Optimisation and characterisation of protein extraction from coffee silverskin assisted by ultrasound or microwave techniques

Coffee silverskin (CSS) is a coffee by-product obtained during the coffee roasting process and a potential source of proteins (14–19% protein content). In this study, conventional extraction (CE) and novel extraction methods were investigated for protein extraction from CSS. Optimum extraction pH and concentration for conventional acid and alkali extraction were studied. In addition, ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE), which have been widely recognised as efficient and economic novel extraction techniques, were employed to enhance the protein extraction from CSS using alkaline and acid extraction. Among the extraction techniques studied, MAE was found to generate the highest yield of protein recovery, 43.53% of recovery with an average molecular weight of 6.64 kDa. Comparing with the conventional sequential extraction using NaOH followed by HCl at two different concentrations (0.2 M and 0.6 M), the recovery yields were significantly increased by 2.8-fold and 2.3-fold by applying UAE, and by 5.8-fold and 7-fold by applying MAE. The present work shows that UAE and MAE have potential to be rapid and effective tools for protein extraction from coffee silverskin. In this study, extracted proteins and raw material were characterised considering the molecular weight and the amino acid profile as well as its nutritional composition and its mineral contents.