In fungal fermentation for producing alcohol, vinegar, soy sauce, or miso, waste is generated after the process, such as liquor meal or distillers' grains. Some researchers have used beer spent grain (BSG) to extract proteins, modified their properties, and tested their potential as wood adhesives. Using six fungal strains, and protein gels were produced through processes such as centrifugation, alkali hydrolysis, acid neutralization, and centrifugal concentration. The best results in the small-scale adhesive tests were those of the protein extracted from red yeast (Monascus purpureus) and koji rice bacteria (Aspergillus oryzae). Using the compressive load and tension load methods specified in the ASTM (American Society for Testing and Materials) as reference, the adhesive properties of the wood panels were tested by the Taiwan Testing and Certification Center (ETC).
1. The results of the compressive load method (ASTM D905) showed that the shear strength of red yeast protein gel is 156.1 kgf, while the koji rice protein gel is 51.3 kgf, which are 82.2% and 27.0% of the control group, respectively.
2. The results of the tension load method (ASTM D2339) revealed that the shear strength of red yeast protein gel is 88.1 kgf, while the koji rice protein gel is 40.2 kgf, which are 195.1% and 89.0% of the control group, respectively.
The experimental results indicate that the shear strength of the red yeast protein gel is similar to those of the control group (NanPao Resin White Glue adhesive). In the compressive load method (ASTM D905), the shear strength in the tension load method (ASTM D2339) is significantly better than those of the control group (common glue). This suggests that red yeast protein gel provides a natural and non-toxic alternative choice for wood adhesive applications.