Reduction of non-digestible oligosaccharides in soymilk: application of engineered lactic acid bacteria that produce alpha-galactosidase.

Human consumption of soy-derived products has been limited by the presence of non-digestible oligosaccharides (NDO), such as the alpha-galactooligosaccharides raffinose and stachyose. Most mammals, including man, lack pancreatic alpha-galactosidase (alpha-Gal), which is necessary for the hydrolysis of these sugars. However, such NDO can be fermented by gas-producing microorganisms present in the cecum and large intestine, which in turn can induce flatulence and other gastrointestinal disorders in sensitive individuals. The use of microorganisms expressing alpha-Gal is a promising solution to the elimination of NDO before they reach the large intestine. In the present study, lactic acid bacteria engineered to degrade NDO have been constructed and are being used as a tool to evaluate this solution. The alpha-Gal structural genes from Lactobacillus plantarum ATCC8014 (previously characterized in our laboratory) and from guar have been cloned and expressed in Lactococcus lactis. The gene products were directed to different bacterial compartments to optimize their possible applications. The alpha-Gal-producing strains are being evaluated for their efficiency in degrading raffinose and stachyose: i) in soymilk fermentation when used as starters and ii) in situ in the upper gastrointestinal tract when administered to animals orally, as probiotic preparations. The expected outcomes and possible complications of this project are discussed.