flavour attributes of lupin protein products. Therefore, the aim of this study was to characterise the odour-active compounds of freshly milled lupin flour of Lupinus angustifolius cv. Boregine – a common lupin variety harvested in the north of Germany – using high-resolution gas chromatography–olfactometry (HRGC-O) and one- and two- ∗ Correspondence to: Stephanie Bader, Fraunhofer Institute for Process Engi- neering and Packaging IVV, Giggenhauser Str. 35, D-85354 Freising, Germany. E-mail: stephanie.bader@ivv.fraunhofer.de a Fraunhofer Institute for Process Engineering and Packaging IVV, D-85354 Freising, Germany b Institute of Pharmacy and Food Chemistry, Department of Food Chemistry, University Erlangen-N¨ urnberg, 91052 Erlangen, Germany J Sci Food Agric 2009; 89: 2421–2427 www.soci.org c  2009 Society of Chemical Industry