# The Optimized Production of 5-(Hydroymethyl)furfural and Related Products from Spent Coffee Grounds
## 3 Results
### Hemicellulose Enriched Fraction (HEF)  
Characterization  
To characterize the HEF, samples were submitted to various different analysis methods, HPLC was used to evaluate what type of sugars and their quantities are present in this fraction. Total organic carbon (TOC) was performed to assess the amount of carbon present in the organic compounds (mainly carbohydrates) that can be used as a substrate to grow yeast/microalgae or to convert to furans. In addition to this, the amount of nitrogen in these fractions was obtained by a total nitrogen (TN) analysis (Figure 2). Finally, inductively coupled plasma optical emission spectrometry (ICP-OES) was used to quantify the metal composition of HEF samples to determine the suitability as a fermentation broth. Figure 1: Cellulose-enriched fraction (CEF), hemicellulose-enriched fractions (HEF) and lignin-enriched fraction (LEF) yields obtained in the six different types of fractionation with two feedstock (pistachio hull and spent coffee grounds, SCG) and three solvent systems (MEW—MIBK, ethanol and water; MAW—MIBK, acetone and water; MW—MIBK and water). All the processes release suitable levels of micronutrients into the broth for fermentation (Table 1). Using the MW solvent system for SCG led to increases in sulfur and reduced levels of Na, though all other elements were widely similar irrespective of the system used. Pistachio hulls had higher concentration of calcium and potassium regardless of the solvent system, in line with the elemental composition of the initial feedstock. HPLC analysis using a refractive index detector was used to quantify the concentration of the sugars present in this fraction (Table 2). Interestingly, while xylose (and possibly arabinose which elutes at the same time) are present in the HEF produced from pistachio hulls, there were very few C\({}_{5}\) sugars produced from SCG. Instead the soluble HEF fraction contained high levels of galactose and mannose, in addition to glucose, maltose and cellobiose. This demonstrates that SCG would be entirely unsuitable for the production of furfural but rather that fermentation would be a suitable processing step for this fraction. To determine the suitability of HEF from SCG for fermentation, the substrate was used with _Metslnikowia pulcherrima_, an oleaginous yeast species which can ferment a large range of alternative sugars and has excellent inhibitor tolerance [31]. The yeast could not grow on the MEW and MAW derived HEF fractions (data not shown) presumably due to the elevated levels of both ethanol and acetone in the broth. The number of cells per mL increased with time for all the samples (Figure 3a). An increase in the concentration of the medium was directly proportional to an increase in the number of cells. At the end of the first day, the 25% concentrated medium achieved an increase of 1,204,375 cells per mL, the 50% concentrated medium increased by 2,530,000 in the number of cells per mL, the medium with 75% HEF registered an increase of 3,792,500 in the number of cells per mL while the fully concentrated medium increased by 7,665,625. This demonstrated that HEF was not toxic to the yeast and rather was limited by the carbon available. The fully concentrated medium therefore could potentially be used for fermentation as long as no ethanol or acetone were used in this fractionation process, or were removed prior to use. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**System** & **Ca (ppm)** & **K (ppm)** & **Mg (ppm)** & **Na (ppm)** & **P (ppm)** & **S (ppm)** & **Others (ppm)** \\ \hline Pist–MEW & 46.1 & 123.3 & 42 & 503.8 & 6.9 & 123 & 6.0 \\ SCG–MEW & 13.2 & 56.1 & 6.2 & 355.5 & 7.4 & 137 & 10.3 \\ Pist–MAW & 37.9 & 130.9 & 1.9 & 480.2 & 6.3 & 105 & 7.1 \\ SCG–MAW & 21.7 & 37.0 & 8.2 & 10.7 & 9.9 & 134 & 5.8 \\ Pist–MW & 61.9 & 85.0 & 6.1 & 10.7 & 7.2 & 258 & 14.8 \\ SCG–MW & 16.1 & 24.3 & 7.4 & 3.9 & 7.4 & 225 & 5.7 \\ \hline \hline \end{tabular}
\end{table}