Biopolymer Composites Filled with Brewer's Spent Grain for Yeast Immobilization

Biopolymer-based composites incorporating natural fillers were developed as carriers for various microbiological applications. Three commercially available biodegradable and bio-based polymers: poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and polylactide (PLA)were used as matrices. Brewer's spent grain (BSG), a by-product of the brewing industry, was employed as a natural filler. A series of biocomposites containing 20, 30, and 40 wt% BSG were fabricated. The structure and thermal properties of the composites were characterized using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Surface properties were evaluated by measuring contact angles with two probe liquids, enabling calculation of surface energy and its polar and dispersive components. In turn, microscopic studies were conducted to evaluate the adhesion and colonization of Metschnikowia andauensis cells on the prepared carriers. The biocontrol activity of the cell-carrier system was assessed using the agar plate method. The results identified the most promising formulations: PHBV with 40 wt% BSG and PLA with 20-40 wt% BSG, especially with 30 wt% BSG. However, the highest biocontrol efficacy among cells adhered to the biocomposite materials was observed with the last one. This study explored the relationship between the physicochemical properties of BSG-filled biopolymers and their suitability for microbial colonization, highlighting their potential as functional carriers for yeast cells.