Supercritical CO2 Extraction of Lipids from Coffee Silverskin: From Laboratory to Industrial scale

Coffee is the most important food commodity worldwide and ranks second, after crude oil, among all commodities1. Since more than 50% of the coffee bean fruit is not used for production of the commercialized green coffee and, therefore, is discarded during processing, it should be interesting to find applications for these by-products. Coffee silverskin (CS) is the thin tegument that covers each hemisphere of the green coffee beans and is the only waste that comes from coffee roasting. Despite promising applications, CS is still underutilized and nowadays still discarded by the roasters or used for fuel or for composting. In terms of composition, CS displays an interesting content of dietary fibres, proteins, carbohydrates, lipids and antioxidants. Considering its composition, the rECOBIOpack project (funded by MUR, PRIN 2022), promoting a strategy close to “zero waste”, aims to develop a functional food packaging material completely exploiting the CS added value, in the sense that it uses its 5 main components: cellulose as polymeric backbone and lipids, proteins and polyphenols as additives. The aim of this work was the scaling-up of the lipid extraction from CS (Illycaffè S.p.A) using supercritical CO2 (sc-CO2). Laboratory extraction was scaled up at ILSA S.p.A. (Arzignano, Italy) using an industrial sc-CO2 apparatus. The biomass used as starting material was CS derived from a mixture of Arabica coffee beans. CS has been kindly supplied by the Italian coffee company Illycaffè S.p.A (Trieste, Italy). The optimal extraction conditions in term of yield of extraction were defined at lab-scale as 50 ºC and 400 bar, using Design of Experiments. The industrial extraction was performed at ILSA S.p.A. at 400 bar and 50-60 °C for 3 h and in dynamic conditions. The biomass was extracted using two vessels (10 L) in series each one containing 0.7-0.9 kg of CS. Five replicates of the extraction were performed and a total of 8 kg of biomass were processed. The extract was characterized in term of free fatty acid (FFA%) content using an acid-base titration with NaOH 0.1 M. The fatty acid composition of the lipidic extract was evaluated using GC-MS (Bruker Scion SQ Instrument, Milan, Italy) equipped with a quadrupole mass spectrometer, after derivatization (both transesterification and sylilation were employed). The quantification of the caffeine present in the extracts was performed, using a Waters ACQUITY UPLC system (Waters corp., United States) equipped with a UV–Vis photo diode array (PDA). The industrial extraction was thus performed using the optimal conditions determined in a lab-scale optimization trial. The extract obtained at ILSA comprised two phases, as shown in Figure 1: a solid fraction and a liquid aqueous fraction. 8 kg of CS were extracted in different batches, obtaining an average yield of 4 ± 1%, considering only the solid fraction. The FFA% was determined at 141 %. The fatty acid composition results are shown in Figure 2. In agreement with literature data2 and with the lab-scale extractions, the fatty acids found in the extracts were palmitic acid, linoleic acid, oleic acid, stearic acid, arachidic acid, behenic acid and lignoceric acid. It is worth noticing that the heavier fatty acids show, at first glance, no significant variability between the two types of derivatizations, an aspect that did come up in the lab-scale extractions. A relevant aspect was the presence of needle-shaped crystals in the liquid (aqueous) extract after storing it overnight at +4ºC. The crystals were separated and analyzed with UPLC-PDA to identify and quantify the caffeine content, observing a purity equal to 99.4% and thus confirming their nature. The scale-up of the extraction of lipids from CS using supercritical CO2 extraction was successful. The industrial-scale extraction showed higher extraction yield (4 ± 1%) than the optimized lab-scale extraction (2.5%). The fatty acid profile of the extracts consists of palmitic acid, linoleic acid, oleic acid, stearic acid, arachidic acid, behenic acid and lignoceric acid. Caffeine was found in the liquid part of industrial extracts, easily separated in pure crystals.