As most of us know, coffee is definitely among the most consumed commodity around the world and many people are drawn to it thanks to its peculiar flavour and taste which may range between woody and/or caramelised.

75% of the coffee that is produced around the worlds consist in Arabica (Coffea Arabica) while for its 25% it consists of Robusta (Coffea Canephora) (Mussatto et al., 2011).

The manufacturing of coffee –from fruit to roasted and/or grounded bean- may lead to the production of by-products which can be recapped into three major ones:

• Coffee pulp and husk

Pulp and husk are respectively a product derived from the wet or dried process of removal of external components. Both pulp and husk are rich in carbohydrates, proteins and minerals but they are also a source of tannins, chlorogenic acid and caffeine (Fan et al., 2003).

• Coffee Silver Skin

Coffee Silver Skin counts for 1% to 2% of the fruit, it is the internal integument of the coffee bean and is normally produced during the roasting process. The coffee silver skin is rich in dietary fibres and phenolic compounds (Murthy and Naidu, 2012).

• Spent Coffee Ground

This type of coffee by-product is the final one that is produced in the coffee industry and is commonly used to obtain instant coffee.

The roasted coffee beans are then used to produce coffee via extraction and is the final step for the manufacturing of a finished product.

Nowadays, given sustainability issues and the urge to use waste products coming from food processing in a novel and smart way, our understanding of the use of by-products of coffee for other purposes has advanced.

So, what can coffee by-products be also used for?

1 – Mushrooms

Coffee by products can be used as potential substrate for mushrooms cultivation and this has been happening already for three decades. Since coffee pulp and husk are powerful sources of organic compounds, they have been used in blends with coffee leaves and coffee cherry waste in order to produce an effective substrate for mushrooms cultivation. An alternative use of coffee by-products is also as compost to produce fertiliser for soils (Martinez-Carrera et al., 2000).

2- Enzymes

Recent research from Buntic and co-workers (2016) showed the potential of coffee grounds as a substrate for the production of cellulose –an enzyme that catalyses the hydrolysis of cellulose – by Paenicillium chitinolyticus. Other evidence showed feasibility and extraction of other enzymes like pectinase, tannase and xylanase, among the many others (Battesin and Macedo, 2007; Murthy and Naidu, 2012; Ngo and Phan, 2016). Such enzymes are normally used for food applications in order to improve textural characteristics or influence aroma and flavour (Kuhad et al., 2011).

3 – Biofuels:

The potential for production from coffee by-products has been investigated and positive results have been obtained with yields of ethanol ranging between 50 and 78% (Gouvea et al., 2009; Woldesenbet et al., 2016).

4- Dietary Fibre:

It is no secret that dietrary fibres can contribute to gastrointestinal health and cause many beneficial effects to human health in general. Coffee ground and coffee silver skin are characterised by their high percentage in dietary fibre (60 to 54 % w/w) (Ballesteros et al., 2014) and can be used in food formulation for the development of functional foods.

It looks like we will talk about coffee by-products for a while in the coming years.

References:

Kuhad R. C., Gupta R., Sing A. (2011). Microbial Cellulase and their industrial applications. Enzyme Research. 1, 1-10.

Janissen B., Huyunh T. (2018). Chemical composition and value-adding applications of coffee industry by-products: a review. Resources, Conservation and Recycling. 128, 110 -117.

Mussatto S. I., Carneiro L.M., Silva J.P.A., Roberto I.C., Teixeira J.A. (2011). A study on chemical constituents and sugars extraction from spent coffee grounds. Carbohydrate Polymers. 83 (2), 368 – 374.

Fan L., Soccol A.T., Pandey A., Soccol C.R. (2003). Cultivation of Pletorus mushrooms on Brazilian coffee husk and effect of caffeine and tannic acid. Micologia Aplicada Internacional. 15 (1), 15 – 21.

Murthy P.S, Naidu M.M. (2012). Production and application of xylanase from penicillium ssp. Utilizing coffee by-products. Food Bioprocess Technology. 5 (2), 657 – 664.

Martinez-Carrera D., Aguilar A., Martinez W., Bonilla M., Morales P., Sobal M. (2000). Commercial production and marketing of edible mushrooms cultivated on coffee pulp in Mexico. Coffee Biotechnology and Quality. Springer. Pp. 471 – 488.

Buntić A.V., Pavlović M.D., Antonović D.G., Şiler-Marinović S.S., Dimitrijević-Branković S.I. (2016). Utilization of spent coffee grounds for isolation and stabilization of Paenibacillus chitinolyticus CKS1 cellulase by immobilization. Heliyon 2 (8), e00146.

Battestin V., Macedo G.A. (2007). Tannase production by Paecilomyces variotii. Bioresources Technology. 98 (9), 1832 – 1837.

Ngo N. T.T., Phan H.T. (2016). Screening of fungal strains grown in solid-state culture for production of pectinase from coffee husk. International journal on advanced science. Engl. Ing. Technol. 6 (3), 273.

Gouvea B., Torres C., Franca A., Oliveira L., Oliveira E. (2009). Feasibility of ethanol production from coffee husk. Biotechnol. Lett. 31 (9), 1315 – 1319.

Ballesteros L., Teixeira J., Mussatto S. (2014). Chemical, functional and structural properties of spent coffee grounds and coffee silversking. Food Bioprocess Technol. 7 (12), 3493 – 3503.