Simultaneous quantification of 30 different bioactive compounds including polyphenols in spent coffee ground and coffee silverskin by HPLC-MS/MS triple quadrupole

Coffee is one of the most consumed beverages worldwide and according to the latest statistics the global consumption is more than 150 million of 60 kg coffee bags per year. As a consequence, large amount of coffee residues need to be disposed of [1]. Although many studies related to coffee and health have been carried out in green, ground and espresso coffee, two components of the coffee processing chain have been less investigated, i.e. coffee silverskin (CS) and spent coffee ground (SCG), the two main by-products presenting a huge potential to be valorized [2]. It is well known that coffee is a rich source of polyphenols, phytochemicals associated with many biological activities, and they are partially extracted from the beans during brewing; so, the resulting spent coffee is still a rich source of polyphenolic compounds. Similarly, silverskin is also considered to be a potential source of polyphenolic compounds because this tegument is in direct contact with the beans; therefore, it keeps part of the polyphenolic compounds constituents present in coffee beans [3]. On these bases, general aim of this project was to deepen the knowledge on CS and SCG, in the future perspective of their re-use as nutraceuticals by a) developing an efficient and low-cost method to extract different bioactive compounds including polyphenols from these by-products b) quantifying these bioactive compounds (chlorogenic acids, caffeine and other important coffee polyphenols such as flavonoids and phenolic acids) from different CS and SCG extracts by developing new HPLC-MS/MS analytical method. SCG and CS samples were extracted by using different solvents and extraction procedures (i.e. magnetic stirrer, ultrasound extraction). From an analytical point of view, UHPLC–MS/MS studies were performed using an Agilent 1290 Infinity series and a Triple Quadrupole 6420 from Agilent Technology equipped with an ESI source operating in negative ionization mode. The separation was achieved using a Kinetex C18 analytical column (50 mm × 2.10 mm i.d., 2.6 μm) using a binary gradient of 0.1% formic acid in water (A) and 0.1% formic acid in acetonitrile (B). The method was sensitive (LOQs for all compounds were in the range 1-100 μg kg-1), linear (R2 for all analytes was higher than 0.9907), accurate and robust. The best extraction procedure in term of amount of bioactive compounds extracted was ultrasound extraction with a mixture of ethanol:water 70:30 v/v; in this case, the highest amount of total bioactive compounds concentration was found. In the future, the most promising extracts in terms of bioactive compounds will be tested to evaluate theirs prebiotic and antimicrobial activity, in the perspective of their re-use as nutraceuticals.