Effects of fermentations using Aspergillus spp. towards extraction yield and bioactivity of coffee pulp extract

Coffee pulp contains a considerable number of phenolic compounds such as chlorogenic acid and ferulic acid that can be extracted with the help of biological agents to produce bioactive phenolic compounds. This study investigated the impact of solid-state fermentation of coffee pulp using Aspergillus spp. The research focused on evaluating the effects of fermentation on the yield of coffee pulp extract, as well as its total phenolic content, antioxidant activity, and anti-inflammatory activity. Fermentation was carried out at room temperature (\(27^\circ{\rm C}\)) for 7 d using Aspergillus niger, Aspergillus oryzae, and mixed cultures of A. niger and A. oryzae to enhance the yield and bioactivities of the coffee pulp extract. Biomass dry weight and substrate consumption were monitored daily, followed by extraction of the fermented coffee pulp. The yield, total phenolic content, antioxidant activity, and anti-inflammatory activity of the extract were also determined. The growth of A. niger cultures was found to be optimum on the 5th day of fermentation while A. oryzae and mixed cultures were optimal on the 4th day of fermentation. Fermentation of coffee pulp with Aspergillus spp. effectively increased the extract yield (6.2–8.8%) and total phenolic content (59.9–64.4 mg GAE g^-1) up to 83% and 111% as compared to the control (unfermented coffee pulp). The fermentation also enhanced the antioxidant and anti-inflammatory activity of the coffee pulp extract with the \({\text{IC}}_{50}\) (half of the maximal inhibitory concentration) decreased up to 69% and 51%, respectively. Statistically, the total phenolic content in the extract had a significant negative effect on the IC₅₀ values of the antioxidant activity and anti-inflammatory activity of the fermented samples. This indicates that the higher the total phenolic content, the stronger the antioxidant activity and anti-inflammatory activity of the extract. The findings suggest that the coffee pulp can be utilized as an alternative source of phenolic compounds with good bioactivity.