Antioxidative phenolic constituents of skins of onion varieties and their activities

Interactions of flavonoids from yellow onion skins with whey proteins: Mechanisms of binding and microencapsulation with different combinations of polymers

The interaction of flavonoids extracted from yellow onion skins with whey proteins isolate was studied using fluorescence spectroscopy and simulation methods from the perspectives of microencapsulation. The fluorescence spectroscopy revealed a static quenching mechanism and the involvement of van der Waals and H bonding in complexes formation. The in silico methods suggested that the heat treatment of the major whey proteins affected the binding pockets and therefore the affinity for the main flavonoids. The interaction surface decreased and the interaction energy increased, suggesting lower binding strength. Further, the yellow onion skins extract was successfully encapsulated in whey proteins isolate and different combinations of polymers, including chitosan, maltodextrin and pectin by freeze drying. The resulted powder showed a total flavonoid content of 5.84 ± 0.23 mg quercetin equivalents/g DW in whey protein-chitosan combination and 104.97 ± 5.02 mg quercetin equivalents/g DW in whey protein-maltodextrin-pectin combinations, with antioxidant activity of 175.93 ± 1.50 mM mM Trolox/g DW and 269.20 ± 3.59 mM Trolox/g DW, respectively. The confocal microscopy indicated that the flavonoids aggregated inside the matrix formed between the whey proteins and various polymers and irregular and compact clusters. Therefore, a comprehensive approach involving the extraction of flavonoids from underutilized food by-products, such as yellow onion skins, evaluation of binding mechanisms with whey proteins, whereas tailoring their functional benefit through microencapsulation in order to obtain active ingredients are reported.

Onion (Allium cepa L.) is potentially a good source of important antioxidants

Six different cultivars of onions available in the Kuwaiti market were analyzed for various physic-chemical properties, such as, moisture content, sugar composition, TBARS as malondialdehyde, total phenolic content, as well as trolox equivalent antioxidant capacity, these cultivars comprised of US onions white, US onions yellow, Indian onions red, Egyptian onions red, New Zealand onions golden and Saudi onions white. Layers from each onion bulb were manually cut and separated into three nearly equal portions, i.e., outer layers, middle layers and the inner layers. The outermost layers of the bulb showed the highest concentration of antioxidant compounds and a distinct decreasing trend was observed towards the innermost layers in all types of onion samples. The onion samples studied showed variations in carbohydrate contents (glucose, fructose and sucrose), which would have important implications in affecting the flavor (sweetness and pungency) and the suitability of these onions for processing. An important observation is about the distribution of antioxidant compounds with the highest contents in the outmost layers of the onions than in their middle and inner layers. Unfortunately, these outer layers are generally discarded by the consumers thus depriving them of the important health-promoting phytochemicals.

Date palm wood as a new source of phenolic antioxidants and in preparation of smoked salmon

The potential of date palm wood (DPW) as a new source of phenolic antioxidants was investigated in this contribution. The total phenolic content and antiradical activity of soluble and insoluble-bound fractions of DPW was compared to those of maple wood (MW). Furthermore, salmon was smoked with DPW and MW. Irrespective of the wood type, volatile phenolic compounds were mainly methoxyphenols, with the highest contribution from eugenol followed by guaiacol and their corresponding derivatives, as evaluated by solid-phase microextraction and gas chromatography-mass spectrometry. Salmon smoked with DPW showed a higher oxidative stability than that of MW during 21 days of storage at 4°C, which was explained by the higher content of volatile phenolic compounds in the smoke generated from DPW. Minor differences were detected for the instrumental color between both samples of smoked salmon. Therefore, smoking with DPW may be used for industrial meat and fish smoking purposes. PRACTICAL APPLICATIONS: Smoking has long been used to preserve fish and meat products. The process changes the appearance and gives a desirable flavor to the product. However, high temperatures applied during smoking may also induce lipid oxidation, the extent of which is counterbalanced by the antioxidant action of phenolics in woodsmoke. In this sense, the desired interactions of the smoke volatiles in the food matrix dictates the quality of the final product. Volatile phenolics released upon smoking are dependent on the type of wood. Thus, use of a specific wood might provide unique products, hence date palm wood (DPW) used in this work may not only provide special smoked fish products but its use could be extended to other smoked products. Hence, this contribution extends the possible feedstocks for the preparation of smoked products.

Total Phenolic Content and Antioxidant Capacity of Different Parts of Cucumber (Cucumis sativus L.)

The aims of this research were to estimate the polyphenol content and antioxidant capacity from different parts of cucumber. The antioxidant activity was investigated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP), total flavonoid and phenolic contents were estimated using aluminium chloride and Folin-Ciocalteau reagents assays, respectively. Our finding showed that the ethanolic peel extract contained the highest phenolic (23.08 mg GAE/g) and flavonoids (14.02 mg QE/g). Also, ethanolic peel extract demonstrated significantly (p<0.05) higher FRAP value. Pearson correlation revealed that there were positive correlations (p<0.01) between TPC and TFC with FRAP assay. These findings suggest that consumption of cucumber with peel may provide optimum health benefit than its peeled counterpart.

In vitro protein tyrosine phosphatase 1B inhibition and antioxidant property of different onion peel cultivars: A comparative study

The aim of the present study was a comparative investigation of water and 70% ethanol extracts derived from yellow and red onion (Allium cepa L.) peels against diabetes and diabetic complications. The total phenolic contents (TPCs) and total flavonoid contents (TFCs) of each cultivar, measured to assess phytochemical characteristics, showed a direct correlation with the in vitro antioxidant effects. Among the two captives, the yellow onion peel extract showed higher antioxidant activity than red one. However, all extracts exhibited significant protein tyrosine phosphatase 1B (PTP1B) inhibitory activity (IC50; 0.30-0.86 μg/ml), showing water extracts more potent (IC50; approximately 0.3 μg/mL), than the 70% ethanol extracts (IC50; approximately 0.8 μg/ml). Similarly, in insulin-resistant HepG2 cells, all extracts enhanced the glucose uptake and reduced the expression of PTP1B in a concentration-dependent manner, water extract displaying better activity. Our results overall suggest that in vitro antioxidant and antidiabetic potentials vary among red and yellow cultivars and extracting solvents, which could therefore be a promising strategy to prevent diabetes and associated complications.

1-Methylcyclopropene Treatment on Phenolics and the Antioxidant System in Postharvest Peach Combined with the Liquid Chromatography/Mass Spectrometry Technique

In the present study, the potential effect of 1-methylcyclopropene (1-MCP) treatment on phenolics and antioxidant capacity in postharvest peach was assessed. Peach fruit (cv. Xiahui-8) treated with 1-MCP or without treatment was stored in 25 °C for 2, 4, 6, and 8 days. The phenolic composition and change trend were evaluated by liquid chromatography/mass spectrometry. The reactive oxygen species production and scavenging capacity against DPPH, O₂^• -, and HO^• were determined. Gene expression of enzymes in the flavonoid biosynthetic pathway was assayed by quantitative reverse transcription polymerase chain reaction analysis. 1-MCP application inhibited the ethylene and CO₂ production and stimulated the total phenol and total flavonoid contents. Total anthocyanin formation may be influenced directly or indirectly by the level of ethylene. The scavenging capacities of DPPH, HO^•, and O₂^• - after 1-MCP treatment were enhanced. 1-MCP treatment affected the tissue color change, stimulated gene expression of PpaPAL, PpaCHS, PpaF3H, and PpaUFGT, and promoted the biosynthesis of flavonoids and stability of anthocyanin. PpaDFR and PpaUFGT played crucial roles in rapid color change stages. Kaempferol and kaempferol 3- O-galactoside increased distinctively during storage time.

Red onion scales ameliorated streptozotocin-induced diabetes and diabetic nephropathy in Wistar rats in relation to their metabolite fingerprint

AIM

The present study was designed to investigate the effect of red onion scales extract (ROS) against diabetic nephropathy, in relation to its metabolic profiling.

METHODS

Four groups of male Wistar rats were assigned as follows; 1st untreated group, 2nd group (animals with diabetes) treated with streptozotocin (STZ, 50 mg/kg) IP, 3rd group co-treated with ROS (150 mg/kg + STZ, 50 mg/kg) and 4th group co-treated with ROS by a dose (300 mg/kg + STZ, 50 mg/kg) daily. After four weeks, random and fasting blood glucose (FBG) levels, serum insulin, advanced glycation end products (AGEs), urea, uric acid and inflammatory and fibrotic gene expression were evaluated. Moreover, histopathological examination of the renal tissues was performed. In addition, the metabolic profiling of ROS was performed via RP-HPLC-DAD-QTOF-MS and -MS/MS.

RESULTS

The metabolic profiling of ROS revealed that protocatechuic acid and cyanidin-3-O-glucoside were the predominant compounds among 32 metabolites identified in the extract. ROS treated groups showed improvement of FBG and AGEs levels, whereas serum insulin level showed significant elevation. In addition, down-regulation of inflammatory mRNA expression associated with the hyperglycemic condition and amelioration in histopathological alterations in kidney tissues were observed.

CONCLUSION

This study displayed the presence of 32 phenolic compounds in the ethanolic extract of ROS, a common by-product of the industrial production of onion in Egypt. This study proved the therapeutic potential of ROS as antidiabetic agent and its preventive effect against diabetic nephropathy. Therefore, this study represents a perspective of the utilization of food waste products.

Comparative Evaluation of Soluble and Insoluble-Bound Phenolics and Antioxidant Activity of Two Chinese Mistletoes

Mistletoes are used medicinally in order to treat various human illnesses. Few studies have reported on the phenolic content and antioxidant properties of Chinese mistletoes (CMs). In this work, the total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activities of soluble and insoluble-bound phenolic extracts from CMs hosted by Camellia assamica (Mast.) Chang (CMC) and Pyrus, i, f. (CMP) were compared. Phenolic compounds in CMC and CMP were identified and quantified using high-performance liquid chromatography (HPLC). The results indicated that the TPC of soluble phenolic extracts was higher than insoluble-bound phenolic counterparts in both CMC and CMP. In addition, the TPC of soluble, insoluble-bound and total phenolic fractions (9.91 ± 0.23, 4.59 ± 0.27 and 14.50 ± 0.35 μmol ferulic acid equivalents per gram (FAE/g) dry sample) extracted from CMP were higher than those extracted from CMC. The soluble phenolic extracts in CMP showed higher antioxidant activities than those in CMC. Eighteen phenolic compounds from soluble and insoluble-bound phenolic extracts from the CMs were identified and quantified by HPLC. This study indicates that CMC and CMP, especially the latter, could be sources of antioxidants in human health care.

Moisture Transport Mechanism and Drying Kinetic of Fresh Harvested Red Onion Bulbs under Dehumidified Air

Drying plays an important role in post-harvest handling of onion for prolonging storage time. This research focuses on the drying studies of red onion bulbs using dehumidified air. The works were carried out by observing the microscopic structure of red onion bulbs layer and followed by developing mass transfer model for moisture diffusion during drying. Moisture diffusivity was estimated from drying experiments conducted at various temperatures (40, 50 and 60 °C) using the unsteady state solutions of Fick’s second law model. The diffusivity values were used to predict the drying kinetics as well as effective drying time for different air relative humidity. Results showed that combination of low relative humidity and low drying temperature significantly improved drying rate and reduced drying time.

Enzymatic production of pectic oligosaccharides from onion skins

Onion skins are evaluated as a new raw material for the enzymatic production of pectic oligosaccharides (POS) with a targeted degree of polymerization (DP). The process is based on a two-stage process consisting of a chelator-based crude pectin extraction followed by a controlled enzymatic hydrolysis. Treatment of the extracted crude onion skin's pectin with various enzymes (EPG-M2, Viscozyme and Pectinase) shows that EPG-M2 is the most appropriate enzyme for tailored POS production. The experiments reveal that the highest amount of DP2 and DP3 is obtained at a time scale of 75-90min with an EPG-M2 concentration of 26IU/mL. At these conditions the production amounts 2.5-3.0% (w/w) d.m for DP2 and 5.5-5.6% (w/w) d.m for DP3 respectively. In contrast, maximum DP4 production of 5.2-5.5% (w/w) d.m. is obtained with 5.2IU/mL at a time scale of 15-30min. Detailed LC-MS analysis reveals the presence of more methylated oligomers compared to acetylated forms in the digests.

Phenolic profiles and chemical- or cell-based antioxidant activities of four star fruit (Averrhoa carambola) cultivars

Phenolic profiles and chemical- or cell-based antioxidant activities of differentAverrhoa carambolacultivars cultivated in South China.

Review of natural compounds for potential skin cancer treatment

Most anti-cancer drugs are derived from natural resources such as marine, microbial and botanical sources. Cutaneous malignant melanoma is the most aggressive form of skin cancer, with a high mortality rate. Various treatments for malignant melanoma are available, but due to the development of multi-drug resistance, current or emerging chemotherapies have a relatively low success rates. This emphasizes the importance of discovering new compounds that are both safe and effective against melanoma. In vitro testing of melanoma cell lines and murine melanoma models offers the opportunity for identifying mechanisms of action of plant derived compounds and extracts. Common anti-melanoma effects of natural compounds include potentiating apoptosis, inhibiting cell proliferation and inhibiting metastasis. There are different mechanisms and pathways responsible for anti-melanoma actions of medicinal compounds such as promotion of caspase activity, inhibition of angiogenesis and inhibition of the effects of tumor promoting proteins such as PI3-K, Bcl-2, STAT3 and MMPs. This review thus aims at providing an overview of anti-cancer compounds, derived from natural sources, that are currently used in cancer chemotherapies, or that have been reported to show anti-melanoma, or anti-skin cancer activities. Phytochemicals that are discussed in this review include flavonoids, carotenoids, terpenoids, vitamins, sulforaphane, some polyphenols and crude plant extracts.

Bound phenolics in foods, a review

Among phytochemicals, phenolic compounds have been extensively researched due to their diverse health benefits. Phenolic compounds occur mostly as soluble conjugates and insoluble forms, covalently bound to sugar moieties or cell wall structural components. Absorption mechanisms for bound phenolic compounds in the gastrointestinal tract greatly depend on the liberation of sugar moieties. Food processes such as fermentation, malting, thermoplastic extrusion or enzymatic, alkaline and acid hydrolyses occasionally assisted with microwave or ultrasound have potential to release phenolics associated to cell walls. Different kinds of wet chemistry methodologies to release and detect bound phenolic have been developed. These include harsh heat treatments, chemical modifications or biocatalysis. New protocols for processing and determining phenolics in food matrices must be devised in order to release bound phenolics and for quality control in the growing functional food industry.