Impact of kilning on the fermentability of oat wholemeal flour and related bioconversion of starch, protein, dietary fibre and phytate

Considering the beneficial nutritional profile of whole oats and the potential health-enhancing effect of fermentation, oat fermentation offers significant potential for developing nutritious foods. However, fermenting oat wholemeal flour proves challenging. We hypothesise this to be related to the kilning step typically applied to oat groats, causing complete enzyme inactivation, thereby impeding necessary constituents' bioconversions during fermentation, and associated microbial growth and acidification. As such, use of non-kilned oat wholemeal flour is expected to result in a more rapid acidification and faster microbial growth, which might lead to a more pronounced effect on its constituent physicochemical properties. To investigate this, kilned and non-kilned oat wholemeal flour suspensions were fermented using a strain of Lactiplantibacillus plantarum as a starter culture. The ferments were characterised microbiologically, i.e., microbial growth and starter culture prevalence and biochemically, i.e., acidification, metabolite content, soluble fibre content, soluble protein content, phytate reduction, over time. Non-kilned oat wholemeal flour suspensions were acidified much faster than kilned oat wholemeal flour suspensions, which was related to faster microbial growth, faster fermentable saccharide consumption and higher lactic acid production. In addition, fermentation of non-kilned oat wholemeal flour suspensions resulted in increased arabinoxylan, ß-glucan and protein extractability and reduced phytate content, whereas these effects were very limited in kilned oat wholemeal flour. These results highlight the importance of having an intact oat endogenous enzyme system to provide nutrients for the fermenting microorganisms and to achieve desired changes of the matrix during fermentation.