Effects of germination on flavour and nutritional properties of Lupin

Abstract

Australian sweet lupin is an excellent protein and dietary fibre source, but is largely underutilised in the human diet. The barrier to greater consumption of lupin are oligosaccharides which cause bloating and flatulence and beany flavour which are not acceptable to the consumers. To overcome these limitations 72 h of germination was applied to lupin and the resultant germinated flours were tested for their nutritional and flavour properties. Soybean was also germinated and served as a control. Protein content of lupin and soybean was 37 %. Lupin seeds contained 5 % of starch, 1.3 % sugars, 15.6 % oligosaccharides, 16 % dietary fibre, 1 % soluble dietary fibre and 15 % insoluble dietary fibre. Soybean seeds had 3.5 % of starch, 3.6 % sugars, 15.8 % oligosaccharides, 7 % total dietary fibre, 0.1 % soluble dietary fibre and 7 % insoluble dietary fibre. Germination of lupin under both conditions significantly reduced oligosaccharides concentration to 0.6 % and 8.6 % under uncontrolled (room temp., 12 h of light and 12 h of darkness) and controlled (25°C, 93% relative humidity and 24 h of darkness) conditions, respectively. Total, soluble and insoluble dietary fibre, and starch content were not significantly (p≥0.05) affected by the germination of lupin under both conditions. Total sugars increased in germinated lupin under both conditions up to 3.8 %. Germination of soybean significantly reduced oligosaccharides to 4.8 % and 2.6 %, and starch to 2 % and 1.6 % under uncontrolled and controlled conditions, respectively. Total sugars reduced to 2.6 % in soybean germinated under controlled conditions. Total, soluble and insoluble dietary fibre were not significantly affected by the germination. The aroma profile of germinated lupin and soybean flours were characterised for the first time. Soybean had significantly higher concentrations of volatiles associated with beany flavour in legumes compared to lupin. Germination resulted in increased levels of many volatiles and sweet, woody, mushroom and baked aroma notes. Muffins incorporating germinated lupin and soybean flours had the highest concentrations of volatiles, followed by wheat muffins. Germination of lupin may be a successful strategy to increase acceptability and mask beany aroma of legumes.