Efficiency Improvement and SEM Visualization of Enzymatic Hydrolysis-Based Valorization of Oat Hulls

The utilization of agro-industrial waste in the bioeconomy is crucial for reducing the environmental impact. This study investigated the valorization of a common oat processing waste—oat hulls—using enzyme preparations of different origin and enzyme cocktails based on them. Oat hulls were used in native form and after chemical pretreatment. The following three enzyme preparations were used for enzymatic hydrolysis: Agrocell Plus, CelloLux-A, and Ultraflo Max. An enzyme cocktail consisting of the three enzyme preparations was found to provide a conversion degree of 45% for native oat hulls with simultaneous hydrolysis of cellulose and hemicelluloses, with glucose accounting for only 41% of the total reducing sugars. Enzymatic hydrolysis of the chemically pretreated product confirmed the effectiveness of using enzyme cocktails: the yield of reducing sugars increased 1.4–1.8 times compared to the individual enzymes. The use of the enzyme cocktail consisting of the three enzyme preparations provided a 99% conversion of the accessible fraction of the substrate. Visualization by scanning electron microscopy (SEM) of the hydrolysis of native oat hulls revealed the disappearance of substrate surface irregularities, while in the case of the chemically pretreated product, the substrate disintegration was observed. The comparison of the SEM results of the two substrates before and after hydrolysis confirms the effectiveness of the enzyme cocktails. The contribution of glucose to the total concentration of reducing sugars in the hydrolyzates obtained from the chemically pretreated oat hulls was 85–91%, which allows for predicting the successful application of these hydrolyzates as nutrient media for the biosynthesis of value-added products.