Espresso Coffee preparation: analytical study to improve the quality of the product

The PhD project was divided into three main parts. The first part aimed to develop and optimize efficient and simply methods for the quantification of nine phytoestrogens in green coffee, and three lignans in ground and espresso coffee (EC), using HPLC-MS/MS. For this purpose, different extraction processes, i.e., acid and base hydrolysis, enzymatic hydrolysis, organic solvent extraction, and a combination of these, have been studied. The best performing procedures, in term of recovery and quantitative data, were chosen, validated and finally applied to different samples coming from diverse geographical origins. The final objective was to characterize the content of these compounds in the whole coffee chain, from green beans to cup. The second part concerned the optimization of espresso coffee extraction, by modifying some machine variables aiming to produce a good quality espresso coffee, lowering the amount of coffee powder used for espresso preparation. The variables under study were the particle size distribution (PSD) of roast and ground (R&G) coffee, the design of the filter basket and the height of perforated disc. The EC quality was investigated from chemical point of view and it concerned the total solids (TS) analysis and the quantification of caffeine, chlorogenic acids and trigonelline. In addition, some analysis on volatile fraction were also performed. The third part of the project focused on promoting and adding value to coffee silverskin (CS) in the perspective of its application in the food industry. The work aimed to characterize the odor-active compounds in CS and compare them with those present in coffee beans. The characterization of aroma fraction was carried out by gas chromatography-olfactometry/flame ionization detector (GC-O/FID) and by comparing the odors and odorants with those found in coffee beans. The identification was carried out by comparing with reference compounds the retention index and the odor quality. Finally, for unequivocal identification, after fractionation, the samples were analysed into comprehensive two-dimensional gas chromatography-mass spectrometry (GCxGC- MS). Moreover, the Aroma Extract Dilution Analysis (AEDA) was performed to assess the potency of each odors/odorants. 7 Regarding the phytoestrogen characterization, we found two enzymatic digestions, i.e., clara-diastase (Method 3.10-EC) and taka-diastase (Method 5-R&G), as the most performing processes for lignan extraction from espresso and R&G coffee, respectively. Secoisolariciresinol was the lignans present at the highest concentration in espresso (27.9-52.0 μg L-1) and in R&G coffee (84.4-257.8 μg kg-1). Moreover, the extraction yield of lignans revealed that they are almost completely extracted during coffee percolation. For green coffee matrix, the best performing process was Method 7-GC, a double extraction composed of base hydrolysis in MeOH and enzymatic digestion with clara-diastase and we found that lignans (total content: 286.5-8131.8 μg kg-1) were more abundant than isoflavones (total content: 3.4-300.0 μg kg-1). Our studies on espresso coffee optimization showed higher levels of TS, caffeine, trigonelline and chlorogenic acids for reference samples (ECs extracted with mixed particles) and for 200-300 μm mesh size, when standard filter (A) was set in the machine. By decreasing the amount of R&G coffee, similar TS levels and contents of bioactive compounds to standard condition, were obtained for reference compounds. The best filter baskets, in term of quantitative data, were A and B and the study on perforated discs suggested that using lower amount of ground coffee permits to obtain the same extraction yield increasing the height of perforated disc. From our investigations on CS, four volatile compounds were identified for the first time in coffee. In detail, 4-methyloctanoic acid and trans-4,5-epoxy-(E)-2-decenal were characterized in coffee beans and silverskin, while 6-acetyl-2,3,4,5-tetrahydropyridine and 5-methyl-2-methoxyphenol only in coffee beans. The highest flavour dilution (FD) factors in CS were obtained for furaneol, 2- methoxy-4-vinylphenol and 2-methoxyphenol and, moreover, other typical coffee aroma volatiles were found, e.g., 2-furfurylthiol, 2,3-butanedione, vanillin, 2-isobutyl-3-methoxypyrazine, etc. Some aromas, such as furaneol, 2-methoxy-4-vinylphenol, vanillin, trans-4,5-epoxy-(E)-2-decenal, 2- acetyl-1-pyrroline and 2-acetylpyrazine, occurred with similar FD factors in CS and coffee beans. Our studies demonstrated that CS contains an interesting odor-active compound fraction with high similarity to coffee beans.