Oat Hulls: Under-Utilized Biomass for Fermentative Generation of Value-Added Products

Oat (Avena sativa L.) is generally considered a healthy and nutritious cereal and has gained further interest due to the generation of oat milk as an alternative nutritious beverage. However, during oat milling, about 20–30% hulls are produced. These are of low value, with small amounts used as feed or for combustion or are simply discarded. One of the downsides to consuming oat hulls is their abrasiveness because of high silica content but otherwise present a significant opportunity for biotransformation into value-added products derived from the milling industry in a context of upcycling. This review addresses some of the physico-chemical properties of oat hulls and discusses fermentative systems such as solid-state (SSF), semi-solid state (Semi-SSF) and submerged (SmF) fermentation to break down and texturize oat hulls into valuable products which can be used as food, feed or pet food. We also discuss the three fermentation systems (SSF, Semi-SSF and SmF) and their potential for oat hull valorization. With increasing interest in mycoproteins, we also discuss edible fungi as the ideal microorganisms capable not only of degrading oat hulls and increasing nutrient bioavailability but also of contributing microbial protein.