Valorization of Onion Waste by Obtaining Extracts Rich in Phenolic Compounds and Feasibility of Its Therapeutic Use on Colon Cancer

Abstract

In this study, the total phenolic content, the antioxidant and antiproliferative activities of onion waste extracts were characterized. Some phenolic compounds present in the extracts were also identified and quantified by HPLC-DAD. Additionally, an in-silico analysis was performed to identify the phenolic compounds with the highest intestinal absorption and Caco-2 permeability. The onion extract possessed a high amount of phenolic compounds (177 ± 9 mg/g extract) and had an effective antioxidant capacity measured by ABTS, FRAP and DPPH assays. Regarding the antiproliferative activity, the onion extracts produced cell cycle arrest in the S phase with p53 activation, intrinsic apoptosis (mitochondrial membrane potential modification) and caspase 3 activation. Likewise, onion waste increased intracellular ROS with possible NF-kB activation causing a proteasome down regulation. In addition, the extracts protected the intestine against oxidative stress induced by H2O2. According to the in-silico analysis, these results could be related to the higher Caco-2 permeability to protocatechuic acid. Therefore, this study provides new insights regarding the potential use of these types of extract as functional ingredients with antioxidant and antiproliferative properties and as medicinal agents in diseases related to oxidative stress, such as cancer. In addition, its valorization would contribute to the circular economy.

Anti-Inflammatory and Chondroprotective Effects Induced by Phenolic Compounds from Onion Waste Extracts in ATDC-5 Chondrogenic Cell Line

“…Onion extracts and their characterization regarding the presence of phenolic compounds were developed as we previously described [ 28 ]. In brief, onion extract from household waste was obtained by drying at 30 °C and milling through a coffee grinder to sieve the material by using a 300 µm sieve.…”

“…The phenolic components in the extracts were characterized by HPLC-DAD as described before [ 28 , 29 ]. In brief, 350 mL of methanol was used to reconstitute 30 mg of freeze-dried extract.…”

“…As previously reported [ 28 , 30 , 31 ], three spectrophotometric techniques were employed to assess the antioxidant capacity of onion extracts. In brief, the DPPH (2,2-diphenyl-1-pycrilhydracyl) method was carried out by dissolving the extracts (49.1–53.1 mg) in methanol (5 mL), filtering, and then diluting them 10 times in methanol.…”

“…In brief, the DPPH (2,2-diphenyl-1-pycrilhydracyl) method was carried out by dissolving the extracts (49.1–53.1 mg) in methanol (5 mL), filtering, and then diluting them 10 times in methanol. The ABTS (2,20-azinobis(3-ethylbenzothiazoline-6-sulphonic acid)) [ 30 ] and the FRAP [ 31 ] assays were performed as published [ 28 , 30 , 31 ]. Trolox (0.05–1.2 mM) was used as a standard in the three spectrophotometric methods (R 2 = 0.99).…”

“…Total phenolic and flavonoid quantification was carried out as previously described [ 28 , 32 , 33 ]. Briefly, 50 mg of the extract was dissolved in 5 mL of methanol and filtered to be further diluted in methanol (4 times for total phenolic content and 30 times for total flavonoid quantification).…”