Antioxidative phenolic constituents of skins of onion varieties and their activities

Onion (Allium cepa L.) and Drought: Current Situation and Perspectives

Onions (Allium cepa L.) are the second most commonly produced and consumed vegetable worldwide due to their economic, nutritional, and medicinal benefits. However, drought hinders vegetative growth, lowers yields and bulb quality, reduces photosynthetic activity, and alters the onion plant's metabolism. This review provides a summary of global research on the impact of drought on onions. It specifically seeks to shed light on aspects that remain unclear and generate research avenues. Relevant scientific articles were sourced from the AGORA database, Web of Science (WoS), and search engines such as Google Scholar, Scopus, MEDLINE/PubMed, and SCImago to achieve this objective. A total of 117 scientific articles and documents related to onion and drought were critically examined. The review revealed agromorphological, physiological, biochemical, and genomic studies depicting factors that contribute to drought tolerance in onion genotypes. However, there was little research on the physiological, biochemical, and genetic characteristics of drought tolerance in onions, which need to be deepened to establish its adaptation mechanisms. Understanding the mechanisms of onion response to water stress will contribute to fast-tracking the development of drought-tolerant genotypes and optimize onion production. Future research should be more focused on investigating onion drought tolerance mechanisms and structural and functional genomics and identifying genes responsible for onion drought tolerance.

Comparative Analysis of Polyphenol Content and Antioxidant Activity of Different Parts of Five Onion Cultivars Harvested in Korea

Onions are typically consumed as the bulb, but the peel and root are discarded as by-products during processing. This study investigated the potential functional use of these by-products by analyzing the polyphenols, antioxidant compounds, and antioxidant activity contained in onions. In this study, the bulb, peel, and root of five onion cultivars ('Tank', 'Bomul', 'Gujji' 'Cobra', and 'Hongbanjang') harvested in Korea were investigated. Caffeic acid and quercetin were most abundant in the peel, whereas methyl gallate was the predominant polyphenol in the bulb. Both DPPH and ABTS radical scavenging activity were higher in onion peel and root than in the bulb. These findings suggest that onion peel and roots, which are often discarded, have abundant antioxidant substances and excellent antioxidant activity. This study provides basic data for the future use of onion peel and roots as functional ingredients with high added value.

Red Onion Peel Powder as a Functional Ingredient for Manufacturing Ricotta Cheese

Onion (Allium cepa L.) is a vegetable widely cultivated and consumed due to its rich content in bioactive compounds. Red onion peel (ROP) powder, which is a by-product derived from the onion industry, has been attracting significant interest as a potential functional ingredient for improving the overall quality of foods. The present study explores the potential of ROP powder as a functional ingredient to improve the quality and nutritional value of whey cheese. Despite being frequently viewed as a food processing waste byproduct, ROP is a rich source of bioactive substances, including antioxidants, flavonoids, and dietary fiber, having antioxidant and antibacterial effects. The ROP extract exhibited high amounts of total polyphenols (119.69 ± 2.71 mg GAE/g dw) and antioxidant activity (82.35 ± 1.05%). Different quantities (1 and 3%) of ROP powder were added to cheese formulations, and the subsequent impact on the texture characteristics, sensory attributes, and phytochemical composition of the value-added cheeses was evaluated. The findings show that the addition of ROP powder improved the texture and the color of the cheeses, providing a visually appealing product. Additionally, adding the ROP powder significantly raised the amount of phytochemicals and antioxidant activity (17.08 ± 0.78 µmol TE/g dw for RCROP1, 24.55 ± 0.67 µmol TE/g dw for RCROP2) in the final product's formulation. Moreover, adding powder to cheese is an effective way to increase the value of onion by-products and produce polyphenol-enriched cheese.

Valorization of onion peel waste: From trash to treasure

Globally, fruits and vegetables are consumed as raw, processed, or as an additive, accounting for approximately 50% of total food wastage. Among the fruits and vegetables, onion is well known for its potential bioactive components; however, peels of onion are a major concern for the environmental health and food industries. Effective utilization methods for valorizing the onion peel should be needed to develop value-added products, which are more eco-friendly, cost-effective, and sustainable. Therefore, this review attempts to emphasize the conventional and emerging valorization techniques for onion peel waste to generate value-added products. Several vital applications including anticancerous, antiobesity, antimicrobial, and anti-inflammatory activities are thoroughly discussed. The findings showed that the use of advanced technologies like ultrasound-assisted extraction, microwave-assisted extraction, and enzymatic extraction, demonstrated improved extraction efficiency and higher yield of bioactive compounds, which showed the anticancerous, antiobesity, antimicrobial, and anti-inflammatory properties. However, in-depth studies are recommended to elucidate the mechanisms of action and potential synergistic effects of the bioactive compounds derived from onion peel waste, and to promote the sustainable utilization of onion peel waste in the long-term.

Comparison of the effect of extraction methods on waste cotton (Gossypium hirsutum L.) flowers: metabolic profile, bioactive components, antioxidant, and α-amylase inhibition

BACKGROUND

Waste cotton flowers, as a by-product of cotton cultivation, are enriched with bioactive substances that render them a promising natural source of health-promoting benefits. In this study, ultrasound-assisted extraction (UAE), subcritical water extraction (SWE), and conventional extraction (CE) approaches were applied to extract bioactive compounds from waste cotton flowers, and the metabolic profiles, bioactive components, antioxidants, and α-amylase inhibition of different extractions were systematically analyzed and compared.

RESULTS

It was observed that UAE and CE extracts had similar metabolic profiles compared with SWE. The flavonoids and amino acids and derivatives were more prone to be extracted by UAE and CE, whereas phenolic acids tended to accumulate in SWE extract. The UAE extract had the highest amounts of total polyphenols (214.07 mg gallic acid equivalents per gram dry weight) and flavonoids (33.23 mg rutin equivalents per gram dry weight) as well as the strongest inhibition on oxidation (IC50  = 10.80 μg mL-1 ) and α-amylase activity (IC50  = 0.62 mg mL-1 ), indicating that chemical composition was closely related to biological activity. Additionally, microstructures and thermal behaviors of the extracts were investigated and highlighted the ability of UAE.

CONCLUSION

Overall, it can be concluded that UAE is an efficient, green, and economical extraction method to produce bioactive compounds from cotton flowers, and the UAE extracts could be used in food and medicine industries because of their high antioxidant and α-amylase inhibitory activity. This study provides a scientific basis for the development and comprehensive utilization of cotton by-products. © 2023 Society of Chemical Industry.

From Waste to Green: Water-Based Extraction of Polyphenols from Onion Peel and Their Adsorption on Biochar from Grapevine Pruning Residues

Onion peels (OP) are rich in bioactive compounds with a plethora of benefits for human health, but this valuable material is often wasted and underutilized due to its inedibility. Likewise, grapevine pruning residues are commonly treated as agricultural waste, but biochar (BC) obtained from this material has favorable characteristics as an adsorbent. This study investigated the potential of BC in removal of targeted polyphenolic compounds from OP extracts. The OP extracts were obtained adhering to green chemistry principles using deionized water amplified by three methods: maceration (MAC), ultrasound-assisted extraction (UAE), and microwave-assisted extraction (MAE). The extraction efficiency on the polyphenolic profile and antioxidant capacity was investigated with different extraction temperatures and solid-to-liquid (s/l) ratios. For further analysis, UAE at 90 °C with an s/l ratio of 1:100 was used due to higher polyphenolic compound yield. The BC adsorption capacity of individual polyphenols was fitted with the Langmuir and Freundlich isotherm models. Quercetin-3,4'-diglucoside obtained the highest R2 coefficient in both models, and the highest qmax value. The optimum conditions in the dosage experiment suggested an amount of 0.5 g of BC using 3 g/L extracts. The studied BC showed a high affinity for targeted phytochemicals from OP extracts, indicating its potential to be applied for the green adsorption of valuable polyphenolic compounds.

Evaluation of deodorization techniques using cyclodextrins on the headspace volatiles and antioxidant properties of onion

Sulphur-containing volatiles in onion produce unpleasant odors and this limit their usage in foods. To expand its application, several additives including α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), and chitosan were added to onion solution and evaluated for their effect on sulphur-containing volatiles. Also, antioxidant property using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay and oxidative stabilities in an oil-in-water (O/W) emulsion were carried out. The total volatile contents were decreased in the order of α-CD (50.1%), β-CD (49.3%), HP-β-CD (46.2%), and chitosan (7%). Meanwhile, HP-β-CD showed the highest DPPH radical scavenging ability followed by β-CD, α-CD, and chitosan with decreasing order. The β-CD significantly enhanced the oxidative stability of the O/W emulsion, whereas α-CD and β-HP-CD showed prooxidative behavior. Overall, β-CD might be used as a sulphur-containing volatile decreasing agent, which could keep the antioxidant properties of onion in the O/W emulsion.

Quercetin extraction from small onion skin (Allium cepa L. var. aggregatum Don.) and its antioxidant activity

In the present study, the maximum yield of quercetin was optimized for the ethanol extraction of small onions (Allium cepa L. var. aggregatum Don.), and the antioxidant activity was investigated in vitro. The extraction of quercetin from the small onion skin was carried out through ethanol solvent extraction with different ratios of ethanol and water. Ethanol: water ratio produced the highest quercetin from the onion skin. RP-HPLC analysis of the extracted material showed 2, 122 mg/g of quercetin and 0.34 mg/g of isorhamnetin. A total of 301.03 mg GAE/g dry weight and 156 mg/g quercetin equivalents were found in the onion skin extract. DPPH and ABTS free radical scavenging potentials of the tested extract (90:10 v/v) were dose-dependent, with IC₅₀ values of 62.27 μg/mL and 53.65 μg/mL, respectively. Therefore, the present study reports that small onion skin extract rich in quercetin may serve as a promising antioxidant and anticancer agent.

The ‘Edge Effect’ Phenomenon in Plants: Morphological, Biochemical and Mineral Characteristics of Border Tissues

The ‘edge’ effect is considered one of the fundamental ecological phenomena essential for maintaining ecosystem integrity. The properties of plant outer tissues (root, tuber, bulb and fruit peel, tree and shrub bark, leaf and stem trichomes) mimic to a great extent the ‘edge’ effect properties of different ecosystems, which suggests the possibility of the ‘edge’ effect being applicable to individual plant organisms. The most important characteristics of plant border tissues are intensive oxidant stress, high variability and biodiversity of protection mechanisms and high adsorption capacity. Wide variations in morphological, biochemical and mineral components of border tissues play an important role in the characteristics of plant adaptability values, storage duration of roots, fruit, tubers and bulbs, and the diversity of outer tissue practical application. The significance of outer tissue antioxidant status and the accumulation of polyphenols, essential oil, lipids and minerals, and the artificial improvement of such accumulation is described in connection with plant tolerance to unfavorable environmental conditions. Methods of plant ‘edge’ effect utilization in agricultural crop breeding, production of specific preparations with powerful antioxidant value and green nanoparticle synthesis of different elements have been developed. Extending the ‘edge’ effect phenomenon from ecosystems to individual organisms is of fundamental importance in agriculture, pharmacology, food industry and wastewater treatment processes.

Mechanisms Underlying Neurodegenerative Disorders and Potential Neuroprotective Activity of Agrifood By-Products

Neurodegenerative diseases, characterized by progressive loss in selected areas of the nervous system, are becoming increasingly prevalent worldwide due to an aging population. Despite their diverse clinical manifestations, neurodegenerative diseases are multifactorial disorders with standard features and mechanisms such as abnormal protein aggregation, mitochondrial dysfunction, oxidative stress and inflammation. As there are no effective treatments to counteract neurodegenerative diseases, increasing interest has been directed to the potential neuroprotective activities of plant-derived compounds found abundantly in food and in agrifood by-products. Food waste has an extremely negative impact on the environment, and recycling is needed to promote their disposal and overcome this problem. Many studies have been carried out to develop green and effective strategies to extract bioactive compounds from food by-products, such as peel, leaves, seeds, bran, kernel, pomace, and oil cake, and to investigate their biological activity. In this review, we focused on the potential neuroprotective activity of agrifood wastes obtained by common products widely produced and consumed in Italy, such as grapes, coffee, tomatoes, olives, chestnuts, onions, apples, and pomegranates.

Optimization of Wall Material of Freeze-Dried High-Bioactive Microcapsules with Yellow Onion Rejects Using Simplex Centroid Mixture Design Approach Based on Whey Protein Isolate, Pectin, and Sodium Caseinate as Incorporated Variables

For the food sector, onion rejects are an appealing source of value-added byproducts. Bioactive compounds were recovered from yellow onion rejects using a pulse electric field process at 6000 v and 60 pulses. The onion extract was encapsulated with whey protein isolate (WPI), pectin (P), and sodium caseinate (SC) with a mass ratio of 1:5 (extract/wall material, w/w). A Simplex lattice with augmented axial points in the mixture design was applied for the optimization of wall material for the encapsulation of onion reject extract by freeze-drying (FD). The optimal wall materials were 47.6 g/100 g (SC), 10.0 g/100 g (P), and 42.4 g/100 g (WPI), with encapsulation yield (EY) of 85.1%, total phenolic content (TPC) of 48.7 mg gallic acid equivalent/g DW, total flavonoid content (TFC) of 92.0 mg quercetin equivalent/g DW, and DPPH capacity of 76.1%, respectively. The morphological properties of the optimal encapsulate demonstrated spherical particles with a rough surface. At optimal conditions, the minimum inhibitory concentration (MIC) of the extract (mean diameter of inhibition zone: 18.8 mm) was shown as antifungal activity against Aspergillus niger.

Value-added salad dressing enriched with red onion skin anthocyanins entrapped in different biopolymers

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The microencapsulation of ROS extract was performed by gelation and freeze-drying.

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The powders were rich in valuable antioxidants, with over 80% EE for anthocyanins.

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Good stability of phytochemicals over storage and digestion was noticed.

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V2 powder’s functionality was tested by its addition to salad dressing.

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Our results are promising in developing multifunctional ingredients for foods.

In this study, red onion skin extract was used to obtain food ingredients. Complex biopolymeric matrices were dissolved in the anthocyanin-rich aqueous extract, followed by gelation and freeze-drying. Powders were characterized regarding encapsulation efficiency (EE), phytochemical content, color, antioxidant activity, and microstructure. Storage and simulated digestion stability were also assessed. Two powders with high contents of bioactives and antioxidant activity were obtained. The highest EE was acquired for the powder with a higher polysaccharides concentration (V2). In addition, V2 exhibited the best storage stability. The in vitro studies demonstrated that increased carbohydrate concentration delivers the best anthocyanins protection. To prove its functionality, V2 was added to a salad dressing. The addition of powder has improved the concentration of biologically active compounds and the antioxidant activity of the salad dressings. These results support the assumption that microencapsulation may deliver bioactives from red onion skin as functional ingredients for value-added foods.

Onion waste based-biorefinery for sustainable generation of value-added products

Waste derived from the onion processing sector can be harnessed for the production of organic acids, polyphenols, polysachharides, biofuels and pigments. To sustainably utilize onion processing residues, different biorefinery strategies such as enzymatic hydrolysis, fermentation and hydrothermal carbonization have been widely investigated. This review discusses the recent advances in the biorefinery approaches used for valorization of onion processing waste followed by the production of different value-added products from diverse classes of onion waste. The review also highlights the current challenges faced by the bioprocessing sector for the utilization of onion processing waste and perspectives to tackle them.

Red onion skin active ingredients, extraction and biological properties for functional food applications

Onion is an important vegetable in the world and the second most important vegetable crop after tomato.Hence, the onion waste, such as onion skin, is produced in abundance causing environmental problems. Due to its bioactive compounds, especially phenolics and flavonoids, red onion skin can be used through appropriate methods for producing value-added products. These phytochemicals are proven to prevent oxidative stress and broad spectrum of microorganisms beside having diverse beneficial biological properties. Extraction step is the most critical processing in making phytonutrient available. Various approaches including conventional and non-conventional technologies applied for extracting different compounds from red onion wastes was summarized in this study. To evaluate the industrial application potential, the use of natural bioactives derived from red onion skin for elaboration of various food systems has been also investigated.

Effects of Onion Extract and Onion Peel Extract on the Formation of Polycyclic Aromatic Hydrocarbons in Charcoal-Grilled Pork Patties

ABSTRACT

This study investigated the effects of different concentrations (0.0005, 0.005, 0.05, 0.25, and 0.5%) of onion extract (OE) and onion peel extract (OPE) on the formation of four polycyclic aromatic hydrocarbons (PAHs) in charcoal-grilled pork patties. Both OE and OPE inhibited the formation of four PAHs in charcoal-grilled pork patties, with the highest inhibition rate reaching 88.33% on 0.50% OE addition and 98.79% on 0.05 and 0.25% OPE addition. OPE has greater inhibitory effect on the formation of four PAHs than OE does; this may be related to OPE's higher concentrations of flavonoids and higher free-radical scavenging activities. Both OE and OPE worked to lower thiobarbituric acid reactive substance values of charcoal-grilled pork patties. The inhibitory effect of OE and OPE on four PAHs showed the same trend as their antilipid oxidation effects, but the correlation was not strong. In addition to antilipid oxidation, other pathways are also involved in the inhibition of PAH formation.

HIGHLIGHTS

Differences in Antioxidant Potential of Allium cepa Husk of Red, Yellow, and White Varieties

The effective management of agro-industry organic waste for developing high-commercial-value products is a promising facet of the circular economy. Annually, more than 550,000 tons of waste that is potentially rich in biologically active substances is generated worldwide while processing onions (Allium cepa L.). The antioxidant potential of red, yellow, and white onion husks was studied using FRAP, ORAC, chemiluminescence, and UPLC-ESI-Q-TOF-MS analysis methods. The extraction of phenolic compounds from onion husks was more effective when using an aqueous solution of 70% ethanol as compared with water. Ethanolic extract from red onion husks exhibited the highest TAC_ORAC and TAC_FRAP values, averaging 2017.34 µmol-equiv. Trolox/g raw material and 2050.23 µmol-equiv. DQ/g raw material, respectively, while the white onion exhibited much lower levels of antioxidants. According to the chemiluminescence results, it was determined that the red and yellow onion husks contained antioxidants of three types of power, while white onion husks only contained medium and weak types. The highest content of flavonoids was found in red onion husks, averaging 1915.90 ± 9.92 µg-eq. DQ/g of raw material and 321.42 ± 2.61 µg-eq. DQ/g of raw material for ethanol and water, respectively, while yellow onion husks exhibited 544.06 ± 2.73 µg-eq. DQ/g of raw material and 89.41 ± 2.08 for ethanol and water, respectively. Quercetin and its glycosides were the most representative flavonoids, and a number of substances with different pharmacological and biological properties were also identified.

Development and evaluation of onion bulb descaler for removal and collection of surface dry peel

Onion bulbs contain outer papery dry peel which is rich with industrially important high-value compounds. Removal of dry peel/scale of onion is the common practice during bulb processing, storage and marketing. A conventional manual method of scale removal involves huge labour, drudgery and means of environmental pollution. An onion descaler machine has been therefore developed to mechanize this operation, reduce drudgery and effectively collect the dry scales for industrial use. The operating parameters of the developed machine were optimized for its best performance using RSM. During optimization study, roller speed, roller slope and hopper opening were taken as independent variables. The performance of the machine was evaluated through descaling efficiency and descaling loss. During experimentation, descaling efficiency and descaling loss were obtained in the range of 35.92-98.55% and 0.82-9.07%. The optimum performance of the machine was obtained at 450 rpm roller speed, 2% roller slope and 380 mm of the hopper opening with maximum descaling efficiency (88.29%) and minimum descaling loss (3.65%). The optimization of the onion descaler parameters and their statistical relation provided the necessary information on the combination of material-machine alignment, and design parameters for enhanced descaling efficiency.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-021-05264-5.

Value-Added Crackers Enriched with Red Onion Skin Anthocyanins Entrapped in Different Combinations of Wall Materials

The objective of this study was to encapsulate anthocyanins from red onion skins into different biopolymeric matrices as a way to develop powders with multifunctional activities. Two different variants of powders were obtained using a combination of gelation and freeze-drying techniques and characterized by encapsulation efficiency, antioxidant activity, phytochemical content, and color. Stability during storage and the bioavailability of anthocyanins in the in vitro simulated digestion were also examined. Powder V2, with a higher concentration of polysaccharides than V1, allowed a better encapsulation efficiency (90.53 ± 0.29%) and good stability during storage. Both variants had a high content of phytochemicals and antioxidant activity. In vitro investigations proved that an increased polysaccharides concentration offers the best protection for anthocyanins. Thus, a controlled release of the anthocyanins in the intestinal medium was achieved. The powder with the highest encapsulation efficiency was added to crackers, followed by phytochemical characterization to assess its potential added value. The addition of the micro-particles improved the functional characteristics such as antioxidant activity, showing its suitability for the development of bakery products. The attained results may bring implicit benefits to consumers, who can benefit from improved bioactive concentrations in foodstuffs, with significant health benefits.

Valorization of ‘Rossa di Tropea’ Onion Waste through Green Recovery Techniques of Antioxidant Compounds

The aim of this work was to maximize the recovery of the bioactive components from an important solid waste derivate from Tropea onion processing. To achieve this, three different extractive procedures (conventional for maceration, ultrasound, and microwave-assisted) were employed, using only food-grade extraction solvents such as water and ethanol:water (50:50). Solvent, temperature, microwave power, time, and their interaction were studied as the principal factors that might affect the extractability rates. The obtained data suggest that the hydroalcoholic mixture proved to be the best for each of the techniques developed and at each time and temperature considered. In particular, the best results were achieved by conventional extraction for 60 min at 40 °C (total flavonoids content: 25.64 ± 1.40 mg QE g−1 d.w.; total anthocyanins content: 0.78 ± 0.01 mg C-3-GLUC g−1 d.w.). The UHPLC analysis of the optimally obtained extract revealed that the principal phytochemicals recovered were quercetin (5322.61 ± 0.32 mg kg−1) and quercetin 3-4′-diglucoside (1023.80 ± 0.34 mg kg−1) after conventional and ultrasound-assisted extraction, respectively. In this perspective, the implementation of sustainable, food-grade extraction processes to recover value-added substances from solid onion waste could play a crucial role both in reducing the waste load and in formulating natural food additives with functional properties, with a potential direct industrial impact.

Using Transcriptome Analysis to Explore Gray Mold Resistance-Related Genes in Onion (Allium cepa L.)

Gray mold disease caused by Botrytis in onions (Allium cepa L.) during growth and storage negatively affects their yield and quality. Exploring the genes related to gray mold resistance in onion and their application to the breeding of resistant onion lines will support effective and ecological control methods of the disease. Here, the genetic relationship of 54 onion lines based on random amplified polymorphic DNA (RAPD) and in vitro-cultured onion lines infected with gray mold were used for screening resistance and susceptibility traits. Two genetically related onion lines were selected, one with a resistant and one with a susceptible phenotype. In vitro gray mold infection was repeated with these two lines, and leaf samples were collected for gene expression studies in time series. Transcript sequences obtained by RNA sequencing were subjected to DEG analysis, variant analysis, and KEGG mapping. Among the KEGG pathways, ‘α-linoleic acid metabolism’ was selected because the comparison of the time series expression pattern of Jasmonate resistant 1 (JAR1), Coronatine-insensitive protein 1 (COI 1), and transcription factor MYC2 (MYC2) genes between the resistant and susceptible lines revealed its significant relationship with gray-mold-resistant phenotypes. Expression pattern and SNP of the selected genes were verified by quantitative real-time PCR and high-resolution melting (HRM) analysis, respectively. The results of this study will be useful for the development of molecular marker and finally breeding of gray-mold-resistant onions.

Onion (Allium cepa L.) peels: A review on bioactive compounds and biomedical activities

Huge quantities of byproducts/wastes generated in onion processing are usually discarded, but they are excellent sources of bioactive compounds and phytochemicals. However, with growing interest in the sustainable use of resources and the circular economy to reduce adverse impacts on the environment, food processing wastes such as onion peel/skin can be extracted and employed as inputs in developing or reformulating nutrient supplements, and pharmacological drugs. This review highlights major bioactive components, especially total phenolics, total flavonoid, quercetin and its derivatives present in onion peel/skin and their therapeutic applications as cardioprotective, neuroprotective, antiobesity, antidiabetic, anticancer and antimicrobial agents. The present review emphasized that onion peel is one of the important agricultural by-products which is rich in bioactive compounds and can be utilized as health promoting ingredient especially in pharmacological and biomedical fields. Thus, with increasing burden of life style disorders/non-communicable diseases, finding suitable natural alternative for their treatment is one major concern of the researchers and onion peel and its extract can be exploited as a prime ingredient.

Bioactive's Characterization, Biological Activities, and In Silico Studies of Red Onion (Allium cepa L.) Skin Extracts

This study aimed to investigate the thermal stability and biological activities of the phytochemicals from the red onion skins extract, which are a rich source of anthocyanins. Eight anthocyanins were identified in the extract by high-performance liquid chromatography, the most abundant ones being cyanidin 3-O-laminaribioside and cyanidin 3-O-(6″-malonoyl-laminaribioside). The study also involved the assessment of the thermal degradation kinetics of anthocyanins and antioxidant activity in the 75-155 °C temperature range. The thermal degradation kinetics was described using the first-order kinetics model. In terms of thermal stability, increasing the temperature resulted in lower half-life values (t_1/2) and higher degradation rate constant values (k) for both anthocyanins and antioxidant activity. The thermodynamic parameters revealed that the phytochemicals' degradation is a non-spontaneous and endothermic reaction. Furthermore, the inhibitory effect of the extract was investigated against the enzymes affiliated with metabolic syndrome, oxidative stress, and inflammatory process diseases. Thus, we also demonstrated that the red onion skins extract exerted inhibitory activity on α-glucosidase, α-amylase, lipase, and lipoxygenase. Considering the high content of bioactives and various biological properties, the red onion skins extract is suitable for multiple applications.

Underutilized Northern plant sources and technological aspects for recovering their polyphenols

Consumers worldwide are increasingly interested in the authenticity and naturalness of products. At the same time, the food, agricultural and forest industries generate large quantities of sidestreams that are not effectively utilized. However, these raw materials are rich and inexpensive sources of bioactive compounds such as polyphenols. The exploitation of these raw materials increases income for producers and processors, while reducing transportation and waste management costs. Many Northern sidestreams and other underutilized raw materials are good sources of polyphenols. These include berry, apple, vegetable, softwood, and rapeseed sidestreams, as well as underutilized algae species. Berry sidestreams are especially good sources of various phenolic compounds. This chapter presents the properties of these raw materials, providing an overview of the techniques for refining these materials into functional polyphenol-rich ingredients. The focus is on economically and environmentally sound technologies suitable for the pre-treatment of the raw materials, the modification and recovery of the polyphenols, as well as the formulation and stabilization of the ingredients. For example, sprouting, fermentation, and enzyme technologies, as well as various traditional and novel extraction methods are discussed. Regarding the extraction technologies, this chapter focuses on safe and green technologies that do not use organic solvents. In addition, formulation and stabilization that aim to protect isolated polyphenols during storage and extend shelflife are reviewed. The formulated polyphenol-rich ingredients produced from underutilized renewable resources could be used as sustainable, active ingredients--for example, in food and nutraceutical industries.

Development of active packaging film from sodium alginate/carboxymethyl cellulose containing shallot waste extracts for anti-browning of fresh-cut produce

Owing to growing concerns about making pollution-free sustainable environment by reducing the dumping of agricultural waste and convert it into valuable product is a key to carry out the present study. The ultimate goal of this study is to convert onion solid wastes (OSWs) into active packaging and evaluating the anti-browning effect due to the OSWs holding rich polyphenols and antioxidants. The active packaging film was fabricated by using sodium alginate (SA) and carboxymethyl cellulose (CMC) along with SOWEs such as peel and stalk at 0.2% and 0.5% concentration. The film made with SA/CMC/SOWEs had good physical, mechanical, optical and barrier property, higher phenolic and antioxidant activity compared to control. In addition, the effect of SA/CMC/SOWEs film packaging on anti-browning and quality of fresh-cut apple and potato stored at 4 °C was studied. The results show the SA/CMC/SOWEs film had better effect on controlling browning index in fresh-cut apple and potato over the storage of 12 days and 5 days. This study concludes that the SA/CMC film developed with shallot stalk extract can be used for wrapping of fresh-cut fruits and vegetables. It also prevents browning and maintains the overall quality than control and shallot peel incorporated film.

Onion (Allium cepa L.) peel extracts characterization by conventional and modern methods

The impact of different extraction methods on bioactive compounds (total phenols and flavonoids) recovery from onion wastes recovered from the market was investigated. The results revealed a total polyphenol content from 25.19 ± 3.56 mg gallic acid equivalents/g for enzyme-assisted extraction (EAE) to 212.56 ± 1.18 mg gallic acid equivalents/g for supercritical extraction (SFE). The total flavonoid content registered from 108.36 ± 3.62 mg quercetin equivalents/g for EAE to 334.97 ± 19.41 mg quercetin equivalents/g for conventional solvent extraction (CSE). The antioxidant activity (404.93 ± 1.39 mM Trolox/g) for SFE was the highest compared to all the extraction procedures used. The chromatographic profiles were conducted at five primary compound identification (quercetin 7,4-diglycoside, quercetin 3,4-diglycoside, quercetin 4-glucoside, quercetin, and kaempferol) and GC-MS analysis allowed the identification of 26 compounds, manly identified in EAE. The results also revealed that the SFE method, as a non-invasive technique, recorded the highest concentration of bioactive compounds and antioxidant activity, confirmed by chromatographic profiles.

Formulation and development of herbal microsponge sunscreen gel

PURPOSE

The endeavor of this study is to prepare and developed a method for microsponge gel as a polyherbal formulation along with their evaluation methods for sunscreen properties.

METHOD

Polyherbal extracts as an active component for preparing microsponge formulation used in ratio of a drug, i.e. Poly herbal extracts, ethyl cellulose used as polymer, Polyvinyl alcohol as an emulsifier present in the formulation was successfully obtained by using method quasi-emulsion solvent diffusion. The formulations prepared were considered for substantial characterization. The physical description of microsponge formulation, having a coating of Gel-3 exhibits more loading efficiency and production yield. The mentioned formulation of microsponge was formulated with the help of gel using carbopol and then test performed are pH, viscosity, spreadability, drug content, and in-vitro release. Most of the microsponge preparations are prepared by drug loading in it and the consequences are good to reproduce. The best formulation was prepared and then comparison study was done with one of the marketed simple gel of polyherbal extract and other one is microsponge loaded gel of polyherbal extract by using Franz diffusion cell.

RESULT

The release profile details about that the microsponge loaded gels are showing excellent release rate while comparing to simple marketed gel of polyherbal extract.

Waste streams in onion production: Bioactive compounds, quercetin and use of antimicrobial and antioxidative properties

Onion production generates abundant waste with high contents of bioactive compounds. These might have several beneficial functional properties for fortification of foods. To understand the variety and potential for further use, we examined various parts of the plants (edible/inedible waste/outer skin of onion), as well as extraction in water/ethanol and by shaking/sonication. Quercetin content and antioxidant capacity were initially determined for extracts of edible and waste parts of red, yellow and white onions, and red shallots. Ethanol extracts of the waste fraction had the highest quercetin content and antioxidant capacity. Except white onion, which contained no quercetin, the dried waste ethanol extracts contained up to 15 mg quercetin g^-1 and had an antioxidant capacity of nearly 40 mg Trolox equivalents g^-1. Furthermore, the dried skin ethanol extract of yellow onion, which is commercially the most available fraction, contained 8 mg quercetin g^-1, with antioxidant capacity of 25 mg Trolox equivalents g^-1 and high antimicrobial activity. Dried yellow onion skin showed good stability for the quercetin content under various storage conditions (4, 25, 37, 40 °C; dark/light; dry/moist air/in water). Bacteria, bacterial spores, yeast and mould counts remained unchanged for dried onion skin over 5 days under storage conditions that can promote food spoilage, indicating exceptional microbial stability. Finally, two different applications are demonstrated for dried yellow onion skin: tablets for home use (tablets as more convenient form of storage and for simple dosing in cooking), and a stabilisation additive (prolonged shelf-life of olive oil). Both represent efficient and straightforward approaches through waste prevention and food fortification.

Effect of temperature fluctuation on colour change and softening of postharvest sweet cherry

The inevitable temperature fluctuation during cold chain transport accelerates the colour change and softening of postharvest sweet cherry, leading to further deterioration of quality and decline of the marketable value of cherries. The influences of temperature fluctuation on the contents of total anthocyanin, phenolic, malondialdehyde, and sodium carbonate-soluble pectin (SSP), as well as the activities of polyphenoloxidase (PPO) and peroxidase (POD) in sweet cherry, were assessed. In addition, the effects of temperature fluctuation on the activities of polygalacturonase (PG), pectin methyl esterase (PME), and beta-galactosidase (β-Gal) activities, and the paPG, paPME, and paPME genes expression were studied. The evolution of SSP nano-morphology was measured by atomic force microscopy. The results showed that the temperature fluctuation promoted anthocyanin synthesis, phenolic metabolism, and malondialdehyde accumulation, which immediately affected the brightness (6.2% lower than that of the cherry stored at 5 °C) of sweet cherry. Temperature fluctuation also led to a significant increase in POD and PPO activities during subsequent isothermal storage, accelerating the colour change (24.8% more than that of the cherry stored at 5 °C), which almost reached the level observed during constant 10 °C storage. In addition, temperature fluctuation not only affected the firmness (13.7% lower than that of the cherry stored at a constant temperature of 5 °C) of fruit immediately, but also, during subsequent isothermal storage, accelerated the deterioration of firmness (19.6% lower than that of the cherry stored at a constant temperature of 5 °C). This could be explained by temperature fluctuation inducing the upregulation of paPG1-3, paPME3, and paPME4 expression, which led to a 3.5 and 1.5-fold increase in PG and PME activity, respectively. This led to degradation of the aggregated SSP to its nanostructural basic units. Furthermore, temperature fluctuation resulted in upregulated expression of paβ-Gal1 and paβ-Gal3 and enhanced β-Gal activity during subsequent isothermal storage. The results provide theoretical guidance for the transportation, storage, and preservation of postharvest sweet cherry.

The inevitable temperature fluctuation induced anthocyanin synthesis, phenolic metabolism, and alkali-soluble pectin degradation, which lead to sweet cherry enzymatic browning and softening.

Phytochemical constituents of sterol-rich fraction from Allium cepa L. and its cytotoxic effect on human embryonic kidney (HEK293) cells

The present study investigates the cytotoxic effect of the chemical fractions of Allium cepa (yellow variety) on Human Embryonic Kidney (HEK293) cells. Allium cepa was blended into paste and macerated in distilled water before subjecting to liquid-liquid fractionation, yielding the dichloromethane, ethyl acetate (EtOAc), butanol, and aqueous fractions. Their cytotoxicity on HEK293 cells were evaluated via MTT assay. The cytotoxic fraction (EtOAc) was further evaluated for its oxidative, pro-inflammatory, and apoptotic effects on the cells. The incubation of cells with EtOAc led to depleted level of GSH, SOD, and catalase activities, and elevated levels of malondialdehyde, nitric oxide, and myeloperoxidase as well as apoptotic activities. GC-MS analysis of EtOAc revealed allyl ionone, pentadecanoic acid, and phytol acetate as the predominant fatty acids, while ergost-7-en-3β-ol, campesterol, cycloartenol-3β acetate, sitosterol, and fucosterol as the predominant sterols. These results portray the cytotoxic effect of the EtOAc fraction of A. cepa on HEK293 cells. PRACTICAL APPLICATIONS: There have been increasing concerns in the toxicity and safety of foods. Allium cepa (onions) is among the common globally grown and consumed plant food. This study investigated its cytotoxic effect on normal Human Embryonic Kidney (HEK293) Cells. Although only the ethyl acetate fraction was cytotoxic against the cell line, it, however, portrays a need for caution in its usage.

Optimization of extraction parameters and stabilization of anthocyanin from onion peel

A large amount of onion waste is produced by the food industries. This onion waste contains high-value functional ingredients, since several compounds and nutrients are present in onion peel. The objective of this work is to extract and stabilize the anthocyanin from onion peel waste in various forms. The major component present in onion peel is anthocyanin. The anthocyanin was extracted from onion peel by the microwave-assisted extraction process. A fractional factorial experiment was used to carry out 16 possible extractions instead of 64 possible extractions. The highest yield of total anthocyanin content such as 21.99 attains when using 2 g of onion peel with the extraction time 5 minutes, power as 700 W, ethanol concentration as 75 mL, and solvent feed ratio as 20 g/mL. The anthocyanin was stabilized in three ways such as co-pigmentation, a combination of buffer and hardpan coating. The most stable and colorless anthocyanin was observed by the co-pigmentation method. Stable and red color anthocyanin is obtained using a combination of buffer and dark brown color stable anthocyanin is perceived using hard pan coating. The antioxidant activity of each sample was studied during 3 weeks of storage. Sample A (co-pigmented sample) showed 75% of antioxidant activity, sample B (hardpan coating) exhibited 60% of antioxidant activity and sample C (buffer combination) confirmed 81% of antioxidant activity. This anthocyanin study can be used in future studies for various applications such as the preservation of meat and natural colorant.

Subcritical Water Extraction of Phenolic Compounds from Onion Skin Wastes (Allium cepa cv. Horcal): Effect of Temperature and Solvent Properties

The valorization of onion skin wastes (OSW) through the extraction, identification, and quantification of phenolic compounds was studied in this work, using subcritical water in a semicontinuous extractor (2.5 mL/min; 105-180 °C; 5 MPa). The extraction of flavonoids resulted to be fast (<30 min) and temperature sensitive (maximum at 145 °C; total flavonoids, 27.4 ± 0.9 mg/g dry OSW (DOSW)). The experimental results were fitted to the Weibull model. The influence of the solvent properties on the flavonoids quantification was found to be critical. A precipitate was formed once the extracts cooled down. If removed, a significant fraction of the high temperature extracted flavonoids (as much as 71%, at 180 °C) was lost. Such a condition affected especially those compounds that show extremely low solubility in water at room temperature, whereas quercetin glycosylated derivatives were less affected by the polarity change of the medium induced by the temperature change. It was demonstrated that it is necessary to re-dissolve the subcritical water extracts by the addition of ethanol, which led to a medium with a polarity equivalent to that obtained with water at high temperature. At 145 °C, quercetin (15.4 ± 0.4 mg/g DOSW) and quercetin-4'-glucoside (8.4 ± 0.1 mg/g DOSW) accounted for the 90% of the total flavonoids identified. By recovering high added value bioactive compounds from OSW the principles of circular economy were fulfilled, providing a new use for this agricultural waste.

Bovine β-lactoglobulin peptides as novel carriers for flavonoids extracted with supercritical fluids from yellow onion skins

Our study describes in detail the binding mechanism between the main flavonoids that were extracted from onion skins by supercritical CO₂ and peptides from whey proteins, from the perspective of obtaining multifunctional ingredients, with health-promoting benefits. The supercritical CO₂ extract had 202.31 ± 11.56 mg quercetin equivalents/g DW as the major flavonoid and antioxidant activity of 404.93±1.39 mM Trolox/g DW. The experiments on thermolysin-derived peptides fluorescence quenching by flavonoids extract allowed estimating the binding parameters, in terms of binding constants, and the number of binding sites. The thermodynamic analysis indicated that the main forces involved in complex formation were hydrogen bonds and van der Waals interactions. Molecular docking tests indicated that peptide fluorescence quenching upon gradual addition of onion skin extract might be due to flavonoids binding by Val¹⁵ -Ser²¹ . All 7 to 14 amino acids long peptides appeared to have affinity toward quercetin-3,4'-O-diglucoside and quercetin-4'-O-monoglucoside. The study is important as a potential solution for reuse of valuable resources, underutilized, such as whey peptides and yellow onion skins flavonoids for efficient microencapsulation, as a holistic approach to deliver healthy and nutritious food. PRACTICAL APPLICATION: A growing interest was noticed in the last years in investigating the interactions between proteins and different biologically active compounds, such as to provide knowledge for efficient development of new food, pharmaceutical, and cosmetic products. Recent studies suggest that flavonoid-protein complexes may be designed to improve the functional performance of the flavonoids. The results obtained in this study bring certain benefits in terms of exploiting the bioactive potential of both flavonoids and bioactive peptides, for developing of formulas with improved functional properties.

Isolation and characterization of components responsible for neuroprotective effects of Allium cepa outer scale extract against ischemia reperfusion induced cerebral injury in mice

The antioxidant-mediated neuroprotective effect of Allium cepa outer scale extract (ACE) in mice with cerebral ischemia-reperfusion (I-R) injury was demonstrated in our earlier work. The current investigation aimed at establishing the bioactive component(s) responsible for this activity. Thus ACE was fractionated into ethyl acetate (EF) and aqueous (AF) fractions. These fractions were evaluated against cerebral I-R injury in mice. I-R injury in mice was induced by bilateral common carotid artery occlusion followed by 24 hr reperfusion. Memory, sensorimotor functions, cerebral infarct size, and oxidative stress were measured to address the neuroprotective mechanism of test substances. EF showed marked improvement of memory and sensorimotor functions by reducing brain oxidative stress and infarct size in mice after I-R injury. The bioactive EF was subjected to chromatographic (HPLC-PDA, HPLC-MS, preparative HPLC) and spectroscopic studies to isolate and identify the neuroprotective compounds. This lead to separation of three components, namely quercetin, quercetin 4'-O-glucoside, and the remaining fraction, from EF. The separated components were biologically evaluated. These components showed improvement in mice with I-R injury. But, EF displayed more marked neuroprotective effects as compared to the isolated components. The distinct neuroprotective outcome of EF may be credited to the synergistic action of compounds present in EF. Further studies such as evaluation of neurotoxic effects and other possible neuroprotective mechanisms are required to develop EF as a neuroprotective drug.

Minimization of the adverse environmental effects of discarded onions by avoiding disposal through dehydration and food-use

Onion is a commonly used vegetable in the Cuyo Region, Argentina, and important in the world global vegetable production ranking. Production levels often exceed immediate markets of fresh sale, and excesses, although still edible, are currently discarded (mostly incinerated and disposed in landfill, creating numerous environmental hazards). To minimize these adverse environmental problems, this research investigates upgrading the discarded products by dehydration, hence guaranteeing their ultimate food-use. The dehydration process of discarded onion cv. Crioula Roxa was hence studied at 60 and 70 °C, temperatures selected to maintain the main physicochemical characteristics of the onions, while also creating optimum heat and mass transfer coefficients while significantly reducing the energy consumption and CO₂ emissions. When using an electrically-heated convective dryer, the Specific Energy Consumption (SEC) values and the CO₂ emissions during dehydration at 70 °C are 738.89 kWh.kg^-1 and 264.74 kg of CO₂ kg^-1, respectively. These values are only 41.61 kWh.kg^-1 and 2-4 kg of CO₂ kg^-1 if a solar dryer is applied. The thermal diffusivities were 1.86✕10^-10 m² s^-1 (dehydration) and 1.08✕10^-10 m² s^-1 (rehydration), showing a weak effect of the dehydration process on the solid structure and properties.

Effects of onion bulb processing conditions on drying characteristics, physicochemical and functional properties profile of onion (Allium cepa L.) powder

Onion (Allium cepa L.) is one of the most perishable consuming vegetable in the world as an aromatic seasoning and for its health promoting bioactive compounds. However, drying and blanching are two essential thermal treatments in vegetables processing which lead to considerable changes in their properties. This study investigated the effects of temperature (70, 80, and 90 °C), time (2, 4, 6, and 8 hr), and blanching (100 °C for 5 min) followed by drying at 70 °C for 8 hr on the drying kinetics, physicochemical (Ash and total polyphenol content, pH, and titratable acidity), and functional (water solubility index and particle size) properties of onion powder, as well as compared to local market powders. The variety violet of Galmi was used. The results revealed that the moisture content of non-blanching powder was below 13 ± 0.76 g/100 g with pH under 4. In addition, total polyphenol contents were higher than 512 ± 15.06 mg GAE/100 g DM. These powder showed a small particle size (under 400 µm) and high solubility (≤81.36 ± 2.3 g/100 g DM). Blanching did not affect the powders quality. Local market powders showed a lowest total polyphenol content (386.60 ± 10.02 mg GAE/100 g DM) with large particles (≤800 µm) and a lowest solubility (65.33 ± 1.62 g/100 g DM). Drying at 80 °C for 8 hr without blanching emerge as the best compromise drying conditions resulting in optimal physico-chemical and functional properties (10.8 ± 0.8 g/100 g, 846.6 ±15.09 mg GAE/100 g DM and 88.12 ± 2.31 g/100 g DM of moisture content, total polyphenol content, and water solubility index, respectively. These findings can contribute to reduce postharvest losses in onion and to stimulate the industrialization of onion enriched-powder production in Africa. PRACTICAL APPLICATION: This study provides critical information on onion properties profile during its transformation, on which processor might build on its decision to make an appropriate choice of processing parameters and tools for producing health promoting onion powder meeting modern consumer requirements. In this study, oven-drying at 80 °C for 8 hr without blanching might be the suitable condition to deliver innovative onion powder tailored specifically to functional ingredients of many food formulations.

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.

Effects of edible plant polyphenols on gluten protein functionality and potential applications of polyphenol-gluten interactions

Expanding plant-based protein applications is increasingly popular. Polyphenol interactions with wheat gluten proteins can be exploited to create novel functional foods and food ingredients. Polyphenols are antioxidants, thus generally decrease gluten strength by reducing disulfide cross-linking. Monomeric polyphenols can be used to reduce dough mix time and improve flexibility of the gluten network, including to plasticize gluten films. However, high-molecular-weight polyphenols (tannins) cross-link gluten proteins, thereby increasing protein network density and strength. Tannin-gluten interactions can greatly increase gluten tensile strength in dough matrices, as well as batter viscosity and stability. This could be leveraged to reduce detrimental effects of healthful inclusions, like bran and fiber, to loaf breads and other wheat-based products. Further, the dual functions of tannins as an antioxidant and gluten cross-linker could help restructure gluten proteins and improve the texture of plant-based meat alternatives. Tannin-gluten interactions may also be used to reduce inflammatory effects of gluten experienced by those with gluten allergies and celiac disease. Other potential applications of tannin-gluten interactions include formation of food matrices to reduce starch digestibility; creation of novel biomaterials for edible films or medical second skin type bandages; or targeted distribution of micronutrients in the digestive tract. This review focuses on the effects of polyphenols on wheat gluten functionality and discusses emerging opportunities to employ polyphenol-gluten interactions.

Quantification of flavonoids, total phenols and antioxidant properties of onion skin: a comparative study of fifteen Indian cultivars

Onion waste disposal issue could be solved by using onion skin as food ingredient. Therefore, the aim of present study is the estimation of flavonoid concentration, total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activities of onion skin of fifteen Indian cultivars. Flavonoid quantification was achieved by high performance liquid chromatography, which showed highest concentration of quercetin, quercetin 3-β-D-glucoside, luteolin and kaempferol in cv. 'NHRDF Red' (11,885.025 mg/kg), 'Hissar-2' (1432.875 mg/kg), 'Pusa Riddhi' (1669.925 mg/kg) and 'Bhima Shakti' (709.975 mg/kg), respectively in dry weight. Highest TPC and TFC were found in cv. 'NHRDF Red' while lowest were measured in cv. 'Bhima Shubhra'. DPPH assay (%), ABTS assay (%) and FRAP assay (µmol gallic acid/g) were showed maximum antioxidant capacity for cv. 'NHRDF Red' whereas least obtained for cv. 'Bhima Shubhra'. Skin of cv. 'Hissar-2' and 'NHRDF Red' are the best source of flavonoids and natural antioxidants.

Valorization of Red Onion Peels for Quercetin Recovery Using Quercetin-Imprinted Polymer

Quercetin (QC) is one of the most prominent dietary antioxidants present in vegetables/fruits, specifically in onions that rank second in consumption following tomato. QC with proven health benefits is now largely utilized as a nutritional supplement. In this work that aims to isolate QC from red onion peels forming a huge agricultural waste, a QC-molecularly imprinted polymer (QC-MIP) in a molar ratio of 1:4:20 (QC:4-vinylpyridine:ethylene glycol dimethacrylate) was prepared thermally through bulk polymerization. Molecularly imprinted solid phase extraction (MISPE) procedures were applied for the selective pre-concentration and purification of QC from both red onion peel methanolic extract with 58% recovery and from the extract hydrolyzate with 86% recovery. The hydrolysis process increased both the QC amount as expected and the recovery yield due to changing matrix components. The results demonstrated that onion peel can easily and efficiently be converted to a valuable product, QC, using QC-MIP as SPE sorbent.

Densification and Fuel Properties of Onion Husks

The aim of the described research was to assess the suitability of onion husk waste as a material for the production of solid fuels in the form of granules (pellets). Due to the low susceptibility to thickening of onion husks, the addition of a binder in the form of potato pulp was used (waste with a high starch content). Both wastes were subjected to elemental analysis determining the content of C, H, N, S, Cl, and their HHV (High Heating Value) and LHV (Low Heating Value). Mixtures containing the addition of 10%, 15%, and 20% potato pulp to onion husks were subjected to granulation in a “flat matrix–thickening rollers” operating system at three rotational speeds of the granulator matrix a 170, 220, and 270 rpm. The influence of the potato pulp addition and matrix rotational speed on the quality of the obtained pellet was determined. The highest quality product was combusted in a low-power boiler with a retort grate, and the content of CO, CO2, SO2, NO, and HCl in the exhaust gas was determined. The highest quality granulate was obtained from a mixture containing 10% potato pulp, which was compacted at 170 rpm matrix, where the kinetic strength was 99.50% and the density was about 650 kg·m−3. The results of the combustion emissions from onion husk granules exceed the requirements of the EcoDesign Directive with the greatest being the case of CO.