Insights into physicochemical and functional properties of polysaccharides sequentially extracted from onion ( Allium cepa L.)

Recent advances in dietary polysaccharides from Allium species: Preparation, characterization, and bioactivity

Allium plants, including garlic, onions, shallots, and leeks, belong to the Alliaceae family and are utilized as vegetable, medicinal, and ornamental plants. These plants are consumed both raw and cooked and are noted in traditional medicine for their antibacterial, antitumor, and diuretic properties. Allium plants are a rich source of polyphenols, organosulfur compounds, flavonoids, alkaloids, and polysaccharides, which contribute to their health benefits. As consumer interest in the association between diet and health grows, there is an increasing market demand for foods that promote health, particularly those rich in dietary fiber or non-starch polysaccharides. Allium polysaccharides (APS) have molecular weights of 1 × 103-1 × 106 Da containing small amounts of pectin, glucofructan, or glycoproteins and large amounts of fructans. APS, despite its complex structure, is one of the principal active components of Allium plants but is often overlooked, which restricts its practical application. This paper provides a comprehensive overview of the extraction and purification, structural and functional characteristics, bioactivities, structure-function relationships, and chemical modifications of APS, as well as the effects of APS processing and storage. Additionally, this paper outlines future research directions for APS, which will inform its development and application in the food, pharmaceutical, and cosmetic industries.

Regulation strategy, bioactivity, and physical property of plant and microbial polysaccharides based on molecular weight

Structural features affect the bioactivity, physical property, and application of plant and microbial polysaccharides. However, an indistinct structure-function relationship limits the production, preparation, and utilization of plant and microbial polysaccharides. Molecular weight is an easily regulated structural feature that affects the bioactivity and physical property of plant and microbial polysaccharides, and plant and microbial polysaccharides with a specific molecular weight are important for exerting their bioactivity and physical property. Therefore, this review summarized the regulation strategies of molecular weight via metabolic regulation; physical, chemical, and enzymic degradations; and the influence of molecular weight on the bioactivity and physical property of plant and microbial polysaccharides. Moreover, further problems and suggestions must be paid attention to during regulation, and the molecular weight of plant and microbial polysaccharides must be analyzed. The present work will promote the production, preparation, utilization, and investigation of the structure-function relationship of plant and microbial polysaccharides based on their molecular weight.

Evaluation of carbon dioxide elevation on phenolic compounds and antioxidant activity of red onion (Allium cepa L.) during postharvest storage

Carbon dioxide (CO₂) is considered one of the eco-related key factors that negatively affect global climatic change. Also, CO₂ can play an important role in the postharvest quality of the agri-products. In this study, the impact of CO₂ on the quality of postharvest onions that were stored at 23 °C for 8 weeks was investigated. The weight loss, phenolic, flavonoid, flavanol, anthocyanin, antioxidant activity, and soluble sugar were analyzed during the study period. The results showed that 20% CO₂ treatment was significantly (P > 0.05) more effective than 15% CO₂ and control in inhibiting weight loss. Additionally, 20% CO₂ treatment significantly retained higher antioxidant enzyme activities such as CAT, APX, and SOD than 15% CO₂ and control. During storage, 20% CO₂ treatment significantly (P < 0.05) improved glucose, fructose, and sucrose levels by more than 15% CO₂ exposure and control groups. Besides the chlorogenic acid, kaempferol and quercetin were significantly (P < 0.05) higher in the 20% CO₂ than in the 15% CO₂ after 2 weeks of storage. In conclusion, this study's novelty comes from the broad prospects of using CO₂ for maximizing the stored onion phytochemical functionality that is usually affected by the room temperature long storage. This will help in the onion shelf-life extension by considering the quality-related attributes.

Acetyl-glucomannan from Dendrobium officinale: Structural modification and immunomodulatory activities

To understand the mechanisms of immunomodulatory effect, Dendrobium Officinale polysaccharides (DOP) were treated by ultrasound and mild base separately to generate fractions of various weight-average molecular weight (Mw) and degrees of acetylation (DA). The structural features, conformational properties, functional properties and immunomodulatory activities of original and modified DOPs were investigated. Ultrasonic treatment decreased the Mw and apparent viscosity and improved the water solubility of DOP. Mild base treatment remarkably reduced the DA and the water solubility, while the overall apparent viscosity was increased. Conformational analysis by triple-detector high performance size-exclusion chromatography showed that the molecular chain of DOP turned more compact coil conformation with decreased DA. Results from the macrophages RAW 264.7 analysis showed that samples sonicated for 200 min (Mw 34.2 kDa) showed the highest immune-regulation effects. However, the immunomodulatory effects of the samples after de-acetylation were all compromised compared to the original DOP. This study inspires further research to establish the structural-immunomodulatory relationships, which promote the application of DOP in both the food and medicine fields.

Characterization of Polysaccharides Sequentially Extracted from Allium roseum Leaves and Their Hepatoprotective Effects against Cadmium Induced Toxicity in Mouse Liver

Allium roseum is one of the medicinal plants of the Liliaceae family, widely used in the food industry and traditional medicine. It is known for its various biological properties, such as its antioxidant, antiviral, antidiabetic, and anti-inflammatory activities. The present work aims to extract the polysaccharides from Allium roseum leaves and evaluate their antioxidant activities and hepatoprotective effects in vivo. Three polysaccharides from the leaves of Allium roseum were sequentially extracted in three media: water, chelating, and basic, respectively. They were characterized by size exclusion chromatography, gas chromatography mass spectrometry, FTIR-ATR, and NMR spectroscopy (1D and 2D). The different polysaccharides principally consist of glucose, galactose, mannose, rhamnose, xylose, and galacturonic acid. The antioxidant activity and hepatoprotective effect of the extracts against Cd-caused oxidative stress in liver mouse were tested. Cd treatment, during 24 h, enhanced significantly lipid peroxidation by a high production of malondyaldehyd (MDA) and superoxide dismutase (SOD) activity. In contrast, catalase activity (CAT) was decreased after the same period of exposure to the metal. The polysaccharides pre-treatment improved the antioxidant defense system to a great degree, mainly explained by the modulating levels of oxydative stress biomarkers (MDA, SOD, and CAT). This research clearly shows that Allium roseum polysaccharides, especially those extracted in aqueous medium, can be used as natural antioxidants with hepatoprotective properties.

Onion and garlic polysaccharides: A review on extraction, characterization, bioactivity, and modifications

Allium cepa (onion) and Allium sativum (garlic) are important members of the Amaryllidaceae (Alliaceae) family and are being used both as food and medicine for centuries in different parts of the world. Polysaccharides have been extracted from different parts of onion and garlic such as bulb, straw and cell wall. The current literature portrays several studies on the extraction of polysaccharides from onion and garlic, their modification and determination of their structural (molecular weight, monosaccharide unit and their arrangement, type and position of glycosidic bond or linkage, degree of polymerization, chain conformation) and functional properties (emulsifying property, moisture retention, hygroscopicity, thermal stability, foaming ability, fat-binding capacity). In this line, this review, summarizes the various extraction techniques used for polysaccharides from onion and garlic, involving methods like solvent extraction method. Furthermore, the antioxidant, antitumor, anticancer, immunomodulatory, antimicrobial, anti-inflammatory, and antidiabetic properties of onion and garlic polysaccharides as reported in in vivo and in vitro studies is also critically assessed in this review. Different studies have proved onion and garlic polysaccharides as potential antioxidant and immunomodulatory agent. Studies have implemented to improve the functionality of onion and garlic polysaccharides through various modification approaches. Further studies are warranted for utilizing onion and garlic polysaccharides in the food, nutraceutical, pharmaceutical and cosmetic industries.

Structure Identification of Two Polysaccharides from Morchella sextelata with Antioxidant Activity

Mushrooms of the Morchella genus exhibit a variety of biological activities. Two polysaccharides (MSP1-1, 389.0 kDa; MSP1-2, 23.4 kDa) were isolated from Morchella sextelata by subcritical water extraction and column chromatography fractionation. Methylation and nuclear magnetic resonance analysis determined MSP1-1 as a glucan with a backbone of (1→4)-α-D-glucan branched at O-6, and MSP1-2 as a galactomannan with coextracted α-glucan. Light scattering analysis and transmission electron microscopy revealed that MSP1-1 possessed a random coil chain and that MSP1-2 had a network chain. This is the first time that a network structure has been observed in a polysaccharide from M. sextelata. Despite the differences in their chemical structures and conformations, both MSP1-1 and MSP1-2 possessed good thermal stability and showed antioxidant activity. This study provides fundamental data on the structure-activity relationships of M. sextelata polysaccharides.

Structural properties of diluted alkali-soluble pectin from Pyrus communis L. in water and salt solutions

The self-assembly and gelation of low-methoxyl diluted alkali-soluble pectin (LM DASP) from pear fruit (Pyrus communis L. cv. Conference) was studied in water and salt solutions (NaCl and CaCl₂, constant ionic strength) without pH adjustment at 20 °C. The samples at different LM DASP concentrations were characterized using rheological tests, Fourier-transform infrared spectroscopy, dual-angle dynamic light scattering and atomic force microscopy. LM DASP from pear fruit (Pyrus communis L.) showed gelling ability. The indices (aggregation index and shape factor) based on light scattering may be useful for the characterization of structural changes in polysaccharide suspension, particularly for the determination of a gel point. The results obtained may be important for the food, cosmetic and pharmaceutical industries where pectin is used as a texturizer, an encapsulating agent, a carrier of bioactive substances or a gelling agent.

Characterization of functional chocolate formulated using oleogels derived from β-sitosterol with γ-oryzanol/lecithin/stearic acid

With an aim to prepare the functional chocolate, corn oil was used as the base oil and β-sitosterol was combined with oryzanol/stearic acid/lecithin to prepare respective oleogels (GO, SO, and LO). Oleogels (12%) were prepared by adding compound oleogelators at different ratios [GO-2:3, SO-1:4, and LO-4:1 (w/w)] in corn oil. The microstructure, interaction, thermodynamic, crystalline, and rheological behavior of formulated oleogels were studied by microscopic observation, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and rotational rheometer, respectively. The results showed that GO had the strongest gel forming ability and the densest gel crystallization network. Moreover, chocolate prepared with GO (cocoa butter and oleogels-1:1) had the similar texture, crystal structure, rheological, and sensory properties to that of dark chocolate. This study provides the possibility for the wider application of oleogel prepared with lower saturated and trans-fatty acids in the chocolate industry.

Effect of particle size, concentration, temperature and pH on rheological properties of shallots flour

Shallot flour was prepared and sieved into three different particle sizes of < 180 μm (sample A), 180 μm (sample B) and 250 μm (sample C). Effect of concentration [0.5%, 1.0%, 1.5% and 2.0% (w/w)], temperature (20, 30, 40, 60 and 80 °C), pH (4, 7 and 10) and freezing (- 20 °C) on rheological properties of shallot flour were studied at increasing shear of 0.1-100 s^-1. Effect of dynamic change in temperature (15-95 °C) was also measured at constant shear rate of 50 s^-1. Power law (Eq. 2) model with coefficient of determination (R²) above 0.90, well described the rheological behavior of the shallot flour as a shear thinning, non-Newtonian fluid at different concentration, temperature and pH. All the samples had n values below 1 and increase in viscosity or consistency index (k) value with increase in concentration of the sample was observed, while inverse relation was observed when temperature was increased. All samples showed increase in k value when the pH of the dispersion was varied from acidic to alkaline condition. Viscosity of samples were found unaffected even after freezing in freeze-thaw cycle. These data show sample A to be most suitable for their application as thickener, having highest k value. The obtained research provides information for utilization of shallot as a thickener in various food industries.

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.

Evaluation of structural, functional, and anti-oxidant potential of differentially extracted polysaccharides from potatoes peels

Potato peel was used for the extraction of three types of polysaccharides (PW, PAL, and PAC) using water, alkaline, and acid treatments, respectively. The structure of the PP polysaccharides was examined by means of Fourier transform infrared spectroscopy (FT-IR) analysis and Gas chromatography-mass spectrometry (GC-MS). The results suggest that the extracted polysaccharides constituted essentially three functional groups: CO, CH, and OH. The polysaccharides were comprised of low proportions of proteins, 17-23% uronic acids, and approximately 70% carbohydrates. PAL, PW, and PAC with molecular weights of 2.25 × 10³, 2.18 × 10³, and 1.92 × 10³ kDa, respectively, were composed of rhamnose, xylose, mannose, arabinose, glucose, and galactose. Functional properties (solubility, oil holding capacity, foaming, and emulsion properties) of these polysaccharides were evaluated. Among three, PAL showed the highest fat-binding capacity which was 7.50 g/g with the solubility of 95.06%. The three polysaccharides possessed appreciable in vitro anti-oxidant (scavenging DPPH and ABTS⁺ radicals, chelating ferrous ions, and reducing power) potential. PAL exhibited the strongest reducing power, scavenging activity on DPPH radicals and chelating capability on ferrous ions. PP polysaccharides can be used as promising natural antioxidants in food, pharmaceutical, and cosmetic preparations.

Biosynthesized Highly Stable Au/C Nanodots: Ideal Probes for the Selective and Sensitive Detection of Hg2+ Ions

The enormous ongoing industrial development has caused serious water pollution which has become a major crisis, particularly in developing countries. Among the various water pollutants, non-biodegradable heavy metal ions are the most prevalent. Thus, trace-level detection of these metal ions using a simple technique is essential. To address this issue, we have developed a fluorescent probe of Au/C nanodots (GCNDs-gold carbon nanodots) using an eco-friendly method based on an extract from waste onion leaves (Allium cepa-red onions). The leaves are rich in many flavonoids, playing a vital role in the formation of GCNDs. Transmission electron microscopy (TEM) and Scanning transmission electron microscopy-Energy-dispersive X-ray spectroscopy (STEM-EDS) elemental mapping clearly indicated that the newly synthesized materials are approximately 2 nm in size. The resulting GCNDs exhibited a strong orange fluorescence with excitation at 380 nm and emission at 610 nm. The GCNDs were applied as a fluorescent probe for the detection of Hg2+ ions. They can detect ultra-trace concentrations of Hg2+ with a detection limit of 1.3 nM. The X-ray photoelectron spectroscopy results facilitated the identification of a clear detection mechanism. We also used the new probe on a real river water sample. The newly developed sensor is highly stable with a strong fluorescent property and can be used for various applications such as in catalysis and biomedicine.

Thermal and Antioxidant Properties of Polysaccharides Sequentially Extracted from Mulberry Leaves (Morus alba L.)

Polysaccharides from natural plant products are gaining considerable attention due to their multi-faceted health effects, as well their functional applications in food production. We reported the sequential extraction of mulberry leaf polysaccharides (MLPs) with hot buffer (HBSS), chelating agent (CHSS), dilute alkali (DASS) and concentrated alkali (CASS), in order to obtain polysaccharide fractions. Monosaccharide analysis proved that galactose (27.07%) and arabinose (25.99%) were the major sugars in HBSS, whereas arabinose (30.55%) was the major sugar in CHSS, and glucose was the major sugar in DASS (24.96%) and CASS (27.51%). The molecular weights of the polysaccharide fractions were 7.812 × 10³ (HBSS), 3.279 × 10³ (CHSS), 6.912 × 10³ (DASS), and 1.408 × 10³ kDa (CASS). HBSS and CASS showed the largest peak temperature and the highest endothermic enthalpy, respectively. Different antioxidant assays showed that the MLPs possessed appreciable antioxidant activities in a dose-dependent manner. At 5 mg/mL, HBSS and DASS possessed the largest 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) radical scavenging activity (96.82%). HBSS exhibited the highest reducing power, and DASS rendered the strongest ABTS radical scavenging activity (99.69%). CHSS performed the best hydroxyl radical scavenging activity (64.22%) and Fe²⁺-chelating ability (96.36%). Our results suggested that MLPs could be a promising source of natural antioxidants for use in the food, pharmaceutical, and cosmetic industries.