Valorization of spent coffee grounds: A review

Spent coffee grounds (SCGs) arise as waste products through the production of instant coffee and coffee brewing. This work reviews the composition of SCGs, the methods used for the isolation of individual compounds present in SCGs, the ways of utilizing SCGs presented in the literature so far, including use of SCGs' bioactive compounds, carbohydrates, oil fraction, as well as SCGs as the whole composite without treatment or with some physical and chemical modifications. However, this work mainly focuses on biotechnological processing of SCG hydrolysates and the reason why the fermentable sugars present in SCG hydrolysates cannot support sufficiently the growth of bacteria or yeasts. The reason is basically the presence of toxic co-contaminants, which have antibacterial properties. One suggestion for how to lower the presence of such co-contaminants in SCG hydrolysates is pre-extraction of them or the inclusion of a detoxification step. This review suggests that the fractionation of SCGs and detoxification of SCG hydrolysates might contribute to increased multiple utilization of this waste in many industrial sectors.