Spent Coffee Grounds (SCG) Contain Large Mexico (Tel.: D52 55 1921304; E-Mail: Chio Cve@ Amounts of Organic Compounds (I.E

Trends in Food Science & Technology 45 (2015) 24e36

Review Spent coffee

commodity after petroleum (Murthy & Naidu, 2012a). grounds: A review on Global green coffee production increased by almost 17%, probably due to increased yield (24%), between 2000 and 2012. Several residues are obtained during coffee process- current research and ing. Coffee producing countries generate residues from the coffee fruit amounting to >50% of the fruit mass (Tsai, future prospects Liu, & Hsieh, 2012). Spent coffee ground (SCG) is the residue obtained during the brewing process (Cruz et al., a, 2012). The huge amount of residue generated annually in Rocio Campos-Vega *, the production of soluble coffee requires waste manage- ~ a ment plan consistent with existing national regulations. Guadalupe Loarca-Pina , c For example, Nestle, the world’s biggest food company Hayde A. Vergara-Castaneda~ pledges to reduce waste in Europe by 2020 using spent cof- b,1 fee grounds as a source of renewable energy in more than and B. Dave Oomah 20 Nescafe factories. In most of the soluble coffee produc- aPrograma en Alimentos del Centro de la Republica ing industries, the waste is collected by specialized (PROPAC), Research and Graduate Studies in agencies, which sell the residues for different purposes Food Science, School of Chemistry, Universidad (i.e. composting, gardening, bioenergy production, mush- Autonoma de Queretaro, Queretaro, Qro 76010, room growth). Spent coffee grounds (SCG) contain large Mexico (Tel.: D52 55 1921304; e-mail: chio_cve@ amounts of organic compounds (i.e. fatty acids, lignin, cel- yahoo.com.mx) lulose, hemicellulose, and other polysaccharides) that can be exploited as a source of value-added products. Thus, cof- bNational Bioproducts and Bioprocesses Program, fee residue has been investigated for biodiesel production Pacific Agri-Food Research Centre, Agriculture and (Caetano, Silva, & Mata, 2012), as source of sugars Agri-Food Canada, Summerland V0H 1Z0, BC, Canada (Mussatto, Carneiro, Silva, Roberto, & Teixeira, 2011), pre- c Nucitec, S.A. de C.V., Comerciantes 15-3, Colonia cursor for activated carbon production (Kante, Nieto- ~ Penuelas, Queretaro, Mexico Delgado, Rangel-Mendez, & Bandosz, 2012), compost (Preethu, BhanuPrakash, Srinivasamurthy, & Vasanthi, Spent coffee ground (SCG) contains large amounts of organic 2007), and as sorbent for metal ions removal (Fiol, compounds (i.e. fatty acids, amino acids, polyphenols, minerals Escudero, & Villaescusa, 2008). and polysaccharides) that justify its valorization. Earlier innova- By-products of coffee fruit (Fig. 1) and bean processing tion explored the extraction of specific components such as oil, can also be considered as potential functional ingredients flavor, terpenes, and alcohols as value-added products. Howev- for the food industry. The coffee husks, peel and pulp, er, by-products of coffee fruit and bean processing can also be comprising nearly 45% of the cherry, are the main by- considered as potential functional ingredients for the food in- products of coffee agro-industry and can be a valuable ma- dustry. There is an urgent need for practical and innovative terial for several purposes, including caffeine and polyphe- ideas to use this low cost SCG and exploit its full potential nols extraction. Coffee husks and skins are traded as crops increasing the overall sustainability of the coffee agro-industry. and livestock products with export and import range of 857e27,209 and 490e11,474 tonnes from 2000 to 2012 according to FAO Statistics. These export and import were Introduction valued at 2.2e62.7 and 1.7e24.3 million US$, respectively Coffee, grown in about 80 countries, is one of the world’s for the same period. Other by-products of coffee processing most popular beverage and second largest traded such as mucilage and parchment have been less studied; however, they are potential sources of important ingredi- * Corresponding author. ents. The pulp is easily fermented by yeast or metabolized 1 Retired. by lactic acid bacteria producing alcoholic beverages and http://dx.doi.org/10.1016/j.tifs.2015.04.012 0924-2244/Ó 2015 Elsevier Ltd. All rights reserved. R. Campos-Vega et al. / Trends in Food Science & Technology 45 (2015) 24e36 25

components in developing a bioreﬁnery platform to add Abbreviations value to this inexpensive waste product.

SCG Spent coffee grounds Carbohydrates MOS Mannooligosaccharides The coffee bean is a rich source of polysaccharides AAA Aromatic amino acids (w50% of the green bean’s dry weight) mainly consisting MAE Microwave assisted extraction of mannans or galactomannans, type II arabinogalactans, FOSHU Food for Specified Health Uses and cellulose. Mannan, the main polysaccharide of coffee DF Dietary fiber extract, is responsible for its high viscosity, which in turn AACC American Association of Cereal Chemists negatively affects the technological processes involved in BCAA Branched chain amino acids instant coffee production. This polysaccharide consists of SFE Supercritical fluid extraction b-(1 / 4)-linked mannan chains substituted at approxi- HMW High molecular weight mately every 100 residues in the O-6 position with single HMWM High molecular weight melanoidins galactose residues. Arabinogalactans have an arabinose/ COM Cost of manufacturing galactose ratio of 0.4/1 and consist of b-(1 / 3)-linked scCO2 Supercritical carbon dioxide galactose backbone substituted at the O-6 position with CGA Chlorogenic acid arabinose and/or galactose residues. The side-chains CQA Caffeoylquinic acids contain arabinose and galactose residues with arabinose GAE Gallic acid equivalents as terminal residue. These linkages are characteristic of PHB Poly 3-hydroxybutyrate type-II arabinogalactans, a polymer usually covalently linked to protein (Bradbury & Halliday, 1990). The roasting process increases both bean arabinogalactan and mannan vinegars. Furthermore, roasted coffee silver skin has been solubility by loosening the cell-wall structure as it swells evaluated for use as a dietary fiber rich ingredient with anti- and by polysaccharide depolymerization (Wei et al., oxidant properties. Finally, SCG have been studied mainly 2012). The water-soluble polysaccharides that appear after for their antioxidant activities (Esquivel & Jimenez, 2012). roasting play an important role in retaining volatile sub- These antioxidants have been associated with health bene- stances, and contribute to the coffee brew viscosity and, fits (Campos-Vega, Oomah, Loarca-Pina,~ & Vergara- thus, to the creamy sensation known as “body” in the mouth Castaneda,~ 2013; Campos-Vega et al., 2009; Vergara-Casta- (Illy, Viana, & Roasting, 1995). neda,~ Oomah, & Campos-Vega, 2013). These galactomannans and arabinogalactans are ex- Spent coffee ground was rarely investigated until the tracted upon coffee roasting, during the beverage prepara- beginning of this decade with half (36 out of 72) of the total tion, using hot pressurized water (Nunes & Coimbra, number of papers published in the last 4 years since 1973. 2010). However, most of these polysaccharides remain as A cursory search of ‘spent coffee ground’ on “Scopus” pro- insoluble material bound to the SCG matrix (Mussatto, duces similar result with 11, 27, 14, 15 and 2 publications Carneiro, et al., 2011; Simoes,~ Nunes, Domingues, & annually from 2014 to 2010. This review aims to use exist- Coimbra, 2013). Galactomannans exhibit different physico- ing knowledge on spent coffee ground and/or its chemical properties and are therefore used in many applications: they are excellent stiffeners and emulsion stabilizers, and the absence of toxicity allows their use in the textile, The Coffee Cherry (Fruit) pharmaceutical, biomedical, cosmetics and food industries. The main applications of galactomannans in food are in Skin dairy products, fruit-based water gels, powdered products, Beann Pulp bakery, dietary products, coffee whiteners, baby milk for- mulations, seasonings, sauces and soups, tinned meats 5-10 % and frozen and cured meat foods (Prajapati et al., 2013). Mucilage Spent coffee ground is rich in sugars polymerized into 45-50 % Parchment 90 % cellulose and hemicellulose structures, which correspond (Hull) total waste 45-50 % to almost half (45.3%, w/w, dry weight) of the material. Spent coffee ground SCG contains 46.8% mannose, 30.4% galactose, 19% Silverskin glucose, and 3.8% arabinose, with mannans as the major polysaccharides (Mussatto, Carneiro, et al., 2011). Howev- er, further investigation by the same group (Mussatto, Machado, Carneiro, & Teixeira, 2012) revealed a lower (2.2-fold) sugar composition for the same SCG consisting Fig. 1. The coffee cherry fruit wastes (With information of: Murthy & of 21.2% mannose, 13.8% galactose, 8.6% glucose, and Naidu, 2012a; Esquivel & Jimenez, 2012). 1.7% arabinose. This SCG can be hydrolyzed 26 R. Campos-Vega et al. / Trends in Food Science & Technology 45 (2015) 24e36

(100 mg H2SO4/g dry matter; liquid/solid ratio 10 g/g; SCG are primarily composed of neutral detergent fiber 163 C, 45 min), and efficiently (>85%) fermented to (45.2%) occurring as hemicellulose, cellulose, and lignin- ethanol by yeast (Mussatto et al., 2012). Simoes~ et al., associated compound, and acid detergent fiber (29.8%), (2009) reported the presence of mannose (57%), followed consisting of cellulose and lignin (Vardon et al., 2013). by galactose (26%), glucose (11%), and arabinose (6%); The isolation of dietary fiber (DF) from plant by-products the differences in chemical composition of SCG probably can be accompanied by the recovery of other constituents reflect the variety of beans and processes used in roasting like antioxidants or proteins; SCG, for example contains and extraction. Earlier study (Stahl, Bayha, & Fulger, 43% total fiber (35% and 8% soluble and insoluble, respec- 1984) showed that mannan, more prevalent than cellulose tively) (Murthy & Naidu, 2012b). Furthermore, the coffee in SCG, is substantially separately from cellulose enabling fibers from SCG exhibit antioxidant properties: 2.4 mmol production of pure mannan hydrolysate. This hydrolysate of trolox/100 g of dry weight (Murthy & Naidu, 2012b) produces high (40%) mannitol yield with sorbitol as a co- similar to well-known food antioxidant such as red wine product. products (43%) and peaches (36%). Therefore, DF from Mannooligosaccharides (MOS), non-digestible oligo- SCG can be categorized as antioxidant dietary fiber, useful saccharides composed principally of mannose, has also as potential dietary supplement. been derived by hydrolyzing mannan in spent coffee grounds at high temperature (220 C) and pressure Proteins (Asano et al., 2001). The major components of manno- SCG contain significant amount of proteins (13.6%, w/ oligosaccharides were mannobiose, mannotriose, and man- w). Total coffee nitrogen compounds are relatively stable notetraose. Studies in Japan (Takao et al., 2006 and refer- between species or even during roasting, ranging from 8.5 ences therein) showed that MOS could promote to 13.6% (Belitz, Grosch, & Schieberte, 2004). Crude pro- bifidobacteria growth in the intestines and improve the tein reported by Cruz et al., (2012) in espresso coffee res- fecal characteristic on human subjects. Furthermore, a idues vary between 12.8 and 16.9%. The mean protein daily intake of a 300 ml drink containing MOS (1 or content of SCG is 13.6% after soluble coffee preparation 2 g/100 ml) reduced abdominal and subcutaneous fat level (Mussatto, Ballesteros, et al., 2011; Silva, Nebra, in humans when administered daily for twelve weeks. Machado Silva, & Sanchez, 1998). Further studies showed that MOS inhibited intestinal fat According to Arya and Rao (2007), roasted coffee con- absorption from a high fat diet by decreasing fat accumu- tains on average 3.1% (w/w) protein. The protein content in lation in the parametrial adipose tissue and liver, while SCG is higher than in the coffee bean due to concentration simultaneously increasing fat excretion. MOS derived of the non-extracted components during instant coffee prep- from coffee mannan has been developed as active prebiotic aration. The protein content in SCG may be overestimated ingredient in Japan (Aginomoto Co. Inc.) and approved as due to the presence of other nitrogen-containing substances Food for Specified Health Uses (FOSHU) oligosaccharide (caffeine, trigonelline, free amines and amino acids) functional food ingredient (Fukami, 2010). (Delgado, Vignoli, Siika-aho, & Franco, 2008). However, Espresso (dark roasted Arabica) SCG consisted mainly many authors report similar protein contents, varying be- of mannose (46%), galactose (27%), glucose (20%), and tween 6.7% and 9.9% (Lago, Antoniassi, & Freitas, 2001) arabinose (7%) with galactomannans as the major polysac- and up to 14% (Ravindranath, Khan, Obi Reddy, charide accounting for approximately 50% the total carbo- ThirumalaRao, & Reddy, 1972). hydrates (Simoes~ et al., 2013). Roasting SCG (160 C) Data on amino acids content is limited to a single report improves the extractability of galactomannans (total 56%) (Lago et al., 2001) of SCG collected from three instant cof- without degradation, preserving their b-(1-4)-Man back- fee producers using four different extractors. SCG protein bone, Gal and Ara side chains, and acetylation. Microwave has similar or higher levels of the essential amino acids assisted extraction (MAE) allows the recovery of arabino- leucine, valine, phenylalanine, and isoleucine than conven- galactans, while a re-extraction of the residual material tional feed products such as soybean meal (Table 1). Isoleu- (MAE2) enables higher galactomannan yield. Through cine, leucine and valine contents of SCG are over twice the this method 74% and 66% of total galactose and mannose levels in soybean meal. Lysine content is low in SCG, could be extracted from SCG (Passos & Coimbra, 2013). although it is as high in coffee pulp and 11S protein as in The carbohydrate composition of exhausted coffee waste soybean meal (on a per gram nitrogen basis) (Elıas, is reduced to only two monomers: glucose (59.2 and 62.9% 1979). The essential amino acids comprise almost half of total sugars) and mannose (40.8 and 37.1%) by alkali (w49%) of the total SCG amino acid mainly leucine extraction (Pujol et al., 2013). However, the hemicelluloses contributing 13 or 21% of the total content. Most SCG reported by these authors contrast with previous studies amino acid contents, except arginine, aspartic acid, lysine, (Mussatto, Ballesteros, Martins, & Teixeira, 2011; Simoes~ phenylalanine, serine and threonine are considerably higher et al., 2009) indicating the presence of galactose and arab- than those in coffee pulp and/or 11S protein. The 11S pro- inose in SCG. These two monosaccharides are probably tein, similar to other plant storage proteins, accounts for easily hydrolyzed during alkali extraction. approximately 45% of total proteins in coffee endosperm R. Campos-Vega et al. / Trends in Food Science & Technology 45 (2015) 24e36 27

Table 1. Amino acid content (% protein) and characteristics of cof- have been used to treat patients with hepatic encephalopa- fee protein and by products. thy (Udenigwe & Aluko, 2010); thus the SCG protein could be used to formulate food products with multiple human Amino acids Min Max Instant Pulp 11S Soymeal health benefits during liver diseases, oxidative stress and Alanine 4.8 5.4 4.0 3.5 3.5 2.3 a hypertension. The lysine/arginine ratio, a determinant of Arginine 0.1 0.2 0.5 2.8 8.4 4.0 Aspartic acid 0.2 1.9 3.0 7.1 4.0 6.3 the cholesterolaemic and atherogenic effects of a protein, Cystine nd 5.1 0.3 0.3 1.0 0.8 is high for SCG protein, suggesting that it can contribute Glutamic acid 11.5 13.8 12.9 7.7 8.6 9.8 to hypercholesterolemic and atherogenic physiological ef- Glycine 2.4 7.9 4.7 4.2 5.0 2.3 fects. SCG protein is also an excellent source of arginine, Histidinea 0.1 5.3 1.6 2.5 2.1 1.4 a glutamine and histidine, the three amino acids known to Isoleucine 5.1 5.3 4.2 3.3 4.3 2.3 Leucinea 10.6 10.9 8.5 4.7 8.7 4.2 have strong effects on the immune functions of the body. Lysinea 1.9 2.3 1.4 3.4 6.4 3.3 The high cysteine and methionine content of some SCG Methioninea 1.0 1.9 1.2 0.3 0.3 0.8 protein can boost the body’s antioxidant levels, potentially a Phenylalanine 0.5 6.7 5.2 3.0 7.3 2.6 stabilizing DNA during cell division and reducing the risk Proline 3.1 4.7 5.6 3.7 4.3 3.0 of certain forms of colon cancer. The essential amino index Serine 0.9 1.2 1.6 3.3 4.5 3.1 e Threoninea 0.3 2.2 2.6 3.1 2.9 1.7 of SCG is high (79 129%) relative to soybean protein and Tyrosine 2.9 4.0 3.1 1.9 2.8 1.8 higher than those of soymeal (Table 1) due primarily to the Valinea 6.0 6.8 5.7 3.7 5.7 2.4 contribution of leucine and isoleucine. BCAA 21.7 23.0 18.4 11.7 18.7 8.9 Early studies (Silva et al., 1998 and references therein) AAA 0.9 8.9 7.8 6.1 10.2 4.3 showed that coffee grounds have low nitrogen content Fischer ratio 24.1 2.6 2.4 1.9 1.8 2.1 (w2%), high acidity (w4.2 pH) containing only half of Lys/Arg 19.0 11.5 2.8 1.2 0.8 0.8 the essential amino acids required for animal feed. In vivo Arg þ Glu þ His 11.8 19.3 15.0 13.0 19.1 15.2 Met þ Cys 1.0 7.0 1.5 0.6 1.3 1.6 evaluation of SCG in sheep showed negative metabolisable EAI (%) 79.3 128.8 94.6 74.7 117.3 58.2 energy contents (1.5 & 1.1 MJ/kg dry matter), based þ þ þ primarily on the negative crude protein digestibility BCAA (Val Leu Ile). AAA (Phe Tyr). Fischer ratio (BCAA/ AAA). nd, not detected. Data calculated from Lago et al. (2001). ( 0.53 & 0.92) despite the high gross-energy content Data from http://www.feedipedia.org/node/11612 Data from (Givens & Barber, 1986). However, the high non-protein ni- Rogers et al. (1999). Soymeal data from Karr-Lilienthal, Kadzere, trogen (w46% of the total nitrogen) present in SCG (Sikka, Grieshop, and Fahey (2005). a Bakshi, & Ichhponani, 1985) may partly explain its low Essential amino acid. biological effect observed in several animal feeding studies. SCG (12.55% protein) at 10% of an isonitrogenous concen- trate mixture has been safely incorporated in fattening pig tissue, representing 5e7% of coffee dry bean weight (esti- ration without adverse health effects on carcass quality mated on 11e15% protein). This storage protein consists of (Sikka & Chawla, 1986). However, 15% SCG significantly a high (a-component, w32 kDa) and a low (b-component, depressed daily live weight gains and feed conversion effi- w22 kDa) molecular subunit easily recognized on two- ciency. Feed conversion ratios were 6.88, 6.95, and 8.10 for dimensional profiles of green coffee proteins (Rogers control (conventional feed ingredient formulation), 10% et al., 1999). The low level of the hydroxyl-amino acids and 15% SCG rations, respectively. The poor feedlot per- serine and threonine in SCG relative to those in coffee formance of the pigs was attributed to the higher fiber con- pulp and/or 11S protein reflects their reactivity during the tent (14.8, 16.7, and 19.1% for control, 10%, and 15% brewing process producing volatile heterocyclic com- SCG, respectively), thereby reducing the digestion of pounds, alkylpyrazines (Oestreich-Janzen, 2010). energy-yielding nutrients. SCG has low nitrogen solubility SCG protein is high in the essential branched chain (28.6%) primarily due to protein denaturation and low amino acids (BCAA) and Fischer ratio, higher than those pepsin digestibility (35.3%) resulting from intramolecular of soymeal or soybean protein (Table 1). Some SCG protein linkage formation during coffee bean roasting (200 C, with low (<1%) aromatic amino acid content has high 20 min), limiting enzyme hydrolysis (Sikka et al., 1985). Fischer ratio similar to those generally derived by hydrolysis and extensive purification process. Proteins with high Non-protein nitrogeneous compounds BCAA, Fischer ratio and low content of aromatic amino Nitrogenous compounds (free amino acids, peptides, al- acids are sought for producing physiologically functional kaloids) contribute considerably to the development of cof- foods for specific needs, such as in patients with malnutri- fee flavor and quality during roasting. The protein profile of tion associated with cancers, burns, trauma, and liver fail- coffee changes during roasting, the proteins are both frag- ure, and for nutritional support of children with chronic mented and polymerized, and integrated into melanoidins. or acute diarrhea or milk protein allergies (Oomah, 2001 Other protein components such as peptides and free amino and references therein). Protein with Fischer ratio higher acids constitute up to 1.5% of green coffee, whereas alka- than 20 and aromatic amino acids (AAA) lower than 2% loids (3e4%), of which trigonelline represents about 1%, 28 R. Campos-Vega et al. / Trends in Food Science & Technology 45 (2015) 24e36 are transformed during roasting (Oestreich-Janzen, 2010). et al., 2012). The polar solvent, dichloromethane extracts According to Oestreich-Janzen (2010), total amino acid the most caffeine at low pressure, whereas SFE at high content of Arabica roast and brew amount to 10.1 and pressure (300 bars) is more efficient, both in terms of gener- 6.4% dry weight, respectively, suggesting that 3.7% dry ating higher caffeine yield and environmental footprint. weight of amino acids can be found in SCG. Caffeine obtained from SCG is equivalent to 18e48% of The content of non-protein nitrogenous compounds in those extracted from coffee beans by supercritical CO2 SCG could be useful in agriculture. Compost and reclama- (Saldana,~ Mohamed, Baer, & Mazzafera, 1999)or tion substrates from SCG can be used for intensive remedi- 8e31% of roasted coffee (Ramalakshmi, Rao, Takano- ation, positively affecting microbial activity and reducing Ishikawa, & Goto, 2009). Supercritical CO2 has long leaching of mineral nitrogen (Nmin) from the arable soil been used to decaffeinate coffee beans and therefore can (Elbl et al., 2014). Compost available carbon increases mi- be integrated in processing SCG. Various caffeine concen- crobial activity, resulting in increased capacity for mineral trations (0.007e0.5%) have been reported depending on nitrogen retention (additionally supplied from compost and extraction process and SCG source (Andrade et al., 2012; another mineral fertilizer). Nmin is captured in soil organic Cruz et al., 2012; Murthy & Naidu, 2012a, 2012b; matter (Diaz, Bertoldi, & Bidlingmaier, 2011). In this re- Ramalakshmi et al., 2009). Thus, caffeine content for gards, SCG, after oil extraction, has a carbon/nitrogen ratio Arabica range between 0.9 and 1.6%, Robusta of 19.8:1 (wt) (Kondamudi, Mohapatra, & Misra, 2008), (1.4e2.9%), mix (60 Arabic/40 Robusta) (1.7%). In similar to soil needs (20:1) (Elbl et al., 2014). Despite espresso-style percolation, the very short time available to this, the use of SCG is limited to gardens as compost for extract caffeine from the cellular structure leads to the plants. Recently, the positive soil amendment impact 75e85% extraction yield with only15e25% caffeine left of SCG has been confirmed in enhancing the physical in the SCG (Oestreich-Janzen, 2010). and nutritional features of lettuce, endorsing its potential Spent coffee extracts of both Arabica (0.5%) and use in agroindustry (Cruz et al., 2014). Robusta (0.2%) contain lower caffeine than low-grade green coffee beans (1.7%) (Ramalakshmi et al.,2009). Caffeine However, high caffeine (6e11.5 mg/g dry matter) were de- Caffeine, 1,3,7-trimethyl-xanthine, a purine alkaloid, is tected in the extracts of SCG from coffee bars; the higher the quintessential single most popular compound recog- amount observed in SCG from Robusta was nearly twice nized in coffee and coffee products/ingredients. This alka- that from Arabica (Panusa, Zuorro, Lavecchia, Marrosu, loid is removed from coffee beans by the decaffeinating & Petrucci, 2013). Caffeine was low in SCG extracts process commonly used in the industrial scale. Although from capsules (obtained from an automatic espresso ma- the caffeine content in coffee waste is lower than that in chine), (0.96e0.97 mg/g dry sample) (Panusa et al., coffee beans, a large amount of caffeine still remains. 2013). In this regard, caffeine content ranged from 1.94 Higher caffeine can be extracted from coffee husks to 7.88 mg/g (DW), with a mean of 4.53 mg/g (DW) in (Tello, Viguera, & Calvo, 2011) or coffee pulp (Murthy espresso coffee (Cruz et al., 2012). The caffeine extract- & Naidu, 2012a, 2012b) than from SCG. Caffeine concen- ability coefficient in espresso coffee is 75e85%, so these trations range from 0.734 to 41.3 mg/mg of spent coffee figures correspond to predicted mean caffeine content of ground extracts, obtained by low-pressure extraction (ultra- 22.5 mg/g (DW) in the original roasted beans, in accor- ~ sound and Soxhlet) and supercritical fluid CO2 extraction dance with the literature (Bicho, Leitao, Ramalho, & (SFE) varying in yield from 9 to 15% (Table 2)(Andrade Lidon, 2011; Casal, Oliveira, Alves, & Ferreira, 2000).

Table 2. Caffeine content of SCG and roasted coffee.

Extraction Solvent/condition (mg/mg extract) Yield (%) Content (%) Reference Ultrasound Hexane 0.734 9 0.007 Andrade et al. (2012) Dichloromethane 38.2 9.9 0.378 Ethanol 25.7 12.2 0.314 Soxhlet Hexane 3.27 12 0.039 Dichloromethane 25.9 10.8 0.28 Ethanol 11.8 15 0.177 SFE CO2 200 bar/331.15 K 27.2 9.1 0.248 300 bar/331.15 K 41.3 10.5 0.434 SCG (Arabica-Ar) H2O(92 5 C/6 h) 25 2 0.5 Ramalakshmi et al. (2009) SCG (Robusta-Rb) H2O(92 5 C/6 h) 10 3 0.2 Roasted Coffee (Ar) Medium roast 1.6 Roasted Coffee (Rb) Medium roast 2.4 SCG 0.02 0.1 Murthy and Naidu (2012) SCG (espresso) 0.18 Cruz et al. (2012) R. Campos-Vega et al. / Trends in Food Science & Technology 45 (2015) 24e36 29

Caffeine (1.8 mg/g SCG) present in SCG prepared from of 16% melanoidins, whose chemical composition has not espresso coffee may serve as a chemical defence mecha- yet been established (Nunes & Coimbra, 2010). nism in some plants, while adversely inducing toxicity in other plants such as lettuce (Cruz et al., 2012). Caffeine Lipids in SCG is completely degraded by Pleutotusostreatus Spent coffee grounds have often been reported to LPB 09 fungal cultures enabling economical utilization of contain 10e15 % (Jenkins, Stageman, Fortune, & Chuck, SCG as substrates for edible fungi/mushroom cultivation 2014), and sometimes higher average 20% (range without any pretreatments (Fan, Pandey, Mohan, & 19.9e27.8%) lipids (Lago et al., 2001) or 13.9e29.2% Soccol, 2000). This observation has been used in the devel- ether extract, on dry weight basis (Silva et al.,1998). Dur- opment of a patent application where mycelium is used in ing the brewing process, lipids stick to the spent grounds reducing coffee bitterness. Caffeine presence as a nitrogen and are filtered off, in filter home brew as well as in instant precursor plays an important catalytic role in hydrogen sul- coffee production (Oestreich-Janzen, 2010). Lipid yield phide oxidation in the preparation of activated carbon from (7e13% dry weight) is low when SCG suspended in fresh SCG (Kante et al., 2012). It also contributes significantly in heptane (1:10 weight ratio) is stirred (3 h) at room temper- lowering/reducing interfacial tension equilibrium in oils, ature (Jenkins et al., 2014). SCG extracted with hexane important in defining the emollient characteristics of phar- yield high oil (15.3%), with low acid (3.65%) and saponi- maceutical and/or cosmetic products. fication (173) values, parameters important for fatty acid methyl ester (FAME) manufacturing (Al-Hamamre, Brown-colored compounds Foerster, Hartmann, Kroger,€ & Kaltschmitt, 2012). Com- The nitrogenous brown-colored compounds of coffee mercial ethanol (99%) has been used to recover lipids result from the non-enzymatic browning (Maillard) reaction from industrial spent coffee grounds containing 25.6% oil between reducing sugars and compounds with a free amino (dry weight petroleum ether extraction). Maximum oil group forming various products including the melanoidins yield (82%) was obtained at 1:7 SCG: alcohol ratio, (Moreira, Nunes, Domingues, & Coimbra, 2012). Maillard 75 C and not affected by extraction time (1 or 2 h) and pre- reaction products may be useful for functional food appli- treatment (milling or extrusion). The extracted oil had char- cation and/or as food preservative, since they exhibit anti- acteristics similar to petroleum ether extract (Freitas, oxidant capacity and inhibit lipid peroxidation (Jung, Monteiro, & Lago, 2000). Park, Ahn, & Je, 2014). Melanoidins are the high molecular SCG total lipids range from 9.3 to 16.2% (Cruz et al., weight (HMW) brown products containing nitrogen, end 2012), 10e15% and 14e15.4% from espresso coffee resi- products of the Maillard reaction (Nunes, Cruz, & Coimbra, dues, filter and industrial soluble coffee, respectively 2012) with small amounts (<6%) of amino acids, primarily (Calixto et al., 2011; Couto, Fernandes, da Silva, & glutamic acid and glycine released by acid hydrolysis. Dur- Simoes,~ 2009; Kondamudi et al., 2008). Also, the yield of ing coffee brewing, only 33% of the original green coffee SCG oil extracted using Soxhlet, is a function of extraction bean protein is extracted with hot water, the residual protein conditions, particularly, the choice of solvent and the dura- remains insoluble due partly to denaturation and association of extraction. Supercritical carbon dioxide extracts up tion with cell wall arabinogalactans representing nearly to 85% of the total amount of SCG oil after 3 h (corre- 92% of the total nitrogen present in the high molecular sponding to a maximum yield of 15.4 goil/100 gdry SC) weight melanoidins (HMWM) (Nunes, Cruz, & Coimbra, (Couto et al., 2009). 2012). Ethanol (70e80%)-soluble HMWM has the highest Although hexane is the most widely and commonly used protein content, but amino acid composition similar to all solvent, modern environmentally friendly technology such melanoidin fractions. The amino acid composition of these as SFE is increasingly being used for SCG oil extraction. melanoidin fractions (abundant in alanine, aspartic acid/ A manufacturing cost of US$ 48.60/kg has been estimated asparagine, glutamic acid/glutamine, and glycine) is similar for spent coffee oil obtained by supercritical technology to those reported for roasted coffee beans and roasted cof- (200 bar, 50 C, 90 min) and may reach US$ 460/kg de- fee brews. pending on process conditions (Andrade & Ferreira, 2013). Browning index of SC extracts from Arabica (0.165) and Commercial SCG contains higher oil (16.7 & 17.2%) Robusta (0.145) coffee from filter coffeemaker was 3e5- compared to raw (9e12.6%), roasted (12e15%), or labora- fold higher than those obtained from espresso and plunger tory extracted SCG (7.9e14%); free fatty acids (120e148 coffeemakers (Bravo et al., 2012). Aqueous extracts from vs 4e10 acid value), and lower unsaponifiable matter soluble SCG has lower browning index (0.271) compared (5.9e9.4% vs 9e13.2%) relative to those produced in the to that from roasted coffee brews (0.305) (Yen, Wang, laboratory (Ravindranath et al., 1972). Coffee brews pre- Chang, & Duh, 2005). Furthermore, a solideliquid method pared by different methods showed that lipids (90.2%) has been proposed as an efficient extraction of brown com- mainly remained in SCG with the following lipid composi- pounds measured by absorbance at 420 nm (from 0.090 to tion (% total lipids), 84.4% triacylglycerols, 12.3% diter- 0.160) (Bravo, Monente, Juaniz, De Pena,~ & Cid, 2013). pene alcohol esters, 1.9% sterols, 1.3% polar material, Passos and Coimbra (2013) suggested that SCG consists and 0.1% sterol esters. The lipid composition is similar to 30 R. Campos-Vega et al. / Trends in Food Science & Technology 45 (2015) 24e36 those of boiled or filtered coffee with 87e93% triglycer- linoleic (<40%) acids (Table 3). These clusters result in ides, 7e13% diterpene alcohol esters, 0.2e0.9% sterols, polyunsaturated/saturated ratios <1or>1 of the extracted and up to 0.8% polar material (Ratnayake, Hollywood, oils. SCG oils with polyunsaturated/saturated ratio >1 are O’Grady, & Stavric, 1993). However, the lipid composition less atherogenic and thrombogenic than those with ratio of SCG may vary analogous to those of green coffee oil de- <1 due to the potential favorable reduction of serum pending on the source, although generally up to 80e90% of cholesterol and atherosclerosis and prevention of heart dis- the oil will be glycerides, including free fatty acids, with eases (Rudel, Parks, & Sawyer, 1995). The cholesterol- the rest of the lipids containing terpenes, sterols and to- raising factor from coffee beans has been attributed to the copherols (Jenkins et al., 2014). Raw green coffee oil con- presence and/or concentration of the diterpenes kahweol sists of: triacylglycerols (75%), terpene esters (14%), and cafestol that varies depending on several factors partial acylglycerols (5%), free fatty acids (1%), free sterols (Urgert, Schulz, & Katan, 1995) including the oil extraction (1.5%), sterol esters (1%), and polar lipids (<1%) (Niko- process (Acevedo et al., 2013). lova-Damyanova et al., 1998, cited in De Azevedo et al., High palmitic acid SCG oils represent a rich and suitable 2008). Khan and Brown (1953) provide a good review on source of palmitic acid for soap manufacture and/or the earlier investigation on raw and roasted coffee bean oil acid itself according to Ravindranath et al. (1972). Further- characteristics and composition. Coffee oil contains exces- more, the combination of high linoleic (w44%), palmitic sive amounts of unusual unsaponifiables, 19% (or 24% for (w36%) and oleic (w9%) acids, predominant in SCG defective coffee beans) according to Oliveira, Franca, oils can result in high biomass and polyhydroxylalkanoates Camargos, and Ferraz (2008), the presence of which makes (PHA)-an alternative completely biodegradable synthetic the oil unfit for most uses. However, the unsaponifiables polymer-yields (Obruca et al., 2014). Fatty acid composi- containing the diterpenes kahweol and cafestol known for tions of SCG oils differ significantly under different SFE their beneficial physiological effects (UVB skin protection, (pressure, temperature, co-solvent: CO2 mass ratio) condi- anticarcinogenic, anti-inflammatory and antioxidant activ- tions (Ahangari & Sargolzaei, 2013; Couto et al., 2009). ities) (Silva, Vieira, & Hubinger, 2014) can be completely SCG oil has efficiently been extracted (>90% yield) by su- removed by molecular distillation. percritical carbon dioxide (scCO2) recently in a pilot plant SCG oils consist predominantly of linoleic, palmitic, (Cruz et al., 2014) and used for producing high yielding stearic and oleic acids (Table 3). Arachidic (7%) and lino- PHA (0.77 kg PHA/kg SCG oil; 97 kg per ton of SCG lenic (<5%) acids are also present in most SCG oils, processed). whereas lauric and myristic acids are rarely detected de- SCG oil also contains minor lipid components, such as pending on extraction conditions, processing and origin. sterols well known for their serum cholesterol lowering ef- The contrasting fatty acid profile exemplifies the effects be- fect by reducing intestinal absorption of cholesterol. Sterols tween two processes used in obtaining SCG oil (Todaka, constitute about 5.4% of the total lipids in Arabica coffee Kowhakul, Masamoto, Shigematsu, & Onwona-Agyeman, and consist of sitosterol (53%), stigmasterol (21%), cam- 2013). SCG oils can be conveniently categorized into two pestol (11%), cycloartenol (8%), and the remaining sterols clusters based on their fatty acid profile; those with low pal- are each 5% or less of the total sterol fraction (Spiller, mitic (<40%) and high linoleic (>40%) acids and 1998). Sterol content of SCG depends on the origin and conversely those with high palmitic (>40%) and low source of roasted coffee (Table 4) with sitosterol,

Table 3. Fatty acid composition of SCG.

References C12:0 C14:0 C16:0 C18:0 C18:1 C18:2 C18:3 C20:0 SFA PUFA PUFA/SFA AI TI Acevedo et al. (2013) nd 0.05 32.45 8.35 9.00 45.04 4.12 nd 41.0 50.0 1.22 0.55 1.26 De Melo et al. (2014) nd nd 37.37 7.07 8.31 44.67 1.42 1.16 45.6 46.1 1.01 0.69 1.44 Cruz et al. (2014) nd 0.1 32.80 7.10 10.30 44.20 1.50 2.60 42.5 45.7 1.08 0.58 1.25 Jenkins et al. (2014) nd nd 35.40 6.70 6.70 22.00 nd 0.00 42.1 22.0 0.52 1.23 2.93 Jenkins et al. (2014) nd nd 41.40 13.50 24.00 49.90 1.40 1.50 56.4 51.3 0.91 0.55 1.49 Ahangari and Sargolzaei (2013) 3.58 2.00 43.64 6.55 8.18 32.35 1.31 2.39 58.2 33.7 0.58 1.32 2.15 Todaka et al. (2013) (Hex)Drip nd 0.4 0.50 0.30 12.90 56.90 8.50 9.80 21.7 65.4 3.01 0.03 0.01 Todaka et al. (2013) (Hex)Esp nd 0.3 1.00 28.00 0.60 24.90 5.50 37.80 69.0 30.4 0.44 0.07 0.33 Supercritical Fluid Extraction (SFE) Acevedo et al. (2013) nd nd 35.78 6.25 nd 46.53 2.02 nd 42.2 49.1 1.16 0.62 1.32 De Melo et al. (2014) nd nd 37.48 6.02 9.53 44.52 0.99 1.46 45.0 45.5 1.01 0.68 1.45 Ahangari and Sargolzaei (2013) nd nd 34.04 5.45 5.45 25.83 nd 1.89 41.4 25.8 0.62 1.09 2.52 Couto et al. (2009) nd nd 35.86 5.26 7.56 35.35 nd 1.53 42.7 9.9 0.24 0.84 1.92 Ahangari and Sargolzaei (2013) 11.69 4.36 36.86 11.32 15.87 44.15 2.16 6.91 71.1 46.3 0.65 1.06 1.43 Couto et al. (2009) 7.4 2.42 41.87 10.4 15.79 41.19 1.88 4.29 66.4 46.7 0.91 1.00 1.91 SFA, saturated fatty acids; PUFA, polyunsaturated fatty acids; AI, atherogenic index; TI, thromogenic index; nd, not determined. R. Campos-Vega et al. / Trends in Food Science & Technology 45 (2015) 24e36 31

Table 4. Sterol (%) composition of SCG and their sourced roasted Mg, P, Ca, Na, Fe, Mn, and Cu) content of espresso SC varies coffee. from 0.82 to 3.52%, confirming mineral leaching during espresso coffee preparation, although not as exhaustive as Sterols SCG1 SCG2 Coffee 1 Coffee 2 with soluble coffee (Cruz et al., 2012). Potassium, the major Oil content (%) 26.74 20.34 5.84 5.74 mineral of espresso SC, ranges from 3.12 to 21.88 mg/g Unsaponifiables (% DW) 2.12 1.37 1.23 0.79 et al. Sterols (% oil) (Cruz , 2012). The industrial SCG contains lower abso- Campesterol 16.08 18.36 15.66 16.83 lute (3.55 mg/g) and relative amounts (22%) of this element. Stigmasterol 21.75 22.48 22.82 21.94 Coffee is regarded as an important source of Mg, comprising Sitosterol 52.66 48.00 52.27 48.78 11% of the SCG minerals, again higher than those of indus- D5 Avenasterol 5.30 9.07 4.05 8.81 7 trial SC (Mussatto, Ballesteros, et al., 2011). D Stigmastenol 1.65 0.62 2.01 1.68 D7 Avenasterol 1.42 0.80 1.74 0.70 Phenolic compounds Data derived from Lago et al. (2001). Phenolic compounds are the major determinant of antioxidant potentials found in high concentrations in plants stigmasterol, and campesterol as the most abundant sterols, (Balasundram, Sundram, & Samman, 2006). Recently, in- predominating in higher plants and in typical diets. These terest in plant-derived natural products has grown, mainly three sterols account for 88e92% of the total sterols in because synthetic antioxidants suffer from several draw- SCG or roasted coffee oils. The concentration of the minor backs. SCG contain several human health related com- sterol, D5-avenasterol also varies in accordance with the pounds, such as phenolics with demonstrated antioxidant, level in roasted coffee (Table 4) reaching up to 9% of the anti-bacterial, antiviral, anti-inflammatory and anti- et al. total sterols. In fact, sitosterol and D5-avenasterol are the carcinogenic activities (de Souza , 2004). two most differentiating sterols used to separate Arabica The recovery of phenolic compounds from the coffee in- from Robusta coffee varieties (Carrera, Leon-Camacho, dustry by-products and their antioxidant activity has been Pablos, & Gonzalez, 1998) because its polymerization pro- investigated recently. Phenolic compounds from coffee tects oils from oxidation. by-products (coffee pulp, husk, silver skin, and SC) have Several methods have been devised to extract/prepare been extracted using solvent mixture of isopropanol and the diterpenes, cafestol and kahweol from coffee oil water (Murthy & Naidu, 2012b). The coffee by-products e because of their potential use and applications in pharmaco- contained about 1 1.5% total polyphenols with the highest logical and cosmetic preparations. Cafestol is minimally yield for silver skin (25%), followed by spent waste (19%) affected by various treatments of coffee beans and is one and cherry husk (17%) when pretreated with viscozyme. of the components that remains in spent coffee grounds Chlorogenic acid (CGA) was the major phenolic compo- (1.2%) (Spiller, 1998). Khan and Brown (1953) identified nent when analyzed with high-performance liquid chroma- kahweol as one of the unsaponifiables with characteristic tography. In fact, phenolic compounds are mainly found in green coffee beans as CGA (up to 12% solids) (Esquivel & brown precipitate formation of SCG oil extracted from fresh roasted blend of Brazilian, Colombian, and Venezue- Jimenez, 2012). These CGA are water-soluble esters lan coffees. Direct saponification produces high level of di- formed between quinic acid and one or two moieties of caf- terpenes (2.14 and 4.66 mg/g SCG of kahweol and cafestol, feic acid, a trans-cinnamic acid. Caffeoylquinic acids respectively) compared to saponification of oil extracted by (CQA) are the most abundant phenolic compounds in cof- solid liquid extraction or supercritical extraction (Acevedo fee. Monocaffeoylquinic acids (3-CQA, 4-CQA, 5-CQA) et al., 2013). Diterpene yield from SCG depends on pro- and dicaffeoylquinic acids (3,4-diCQA, 3,5-diCQA, 4,5- diCQA) were identified and quantified in SC obtained cessing conditions during supercritical CO2 extraction; thus concentration of cafestol (0.207 mg/g SCG) and kah- from different coffeemakers (filter, espresso, plunger, and weol (0.114 mg/g SCG) are lower at 40 C/98 bar than mocha) and in their respective coffee brews by Bravo et al. those at 80 C/379 bar (0.828 and 0.425 mg/g SCG for ca- (2012). All SCG, with the exception of those from festol and kahweol, respectively) (Acevedo et al., 2013). the mocha coffeemaker, have relevant amounts of total caffeoylquinic acids ranging from 11.05 mg (espresso) to 13.24 mg (filter) per gram of Arabica SC and from Minerals 6.22 mg (filter) to 7.49 mg (espresso) per gram of Robusta SCG also contains ash (1.6%), which, according to the SC. Espresso SCG shows high variability, with 5-CQA ICP-AES analysis, consists of several minerals. Potassium ranging from 0.397 to 2.642 mg/g (DW) and total CGA is the most abundant element, followed by phosphorus and varying from 2.12 to 7.66 mg/g (DW) (Cruz et al., 2012). magnesium (Mussatto, Ballesteros, et al., 2011). Potassium The antioxidant phenolic compounds from SCG have is also the predominant mineral in coffee beans, correspond- been extracted by the conventional solideliquid method. ing to 40% of the oxide ash (Grembecka, Malinowska, & For example, extraction with 60% methanol (40 ml/g Szefer, 2007). Most minerals are easily extracted with hot SCG solvent/solid ratio, 90 min) produces a high phenolic water during instant coffee preparation. Total mineral (K, extract (16 mg gallic acid equivalents (GAE)/g SCG) with 32 R. Campos-Vega et al. / Trends in Food Science & Technology 45 (2015) 24e36 high antioxidant activity (FRAP of 0.10 mM Fe(II)/g) SCG. Earlier innovation (pre 2005) explored the extraction simultaneously (Mussatto, Ballesteros, et al., 2011). of specific components such as oil, flavor, terpenes, and al- Phenolic compounds from SCG [coffee bars (SCG-1) or cohols as value-added products. Later studies focus exten- coffee capsules (SCG-2)] have been extracted by an envi- sively on innovation in bioenergy and biorefinery using ronmentally friendly and cost-effective process, using SCG as a source product. In reality, there has been minimal aqueous ethanol under mild temperature conditions to pre- attempt in complete integrated fractionation and utilization serve the activity of the phenolic compounds (Zuorro & of SCG components for industrial and/or other use, Lavecchia, 2012). Total phenolic content of SCG-1 and although these components have been individually well re- SCG-2 were 17.75 and 21.56 mg GAE/g, respectively. searched (Fig. 2). Thus phenolic-rich extracts can be obtained from SCG us- Spent coffee grounds represent a resource for an inte- ing an environmentally friendly and simple solvent- grated product focused biorefinery. It has been proven extraction procedure. Ethanol also influenced microwave- that the conversion of biomass waste to bulk chemicals assisted extraction of natural antioxidants from spent filter for example was nearly 7.5 and 3.5 times more profitable coffee (Pavlovic, Buntic, Siler-Marinkovi c, & than its conversion to animal feed or transportation fuel, Dimitrijevic-Brankovic, 2013). The highest total phenolic respectively, highlighting the marginal value of 1st genera- compounds (399 mg GAE/g extract, dry matter) was ob- tion food supply chain waste recycling (anaerobic diges- tained with 20% aqueous ethanol under just 40 s of micro- tion, composting, animal feed) (Pfaltzgraff, Cooper, wave radiation (80 W), implying that the method is very Budarin, & Clark, 2013). The key to go beyond 1st gener- effective, saving time and chemicals. The extracts (20 mg/ ation waste valorization is to make use of all the valuable mL) exhibited high in vitro antioxidant activities inhibiting components in waste, taking into consideration the pres- 90% of DPPH radicals, supporting their biological stability. ence of high-value products. A good example of 2nd gener- This research group later found that total phenolic com- ation products is succinic acid obtained through sugar pounds of SCG were strongly correlated with their DPPH fermentation of enzyme-hydrolyzed carbohydrates from scavenging activity, and therefore mainly responsible for SCG (Koutinas et al.,2013). the antioxidant activity. An UHPLC-PDA-TOF-MS system SCG oil is the single most economically valuable was used to separate, identify, and quantify phenolic and component easily extractable and a potential low-cost and non-phenolic compounds in the SCG extracts. High good quality feedstock source for fatty acid methyl esters amounts of CGA and related compounds as well as caffeine production by direct single step transesterification of SCG demonstrate the high potential of SCG, a waste material oil in supercritical methanol (Calixto et al., 2011). The that is widely available in the world, as a source of natural oil quality can be improved for use in cosmetic and phar- phenolic antioxidants (Panusa et al., 2013). maceutical applications or as a source of other valuable products such as caffeine, sterols, terpenes and tocopherols Ingenuity/knowledge gap by fractionation similar to those used for green coffee oil Table 5 provides a short survey of product and/or pro- (De Azevedo et al., 2008). The fractionated oil or its com- cess innovation using SCG or coffee products including ponents can be stabilized by the spray drying process used

Table 5. Products and/or processes innovation using SCG or coffee products including SCG.

Component Claim References Spent grounds volatile Aromatic flavor components (diacetyl and acetaldehyde) are recovered from an Cale et al. (1990) compounds aroma stream generated by thermal hydrolysis of a partially extracted roasted and ground coffee. The flavor can be used as a natural ingredient and/or in soluble coffee processing. Ground/Green/Whole Antioxidant-rich biofuel is produced by transesterifying triglycerides extracted from Misra, Mohapatra, roasted/spent-coffee beans coffee products including SCG. Glycerin resulting from the transesterification and Kondamudi (2013) process can be isolated, purified and used in foods, pharmaceuticals, cosmetics and other products. Spent coffee grounds A process is described for manufacturing powdered coffee carbons as an Lu and Lee (2013) environmentally friendly activated carbon source Dried spent coffee grounds SCG is converted to an alternative solid combustible fuel-a wax-less fire log White and Burns (2013) Spent coffee grounds Coffee oil is recovered from hydrolyzed SCG simultaneously using the residual Gottesman (1985) aqueous hydrolyzate as an economically valuable soluble coffee solids in soluble coffee processing Coffee extraction residue A process for preparing low-cost high yield manno-saccharide alcohols such as Stahl et al. (1984) mannitol (a value added expensive specialty food, chemical, and pharmaceutical ingredient) Spent coffee grounds Terpenes containing kahweol and cafestol (10.7 and 14.7 mg/g coffee oil, Baechler (2002) respectively) are extracted from SCG. R. Campos-Vega et al. / Trends in Food Science & Technology 45 (2015) 24e36 33

BBrown-coloredrown-colored ccompoundsompounds CaCaﬀeineeine BrowningBrowning indexindex 0.1550.155 116%6% mmelanoidinselanoidins

CCaCarbohydratesrbohydrates ggalactomannansalactomannans andand aarabinogalactansrabinogalactans

MaMannooligosaccharidesnnooligosaccharides SCGSCG

AnAnƟoxidantoxidant dietarydietary ﬁberber MineralsMinerals K,K Mg,Mg, P,P, Ca,Ca, NNa,a, Fe,Fe, Mn,Mn, andand CuCu

NoNon-proteinn-protein nnitrogeneousitrogeneous ccompoundsomompoupounds PhenolicPhenolic ccompoundsompounds Carbon/nitrogenCarbon/nitrogen rraaƟo ofof 19.8:119.8:1 (wt):(wt): microbialmicrobial acacƟvityvity NaturalNatural phenolicphenolic aannƟoxidantsoxidants SoilSoil amendmentamendment iimpactmpact 11–1.5%–11.5% ttotalotal ppolyphenolsolyphenols CChlorogenichlorogenic acidacid ((12%12% ssolids)olids)

LLipidsipids OOilil manufacturingmanufacturing ccostost USUS$$ 448.68.600/kg-/kg- eaearningrning up ttoo USUS$$ 460/kg460/kg PPolyunsaturated/saturatedolyunsaturated/saturated rraaƟo > 1 MixMix linoleic,linoleic, palmipalmiƟc aandnd oleoleicic aacids/cids/ ppolyhydroxylalkanoates-biodegradableolyhydroxylalkanoates-biodegradable synthesyntheƟc ppolymerolymer

Fig. 2. Value-added products/sustainability of the coffee agro-industry. for encapsulating green coffee oil (Silva et al., 2014), coffee grounds contain large amounts of various carboxylic particularly applicable to the unsaponifiable fraction con- acids enabling their further upgrade into biodiesel or other taining the diterpenes for medical and other associated petrochemical products and/or promote their conversion uses. into noncondensable volatiles that may be beneficial for Oil extracted from SCG can be used as a substrate for combustible gas or syngas production from SCG (Kan, the production of poly (3-hydroxybutyrate) (PHB). PHB Strezov, & Evans, 2013). The glyceride portion of SCG is similar in mechanical properties to polypropylene or oil can be transesterified with methanol to produce fatty polyethylene and is therefore considered a completely acid methyl esters, known as biodiesel. Potentially 1.3 biodegradable alternative to synthetic polymers (Obruca billion litres of biodiesel (based on w8 million tonnes of et al., 2014). When compared to other waste/inexpensive globally produced coffee containing 10e15 % wt lipids oils, the utilization of SCG results in the highest biomass [80e95% glycerides] could be added to the world fuel sup- as well as PHB yields (up to 0.88 g of PHB per g of oil ply from SCG, a value comparable to waste cooking oil vs 0.85 for soybean oil, or 0.83 for waste rapessed oil) (Jenkins et al., 2014). Furthermore, spent coffee defatting (de Cruz Pradella, Ienczak, Delgado, & Taciro, 2012; and extract lyophilization produces spent coffee extracts Obruca, Marova, Snajdar, Mravcova, & Svoboda, 2010; powder with high antioxidant capacity that can be used as Obruca et al., 2014). The utilization of oil extracted from an ingredient or additive in food industry with potential SCG as a feedstock for PHB production presents several preservation and functional properties (Bravo et al., 2013). advantages. The coffee industry is steadily growing; the Enzyme technology (hydrolysis) can be used to hydro- annual worldwide production of green coffee beans ex- lyze SCG polysaccharides into valuable food additives ceeded eight million tons (Murthy & Naidu, 2012a). There- such as mannitol and higher mannosaccharide alcohols or fore, SCG are available in millions of tons especially in source raw material for bioethanol production (Jooste, coffee-producing countries. Moreover, since oil extraction Garcıa-Aparicio, Brienzo, van Zyl, & Gorgens,€ 2013; decreased the calorific value of SCG by only about 9% Stahl et al., 1984). Alcohol production similar to process (from 19.61 to 17.86 MJ/kg), residual SCG after oil extrac- generally used in distilled beverages generates a beverage tion can be used as fuel to at least partially cover heat and with 40% ethanol alcohol, comparable to liquors such as energy demands of fermentation, which should even vodka and tequila with a pleasant smell and taste of coffee improve the economic feasibility of the process (Obruca (Sampaio et al., 2013). Additionally, the residual solid ma- et al., 2014). In addition to oil extraction, several processes terial obtained after the hydrothermal process is rich in such as pyrolysis and gasification have been used to convert sugars that can be reused as raw material for the production industrial SCG into fuel, hydrogen-enriched fuel, bio-oils, of other valuable products, which would give additional liquid product mixture comparable to fossil fuel oil and value to spent coffee grounds into a bio-refinery concept. valuable biocide. Bio-oils produced from pyrolysis of Furthermore, the cellulose and hemicellulose fractions of 34 R. Campos-Vega et al. / Trends in Food Science & Technology 45 (2015) 24e36

SCG have potential applications in sorbitol, hydroxyme- Arya, M., & Rao, L. J. M. (2007). An impression of coffee thylfurfural, levulinic acid, formic acid, xylitol, arabitol, carbohydrates. Critical reviews in Food Science and Nutrition, e mannitol, galactitol, furfural and, emulsificant production 47(1), 51 67. et al. Asano, I., Nakamura, Y., Hoshino, H., Aoki, K., Fujii, S., Imura, N., (Mussatto, Carneiro, , 2011). High pressure and tem- et al. (2001). Use of mannooligosaccharides from coffee mannan perature hydrolysis of SCG generates MOS, already mar- by intestinal bacteria. Nippon Nogeikagaku Kaishi, 75(10), keted in Japan as a functional food primarily as a 1077e1083. probiotic for digestive health (Fukami, 2010). Baechler, R. (2002). Process for extracting terpens from spent coffee Waste from brewing coffee could be a valuable resource grounds. E.P. Patent 0819385 B1. Balasundram, N., Sundram, K., & Samman, S. (2006). Phenolic for the production of hydrophilic bioactive antioxidants for compounds in plants and agri-industrial by-products: antioxidant dietary supplements according to Spanish researchers activity, occurrence, and potential uses. Food Chemistry, 99(1), (Bravo et al., 2012). All spent coffee (from filter, plunger 191e203. and espresso-type coffeemakers) had relevant amounts of Belitz, H. D., Grosch, H., & Schieberte, P. (2004). Food chemistry (pp. 939e969). Berlin, Germany: Springer. total caffeoylquinic acids, mainly dicaffeoylquinic acids ~ e Bicho, N. C., Leitao, A. E., Ramalho, J. C., & Lidon, F. C. (2011). that were 4 7-fold higher than their respective coffee Identification of chemical clusters discriminators of the roast brews. Solvent mixture of isopropanol and water can selec- degree in Arabica and Robusta coffee beans. 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