Pretreatment and enzymatic hydrolysis of coffee husk for the production of potentially fermentable sugars

BACKGROUND Coffee husk (CH) is the main agricultural solid waste generated during the coffee bean dry processing. Therefore, it is necessary to investigate other alternatives for the more noble use of this by-product, adding value to it considering the circular economy concept within the coffee production chain. This study aimed to add value to CH by liquid hot water (LHW) pretreatment as an alternative to improve the enzymatic conversion of polysaccharides of this substrate to fermentable sugars through enzymatic hydrolysis. RESULTS Box-Behnken experimental design was used to evaluate the effect of LHW pretreatment on the enzymatic hydrolysis yield (EHY), investigating the independent variables time (t), temperature (T), and liquid-to-solid ratio (LSR). The desirable condition (200 degrees C, 41 min, LSR of 5 mL g(-1)) was selected as the most suitable for the enzymatic hydrolysis, reaching an EHY value of 75.3% with an enzyme load of 40 FPU g PCH-1. The alkaline extraction step applied to pretreated coffee husk (PCH) was not effective to improve the EHY, as the cellulose fraction was not preserved. Two reloads of solids were considered an ideal condition, reaching an EHY value of 69.1% after 24 h of hydrolysis with a total enzyme load of 27 FPU g PCH-1. CONCLUSION The liquid hot water of CHs associated with the reload of solids on enzymatic hydrolysis is an interesting alternative to reduce the cost with enzyme cocktail and hydrolysis time, thus making the process more feasible for technology upscaling. (c) 2021 Society of Chemical Industry (SCI).