Grain by-products and Saccharomyces cerevisiae application in paper packaging material: impact on physical–mechanical and barrier properties
Authors: Markevičiūtė Zita , Lyytikäinen Johanna , Leminen Ville , Varžinskas Visvaldas 
Published: April 2024

Renewable materials and material circularity are key priorities for the coming decades. While paper is the most utilized material in the packaging sector, its applications in food packaging are limited due to low barrier properties. Coating it with petroleum-based polymer barrier coatings renders it unrecyclable both mechanically and biologically. Bio-coated paper packaging, made from agricultural waste or by-products, presents environmentally favorable solutions that can benefit the biological cycle of the circular economy. The main objective of this study is to assess the applicability of grain and beer production by-products in wood pulp food packaging materials. It examines the effects of different grain by-products (industrial wheat grain processing residues and wheat bran) particles and concentrations (15 wt% and 40 wt%), as well as the impact of brewer’s yeast (Saccharomyces cerevisiae) at a concentration of 10 wt%, on the physical–mechanical and barrier properties of Northern bleached softwood kraft (NBSK) and chemithermomechanical (CTMP) pulps. Material composites were fabricated using a standard sheet forming method. Physical–mechanical properties were analyzed through tensile strength, strain at break, tear resistance, and bending stiffness tests. Barrier-related properties were analyzed through roughness, air permeance, and water contact angle tests. Results revealed that the vast majority of physical–mechanical properties decreased with the increase of both types of grain production fillers. Industrial wheat grain processing residues had a lower impact on physical–mechanical properties than wheat bran filler. A higher percentage of property decrease was absorbed in NBSK pulp than in CTMP. Roughness of CTMP can be improved by adding both industrial wheat grain processing residues and wheat bran. Wheat bran particles can increase hydrophobicity. CTMP pulp strength properties can be increased with the addition of yeast; however, the yeast additive’s effect on air permeance demonstrated a negative impact. In the case of NBSK pulp, which has higher primary strength properties, the addition of yeast does not make any significant changes. The conducted experiments demonstrated that, overall, the addition of these fillers resulted in a decline in physical–mechanical properties such as tensile strength, strain at break, tear resistance, and bending stiffness. This decline was more pronounced with higher concentrations of fillers. In the case of CTMP pulp, both types of fillers exhibited similar trends in affecting properties, whereas for NBSK pulp, wheat bran had a more significant impact compared to wheat grain processing residues. The addition of yeast generally led to a reduction in physical–mechanical properties, particularly in tensile strength and tear resistance. However, samples containing yeast displayed increased flexibility compared to controls. The influence on barrier properties varied: while yeast increased air permeability, it also enhanced surface hydrophobicity, thereby reducing the paper’s receptivity to liquids.