Valorization of hazelnut husk as a carbon source for l-DOPA production with Corynebacterium glutamicum

Abstract

Lignocellulosics are abundant carbon sources in nature, therefore they gain increasing attention in biotechnology for production of value-added chemicals. In this proof-of-concept study highlighting the techno-economic potential of l-3,4-dihydroxyphenylalanine (l-DOPA) production from lignocellulosic agro-waste hazelnut husk, first an exploratory model-based optimization was used to release the sugar content of the husk whilst maximizing sugar concentration. The sugar hydrolysate was then evaluated as a feedstock for production using an engineered Corynebacterium glutamicum strain. Optimal treatment conditions were found by Kriging model as 12.5% husk load with 3.8% acid for 50 min at 121 °C, which gave a hydrolysate of 27.67 g L−1 reducing sugar with a yield of 11.07 g sugar/100 g husk. When this hydrolysate was used as the sole carbon source during fermentative production, 20 ± 0.4 mg L−1 of l-DOPA was produced. When cells grown on husk hydrolysate were used for whole-cell biotransformation, a titer of 82 ± 1 mg L−1 of l-DOPA was obtained. From an economical point of view, the titer obtained during fermentative production would allow production of l-DOPA from hazelnut husk right around the breakeven point. However, further engineering of the strains and optimization of bioprocess conditions, would make it possible to bring the revenues to higher levels.