Improving protein extractability from oats using malted cereal extracts under acidic fermentation-like conditions

Liquid oat-based food products typically contain low protein levels due to poor oat protein extractability. Lactic acid food fermentation and associated endogenous oat enzymatic activity have previously been shown not to significantly improve oat protein extractability. Therefore, this study investigates the potential of oat malt extract (OME) and wheat malt extract (WME) addition, as a source of cereal-derived enzymes, to increase protein extractability during oat incubation at fermentation-relevant pH as well as during fermentation. Kilned and non-kilned oat whole meal suspensions were incubated for 24 h at pH 4.0 with added WME or OME and the effects on protein extractability, degree of hydrolysis and molecular weight (MW) distribution were evaluated. OME and WME additions increased protein hydrolysis and extractability, most notably in non-kilned oat, reaching protein extractabilities up to 74.5% after 24 h incubation with 10.0% WME, being triple those of samples incubated without OME/WME. Notably, under specific conditions, significant amounts of 4-85 kDa proteins, including species with MWs consistent with those of intact 12S globulins subunits, were rendered extractable. Comparable results were obtained when oat suspensions were fermented for 24 h with a commercial L. plantarum strain in the presence of WME/OME. Interestingly, in addition to expected proteolytic action, other malt-derived enzymatic as well as non-enzymatic effects were found to contribute to increasing the oat globulin extractability. Further examination suggested that, for the most part, the effect of WME/OME could not be attributed to disulfide bond reduction, altered protein-phytate interactions or removal of structural barriers. Overall, the addition of WME/OME to oat-based fermentation processes enhances protein extractability, which may improve the nutritional and functional characteristics of fermented liquid oat-based foods.