During the production of quince paste, significant waste is generated, including skin, peel, and seeds. Quince is rich in bioactive compounds, such as polyphenols, interesting for their antioxidant and antimicrobial properties. Their extraction is of strategic importance to obtain bioactive ingredients from agro-industrial waste.
Currently, conventional extraction techniques, which are used for their good yields, have disadvantages, such as long extraction times and the requirement of organic solvents. Therefore, alternative, environmentally friendly methodologies are being implemented that comply with the principles of green chemistry, avoiding or reducing the use of organic solvents. The determination of phenolic compounds is commonly performed using the Folin-Ciocalteu (FC) assay. Although it is convenient and simple, it has disadvantages such as the use of non-ecological reagents, long processing time, low specificity, and multiple interferences. The aim of this work was to optimize an alternative method for the extraction of food-grade polyphenols without organic solvents, taking advantage of quince residues and proposing an alternative to the classic determination of phenolic compounds. The work was done with samples of residues obtained during the industrial production of quince jam. For the extraction of polyphenols, two treatments were used, using ultrasound with organic solvents: ethanol/water 50:50 (A), ethanol/water 50:50 with citric acid at 2% W/V (B), methanol/water 50:50 (C) and methanol/water 50:50 with hydrochloric acid at 0.1% V/V (D); and a hydrothermal treatment "steam explosion", with high-pressure saturated steam, in an autoclave, for a short time, followed by rapid decompression, using water (E) or water with citric acid at 2% W/V (F). It was observed that the polyphenol content of the hydrothermal extracts was the highest, with extract F presenting the highest value of µg eq. Gallic Acid/mL (408±24), while the lowest content was A (132±50). The total polyphenol content for extracts D, E and F was compared with that determined by amperometry using a Laccase-based biosensor. The results obtained for samples D, E and F were: (193±23) and (238±34), (253±17) and (258±1), and (408±24) and (255±51), by FC and biosensor, respectively. For extracts D and E, there was a high correlation between the quantification by FC and the biosensor, but not for F, which showed a significant difference between the two quantification methods. According to the results of the biosensor, classical extraction methods would have similar yields to hydrothermal ones. Based on this, the profile of compounds in extracts D, E and F was evaluated by UHPLC-MS/MS, observing similar areas for the majority compounds, coinciding with the results obtained by the biosensor. In conclusion, an eco-sustainable extraction of polyphenols from the quince industry residue was achieved. It was determined that the FC technique presents interferences, so it would be convenient to use another method, such as the Laccase biosensor, a technique that was corroborated with a validated method such as UHPLC-MS/MS.
Keywords: green chemistry, antioxidants, biosensor, Folin, UHPL-MS/MS