Antimicrobial assessment of polyphenolic extracts from onion (Allium cepa L.) skin of fifteen cultivars by sonication-assisted extraction method

An ethnopharmacological, phytochemical, and pharmacological overview of onion (Allium cepa L.)

ETHNOPHARMACOLOGICAL RELEVANCE

Onion (Allium cepa L.) is one of the most widely distributed species within the Allium genus of family Amaryllidaceae. Onion has been esteemed for its medicinal properties since antiquity. It has been consumed for centuries in various indigenous cultures for the management of several ailments including microbial infections, respiratory, gastrointestinal, skin and cardio-vascular disorders, diabetes, renal colic, rheumatism, sexual impotence, menstrual pain, and headache. However, so far, there is a scarcity of recent data that compiles the plant chemistry, traditional practices, biological features, and toxicity.

AIM OF THE WORK

The aim of this review is to provide a comprehensive and analytical overview of ethnopharmacological uses, phytochemistry, pharmacology, industrial applications, quality control, and toxicology of onion, to offer new perspectives and broad scopes for future studies.

MATERIALS AND METHODS

The information gathered in this review was obtained from various sources including books, scientific databases such as Science Direct, Wiley, PubMed, Google Scholar, and other domestic and foreign literature.

RESULTS

Onion has a long history of use as a traditional medicine for management of various conditions including infectious, inflammatory, respiratory, cardiovascular diseases, diabetes, and erectile dysfunction. More than 400 compounds have been identified in onion including flavonoids, phenolic acids, amino acids, peptides, saponins and fatty acids. The plant extracts and compounds showed various pharmacological activities such as antimicrobial, antidiabetic, anti-inflammatory, anti-hyperlipidemic, anticancer, aphrodisiac, cardioprotective, and neuroprotective activities. In addition to its predominant medicinal uses, onion has found various applications in the functional food industry.

CONCLUSION

Extensive literature analysis reveals that onion extracts and bioactive constituents possess diverse pharmacological activities that can be beneficial for treating various diseases. However, the current research primarily revolves around the documentation of ethnic pharmacology and predominantly consists of in vitro studies, with relatively limited in vivo and clinical studies. Consequently, it is imperative for future investigations to prioritize and expand the scope of in vivo and clinical research. Additionally, it is strongly recommended to direct further research efforts towards toxicity studies and quality control of the plant. These studies will help bridge the current knowledge gaps and establish a solid basis for exploring the plant's potential uses in a clinical setting.

Onion (Allium cepa L.) Skin Waste Valorization: Unveiling the Phenolic Profile and Biological Potential for the Creation of Bioactive Agents through Subcritical Water Extraction

Onion skin waste (OSW), the primary non-edible byproduct from onion processing, offers a renewable source of bioactive compounds. This study aims to valorize OSW through subcritical water extraction (SWE), aligning with a circular economy and biorefinery principles. SWE was carried out at 145 °C and 50 bar for 50 min in a discontinuous reactor, producing a phenolic-rich extract (32.3 ± 2.6 mg/g) dominated by protocatechuic acid (20.3 ± 2.5 mg/g), quercetin-4'-O-glucoside (7.5 ± 0.2 mg/g), and quercetin (3.2 ± 0.6 mg/g). Additionally, the extract contains sugars (207.1 ± 20.3 mg sucrose-Eq/g), proteins (22.8 ± 1.6 mg BSA-Eq/g), and free amino acids (20.4 ± 1.2 mg arginine-Eq/g). Its phenolic richness determines its scavenging activity against ●NO and O2●- radicals and its α-glucosidase and aldose-reductase inhibition without affecting α-amylase. Notably, the extract demonstrates significant α-glucosidase inhibition (IC50 = 75.6 ± 43.5 µg/mL), surpassing acarbose (IC50 = 129.5 ± 1.0 µg/mL) in both pure enzyme and cell culture tests without showing cytotoxicity to AGS, HepG2, and Caco-2 human cell lines. The extract's bioactivity and nutritional content make it suitable for developing antioxidant and antidiabetic nutraceutical/food components, highlighting SWE's potential for OSW valorization without using organic solvents.

Perspective of Secondary Metabolites in Respect of Multidrug Resistance (MDR): A Review

Aberrant and haphazard use of antibiotics has created the development of antimicrobial resistance which is a bizarre challenge for human civilization. This emerging crisis of antibiotic resistance for microbial pathogens is alarming all the nations posing a global threat to human health. It is difficult to treat bacterial infections as they develop resistance to all antimicrobial resistance. Currently used antibacterial agents inhibit a variety of essential metabolic pathways in bacteria, including macro-molecular synthesis (MMS) pathways (e.g. protein, DNA, RNA, cell wall) most often by targeting a specific enzyme or subcellular component e.g. DNA gyrase, RNA polymerase, ribosomes, transpeptidase. Despite the availability of diverse synthetic molecules, there are still many complications in managing progressive and severe antimicrobial resistance. Currently not even a single antimicrobial agent is available for which the microbes do not show resistance. Thus, the lack of efficient drug molecules for combating microbial resistance requires continuous research efforts to overcome the problem of multidrug-resistant bacteria. The phytochemicals from various plants have the potential to combat the microbial resistance produced by bacteria, fungi, protozoa and viruses without producing any side effects. This review is a concerted effort to identify some of the major active phytoconstituents from various medicinal plants which might have the potential to be used as an alternative and effective strategy to fight against microbial resistance and can promote research for the treatment of MDR.

Active and Intelligent Biodegradable Packaging Based on Anthocyanins for Preserving and Monitoring Protein-Rich Foods

Currently, active and intelligent packaging has been developed to solve the spoilage problem for protein-rich foods during storage, especially by adding anthocyanin extracts. In such a film system, the antioxidant and antibacterial properties were dramatically increased by adding anthocyanins. The physicochemical properties were enhanced through interactions between the active groups in the anthocyanins and reactive groups in the polymer chains. Additionally, the active and intelligent film could monitor the spoilage of protein-rich foods in response to pH changes. Therefore, this film could monitor the sensory acceptance and extend the shelf life of protein-rich foods simultaneously. In this paper, the structural and functional properties of anthocyanins, composite actions of anthocyanin extracts and biomass materials, and reinforced properties of the active and intelligent film were discussed. Additionally, the applications of this film in quality maintenance, shelf-life extension, and quality monitoring for fresh meat, aquatic products, and milk were summarized. This film, which achieves high stability and the continuous release of anthocyanins on demand, may become an underlying trend in packaging applications for protein-rich foods.

In Vitro and In Vivo Antibiofilm Activity of Red Onion Scales: An Agro-Food Waste

Red onion wastes (ROW) are valuable sources of bioactive metabolites with promising antimicrobial effects. Methicillin-resistant Staphylococcus aureus (MRSA) infections are a growing risk in hospitals and communities. This study aims to investigate the in vitro and in vivo antibiofilm activities of the acidified ethanolic extract of red onion scales (RO-T) and its fractions against an MRSA vaginal colonization model. The RO-T extract, as well as its anthocyanin-rich fraction (RO-P) and flavonoid-rich fraction (RO-S), recorded a promising antibacterial activity against highly virulent strains of bacteria (MRSA, Acinetobacter baumannii, Escherichia coli and Pseudomonas aeruginosa). RO-S showed the highest antibacterial activity (MBC of 0.33 ± 0.11 mg/mL) against MRSA USA300 and significantly eradicated its biofilm formation with an IC₅₀ of 0.003. Using a rat model, in vivo assessment on all samples, which were formulated as a hydrogel, revealed a significant reduction of MRSA bacterial load recovered from an infected vagina compared to that of the negative control group (NCG). RO-T extract and vancomycin groups recorded the highest antibacterial activity with a bacterial load 2.998 and 3.358 logs lower than the NCG, respectively. The histopathological investigation confirmed our findings. RO-T and RO-S were standardized for their quercetin content. Finally, ROW offers a new potent antibiofilm agent mostly due to its high quercetin content.

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.

Synergistic antimicrobial activity of ε-polylysine, chestnut extract, and cinnamon extract against Staphylococcus aureus

A mixed natural preservative composed of ε-polylysine (ε-PL), chestnut 70% ethanol extract (NE), and cinnamon hydrothermal extract (CW), was investigated for the reduction of Staphylococcus aureus. The minimum inhibitory concentration (MIC) and minimum bacterial concentration (MBC) of seven natural extracts were investigated against a cocktail of three strains of S. aureus (ATCC 25923, ATCC 33591, and ATCC 33594). Three important factors (ε-PL, NE, and CW) were selected by using the Plackett-Burman (PB) design for the response surface model (P < 0.001). Following a central composite design, S. aureus were treated with mixtures of natural preservatives that included ε-PL, NE, and CW. The MIC and MBC of ε-PL and the natural extracts and ranged from 1 to 16 mg/mL (R² = 0.9857). The mixed natural preservative presented a synergistic antibacterial effect, at the optimum point. These results suggest that mixed natural preservatives of ε-PL, NE, and CW can lower the economic cost of food processing.

Recent advances in research on Allium plants: functional ingredients, physiological activities, and applications in agricultural and food sciences

Fruits and vegetables (FVs) have long been a major source of nutrients and dietary phytochemicals with outstanding physiological properties that are essential for protecting humans from chronic diseases. Moreover, the growing demand of consumers for nutritious and healthy foods is greatly promoting the increased intake of FVs. Allium (Alliaceae) is a perennial bulb plant genus of the Liliaceae family. They are customarily utilized as vegetable, medicinal, and ornamental plants and have an important role in agriculture, aquaculture, and the pharmaceutical industry. Allium plants produce abundant secondary metabolites, such as organosulfur compounds, flavonoids, phenols, saponins, alkaloids, and polysaccharides. Accordingly, Allium plants possess a variety of nutritional, biological, and health-promoting properties, including antimicrobial, antioxidant, antitumor, immunoregulatory, antidiabetic, and anti-inflammatory effects. This review aims to highlight the advances in the research on the bioactive components, physiological activities and clinical trials, toxicological assessment for safety, and applications of different Allium plants. It also aims to cover the direction of future research on the Allium genus. This review is expected to provide theoretical reference for the comprehensive development and utilization of Allium plants in the fields of functional foods, medicine, and cosmetics.