Rapid growth in the volume and variety of agro-industrial wastes along with the increasing demand for energy, chemicals and materials have fostered global research efforts to develop technologies with low environmental impact based on sustainable and cost-effective raw materials. One attractive concept is the conversion of these wastes into value-added products using biorefinery processes. In this work, the valorisation of two major by-products from the primary processing of peanuts is examined.
A submerged fermentation process was developed to utilise peanut meal as a substrate for biosynthesis of the natural antifungal compound natamycin by Streptomyces chattanoogensis. By optimising the process, the natamycin concentration was increased 25-fold (650 mg L-1). The natamycin produced was capable of inhibiting the growth of known plant pathogens (e.g. Aspergillus niger) at concentrations as low as 100 mg L-1.
The second target molecule, lignin, was extracted from peanut shells and used to replace maleic anhydride in the wood-polymer composite matrix of acrylonitrile butadiene styrene (ABS) and wood flour. This substitution improved the interfacial bonding between the wood flour and ABS in the matrix and consequently increased the density and reduced the water absorption and swelling of the composite. After 2000 h of accelerated UV-weathering, specimens containing lignin did not exhibit either yellowness or significant differences in tensile strength. Such results indicate that the use of lignin as a coupling agent minimises damage associated with exposure to UV radiation, due to the chemical structure of the lignin and decreased porosity and water penetration.
These results demonstrate two novel applications of otherwise under-utilised peanut by-products. Further, these approaches could be potentially applied to other agro-industrial wastes.