Onion Solid Wastes Research Articles

DFT simulated Quercetin imprinted polymer: Selective recovery of Quercetin from onion solid waste

Onion peels (OP) are byproduct of food processing industries that poses economic and environmental challenges. However, being rich source of bioactive compounds like Quercetin (Qt), a polyphenolic antioxidant with potential health benefits, harnessing value from such waste can imbibe sustainable practices and protect environment. With this view, the present study targets selective recovery of Qt from OP waste using rationally designed molecularly imprinted polymer (MIP). Density Functional Theory (DFT) was used for the theoretical selection of the best conformer of Qt (template), methacrylic acid (MAA) as functional monomer, ratio of Qt-MAA for getting stable pre-polymerization complex, and to avoid hit and trial experiments. The theoretical results were validated experimentally by synthesizing MIP/ control polymer (NIP) using MAA as functional monomer, EGDMA as a cross-linker and AIBN as initiator. Synthesized MIP/NIP were characterized using various characterization techniques to confirm successful imprinting. Prepared MIP and NIP could effectively rebind the Qt molecule with binding capacity of 46.67 and 20.89 mg g-1 respectively. Furthermore, synthesized MIP could selectively recover 62.81 % of Qt from 1 g of dry onion peel powder. This study can be effectually used for sustainable recovery of Qt in large scale for various foods, cosmetic and pharmaceutical applications.

Optimization of microwave-assisted extraction of antioxidant compounds from spring onion leaves using Box–Behnken design

Many studies have explored the extraction of bioactive compounds from different onion solid wastes, such as bulb, skin, and peel. However, onion leaves have received limited attention despite their potential as a valuable source of nutraceutical compounds. This study aimed to valorise, for the first time, the agricultural waste in the form of spring onion leaves (CN, Cipollotto Nocerino) to obtain antioxidant-rich polyphenolic extracts. A Box–Behnken design (BBD) was used to assess the impact of microwave-assisted extraction (MAE) variables (temperature, time, extraction volume, and ethanol concentration) on total polyphenol content (TPC) measured by Folin–Ciocalteu method and the antioxidant power determined by FRAP assay. Response surface methodology (RSM) was applied, and regression equations, analysis of variance, and 3D response curves were developed. Our results highlighted that the TPC values range from 0.76 to 1.43 mg GAE g−1 dw, while the FRAP values range from 8.25 to 14.80 mmol Fe(II)E g−1 dw. The optimal extraction conditions predicted by the model were 60 °C, 22 min, ethanol concentration 51% (v/v), and solvent volume 11 mL. These conditions resulted in TPC and FRAP values of 1.35 mg GAE g−1 dw and 14.02 mmol Fe(II)E g−1 dw, respectively. Furthermore, the extract obtained under optimized conditions was characterized by UHPLC-ESI-Orbitrap-MS analysis. LC/MS–MS platform allowed us to tentatively identify various compounds belonging to the class of flavonoids, saponins, fatty acids, and lipids. Finally, the ability of CN optimal extract to inhibit the intracellular reactive oxygen species (ROS) release in a hepatocarcinoma cell line using an H2O2-induced oxidative stress model, was evaluated. The results highlighted the potential of CN extract as a valuable source of polyphenols with significant antioxidant properties, suitable for various applications in the food and pharmaceutical industries.

The use of tailor‐made acidic deep eutectic solvents for preparation of quercetin‐enriched extracts from onion solid wastes

AbstractThe current examination dealt with the development of a methodology to produce quercetin, a multifunctional bio‐flavonoid, by designing task‐specific, highly acidic deep eutectic solvents, based on glycerol and natural organic acids. The purpose was to achieve a simultaneous hydrolysis of spiraeoside, the major quercetin glycoconjugate occurring in onion solid wastes, and quercetin extraction. After an initial performance screening, the combination of glycerol/oxalic acid was identified as the highest‐performing system, and further investigation showed that the most efficacious molar ratio was glycerol/oxalic acid 3:1. Further study of hydrolysis/extractions conditions suggested 30 min, at 130°C, to be the best operating conditions, giving the highest yield of 19.65 mg quercetin per grams of dry mass. The extract obtained under these conditions displayed significantly enhanced antiradical activity, compared to control extracts prepared with water or aqueous ethanol. On the other hand, results on the ferric‐reducing power were rather contradictory. It is proposed that such a methodology may be implemented to valorize onion solid wastes, for the production of extracts significantly enriched in quercetin, with increased antiradical properties.

Conventional and Enzyme-Assisted Extraction of Total Flavonoids from Rotten Onion (Allium cepa L.)

One of the richest sources of dietary flavonoids is the bulb of the onion (Allium cepa L.), which greatly contributes to the daily intake of flavonoids. This research aimed to optimize the yield of Total flavonoids from Onion Solid Waste (OSW). A comparison was drawn between Conventional and Enzyme Assisted extraction methods in terms of the yield of total flavonoids present in OSW extract. The results showed that the highest TFC were obtained at Time/Temp 60 °C for 180 minutes and Pectinase Conc./Time 2g for 120 minutes for Conventional and Enzyme assisted extraction respectively. The yield of TFC by both methods showed that the yield for both was higher in case of enzyme assisted extraction for T13, i.e., 0.472 mg/g respectively than that for conventional extraction for T4 i.e., 0.352 mg/g.

Recent advances and perspectives for effective utilization of onion solid waste in food packaging: a critical review

Recent advances and perspectives for effective utilization of onion solid waste in food packaging: a critical review

Glycerol-Based Deep Eutectic Solvents for Simultaneous Organosolv Treatment/Extraction: High-Performance Recovery of Antioxidant Polyphenols from Onion Solid Wastes

Onion solid wastes (OSW) are a food side-stream with high polyphenolic load and distinguished polyphenolic profile. This study was conducted in order to explore a novel methodology of production of polyphenol-enriched extracts with antioxidant properties from OSW, using glycerol and green deep eutectic solvents (DES), composed of glycerol/citric acid and glycerol/sodium acetate. The organosolv process developed was appraised by establishing models based on severity, but also response surface methodology. Using a linear model, it was, for the first time, proposed that there is a direct correlation between the yield of the process in total polyphenols and the combined severity factor. Furthermore, response surface optimization enabled the establishment of linear models to predict the effects of time and temperature on the total polyphenol extraction yield. Out of the solvents tested, the DES composed of citric acid and glycerol was found to provide the highest yield in total polyphenols (87.90 ± 3.08 mg gallic acid equivalents per g dry mass) at significantly higher combined severity. However, the extraction efficiency of this solvent was virtually equal to that of the two other solvents tested. On the other hand, the polyphenolic composition of the extract obtained with the glycerol/citric acid DES was characterized by exceptionally high quercetin concentration. This extract also displayed the highest antioxidant activity. Based on the evidence emerged, it was proposed that OSW polyphenol extraction with the DES glycerol/citric acid could be used for production of extracts enriched in the bioactive flavonoid quercetin, with enhanced antioxidant activity. Moreover, using this green methodology, 27.59 ± 0.09 g of pure quercetin could be recovered out of 1 kg OSW. Thus, this methodology could be employed as a sustainable means of producing quercetin, through valorization of food wastes in a biorefinery context.

Exploring the Effective Utilization of Shallot Stalk Waste and Tamarind Seed for Packaging Film Preparation

Owing to the increased generation of agricultural bio-waste especially onion solid waste and its impact on environment, the present study mainly focused on the utilization of selected waste streams such as shallot stalk and tamarind seed for development of packaging films which can be used as an alternative to plastic films. Different extraction methods were used for the extraction of xyloglucan (XG). The condition of selected extraction method was optimized by central composite design using response surface methodology. The shallot stalk powder (SSP) packaging film was prepared with extracted XG by casting method. The properties of xyloglucan and SSP packaging film were analyzed and it was compared with commercial pectin based films. Microwave-assisted extraction (MAE) provided a high yield of 21.75% of xyloglucan compared to other methods with optimum process parameters as power level 400 W, liquid to solid ratio 99.43 ml/g, temperature 83.23 °C and time 14.29 min, respectively. The SSP films have less water vapor permeability 1.06 × 10−10−1.49 × 10−10 g/m. s. Pa, high total phenolic content 63.76–69.23 mg/g and antioxidant capacity 23.47–24.09% compared to the control films. Thus, the study provides the rational for effective utilization of not only shallot stalk waste, but also other onion solid waste includes flower, petiole and skin in food packaging applications.

Novel insights on the multi-functional properties of flavonol glucosides from red onion (Allium cepa L) solid waste – In vitro and in silico approach

Flavonol glucosides was extracted from red onion solid waste (ROSW) and multi-functional properties were determined to develop alternative strategy for therapeutic beneficiation and utilisation as functional food. The major flavonol glucosides extracted from ROSW were confirmed as quercetin-3, 4′-O-diglucoside (QDG), quercetin-3-O-glucoside (isoquercetin), quercetin-4′-O-glucoside (spiraeoside), isorhamnetin- 4′-glucoside (IMG), quercetin glycoside (QG), and quercetin (Q) using a combination of chromatographic, spectroscopic and scientific literature data. The ROSW solvent fractions and extracted flavonol glucosides showed significant antioxidant effect with DPPH, ABTS, FRAP, and ORAC radical scavenging assays. The in vitro and in silico study revealed that the QG, QDG, isoquercetin, and spiraeoside from ROSW exhibited potent α-glucosidase, tyrosinase and xanthine oxidase enzyme inhibitory activity. In addition, QG, QDG, isoquercetin, and spiraeoside showed potent anticancer effect on HeLa cancer lines. Considering these results, the utilization of ROSW and their flavonol glucosides might be helpful for developing potential antioxidant, anticancer and enzyme inhibitory agents.

Production of flavonol quercetin and fructooligosaccharides from onion (Allium cepa L.) waste: An environmental life cycle approach

Abstract Onion (Allium cepa L.) is a worldwide culinary ingredient and the second most important vegetable crop. Hence, the amount of onion solid waste (OSW) is really abundant and constitutes an environmental problem due to its pungent odour and the proliferated growth of phytopathogens. However, the content of flavonol quercetin and fructooligosaccharides (FOS) makes it a potentially recoverable residue. The aim of this study is to incorporate a biorefinery approach, developing a full-scale plant for the valorization of OSW into quercetin and FOS, under a circular economy perspective and, in parallel, to evaluate the environmental profile of this alternative according to a Life Cycle Assessment perspective. To do so, inventory data are obtained from modelled processes at large scale. A mass-based allocation approach is established as baseline, although a sensitivity assessment is further developed considering the influence of the different variables on the results obtained. The results identify that the sections responsible for the extraction of quercetin and FOS, based on the use of ethanol as an extractive agent, have significant environmental burdens. Consequently, the use of this solvent is responsible for a high environmental load due to its background production processes, reaching contributing ratios of up to 30% and 50% in some categories for the extraction of quercetin and FOS, respectively. In addition, the consumption of electricity in the different stages of the process is also responsible for high environmental loads (up to 93% for flavonol quercetin and 86% for FOS) due to its dependence on fossil fuels. Therefore, improvement alternatives should be studied (e.g. microwave and ultrasound-assisted extractions) to significantly reduce impacts on the environmental profile.

Development of sodium propionate-based deep eutectic solvents for polyphenol extraction from onion solid wastes

The objective of the study presented herein was the optimisation of onion solid waste (OSW) polyphenol extraction, using sodium propionate-based deep eutectic solvents (DESs) and process variables optimised through response surface methodology. Initial screening of several novel DESs composed of either L-lactic acid or glycerol as hydrogen bond donors, and sodium propionate as the hydrogen bond acceptor, showed that the DES with glycerol/sodium propionate at a molar ratio 8:1 was the highest-performing system. Extraction optimisation showed that theoretical optimal settings were 85% (w/w) aqueous DES, 100 mL g−1 liquid-to-solid ratio and a stirring speed of 900 rpm. Under these conditions, the temperature assay demonstrated that extraction may be performed at 80 °C, without compromising total polyphenol yield and antioxidant activity. Comparison with other green solvents showed that the DES tested could provide extracts with high flavonoid concentration and superior ferric-reducing power. The stability test performed over a period of 30 days suggested that OSW extract may suffer no significant alterations in the polyphenolic profile, but the antiradical activity may be enhanced. Changes in the antioxidant behaviour were not correlated with changes in the two major OSW constituents, quercetin 4′-O-glucoside and quercetin.

Quercetin Recovery from Onion Solid Waste via Solid-Phase Extraction Using Molecularly Imprinted Polymer Nanoparticles

Abstract The present study deals with the valorization of the onion solid waste (i. e. peel) by extracting quercetin (Qu) compound, as a natural antioxidant food ingredient. It is used as a raw material for cosmetic, fine chemical and pharmaceutical industries. The onion peel, as a solid waste, is a highly rich source of Qu that is a valuable source of many useful biological properties, including antioxidant, anti-inflammatory, antiviral, antibacterial and antimicrobial properties. For this purpose, Qu molecular-imprinted polymer nanoparticles (Qu–MIP NPs) and its corresponding non-imprinted polymer (NIP) were prepared using precipitation/polymerization method. The prepared Qu–MIP NPs and its corresponding NIP were characterized using Fourier transform infrared spectrometer, scanning electron microscopy and high-resolution transmission electron microscope. The prepared Qu–MIP NPs and its corresponding NIP could successfully rebind Qu at binding capacities of 60 and 10.0 mM/g, respectively. Thus, the prepared Qu–MIP NPs could successfully recover 260 mg Qu from 1 kg onion peel.

Natural food colourants derived from onion wastes: application in a yoghurt product.

The valorization of onion (Allium cepa) solid wastes, a 450,000 tonnes/year waste in Europe, by a green extraction method is presented. Polyphenols of onion solid wastes were extracted using eco-friendly solvents, such as water and glycerol. The 2-hydroxypropyl-β-cyclodextrin was also used as a co-solvent for the augmentation of the extraction yield. The process has been optimized by implementing a central composite face centered design of experiments, with two replicates in the central point, taking into consideration the following independent variables: glycerol concentration, cyclodextrin concentration and temperature. The assessment of the extraction model was based on two responses: the total pigment yield and the antiradical capacity. LC-MS analysis was also employed in order to identify polyphenols and colourants of the obtained extracts. The main polyphenols found were quercetin and quercetin derivatives and the main colourant was cyanidin 3-O-glucoside. The extract was also tested as a food colourant in a yoghurt matrix. The onion leaf extract was found to be a stable natural colourant and could be utilized as an alternative ingredient to synthetic coloring agents. This article is protected by copyright. All rights reserved.

Valorization of onion solid waste and their flavonols for assessment of cytotoxicity, enzyme inhibitory and antioxidant activities

Onion (Allium cepa L.) is rich with flavonols which perceived benefits to human health. Flavonols like quercetin and quercetin glycosides from onion solid waste (OSW) have been extracted and tested against enzymes of clinical importance in Alzheimer's disease and diabetes and be shown to have cytotoxic and antioxidant effects. A simple high-performance liquid chromatography-diode array detector method using a Zorbax Eclipse XDB C18 column was developed to separate quercetin-3, 4′-O-diglucoside, quercetin-4′-O-monoglucoside, and quercetin from OSW. These compounds were identified using infrared, ultra-violet, 1H, and 13C nuclear magnetic resonance spectroscopic techniques. The OSW solvent fractions and flavonols showed significant antioxidant activities using DPPH (1, 1-diphenyl-2-picrylhydrazyl), FRAP (ferric reducing antioxidant power), and ABTS (2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid) radical scavenging assays. The samples exhibited significant in vitro anti-cholinesterase activity with strong antidiabetic effects. OSW extracted with methanol and ethanol showed greater in vitro anti-cholinesterase and hypoglycemic effects than QDG, QMG, and Q possibly due to interactions between multiple compounds and/or complex multivariate interactions with other factors in OSW. In addition, cytotoxicity assays showed that OSW and QDG, QMG, and Q could inhibit the proliferation of selected cancer cell lines. Results indicate that OSW and flavonol glycosides are potential antioxidant, antidiabetic, anticancer, and sedative agents.

Utilization of quercetin and quercetin glycosides from onion (Allium cepa L.) solid waste as an antioxidant, urease and xanthine oxidase inhibitors

This study aimed to determine the flavonol glycosides from onion solid waste (OSW) using HPLC analysis, with antioxidant and enzyme inhibitory activities. We found considerable amount of quercetin-4′-O-monoglucoside (QMG: 254.85), quercetin-3,4′-O-diglucoside (QDG: 162.34), quercetin (Q: 60.44), and isorhamnetin-3-glucoside (IMG: 23.92) (mg/100g) dry weight (DW) of OSW. For OSW, the methanol and ethanol showed the strongest antioxidant activities, followed by ethyl acetate, chloroform, and n-hexane extracts. Among the flavonols, Q and QDG possessed higher antioxidant activities. OSW and flavonol glycosides displayed significant enzyme inhibitory activity, with IC50 values ranging from 12.5±0.11 to 32.5±0.28 for OSW, 8.2±0.07 to 16.8±0.02 for flavonol glycosides, and 4.2±0.05μg/mL for thiourea (positive control) towards urease; while 15.2±0.8 to 35.8±0.2 (μg/mL) for OSW, 10.5±0.06 to 20.8±0.05 (μg/mL) for flavonol glycosides, and 6.5±0.05μg/mL for allopurinol (positive control) towards xanthine oxidase, respectively. The OSW and flavonol glycosides may thus be considered as potential antioxidant and antigout agents.

Novel Glycerol-Based Natural Eutectic Mixtures and Their Efficiency in the Ultrasound-Assisted Extraction of Antioxidant Polyphenols from Agri-Food Waste Biomass

Several abundant agri-food wastes, including lemon peels, olive leaves, onion solid wastes, red grape pomace, spent filter coffee and wheat bran, were used to test the efficiency of some novel glycerol-based natural eutectic mixtures to extract polyphenolic compounds. Extractions were performed under specified ultrasonication conditions and the eutectic mixtures, tested as 90 % (v/v) aqueous solutions, were glycerol:choline chloride, glycerol:sodium acetate and glycerol:sodium–potassium tartrate:water, with corresponding molar ratios of 3:1, 3:1 and 5:1:4. The latter two mixtures are reported for the first time. Water and 60 % (v/v) aqueous ethanol were also used as control solvents. The results obtained evidenced that glycerol:choline chloride exhibited high efficiency, which was comparable or even surpassed that of aqueous ethanol, but in some instances the same was observed for glycerol:sodium acetate too. In general, glycerol:sodium–potassium tartrate:water displayed lower efficiency in extracting polyphenols. The data also suggested that extracts with high polyphenol concentration may also possess higher antiradical activity and reducing power. The findings of this study were interpreted on the ground of assumptions regarding the polarity of the eutectic mixtures tested.

Kinetics of Ultrasound-Assisted Flavonoid Extraction from Agri-Food Solid Wastes Using Water/Glycerol Mixtures

Red grape pomace (RGP) and onion solid wastes (OSW) were used as raw material to produce flavonoid-enriched extracts, using ultrasound-assisted solid-liquid extraction. The extraction medium used was composed of water and glycerol and under the conditions used the extraction of flavonoids from both materials was shown to obey first-order kinetics. Maximum diffusivities (De) values were 4.01 × 10−11 and 2.35 × 10−11 m2·s−1, for RGP and OSW extraction, respectively, while the corresponding activation energies (Ea) were 14.00 and 15.23 kJ·mol−1.

Kinetic modelling for polyphenol extraction from onion (Allium cepa) solid wastes using acidified water/ethanol mixture

Previous reports highlighted the onion solid wastes as abundant, residual material that might contain a significant load of antioxidant polyphenols. Although there have been studies pertaining to polyphenol recovery from onion wastes, the effect of temperature has not been adequately addressed. In this line, this study was undertaken with the aim of establishing a correlation between the extraction yield in total polyphenols and the extraction temperature, using acidified aqueous ethanol as the solvent system. Extraction of polyphenols from onion solid wastes was found to obey 2nd-order kinetics. On such a basis, the yield in total polyphenols at saturation could be very effectively determined and correlated with temperature using non-linear regression. The results indicated that the extraction yield at saturation is highly correlated with temperature, following a quadratic function. The extract obtained at optimal temperature (40 °C) had a total polyphenol yield of 21.10 mg gallic acid equivalents per gram of dry weight, and it was further analysed by liquid chromatography-mass spectroscopy to characterise its major constituents. The polyphenols detected were quercetin glucosides, as well as quercetin oxidation derivatives, including certain degradation products and dimers. The outcome of this study outlined that temperatures above 40 °C are rather not favourable for polyphenol extraction from onion solid wastes, as suggested by the model established through kinetics. The extract obtained under optimal conditions contained peculiar polyphenolic composition, not encountered in any other food processing residue.

A green ultrasound-assisted extraction process for the recovery of antioxidant polyphenols and pigments from onion solid wastes using Box–Behnken experimental design and kinetics

Onion solid wastes (OSW) were used as raw material to produce polyphenol- and pigment-enriched extracts with antioxidant activity, using ultrasound-assisted solid-liquid extraction. The extraction medium used was free from conventional volatile organic solvents, and it was composed of water and glycerol. Glycerol concentration (Cgl) and liquid-to-solid ratio (RL/S) were first optimised employing Box–Behnken experimental design and then extraction efficiency was further assessed through kinetics. The optimal conditions were found to be Cgl=90% (w/v) and RL/S=90mLg−1, and under these conditions the extraction of total polyphenols and total pigments was shown to obey first-order kinetics. Maximal effective diffusion (De) values were 9.28×10−11 and 13.22×10−11m2s−1, for total polyphenols and total pigments, respectively, while the corresponding activation energies (Ea) were 31.52 and 12.11kJ mol−1. The reducing power (PR) increased as a response to increasing extraction temperature and the extract obtained at 80°C had PR value of 490μmol ascorbic acid equivalents per g of dry weight. Liquid chromatography-diode array-mass spectrometry analysis of this extract showed that the major polyphenols tentatively identified were quercetin 4′-O-glucoside and quercetin, accompanied by other quercetin glycosides, cyaniding 3-O-glucoside and a series of quercetin degradation and oxidation products.

Crude peroxidase from onion solid waste as a tool for organic synthesis. Part III: synthesis of tetracyclic heterocycles (coumestans and benzofuroquinolinones)

In the present study the biocatalytic activity of a crude onion peroxidase extract on the reaction between catechol and heterocyclic 1,3-dicarbonyl compounds is investigated. The crude enzyme preparation promotes effectively the reaction between catechol and 4-hydroxycoumarin, 4-hydroxy-1-methyl-2-quinolinone and 2,4-quinolinediol to afford the corresponding coumestans and benzofuroquinolinones in satisfactory yields. The products of the reaction are fully characterized spectroscopically and are found to possess potent antioxidant activity as evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing antioxidant power (FRAP), and luminol-induced chemiluminescence assays.

Ultrasound‐assisted extraction of quercetin from onion solid wastes

SummaryThe extraction of quercetin with aqueous ethanol solutions from onion solid waste under sonication conditions was investigated using rational experimental design methodologies. It was found that the ethanol concentration (40–80%, v/v) and the temperature (40–60 °C) of extraction are the most influential parameters in the recovery yield, whereas pH (2–6), liquid/solid ratio (30–60 mL g−1) and extraction time (15–35 min) do not significantly influence the completeness of the extraction. The optimal extraction conditions were determined to be an ethanol percentage of 59% and extraction temperature of 49 °C, yielding a total quercetin content of 11.08 mg per g dry weight of onion solid waste. An empirical relationship between extraction parameters and the extraction yield was suggested and verified.