Spent coffee grounds: A review on current research and future prospects

Dave  Oomah

* ! "# $ % & # "++ ,-./..//0123,,11-4 )*+ 1,(1,1567( (.,12(,/(,1. 8+9152: 8 Trends in Food Science & Technology '() " (! "# ( # $(* '()( 0.,123 1,(1,1567( (.,12(,/(,1.( 8 ")9 ; ; ( % (8 % % ; ; (" %; % 7 ( ACCEPTED MANUSCRIPT Spent coffee grounds: A review on current research and future prospects RI PT Rocio Campos-Vegaa*, Guadalupe Loarca-Piñaa, Haydé Vergara-Castañedac and B. Dave Oomahb a Programa en Alimentos del Centro de la República (PROPAC), Research and Graduate Studies in Food Science, School of Chemistry, Universidad Autónoma de Querétaro, Querétaro, Qro. 76010, Mexico SC b (Retired), Formerly with the National Bioproducts and Bioprocesses Program, Pacific Agri-Food Research Centre, Agriculture and Agri-Food Canada, Summerland, BC, Canada V0H 1Z0 M AN U c Nucitec, S.A. de C.V. Comerciantes 15-3, Colonia Peñuelas, Querétaro, México. * Corresponding author. Tel.: (55) 1921304. E-mail address: chio_cve@yahoo.com.mx (R. Campos-Vega). D Abstract Spent coffee ground (SCG) contains large amounts of organic compounds (i.e. fatty acids, 2 amino acids, polyphenols, minerals and polysaccharides) that justify its valorization. Earlier 3 innovation explored the extraction of specific components such as oil, flavor, terpenes, and 4 alcohols as value-added products. However, by-products of coffee fruit and bean 5 processing can also be considered as potential functional ingredients for the food industry. 6 There is an urgent need for practical and innovative ideas to use this low cost SCG and 7 exploit its full potential increasing the overall sustainability of the coffee agro-industry. 8 Keywords: Spent coffee; macronutrients; functional compounds; proteins; phenolics; 9 lipids; minerals; non-protein nitrogeneous compounds; applications. AC C EP TE 1 1 Abbreviations 11 SCG Spent coffee grounds 12 MOS Mannooligosaccharides 13 AAA Aromatic amino acids 14 MAE Microwave assisted extraction 15 FOSHU Food for Specified Health Uses 16 DF Dietary fiber 17 AACC American Association of Cereal Chemists 18 BCAA Branched chain amino acids 19 SFE Supercritical fluid extraction 20 HMW High molecular weight 21 HMWM High molecular weight melanoidins 22 COM Cost of manufacturing 23 scCO2 Supercritical carbon dioxide 24 CGA Chlorogenic acid 25 CQA 26 GAE 27 PHB AC C EP TE D M AN U SC 10 RI PT ACCEPTED MANUSCRIPT Caffeoylquinic acids Gallic acid equivalents Poly 3-hydroxybutyrate 2 ACCEPTED MANUSCRIPT 1. Introduction Coffee, grown in about 80 countries, is one of the world’s most popular beverage and 29 second largest traded commodity after petroleum (Murthy & Naidu, 2012a). Global green 30 coffee production increased by almost 17%, probably due to increased yield (24%), 31 between 2000 and 2012. Several residues are obtained during coffee processing. Coffee 32 producing countries generate residues from the coffee fruit amounting to >50% of the fruit 33 mass (Tsai, Liu, & Hsieh, 2012). Spent coffee ground (SCG) is the residue obtained during 34 the brewing process (Cruz et al., 2012). The huge amount of residue generated annually in 35 the production of soluble coffee requires waste management plan consistent with existing 36 national regulations. For example, Nestlé, the world’s biggest food company pledges to 37 reduce waste in Europe by 2020 using spent coffee grounds as a source of renewable 38 energy in more than 20 Nescafé factories. In most of the soluble coffee producing 39 industries, the waste is collected by specialized agencies, which sell the residues for 40 different purposes (i.e. composting, gardening, bioenergy production, mushroom growth). 41 Spent coffee grounds (SCG) contain large amounts of organic compounds (i.e. fatty acids, 42 lignin, cellulose, hemicellulose, and other polysaccharides) that can be exploited as a 43 source of value-added products. Thus, coffee residue has been investigated for biodiesel 44 production (Caetano, Silva, & Mata, 2012), as source of sugars (Mussatto, Carneiro, Silva, 45 Roberto, & Teixeira, 2011a), precursor for activated carbon production (Kante, Nieto- 46 Delgado, Rangel-Mendez, & Bandosz, 2012), compost (Preethu, BhanuPrakash, 47 Srinivasamurthy, & Vasanthi, 2007), and as sorbent for metal ions removal (Fiol, Escudero, 48 & Villaescusa, 2008). EP TE D M AN U SC RI PT 28 By-products of coffee fruit (Figure 1) and bean processing can also be considered as 50 potential functional ingredients for the food industry. The coffee husks, peel and pulp, 51 comprising nearly 45% of the cherry, are the main by-products of coffee agro-industry and 52 can be a valuable material for several purposes, including caffeine and polyphenols 53 extraction. Coffee husks and skins are traded as crops and livestock products with export 54 and import range of 857 – 27,209 and 490 – 11,474 tonnes from 2000 to 2012 according to 55 FAO Statistics. These export and import were valued at 2.2 – 62.7 and 1.7 – 24.3 million 56 US$, respectively for the same period. Other by-products of coffee processing such as AC C 49 3 ACCEPTED MANUSCRIPT mucilage and parchment have been less studied; however, they are potential sources of 58 important ingredients. The pulp is easily fermented by yeast or metabolized by lactic acid 59 bacteria producing alcoholic beverages and vinegars. Furthermore, roasted coffee silverskin 60 has been evaluated for use as a dietary fiber rich ingredient with antioxidant properties. 61 Finally, SCG have been studied mainly for their antioxidant activities (Esquivel & Jiménez, 62 2012). These antioxidants have been associated with health benefits (Campos-Vega et al., 63 2009; Vergara-Castañeda, Oomah, & Campos-Vega, 2013; Campos-Vega, Oomah, Loarca- 64 Piña, & Vergara-Castañeda, 2013). SC RI PT 57 Spent coffee ground was rarely investigated until the beginning of this decade with half 66 (36 out of 72) of the total number of papers published in the last 4 years since 1973. A 67 cursory search of ‘spent coffee ground’ on “Scopus” produces similar result with 11, 27, 68 14, 15 and 2 publications annualy from 2014 to 2010. This review aims to use existing 69 knowledge on spent coffee ground and/or its components in developing a biorefinery 70 platform to add value to this inexpensive waste product. D M AN U 65 2. Carbohydrates The coffee bean is a rich source of polysaccharides (~ 50% of the green bean’s dry weight) 74 mainly consisting of mannans or galactomannans, type II arabinogalactans, and cellulose. 75 Mannan, the main polysaccharide of coffee extract, is responsible for its high viscosity, 76 which in turn negatively affects the technological processes involved in instant coffee 77 production. This polysaccharide consists of ș-(1Ѝ4)-linked mannan chains substituted at 78 approximately every 100 residues in the O-6 position with single galactose residues. 79 Arabinogalactans have an arabinose/galactose ratio of 0.4/1 and consist of ș-(1Ѝ3)-linked 80 galactose backbone substituted at the O-6 position with arabinose and/or galactose residues. 81 The side-chains contain arabinose and galactose residues with arabinose as terminal 82 residue. These linkages are characteristic of type-II arabinogalactans, a polymer usually 83 covalently linked to protein (Bradbury & Halliday, 1990). The roasting process increases 84 both bean arabinogalactan and mannan solubility by loosening the cell-wall structure as it AC C EP TE 71 72 73 4 ACCEPTED MANUSCRIPT swells and by polysaccharide depolymerization (Wei, Furihata, Koda, Hu, Miyakawa, & 86 Tanokura, 2012). The water-soluble polysaccharides that appear after roasting play an 87 important role in retaining volatile substances, and contribute to the coffee brew viscosity 88 and, thus, to the creamy sensation known as “body” in the mouth (Illy, Viana, & Roasting, 89 1995). 90 These galactomannans and arabinogalactans are extracted upon coffee roasting, during the 91 beverage preparation, using hot pressurized water (Nunes & Coimbra, 2001). However, 92 most of these polysaccharides remain as insoluble material bound to the SCG matrix 93 (Mussatto, Carneiro, Silva, Roberto, & Teixeira, 2011a; Simões, Nunes, Domingues, & 94 Coimbra, 2013). Galactomannans exhibit different physicochemical properties and are 95 therefore used in many applications: they are excellent stiffeners and emulsion stabilizers, 96 and the absence of toxicity allows their use in the textile, pharmaceutical, biomedical, 97 cosmetics and food industries. The main applications of galactomannans in food are in 98 dairy products, fruit-based water gels, powdered products, bakery, dietary products, coffee 99 whiteners, baby milk formulations, seasonings, sauces and soups, tinned meats and frozen M AN U SC RI PT 85 and cured meat foods (Prajapati et al., 2013). 101 Spent coffee ground is rich in sugars polymerized into cellulose and hemicellulose 102 structures, which correspond to almost half (45.3%, w/w, dry weight) of the material. SCG 103 contains 46.8% mannose, 30.4% galactose, 19% glucose, and 3.8% arabinose, with 104 mannans as the major polysaccharides (Mussatto, Carneiro, Silva, Roberto, & Teixeira, 105 2011a). However, further investigation by the same group (Mussatto, Machado, Carneiro, 106 & Teixeira 2012) revealed a lower (2.2-fold) sugar composition for the same SCG 107 consisting of 21.2% mannose, 13.8% galactose, 8.6% glucose, and 1.7% arabinose. This 108 SCG can be hydrolyzed (100 mg H2SO4/g dry matter; liquid/solid ratio 10 g/g; 163 °C, 45 109 min), and efficiently (> 85%) fermented to ethanol by yeast (Mussatto, Machado, Carneiro, 110 & Teixeira, 2012). Simões et al., (2009) reported the presence of mannose (57%), followed 111 by galactose (26%), glucose (11%), and arabinose (6%); the differences in chemical 112 composition of SCG probably reflect the variety of beans and processes used in roasting 113 and extraction. Earlier study (Stahl, Bayha & Fulger, 1984) showed that mannan, more 114 prevalent than cellulose in SCG, is substantially separately hydrolyzable from the cellulose AC C EP TE D 100 5 ACCEPTED MANUSCRIPT 115 enabling production of pure mannan hydrolysate. This hydrolysate produces high (40%) 116 mannitol yield with sorbitol as a co-product. Mannooligosaccharides (MOS), non-digestible oligosaccharides composed principally 118 of mannose, has also been derived by hydrolyzing mannan in spent coffee grounds at high 119 temperature (220 °C) and pressure (Asano et al., 2001). The major components of manno- 120 oligosaccharides were mannobiose, mannotriose, and mannotetraose. Studies in Japan 121 (Takao et al., 2006 and references therein) showed that MOS could promote bifidobacteria 122 growth in the intestines and improve the fecal characteristic on human subjects. 123 Furthermore, a daily intake of a 300 ml drink containing MOS (1 or 2 g/100 ml) reduced 124 abdominal and subcutaneous fat level in humans when administered daily for twelve 125 weeks. Further studies showed that MOS inhibited intestinal fat absorption from a high fat 126 diet by decreasing fat accumulation in the parametrial adipose tissue and liver, while 127 simultaneously increasing fat excretion. MOS derived from coffee mannan has been 128 developed as active prebiotic ingredient in Japan (Aginomoto Co. Inc.) and approved as 129 Food for Specified Health Uses (FOSHU) oligosaccharide functional food ingredient 130 (Fukami, 2010). M AN U SC RI PT 117 Espresso (dark roasted Arabica) SCG consisted mainly of mannose (46%), galactose 132 (27%), glucose (20%), and arabinose (7%) with galactomannans as the major 133 polysaccharide accounting for approximately 50% the total carbohydrates (Simões, Nunes, 134 Domingues, & Coimbra, 2013). Roasting SCG (160 °C) improves the extractability of 135 galactomannans (total 56%) without degradation, preserving their β-(1-4)-Man backbone, 136 Gal and Ara side chains, and acetylation. Microwave assisted extraction (MAE) allows the 137 recovery of arabinogalactans, while a re-extraction of the residual material (MAE2) enables 138 higher galactomannan yield. Through this method 74% and 66% of total galactose and 139 mannose could be extracted from SCG (Passos & Coimbra, 2013). TE EP AC C 140 D 131 141 The carbohydrate composition of exhausted coffee waste is reduced to only two 142 monomers: glucose (59.2 and 62.9% of total sugars) and mannose (40.8 and 37.1%) by 143 alkali extraction (Pujol et al., 2013). However, the hemicelluloses reported by these authors 144 contrast with previous studies (Mussatto, Ballesteros, Martins, & Teixeira, 2011; Simões et 145 al., 2009) indicating the presence of galactose and arabinose in SCG. These two 6 ACCEPTED MANUSCRIPT 146 monosaccharides are probably easily hydrolyzed during alkali extraction. SCG are primarily composed of neutral detergent fiber (45.2%) occurring as 148 hemicellulose, cellulose, and lignin-associated compound, and acid detergent fiber (29.8%), 149 consisting of cellulose and lignin (Vardon et al., 2013). The isolation of dietary fiber (DF) 150 from plant by-products can be accompanied by the recovery of other constituents like 151 antioxidants or proteins; SCG, for example contains 43% total fiber (35% and 8% soluble 152 and insoluble, respectively) (Murthy & Naidu, 2012b). Furthermore, the coffee fibers from 153 SCG exhibit antioxidant properties: 2.4 mmol of trolox/100 g of dry weight (Murthy & 154 Naidu, 2012b) similar to well-known food antioxidant such as red wine products (43%) and 155 peaches (36%). Therefore, DF from SCG can be categorized as antioxidant dietary fiber, 156 useful as potential dietary supplement. M AN U 3. Proteins SC RI PT 147 SCG contain significant amount of proteins (13.6%, w/w). Total coffee nitrogen 160 compounds are relatively stable between species or even during roasting, ranging from 8.5 161 to 13.6% (Belitz, Grosch, Schieberte, 2004). Crude protein reported by Cruz et al., (2012) 162 in espresso coffee residues vary between 12.8 and 16.9%. The mean protein content of 163 SCG is 13.6% after soluble coffee preparation (Mussatto, Ballesteros, Martins, & Teixeira, 164 2011a; Silva, Nebra, Machado Silva, & Sanchez, 1998), EP TE D 157 158 159 According to Arya & Rao (2007), roasted coffee contains on average 3.1% (w/w) 166 protein. The protein content in SCG is higher than in the coffee bean due to concentration 167 of the non-extracted components during instant coffee preparation. The protein content in 168 SCG may be overestimated due to the presence of other nitrogen-containing substances 169 (caffeine, trigonelline, free amines and amino acids) (Delgado, Vignoli, Siika-aho, & 170 Franco, 2008). However, many authors report similar protein contents, varying between 171 6.7% and 9.9% (Lago, Antoniassi, & Freitas, 2001) and up to 14% (Ravindranath, Khan, 172 Obi Reddy, ThirumalaRao, & Reddy, 1972). AC C 165 7 ACCEPTED MANUSCRIPT Data on amino acids content is limited to a single report (Lago, Antoniassi, & Freitas, 174 2001) of SCG collected from three instant coffee producers using four different extractors. 175 SCG protein has similar or higher levels of the essential amino acids leucine, valine, 176 phenylalanine, and isoleucine than conventional feed products such as soybean meal (Table 177 1). Isoleucine, leucine and valine contents of SCG are over twice the levels in soybean 178 meal. Lysine content is low in SCG, although it is as high in coffee pulp and 11S protein as 179 in soybean meal (on a per gram nitrogen basis) (Elias, 1979). The essential amino acids 180 comprise almost half (~ 49%) of the total SCG amino acid mainly leucine contributing 13 181 or 21% of the total content. Most SCG amino acid contents, except arginine, aspartic acid, 182 lysine, phenylalanine, serine and threonine are considerably higher than those in coffee 183 pulp and/or 11S protein. The 11S protein, similar to other plant storage proteins, accounts 184 for approximately 45% of total proteins in coffee endosperm tissue, representing 5-7% of 185 coffee dry bean weight (estimated on 11-15% protein). This storage protein consists of a 186 high (α-component, ~32 kDa) and a low (β-component, ~22 kDa) molecular subunit easily 187 recognized on two-dimensional profiles of green coffee proteins (Rogers, Bézard, 188 Deshayes, Meyer, Pétiard, & Marraccini, 1999). The low level of the hydroxyl-amino acids 189 serine and threonine in SCG relative to those in coffee pulp and/or 11S protein reflects their 190 reactivity during the brewing process producing volatile heterocyclic compounds, 191 alkylpyrazines (Oestreich-Janzen, 2010). TE D M AN U SC RI PT 173 SCG protein is high in the essential branched chain amino acids (BCAA) and Fischer 193 ratio, higher than those of soymeal or soybean protein (Table 1). Some SCG protein with 194 low (< 1%) aromatic amino acid content has high Fischer ratio similar to those generally 195 derived by hydrolysis and extensive purification process. Proteins with high BCAA, 196 Fischer ratio and low content of aromatic amino acids are sought for producing 197 physiologically functional foods for specific needs, such as in patients with malnutrition 198 associated with cancers, burns, trauma, and liver failure, and for nutritional support of 199 children with chronic or acute diarrhoe or milk protein allergies (Oomah, 2001 and 200 references therein). Protein with Fischer ratio higher than 20 and aromatic amino acids 201 (AAA) lower than 2% have been used to treat patients with hepatic encephalopathy 202 (Udenigwe & Aluko, 2010); thus the SCG protein could be used to formulate food products 203 with multiple human health benefits during liver diseases, oxidative stress and AC C EP 192 8 ACCEPTED MANUSCRIPT 204 hypertension. The lysine/arginine ratio, a determinant of the cholesterolaemic and 205 atherogenic effects of a protein, is high for SCG protein, suggesting that it can contribute to 206 hypercholesterolemic and atherogenic physiological effects. 207 excellent source of arginine, glutamine and histidine, the three amino acids known to have 208 strong effects on the immune functions of the body. The high cysteine and methionine 209 content of some SCG protein can boost the body’s antioxidant levels, potentially stabilizing 210 DNA during cell division and reducing the risk of certain forms of colon cancer. The 211 essential amino index of SCG is high (79-129%) relative to soybean protein and higher than 212 those of soymeal (Table 1) due primarily to the contribution of leucine and isoleucine. SC RI PT SCG protein is also an Early studies (Silva et al., 1998 and references therein) showed that coffee grounds have 214 low nitrogen content (~ 2%), high acidity (~ 4.2 pH) containing only half of the essential 215 amino acids required for animal feed. In vivo evaluation of SCG in sheep showed negative 216 metabolisable energy contents (-1.5 & -1.1 MJ/kg dry matter), based primarily on the 217 negative crude protein digestibility (-0.53 & -0.92) despite the high gross-energy content 218 (Givens & Barber, 1986). However, the high non-protein nitrogen (~46% of the total 219 nitrogen) present in SCG (Sikka, Bakshi, & Ichhponani, 1985) may partly explain its low 220 biological effect observed in several animal feeding studies. SCG (12.55% protein) at 10% 221 of an isonitrogenous concentrate mixture has been safely incorporated in fattening pig 222 ration without adverse health effects on carcass quality (Sikka & Chawla, 1986). However, 223 15% SCG significantly depressed daily live weight gains and feed conversion efficiency. 224 Feed conversion ratios were 6.88, 6.95, and 8.10 for control (conventional feed ingredient 225 formulation), 10% and 15% SCG rations, respectively. The poor feedlot performance of the 226 pigs was attributed to the higher fiber content (14.8, 16.7, and 19.1% for control, 10%, and 227 15% SCG, respectively), thereby reducing the digestion of energy-yielding nutrients. SCG 228 has low nitrogen solubility (28.6%) primarily due to protein denaturation and low pepsin 229 digestibility (35.3%) resulting from intramolecular linkage formation during coffee bean 230 roasting (200 °C, 20 min), limiting enzyme hydrolysis (Sikka, Bakshi, & Ichhponani, 231 1985). 232 233 AC C EP TE D M AN U 213 4. Non-protein nitrogeneous compounds 9 ACCEPTED MANUSCRIPT Nitrogenous compounds (free amino acids, peptides, alkaloids) contribute considerably to 235 the development of coffee flavor and quality during roasting. The protein profile of coffee 236 changes during roasting, the proteins are both fragmented and polymerized, and integrated 237 into melanoidins. Other protein components such as peptides and free amino acids 238 constitute up to 1.5% of green coffee, whereas alkaloids (3-4%), of which trigonelline 239 represents about 1%, are transformed during roasting (Oestreich-Janzen, 2010). According 240 to Oestreich-Janzen (2010), total amino acid content of Arabica roast and brew amount to 241 10.1 and 6.4% dry weight, respectively, suggesting that 3.7% dry weight of amino acids 242 can be found in SCG. 243 The content of non-protein nitrogenous compounds in SCG could be useful in agriculture. 244 Compost and reclamation substrates from SCG can be used for intensive remediation, 245 positively affecting microbial activity and reducing leaching of mineral nitrogen (Nmin) 246 from the arable soil (Elbl et al., 2014). Compost available carbon increases microbial 247 activity, resulting in increased capacity for mineral nitrogen retention (additionally supplied 248 from compost and another mineral fertilizer). Nmin is captured in soil organic matter (Diaz, 249 Bertoldi, & Bidlingmaier, 2007). In this regards, SCG, after oil extraction, has a 250 carbon/nitrogen ratio of 19.8:1 (wt) (Kondamudi et al., 2008), similar to soil needs (20:1) 251 (Elbl et al., 2014). Despite this, the use of SCG is limited to gardens as compost for the 252 plants. Recently, the positive soil amendment impact of SCG has been confirmed in 253 enhancing the physical and nutritional features of lettuce, endorsing its potential use in 254 agroindustry (Cruz et al., 2014). EP TE D M AN U SC RI PT 234 255 256 257 Caffeine, 1,3,7-trimethyl-xanthine, a purine alkaloid, is the quintessential single most 258 popular compound recognized in coffee and coffee products/ingredients. This alkaloid is 259 removed from coffee beans by the decaffeinating process commonly used in the industrial 260 scale. Although the caffeine content in coffee waste is lower than that in coffee beans, a 261 large amount of caffeine still remains. Higher caffeine can be extracted from coffee husks 262 (Tello, Viguera, & Calvo, 2011) or coffee pulp (Murty& Naidu, 2012) than from SCG. 263 Caffeine concentrations range from 0.734 to 41.3 µg/mg of spent coffee ground extracts, AC C 4.1. Caffeine 10 ACCEPTED MANUSCRIPT obtained by low-pressure extraction (ultrasound and Soxhlet) and supercritical fluid CO2 265 extraction (SFE) varying in yield from 9 to 15% (Table 2) (Andrade et al., 2012). The 266 polar solvent, dichloromethane extracts the most caffeine at low pressure, whereas SFE at 267 high pressure (300 bars) is more efficient, both in terms of generating higher caffeine yield 268 and environmental footprint. Caffeine obtained from SCG is equivalent to 18 – 48% of 269 those extracted from coffee beans by supercritical CO2 (Saldaña, Mohamed, Baer, & 270 Mazzafera, 1999) or 8-31% of roasted coffee (Ramalakshmi, Rao, Takano-Ishikawa, & 271 Goto, 2009). Supercritical CO2 has long been used to decaffeinate coffee beans and 272 therefore can be integrated in processing SCG. Various caffeine concentrations (0.007 – 273 0.5%) have been reported depending on extraction process and SCG source (Andrade et al., 274 2012; Cruz et al., 2012; Murty & Naidu, 2012; Ramalakshmi, Rao, Takano-Ishikawa, & 275 Goto, 2009). Thus, caffeine content for Arabica range between 0.9 to 1.6%, Robusta (1.4- 276 2.9%), mix (60 Arabic/40 Robusta) (1.7%). In espresso-style percolation, the very short 277 time available to extract caffeine from the cellular structure leads to 75 – 85% extraction 278 yield with only15-25% caffeine left in the SCG (Oestreich-Janzen, 2010). M AN U SC RI PT 264 Spent coffee extracts of both Arabica (0.5%) and Robusta (0.2%) contain lower caffeine 280 than low-grade green coffee beans (1.7%) (Ramalakshmi, Rao, Takano-Ishikawa, & Goto, 281 2009). However, high caffeine (6 – 11.5 mg/g dry matter) were detected in the extracts of 282 SCG from coffee bars; the higher amount observed in SCG from Robusta was nearly twice 283 that from Arabica (Panusa, Zuorro, Lavecchia, Marrosu, & Petrucci, 2013). Caffeine was 284 low in SCG extracts from capsules (obtained from an automatic espresso machine), 285 (0.96−0.97 mg/g dry sample) (Panusa, Zuorro, Lavecchia, Marrosu, & Petrucci, 2013). In 286 this regard, caffeine content ranged from 1.94 to 7.88 mg/g (DW), with a mean of 4.53 287 mg/g (DW) in espresso coffee (Cruz et al., 2012). The caffeine extractability coefficient in 288 espresso coffee is 75−85%, so these figures correspond to predicted mean caffeine content 289 of 22.5 mg/g (DW) in the original roasted beans, in accordance with the literature (Bicho, 290 Leitão, Ramalho, & Lidon 2011; Casal, Oliveira, Alves, & Ferreira, 2000). AC C EP TE D 279 291 Caffeine (1.8 mg/g SCG) present in SCG prepared from espresso coffee may serve as a 292 chemical defence mechanism in some plants, while adversely inducing toxicity in other 293 plants such as lettuce (Cruz et al., 2012). Caffeine in SCG is completely degraded by 294 Pleutotusostreatus LPB 09 fungal cultures enabling economical utilization of SCG as 11 ACCEPTED MANUSCRIPT substrates for edible fungi/mushroom cultivation without any pretreatments (Fan, Pandey, 296 Mohan, & Soccol, 2000). This observation has been used in the development of a patent 297 application where mycelium is used in reducing coffee bitterness. Caffeine presence as a 298 nitrogen precursor plays an important catalytic role in hydrogen sulphide oxidation in the 299 preparation of activated carbon from SCG (Kante, Nieto-Delgado, Rangel-Mendez, & 300 Bandosz, 2012). It also contributes significantly in lowering/reducing interfacial tension 301 equilibrium in oils, important in defining the emollient characteristics of pharmaceutical 302 and/or cosmetic products. SC RI PT 295 303 304 305 The nitrogenous brown-colored compounds of coffee result from the non-enzymatic 306 browning (Maillard) reaction between reducing sugars and compounds with a free amino 307 group forming various products including the melanoidins (Moreira, Nunes, Domingues, & 308 Coimbra, 2012). Maillard reaction products may be useful for functional food application 309 and/or as food preservative, since they exhibit antioxidant capacity and inhibit lipid 310 peroxidation (Jung, Park, Ahn, & Je, 2014). Melanoidins are the high molecular weight 311 (HMW) brown products containing nitrogen, end products of the Maillard reaction (Nunes, 312 Cruz, & Coimbra, 2012) with small amounts (< 6%) of amino acids, primarily glutamic 313 acid and glycine released by acid hydrolysis. During coffee brewing, only 33% of the 314 original green coffee bean protein is extracted with hot water, the residual protein remains 315 insoluble due partly to denaturation and association with cell wall arabinogalactans 316 representing nearly 92% of the total nitrogen present in the high molecular weight 317 melanoidins (HMWM) (Nunes, Cruz, & Coimbra, 2012). Ethanol (70-80%)-soluble 318 HMWM has the highest protein content, but amino acid composition similar to all 319 melanoidin fractions. The amino acid composition of these melanoidin fractions (abundant 320 in alanine, aspartic acid/asparagine, glutamic acid/glutamine, and glycine) is similar to 321 those reported for roasted coffee beans and roasted coffee brews. AC C EP TE D M AN U 4.2. Brown-colored compounds 322 Browning index of SC extracts from Arabica (0.165) and Robusta (0.145) coffee from 323 filter coffeemaker was 3-5-fold higher than those obtained from espresso and plunger 324 coffeemakers (Bravo et al., 2012). Aqueous extracts from soluble SCG has lower browning 12 ACCEPTED MANUSCRIPT 325 index (0.271) compared to that from roasted coffee brews (0.305) (Yen, Wang, Chang, & 326 Duh, 2005). 327 extraction of brown compounds measured by absorbance at 420 nm (from 0.090 to 0.160) 328 (Bravo, Monente, Juániz, De Peña, & Cid, 2013). Passos & Coimbra (2013) suggested that 329 SCG consists of 16% melanoidins, whose chemical composition has not yet been 330 established (Nunes & Coimbra, 2010). RI PT Furthermore, a solid–liquid method has been proposed as an efficient 331 5. Lipids Spent coffee grounds have often been reported to contain 10 – 15 % (Jenkins, Stageman, 335 Fortune, & Chuck, 2014), and sometimes higher average 20% (range 19.9-27.8%) lipids 336 (Lago, Antoniassi & Freitas, 2001) or 13.9 – 29.2% ether extract, on dry weight basis 337 (Silva, Nebra, Machado Silva, & Sanchez, 1998). During the brewing process, lipids stick 338 to the spent grounds and are filtered off, in filter home brew as well as in instant coffee 339 production (Oestreich-Janzen, 2010). Lipid yield (7 – 13% dry weight) is low when SCG 340 suspended in fresh heptane (1:10 weight ratio) is stirred (3 h) at room temperature (Jenkins, 341 Stageman, Fortune, & Chuck, 2014). SCG extracted with hexane yield high oil (15.3%), 342 with low acid (3.65%) and saponification (173) values, parameters important for fatty acid 343 methyl ester (FAME) manufacturing (Al-Hamamre, Foerster, Hartmann, Kröger, & 344 Kaltschmitt, 2012). Commercial ethanol (99%) has been used to recover lipids from 345 industrial spent coffee grounds containing 25.6% oil (dry weight petroleum ether 346 extraction). Maximum oil yield (82%) was obtained at 1:7 SCG: alcohol ratio, 75 °C and 347 not affected by extraction time (1 or 2 h) and pretreatment (milling or extrusion). The 348 extracted oil had characteristics similar to petroleum ether extract (Freitas, Monteiro, & 349 Lago, 2000). AC C EP TE D M AN U SC 332 333 334 350 SCG total lipids range from 9.3 to 16.2% (Cruz et al., 2012), 10-15% and 14-15.4% 351 from espresso coffee residues, filter and industrial soluble coffee, respectively (Kondamudi, 352 Mohapatra, & Misra, 2008; Couto, Fernandes, da Silva, & Simões, 2009; Calixto et al., 353 2011). Also, the yield of SCG oil extracted using Soxhlet, is a function of extraction 354 conditions, particularly, the choice of solvent and the duration of extraction. Supercritical 13 ACCEPTED MANUSCRIPT carbon dioxide extracts up to 85% of the total amount of SCG oil after 3 h (corresponding 356 to a maximum yield of 15.4 goil/100 gdry SC) (Couto, Fernandes, da Silva, & Simões, 2009). 357 Although hexane is the most widely and commonly used solvent, modern environmentally 358 friendly technology such as SFE is increasingly being used for SCG oil extraction. A 359 manufacturing cost of US$ 48.60/kg has been estimated for spent coffee oil obtained by 360 supercritical technology (200 bar, 50 °C, 90 min) and may reach US$ 460/kg depending on 361 process conditions (Andrade & Ferreira, 2013). RI PT 355 Commercial SCG contains higher oil (16.7 & 17.2%) compared to raw (9-12.6%), 363 roasted (12-15%), or laboratory extracted SCG (7.9-14%); free fatty acids (120-148 vs 4-10 364 acid value), and lower unsaponifiable matter (5.9-9.4% vs 9-13.2%) relative to those 365 produced in the laboratory (Ravindranath, Khan, Obi Reddy, ThirumalaRao, & Reddy, 366 1972). Coffee brews prepared by different methods showed that lipids (90.2%) mainly 367 remained in SCG with the following lipid composition (% total lipids), 84.4% 368 triacylglycerols, 12.3% diterpene alcohol esters, 1.9% sterols, 1.3% polar material, and 369 0.1% sterol esters. The lipid composition is similar to those of boiled or filtered coffee with 370 87-93% triglycerides, 7-13% diterpene alcohol esters, 0.2-0.9% sterols, and up to 0.8% 371 polar material (Ratnayake, Hollywood, O'Grady, & Stavric, 1993). However, the lipid 372 composition of SCG may vary analogous to those of green coffee oil depending on the 373 source, although generally up to 80 – 90% of the oil will be glycerides, including free fatty 374 acids, with the rest of the lipids containing terpenes, sterols and tocopherols (Jenkins, 375 Stageman, Fortune, & Chuck, 2014). Raw green coffee oil consists of: triacylglycerols 376 (75%), terpene esters (14%), partial acylglycerols (5%), free fatty acids (1%), free sterols 377 (1.5%), sterol esters (1%), and polar lipids (<1%) (Nikolova-Damyanova et al., 1998, cited 378 in De Azevedo et al., 2008). Khan & Brown (1953) provide a good review on earlier 379 investigation on raw and roasted coffee bean oil characteristics and composition. Coffee oil 380 contains excessive amounts of unusual unsaponifiables, 19% (or 24% for defective coffee 381 beans) according to Oliveira et al., (2008), the presence of which makes the oil unfit for 382 most uses. However, the unsaponifiables containing the diterpenes kahweol and cafestol 383 known for their beneficial physiological effects (UVB skin protection, anticarcinogenic, 384 anti-inflammatory and antioxidant activities) (Silva, Vieira, & Hubinger, 2014) can be 385 completely removed by molecular distillation. AC C EP TE D M AN U SC 362 14 ACCEPTED MANUSCRIPT SCG oils consist predominantly of linoleic, palmitic, stearic and oleic acids (Table 3). 387 Arachidic (≤ 7%) and linolenic (< 5%) acids are also present in most SCG oils, whereas 388 lauric and myristic acids are rarely detected depending on extraction conditions, processing 389 and origin. The contrasting fatty acid profile exemplifies the effects between two processes 390 used in obtaining SCG oil (Todaka, Kowhakul, Masamoto, Shigematsu, & Onwona- 391 Agyeman, 2013). SCG oils can be conveniently categorized into two clusters based on their 392 fatty acid profile; those with low palmitic (< 40%) and high linoleic (> 40%) acids and 393 conversely those with high palmitic (> 40%) and low linoleic (< 40%) acids (Table 3). 394 These clusters result in polyunsaturated/saturated ratios < 1 or >1 of the extracted oils. SCG 395 oils with polyunsaturated/saturated ratio > 1 are less atherogenic and thrombogenic than 396 those with ratio <1 due to the potential favorable reduction of serum cholesterol and 397 atherosclerosis and prevention of heart diseases (Rudel, Parks, & Sawyer, 1995). The 398 cholesterol-raising factor from coffee beans has been attributed to the presence and/or 399 concentration of the diterpenes kahweol and cafestol that varies depending on several 400 factors (Urgert, Schulz, & Katan, 1995) including the oil extraction process (Acevedo et al., 401 2013). M AN U SC RI PT 386 D 402 High palmitic acid SCG oils represent a rich and suitable source of palmitic acid for 404 soap manufacture and/or the acid itself according to Ravindranath, Khan, Obi Reddy, 405 ThirumalaRao, & Reddy (1972). Furthermore, the combination of high linoleic (~44%), 406 palmitic (~36%) and oleic (~9%) acids, predominant in SCG oils can result in high biomass 407 and polyhydroxylalkanoates (PHA)-an alternative completely biodegradable synthetic 408 polymer- yields (Obruca et al., 2014). Fatty acid compositions of SCG oils differ 409 significantly under different SFE (pressure, temperature, co-solvent: CO2 mass ratio) 410 conditions (Ahangari & Sargolzaei, 2013; Couto, Fernandes, da Silva, & Simões, 2009). 411 SCG oil has efficiently been extracted (>90% yield) by supercritical carbon dioxide 412 (scCO2) recently in a pilot plant (Cruz et al., 2014) and used for producing high yielding 413 PHA (0.77 kg PHA/kg SCG oil; 97 kg per ton of SCG processed). AC C EP TE 403 414 SCG oil also contains minor lipid components, such as sterols well known for their 415 serum cholesterol lowering effect by reducing intestinal absorption of cholesterol. Sterols 416 constitute about 5.4% of the total lipids in Arabica coffee and consist of sitosterol (53%), 15 ACCEPTED MANUSCRIPT stigmasterol (21%), campestol (11%), cycloartenol (8%), and the remaining sterols are each 418 5% or less of the total sterol fraction (Spiller, 1998). Sterol content of SCG depends on the 419 origin and source of roasted coffee (Table 4) with sitosterol, stigmasterol, and campesterol 420 as the most abundant sterols, predominating in higher plants and in typical diets. These 421 three sterols account for 88 - 92% of the total sterols in SCG or roasted coffee oils. The 422 concentration of the minor sterol, ∆5- avenasterol also varies in accordance with the level in 423 roasted coffee (Table 4) reaching up to 9% of the total sterols. In fact, sitosterol and ∆5- 424 avenasterol are the two most differentiating sterols used to separate Arabica from Robusta 425 coffee varieties (Carrera, León-Camacho, Pablos, & González, 1998) because its 426 polymerization protects oils from oxidation SC RI PT 417 Several methods have been devised to extract/prepare the diterpenes, cafestol and 428 kahweol from coffee oil because of their potential use and applications in pharmacological 429 and cosmetic preparations. Cafestol is minimally affected by various treatments of coffee 430 beans and is one of the components that remains in spent coffee grounds (1.2%) 431 (Spiller,1998). Khan & Brown (1953) identified kahweol as one of the unsaponifiables with 432 characteristic brown precipitate formation of SCG oil extracted from fresh roasted blend of 433 Brazilian, Colombian, and Venezuelan coffees. Direct saponification produces high level of 434 diterpenes (2.14 and 4.66 mg/g SCG of kahweol and cafestol, respectively) compared to 435 saponification of oil extracted by solid liquid extraction or supercritical extraction 436 (Acevedo et al., 2013). Diterpene yield from SCG depends on processing conditions during 437 supercritical CO2 extraction; thus concentration of cafestol (0.207 mg/g SCG) and kahweol 438 (0.114 mg/g SCG) are lower at 40 °C/98 bar than those at 80 °C/379 bar (0.828 and 0.425 439 mg/g SCG for cafestol and kahweol, respectively) (Acevedo et al., 2013). AC C EP TE D M AN U 427 6. Minerals 440 441 442 SCG also contains ash (1.6 %), which, according to the ICP-AES analysis, consists of 443 several minerals. Potassium is the most abundant element, followed by phosphorus and 444 magnesium (Mussatto, Ballesteros, Martins, & Teixeira, 2011a). Potassium is also the 445 predominant mineral in coffee beans, corresponding to 40% of the oxide ash (Grembecka, 446 Malinowska, & Szefer, 2007). Most minerals are easily extracted with hot water during 16 ACCEPTED MANUSCRIPT instant coffee preparation. Total mineral (K, Mg, P, Ca, Na, Fe, Mn, and Cu) content of 448 espresso SC varies from 0.82 to 3.52%, confirming mineral leaching during espresso coffee 449 preparation, although not as exhaustive as with soluble coffee (Cruz et al., 2012). 450 Potassium, the major mineral of espresso SC, ranges from 3.12 to 21.88 mg/g (Cruz et al., 451 2012). The industrial SCG contains lower absolute (3.55 mg/g) and relative amounts (22%) 452 of this element. Coffee is regarded as an important source of Mg, comprising 11% of the 453 SCG minerals, again higher than those of industrial SC (Mussatto, Ballesteros, Martins, & 454 Teixeira, 2011a). SC RI PT 447 7. Phenolic compounds Phenolic compounds are the major determinant of antioxidant potentials found in high 458 concentrations in plants (Balasundram, Sundram, & Samman, 2006). Recently, interest in 459 plant-derived natural products has grown, mainly because synthetic antioxidants suffer 460 from several drawbacks. SCG contain several human health related compounds, such as 461 phenolics with demonstrated antioxidant, anti-bacterial, antiviral, anti-inflammatory and 462 anti-carcinogenic activities (De Souza et al., 2004). D M AN U 455 456 457 The recovery of phenolic compounds from the coffee industry by-products and their 464 antioxidant activity has been investigated recently. Phenolic compounds from coffee by- 465 products (coffee pulp, husk, silver skin, and SC) have been extracted using solvent mixture 466 of isopropanol and water (Murthy & Naidu, 2012b). The coffee by-products contained 467 about 1–1.5% total polyphenols with the highest yield for silver skin (25%), followed by 468 spent waste (19%) and cherry husk (17%) when pretreated with viscozyme. Chlorogenic 469 acid (CGA) was the major phenolic component when analyzed with high-performance 470 liquid chromatography. In fact, phenolic compounds are mainly found in green coffee 471 beans as CGA (up to 12% solids) (Esquivel & Jimenez, 2012). These CGA are water- 472 soluble esters formed between quinic acid and one or two moieties of caffeic acid, a trans- 473 cinnamic acid. Caffeoylquinic acids (CQA) are the most abundant phenolic compounds in 474 coffee. Monocaffeoylquinic acids (3-CQA, 4-CQA, 5-CQA) and dicaffeoylquinic acids 475 (3,4-diCQA, 3,5-diCQA, 4,5-diCQA) were identified and quantified in SC obtained from AC C EP TE 463 17 ACCEPTED MANUSCRIPT different coffeemakers (filter, espresso, plunger, and mocha) and in their respective coffee 477 brews by Bravo et al (2012). All SCG, with the exception of those from the mocha 478 coffeemaker, have relevant amounts of total caffeoylquinic acids ranging from 11.05 mg 479 (espresso) to 13.24 mg (filter) per gram of Arabica SC and from 6.22 mg (filter) to 7.49 mg 480 (espresso) per gram of Robusta SC. Espresso SCG shows high variability, with 5-CQA 481 ranging from 0.397 to 2.642 mg/g (DW) and total CGA varying from 2.12 to 7.66 mg/g 482 (DW) (Cruz et al., 2012). RI PT 476 The antioxidant phenolic compounds from SCG have been extracted by the conventional 484 solid–liquid method. For example, extraction with 60% methanol (40 ml/g SCG 485 solvent/solid ratio, 90 min) produces a high phenolic extract (16 mg gallic acid equivalents 486 (GAE)/g SCG) with high antioxidant activity (FRAP of 0.10 mM Fe(II)/g) simultaneously 487 (Mussatto, Ballesteros, Martins, & Teixeira, 2011). Phenolic compounds from SCG [coffee 488 bars (SCG-1) or coffee capsules (SCG-2)] have been extracted by an environmentally 489 friendly and cost-effective process, using aqueous ethanol under mild temperature 490 conditions to preserve the activity of the phenolic compounds (Zuorro & Lavecchia, 2012). 491 Total phenolic content of SCG-1 and SCG-2 were 17.75 and 21.56 mg GAE/g, 492 respectively. Thus phenolic-rich extracts can be obtained from SCG using an 493 environmentally friendly and simple solvent-extraction procedure. Ethanol also influenced 494 microwave-assisted extraction of natural antioxidants from spent filter coffee (Pavlović, 495 Buntić, Šiler-Marinković, & Dimitrijević-Branković, 2013). The highest total phenolic 496 compounds (399 mg GAE/g extract, dry matter) was obtained with 20% aqueous ethanol 497 under just 40 s of microwave radiation (80 W), implying that the method is very effective, 498 saving time and chemicals. The extracts (20 µg/mL) exhibited high in vitro antioxidant 499 activities inhibiting 90% of DPPH radicals, supporting their biological stability. This 500 research group later found that total phenolic compounds of SCG were strongly correlated 501 with their DPPH scavenging activity, and therefore mainly responsible for the antioxidant 502 activity. An UHPLC-PDA-TOF-MS system was used to separate, identify, and quantify 503 phenolic and non-phenolic compounds in the SCG extracts. High amounts of CGA and 504 related compounds as well as caffeine demonstrate the high potential of SCG, a waste 505 material that is widely available in the world, as a source of natural phenolic antioxidants 506 (Panusa, Zuorro, Lavecchia, Marrosu, & Petrucci, 2013). AC C EP TE D M AN U SC 483 18 ACCEPTED MANUSCRIPT 8. Ingenuity/knowledge gap Table 5 provides a short survey of product and/or process innovation using SCG or 510 coffee products including SCG. Earlier innovation (pre 2005) explored the extraction of 511 specific components such as oil, flavor, terpenes, and alcohols as value-added products. 512 Later studies focus extensively on innovation in bioenergy and biorefinery using SCG as a 513 source product. In reality, there has been minimal attempt in complete integrated 514 fractionation and utilization of SCG components for industrial and/or other use, although 515 these components have been individually well researched (Figure 2). RI PT 507 508 509 Spent coffee grounds represent a resource for an integrated product focused biorefinery. 517 It has been proven that the conversion of biomass waste to bulk chemicals for example was 518 nearly 7.5 and 3.5 times more profitable than its conversion to animal feed or transportation 519 fuel, respectively, highlighting the marginal value of 1st generation food supply chain waste 520 recycling (anaerobic digestion, composting, animal feed) (Pfaltzgraff, Cooper, Budarin, & 521 Clark, 2013). The key to go beyond 1st generation waste valorization is to make use of all 522 the valuable components in waste, taking into consideration the presence of high-value 523 products. A good example of 2nd generation products is succinic acid obtained through 524 sugar fermentation of enzyme-hydrolyzed carbohydrates from SCG (Koutinas et al., 2013). 525 SCG oil is the single most economically valuable component easily extractable and a 526 potential low-cost and good quality feedstock source for fatty acid methyl esters production 527 by direct single step transesterification of SCG oil in supercritical methanol (Calixto et al., 528 2011). The oil quality can be improved for use in cosmetic and pharmaceutical applications 529 or as a source of other valuable products such as caffeine, sterols, terpenes and tocopherols 530 by fractionation similar to those used for green coffee oil (De Azevedo et al., 2008). The 531 fractionated oil or its components can be stabilized by the spray drying process used for 532 encapsulating green coffee oil (Silva, Vieira, & Hubinger, 2014), particularly applicable to 533 the unsaponifiable fraction containing the diterpenes for medical and other associated uses. 534 Oil extracted from SCG can be used as a substrate for the production of poly (3- 535 hydroxybutyrate) (PHB). PHB is similar in mechanical properties to polypropylene or 536 polyethylene and is therefore considered a completely biodegradable alternative to 537 synthetic polymers (Obruca et al., 2014). When compared to other waste/inexpensive oils, 538 the utilization of SCG results in the highest biomass as well as PHB yields (up to 0.88 g of AC C EP TE D M AN U SC 516 19 ACCEPTED MANUSCRIPT PHB per g of oil vs 0.85 for soybean oil, or 0.83 for waste rapessed oil) (Obruca et al., 540 2014; De Cruz, Ienczak, Delgado, & Taciro, 2012; Obruca, Marova, Snajdar, Mravcova, & 541 Svoboda, 2010). The utilization of oil extracted from SCG as a feedstock for PHB 542 production presents several advantages. The coffee industry is steadily growing; the annual 543 worldwide production of green coffee beans exceeded eight million tons (Murthy & Naidu 544 2012a). Therefore, SCG are available in millions of tons especially in coffee-producing 545 countries. Moreover, since oil extraction decreased the calorific value of SCG by only 546 about 9% (from 19.61 to 17.86 MJ/kg), residual SCG after oil extraction can be used as fuel 547 to at least partially cover heat and energy demands of fermentation, which should even 548 improve the economic feasibility of the process (Obruca et al., 2014). In addition to oil 549 extraction, several processes such as pyrolysis and gasification have been used to convert 550 industrial SCG into fuel, hydrogen-enriched fuel, bio-oils, liquid product mixture 551 comparable to fossil fuel oil and valuable biocide. Bio-oils produced from pyrolysis of 552 coffee grounds contain large amounts of various carboxylic acids enabling their further 553 upgrade into biodiesel or other petrochemical products and/or promote their conversion into 554 noncondensable volatiles that may be beneficial for combustible gas or syngas production 555 from SCG (Kan, Strezov, & Evans, 2014). The glyceride portion of SCG oil can be 556 transesterified with methanol to produce fatty acid methyl esters, known as biodiesel. 557 Potentially 1.3 billion litres of biodiesel (based on ~ 8 million tonnes of globally produced 558 coffee containing 10-15 % wt lipids [80-95% glycerides] could be added to the world fuel 559 supply from SCG, a value comparable to waste cooking oil (Jenkins, Stageman, Fortune, & 560 Chuck, 2014). Furthermore, spent coffee defatting and extract lyophilization produces spent 561 coffee extracts powder with high antioxidant capacity that can be used as an ingredient or 562 additive in food industry with potential preservation and functional properties (Bravo, 563 Monente, Juániz, De Peña, & Cid, 2013). AC C EP TE D M AN U SC RI PT 539 564 Enzyme technology (hydrolysis) can be used to hydrolyze SCG polysaccharides into 565 valuable food additives such as mannitol and higher mannosaccharide alcohols or source 566 raw material for bioethanol production (Jooste, García-Aparicio, Brienzo, van Zyl, & 567 Görgens, 2013; Stahl, Bayha, & Fulger, 1984). Alcohol production similar to process 568 generally used in distilled beverages generates a beverage with 40% ethanol alcohol, 569 comparable to liquors such as vodka and tequila with a pleasant smell and taste of coffee 20 ACCEPTED MANUSCRIPT (Sampaio et al., 2013). Additionally, the residual solid material obtained after the 571 hydrothermal process is rich in sugars that can be reused as raw material for the production 572 of other valuable products, which would give additional value to spent coffee grounds into 573 a bio-refinery concept. Furthermore, the cellulose and hemicellulose fractions of SCG have 574 potential applications in sorbitol, hydroxymethylfurfural, levulinic acid, formic acid, 575 xylitol, arabitol, mannitol, galactitol, furfural and, emulsificant production (Mussato et al., 576 2011a). High pressure and temperature hydrolysis of SCG generates MOS, already 577 marketed in Japan as a functional food primarily as a probiotic for digestive health 578 (Fukami, 2010). SC RI PT 570 Waste from brewing coffee could be a valuable resource for the production of 580 hydrophilic bioactive antioxidants for dietary supplements according to Spanish researchers 581 (Bravo et al., 2012). All spent coffee (from filter, plunger and espresso-type coffee makers) 582 had relevant amounts of total caffeoylquinic acids, mainly dicaffeoylquinic acids that were 583 4–7-fold higher than their respective coffee brews. Solvent mixture of isopropanol and 584 water can selectively extract phenolic antioxidant adjunct for food processing from SCG 585 and other coffee by-products (Murthy & Naidu, 2012b). Melanoidins, another antioxidant 586 component exert bacteriostatic activity at low concentration decreasing pathogenic 587 virulence and may be good candidates as natural antimicrobial agents in thermally 588 processed foods (Rufián-Henares & De La Cueva, 2009). The anti-tumor and anti- 589 allergenic (inhibition of histamine release) activities of SCG extract (Ramalakshmi, Rao, 590 Takano-Ishikawa, & Goto, 2009) provides yet another new opportunities for its 591 pharmaceutical use. 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Spent coffee grounds as a valuable source of AC C EP TE D phenolic compounds and bioenergy. Journal of Cleaner Production, 34, 49-56. 34 ACCEPTED MANUSCRIPT Table 1. Amino acid content (% protein) and characteristics of coffee protein and by products Min 4.8 0.1 0.2 nd 11.5 2.4 0.1 5.1 10.6 1.9 1.0 0.5 3.1 0.9 0.3 2.9 6.0 Max 5.4 0.2 1.9 5.1 13.8 7.9 5.3 5.3 10.9 2.3 1.9 6.7 4.7 1.2 2.2 4.0 6.8 Instant 4.0 0.5 3.0 0.3 12.9 4.7 1.6 4.2 8.5 1.4 1.2 5.2 5.6 1.6 2.6 3.1 5.7 Pulp 3.5 2.8 7.1 0.3 7.7 4.2 2.5 3.3 4.7 3.4 0.3 3.0 3.7 3.3 3.1 1.9 3.7 11S 3.5 8.4 4.0 1.0 8.6 5.0 2.1 4.3 8.7 6.4 0.3 7.3 4.3 4.5 2.9 2.8 5.7 BCAA AAA Fischer ratio Lys/Arg Arg+Glu+His Met+Cys EAI (%) 21.7 0.9 24.1 19.0 11.8 1.0 79.3 23.0 8.9 2.6 11.5 19.3 7.0 128.8 18.4 7.8 2.4 2.8 15.0 1.5 94.6 11.7 6.1 1.9 1.2 13.0 0.6 74.7 18.7 10.2 1.8 0.8 19.1 1.3 117.3 SC M AN U D TE a Soymeal 2.3 4.0 6.3 0.8 9.8 2.3 1.4 2.3 4.2 3.3 0.8 2.6 3.0 3.1 1.7 1.8 2.4 RI PT Amino Acids Alanine Argininea Aspartic acid Cystine Glutamic acid Glycine Histidinea Isoleucinea Leucinea Lysinea Methioninea Phenylalaninea Proline Serine Threoninea Tyrosine Valinea 8.9 4.3 2.1 0.8 15.2 1.6 58.2 AC C EP Essential amino acid BCAA (Val+Leu+Ile) AAA (Phe+Tyr) Fischer ratio (BCAA/AAA) nd, not detected Data calculated from Lago et al., (2001) Data from http://www.feedipedia.org/node/11612 Data from Rogers, Bézard, Deshayes, Meyer, Pétiard, & Marraccini, (1999) Soymeal data from Karr-Lilienthal et al. (2005) ACCEPTED MANUSCRIPT Table 2. Caffeine content of SCG and roasted coffee RI PT 10 ± 3 Reference Andrade et al., (2012) SC H2O(92 ± 5 °C/6 h) Medium roast Medium roast Content (%) 0.007 0.378 0.314 0.039 0.28 0.177 0.248 0.434 0.5 M AN U SCG (Robusta-Rb) Roasted Coffee (Ar) Roasted Coffee (Rb) SCG SCG (espresso) D SCG (Arabica-Ar) Yield (%) 9 9.9 12.2 12 10.8 15 9.1 10.5 TE SFE CO2 (µg/mg extract) 0.734 38.2 25.7 3.27 25.9 11.8 27.2 41.3 25 ± 2 EP Soxhlet Solvent/Condition Hexane Dichloromethane Ethanol Hexane Dichloromethane Ethanol 200 bar/331.15 K 300 bar/331.15 K H2O(92 ± 5 °C/6 h) AC C Extraction Ultrasound 0.2 1.6 2.4 0.02 ± 0.1 0.18 Ramalakshmi, Rao, TakanoIshikawa, & Goto, (2009) Murthy & Naidu, (2012) Cruz et al., (2012) ACCEPTED MANUSCRIPT Table 3. Fatty acid composition of SCG C18:1 9.00 8.31 10.30 6.70 24.00 8.18 12.90 0.60 nd nd nd nd 4.36 2.42 35.78 37.48 34.04 35.86 36.86 41.87 6.25 6.02 5.45 5.26 11.32 10.4 nd 9.53 5.45 7.56 15.87 15.79 C18:2 45.04 44.67 44.20 22.00 49.90 32.35 56.90 24.90 C18:3 4.12 1.42 1.50 nd 1.40 1.31 8.50 5.50 46.53 44.52 25.83 35.35 44.15 41.19 C20:0 nd 1.16 2.60 0.00 1.50 2.39 9.80 37.80 SFA 41.0 45.6 42.5 42.1 56.4 58.2 21.7 69.0 PUFA 50.0 46.1 45.7 22.0 51.3 33.7 65.4 30.4 PUFA/SFA 1.22 1.01 1.08 0.52 0.91 0.58 3.01 0.44 AI 0.55 0.69 0.58 1.23 0.55 1.32 0.03 0.07 TI 1.26 1.44 1.25 2.93 1.49 2.15 0.01 0.33 nd 1.46 1.89 1.53 6.91 4.29 42.2 45.0 41.4 42.7 71.1 66.4 49.1 45.5 25.8 9.9 46.3 46.7 1.16 1.01 0.62 0.24 0.65 0.91 0.62 0.68 1.09 0.84 1.06 1.00 1.32 1.45 2.52 1.92 1.43 1.91 RI PT C18:0 8.35 7.07 7.10 6.70 13.50 6.55 0.30 28.00 SC C16:0 32.45 37.37 32.80 35.40 41.40 43.64 0.50 1.00 M AN U C14:0 0.05 nd 0.1 nd nd 2.00 0.4 0.3 D References C12:0 Acevedo et al. (2013) nd De Melo et al. (2014) nd Cruz et al. (2014) nd Jenkins et al. (2014) nd Jenkins et al. (2014) nd Ahangari & Sargolzaei(2013) 3.58 Todaka et al. (2013)(Hex)Drip nd Todaka et al. (2013)(Hex)Esp nd Supercritical Fluid Extraction (SFE) Acevedo et al. (2013) nd De Melo et al. (2014) nd Ahangari & Sargolzaei(2013) nd Couto et al. (2009) nd Ahangari & Sargolzaei(2013) 11.69 Couto et al. (2009) 7.4 2.02 0.99 nd nd 2.16 1.88 AC C EP TE SFA, saturated fatty acids; PUFA, polyunsaturated fatty acids; AI, atherogenic index; TI, thromogenic index; nd, not determined. ACCEPTED MANUSCRIPT SCG2 20.34 1.37 Coffee 1 5.84 1.23 Coffee 2 5.74 0.79 16.08 21.75 52.66 5.30 1.65 1.42 18.36 22.48 48.00 9.07 0.62 0.80 15.66 22.82 52.27 4.05 2.01 1.74 16.83 21.94 48.78 8.81 1.68 0.70 AC C EP TE D Data derived from Lago, Antoniassi, & Freitas (2001) SC SCG1 26.74 2.12 M AN U Sterols Oil content (%) Unsaponifiables (% DW) Sterols (% oil) Campesterol Stigmasterol Sitosterol Δ5 Avenasterol Δ7 Stigmastenol Δ7 Avenasterol RI PT Table 4. Sterol (%) composition of SCG and their sourced roasted coffee ACCEPTED MANUSCRIPT Table 5. Products and/or processes innovation using SCG or coffee products including SCG SC RI PT Claim References Aromatic flavor components (diacetyl and acetaldehyde) are recovered from an aroma stream Cale et al. (1990) 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. Antioxidant-rich biofuel is produced by transesterifying triglycerides extracted from coffee Misra et al. (2013) products including SCG. Glycerin resulting from the transesterification process can be isolated, purified and used in foods, pharmaceuticals, cosmetics and other products. D M AN U A process is described for manufacturing powdered coffee carbons as an environmentally friendly Lu & Lee (2013) activated carbon source SCG is converted to an alternative solid combustible fuel-a wax-less fire log White & Burns (2013) Coffee oil is recovered from hydrolyzed SCG simultaneously using the residual aqueous Gottesman (1985) hydrolyzate as an economically valuable soluble coffee solids in soluble coffee processing A process for preparing low-cost high yield manno-saccharide alcohols such as mannitol (a value Stahl et al. (1984) added expensive specialty food, chemical, and pharmaceutical ingredient) Terpenes containing kahweol and cafestol (10.7 and 14.7 mg/g coffee oil, respectively) are Baechler & extracted from SCG. Hirsbrunner (2002) TE Component Spent grounds volatile compounds Ground/Green/ Whole roasted/spentcoffee beans Spent coffee grounds Dried spent coffee grounds Spent coffee grounds Coffee extraction residue Spent coffee grounds AC C EP 1 ACCEPTED MANUSCRIPT The Coffee Cherry (Fruit) RI PT Skin 5-10 % M AN U Mucilage 90 % total waste 45-50 % Spent coffee ground EP TE D Parchment (Hull) Silverskin Bean AC C 45-50 % SC Pulp Figure 1. The coffee cherry fruit wastes (With information of: Murthy & Naidu, 2012a; Esquivel & Jiménez, 2012) Brown(colored$compounds$ Browning,index,0.155, 16%,melanoidins,,! ,, $Caﬀeine$$ Carbohydrates$ galactomannans,and, arabinogalactans, , Mannooligosaccharides, , An-oxidant,dietary,ﬁber,, Non(protein$nitrogeneous$compounds$ Carbon/nitrogen,ra-o,of,19.8:1,(wt):,microbial,ac-vity,, Soil,amendment,impact,$ SCG$ Minerals$ K,,Mg,,P,,Ca,,Na,,Fe,,Mn,,and,Cu,$ Phenolic$compounds$ Natural,phenolic,an-oxidants, 1–1.5%,total,polyphenols, Chlorogenic,acid,,,(12%,solids)$ $ Lipids$ Oil,manufacturing,cost,US$,48.60/kgL,earning,up,to,US$,460/kg, Polyunsaturated/saturated,ra-o,>,1,, Mix,linoleic,,palmi-c,,and,oleic,acids/,polyhydroxylalkanoatesLbiodegradable,synthe-c,polymer, $ Figure$2.$ValueLadded,products,/sustainability,of,the,coﬀee,agroLindustry,, ACCEPTED MANUSCRIPT Highlights Most of the polysaccharides remain as insoluble material bound to the SCW RI PT The essential amino acids comprise almost half (~ 49%) of the total SCW amino acid Caffeine obtained from SCW is equivalent up to 48% of those extracted from coffee beans Lipids (90.2%) mainly remained in SCW AC C EP TE D M AN U SC Innovative ideas are needed to use this low cost SCW and exploit its full potential

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Spent coffee grounds: A review on current research and future prospects

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