Coffee silverskin as a substrate for biobased production of biomass and hydrogen by Escherichia coli

Abstract

Currently, coffee consumption reached 9.92 million tons, being responsible for the generation of huge amounts of waste associated with coffee bean processing steps and further operations. Coffee silverskin (CS) and spent coffee grounds having high organic content are generated as a result of roasting and brewing processes. Escherichia coli wild-type and septuple mutant (ΔhyaB ΔhybC ΔhycA ΔfdoG ΔldhA ΔfrdC ΔaceE) growth and hydrogen production were investigated in mediums containing 20 to 200 g L−1 CS with dilutions, hydrolyzed for 25 or 45 min. During utilization of CS, hydrolysate phenolic and flavonoid content does affect bacterial growth, moreover, shorter hydrolyzing was more optimal for biomass generation. Highest specific growth rate of 0.64 ± 0.02 h−1 was observed in wild-type cells when 5 times diluted 200 g L−1 CS was applied to yield 0.495 ± 0.015 g L−1 biomass. Prolonged hydrogen (H2) production determined as an oxidation reduction potential drop was observed during utilization of 20% CS containing twice diluted medium started from 3 h until 72 h. Highest H2 yield was observed in the twice diluted medium after 24 h growth containing 65 g L−1 CS. Particularly it was 1.66 mL (g CS)−1 and 2.15 mL (g CS)−1 in wild-type and septuple mutant, respectively. It can be concluded that CS also can be considered as perspective, cost-effective efficient carbon source for the development of biomass and bio-H2 production technologies.