Effect of Germination and Fermentation on Carbohydrate Composition of Australian Sweet Lupin and Soybean Seeds and Flours

This study investigated the effect of germination and fermentation on the composition of carbohydrates in Australian sweet lupin. Specifically, the amount of sugars (sucrose, fructose, and glucose), starch, oligosaccharides (verbascose, stachyose, and raffinose), and dietary fiber were measured in germinated lupin seeds and fermented lupin flour, and compared with those in soy. High performance liquid chromatography coupled with refractive index was employed for quantitation of sugars, starch, and oligosaccharides, and gas chromatography coupled with a flame ionization detector was used for quantitation of simple sugars in total, and soluble, and insoluble dietary fiber. The enzyme activities of α-amylase and α-glucosidase were compared before and after germination or fermentation. The α-amylase activity in germinated lupin increased to ∼17 nmol/mL/min/0.1 g and in germinated soy∼32; in fermented lupin, the activity increased to ∼52, while in fermented soy it decreased to ∼20. In general, germination or fermentation decreased the oligosaccharide content, and increased the total sugar in samples (p < 0.05). Total oligosaccharides in lupin after uncontrolled germination were reduced by 98% to 6 mg/g, and after controlled germination reduced by 44% to 86 mg/g. Fermentation with yogurt culture lowered the content of total oligosaccharides due to 94% decrease in stachyose. Total oligosaccharides in soy flour prior to fermentation were 180 mg/g and significantly decreased to ∼124 mg/g in fermented soy. Germination did not affect the starch content. There was no significant change in the amounts of total, soluble, and insoluble dietary fiber after germination or fermentation of lupin except for galactose, which was significantly reduced in germinated lupin seeds. Soluble dietary fiber in germinated soy significantly increased. Germination and fermentation are simple and effective techniques to reduce the oligosaccharides while maintaining the composition of dietary fibers.