Aqueous ammonia soaking pretreatment of spent coffee grounds for enhanced enzymatic hydrolysis: A bacterial cellulose production application

In the present work, aqueous ammonia soaking (AAS) was examined as a potential pretreatment stage of spent coffee grounds (SCG), to enhance their enzymatic hydrolysis. The studied parameters were treatment time (30-360 min), SCG solids loading (5-20% w/v), and temperature (40-80 degrees C). Each parameter was studied individually while keeping the other parameters constant. Following the AAS, the pretreated SCG were subjected to enzymatic hydrolysis using commercial preparations of cellulases and hemicellulases. The obtained hydrolysate was subsequently used as an alternative carbon source for the production of bacterial cellulose. Fourier-transform infrared spectroscopy (FT-IR), Confocal Laser Scanning Microscopy (CLSM), and Scanning Electron Microscopy (SEM) of the samples before and after pretreatment were performed in order to evaluate compositional and morphological changes of the biomass materials. Reducing sugars obtained from the ammonia-pretreated and saccharified samples were measured by HPLC. Optimization for total sugars present in the enzymatic hydrolysate was achieved at 120 min, 10% w/v solids concentration, 60 degrees C with the use of similar to 28-30% v/v aqueous ammonia, where 8.34 +/- 1.31 mg(sugars)/mL(hydrolysate) were obtained. The SCG hydrolysate was used as the sole carbon source for the growth of a Komagataeibacter sucrofermentans strain, and 2.04 +/- 0.04 g/L of bacterial cellulose was therefrom produced.