Optimisation of organosolv pretreatment for the extraction of polyphenols from spent coffee waste and subsequent recovery of fermentable sugars

In the present study, organosolv pretreatment strategy was modified for the comprehensive utilisation of spent coffee waste (SCW) for polyphenol extraction and reducing sugar production. A response surface design involving four factors viz. ethanol concentration, temperature, time and H₂SO₄ concentration was created for optimisation of polyphenol extraction from SCW. 11.2 mg GAE of polyphenol content/g of SCW was obtained using ethanol (68% v/v) at 51 °C for 45 min in the presence of 1.5% H₂SO₄ as catalyst. Furthermore, 13.78 of QE of Total Flavonoid Content/g of SCW was obtained following this process which was 7.6-fold higher than control (1.81 QE/g of SCW). Lignin removal of 24.4% was achieved following modified organosolv protocol. Enzymatic hydrolysis of pretreated SCW yielded 29.05 mg/g of total reducing sugar, which was 1.27-fold higher than control (22.8 mg/g). XRD, FTIR, and DSC profiles of the pretreated substrates were analysed for various changes incurred in pretreated SCW.