"Valorization of lentil by-products as novel source of bioactive compounds: a metabolomic investigation"

In the last few decades, from a circular economy perspective, there has been a growing interest in the recovery of antioxidants from by-products and agro-industrial wastes such as peels, kernels, seeds, and pomaces which are often discarded 2, thus causing an environmental problem. Also, lentil (Lens culinaris Medik.) seed coats are generally considered to be a waste by-product. However, this low-value by-product is rich in bioactive compounds and may be considered an eco-friendly source of health-promoting phytochemicals 3. For the first time, a sustainable microwave-assisted extraction technique was applied, and a solvent screening was carried out to enhance the bioactive compound content and the antioxidant activity of green (cv. Eston green) and red (cv. Crimson red) lentil hull extracts. Solvents with different polarity degrees were chosen: ethyl acetate (EtOAc), absolute ethanol (abs EtOH), and water. The aqueous extract of the red and green lentil seed coats showed the highest antioxidant activity, both in terms of the free radical scavenging activity (test ABTS; test DPPH) and the protection of the neuroblastoma cell line (SH-SY5Y), the latter of which has never been investigated so far. To obtain more insights into specific compounds, accounting for the biological activity values that were found for lentil hulls, their aqueous extracts were submitted to liquid chromatography/tandem mass spectrometry (LC-MS/MS) untargeted analysis for the metabolites profiling. The MS spectra were then processed using the commercial software Compound Discoverer v. 3.3.1.111 SP1 (Thermo Fisher, Bremen, Germany), and identification was accomplished by activating the ChemSpider and mzCloud nodes. Each molecule was searched for in the PubChem online database to gather information about their class and their putative function.The metabolic profiles of the lentil hulls reveal that this by-product is generally rich in nutritional and bioactive compounds, and indeed, good percentages of molecules such as phenolic compounds, nucleosides/nucleotides/nitrogenous bases, peptides, vitamins, amino acids, and derivatives were found in the green and red samples. Among this, a consistent fraction of phenolic compounds was observed in the hulls of both the green and red variety, accounting for 15% and 16%, respectively, although the specific composition slightly differs between the two samples. The results that are reported here suggest that our extracts, in perspective, can play the role of nutraceuticals for the prevention and treatment of neurodegenerative diseases, and more generally, they could enter new food formulations for nutrition and health benefits.