Rapid screening and identification of antioxidants in the leaves of Malus hupehensis using off-line two-dimensional HPLC-UV-MS/MS coupled with a 1,1′-diphenyl-2-picrylhydrazyl assay

Bioactive Substances and Biological Functions in Malus hupehensis: A Review

Malus hupehensis (MH), as a natural resource, contains various active ingredients such as polyphenols, polysaccharides, proteins, amino acids, volatile substances, and other components. Increasingly, studies have indicated that MH showed a variety of biological activities, including antioxidant, hypoglycemic, hypolipidemic, anti-cancer, anti-inflammatory activities, and other activities. Hence, MH has attracted wide interest because of its high medical and nutritional value. It is necessary to review the active components and biological activities of MH. This paper systematically reviewed the chemical substances, biological activities, and potential problems of MH to further promote the related research of MH and provide an important reference for its application and development in medicine and food.

Polyphenolics and Chemical Profiles of Domestic Norwegian Apple (Malus × domestica Borkh.) Cultivars

Using modern analytical techniques, a comprehensive study of the chemical composition of fruits from apple cultivars grown in Western Norway during 2019 and 2020 was done. Metals, sugars, organic acids, antioxidant tests, and polyphenol content have been observed. In all investigated samples, the most dominant sugars were glucose, fructose, and sucrose. Among 11 tested organic acids, the dominant was malic acid, followed by citric and maleic acid. The most common metal was potassium, followed by magnesium and zinc. The quantification of polyphenols showed that among the 11 quantified polyphenols, chlorogenic acid, quercetin 3-O-rhamnoside, quercetin 3-O-glucoside, quercetin, and phlorizin were the most abundant. A detailed study of the polyphenolic profile of nine investigated apple samples provided 30 identified polyphenolic compounds from the class of hydroxybenzoic and hydroxycinnamic acids, flavonoids, and dihydrochalcones. In addition to the identified 3-O-caffeoylquinic acid, its two isomers of 5-O-caffeoylquinic acid and three esters were also found. Present polyphenols of the tested apples provided significant data on the quality of Norwegian apples, and they contribute to the distinguishing of these apple samples.

Ultrasonic-Assisted Aqueous Two-Phase Extraction and Properties of Water-Soluble Polysaccharides from Malus hupehensis

Malus hupehensis (M. hupehensis), an edible and medicinal plant with significant antioxidant and hypoglycemic activity, has been applied to new resource foods. However, the structural characterization and biological effects of its polysaccharides (MHP) are less known. The optimum extraction parameters to achieve the highest extraction efficiency (47.63%), the yield (1.68%) and purity of MHP (89.6%) by ultrasonic-assisted aqueous two-phase system (ATPS) were obtained under the liquid-to-solid ratio of 23 g/mL, ultrasonic power of 65 W, and ultrasonic time of 33 min. According to the analysis results, MHP was composed of Man, GlcA, Rha, GalA, Glc, Gal, Xyl, Ara, and Fuc, in which Ara and Gal were the main components, and the content of GlcA was the lowest. In in vitro activity analysis, MHP showed a significant antioxidant capacity, and an inhibition activity of α-glucosidase and the advanced glycation end products (AGEs) formation in the BSA/Glc reaction model. MHP interacted with α-glucosidase and changed the internal microenvironment of the enzyme, and inhibited the AGEs formation, which provides more evidence for the antihyperglycemic mechanism of MHP. The results suggest that ATPS is an efficient and environmentally friendly solvent system, and M. hupehensis has broad application prospects in functional foods, healthcare products, and pharmaceuticals.

Rapid enrichment and separation of two novel minor phenols from Malus hupehensis utilizing liquid-liquid extraction with three-phase solvent system and high-speed counter-current chromatography based on the polarity parameter

For a rapid enrichment and separation of minor components from Malus hupehensis, the selection of suitable solvent system is the great challenge for liquid-liquid extraction with a three-phase solvent system and high-speed counter-current chromatography. According to the concept of "like dissolves like," the similarity of the average polarity between solvent system and target compounds was the significant characteristic of liquid-liquid extraction with a three-phase solvent system and high-speed counter-current chromatography separation. The polarity parameter model provides a way to calculate the polarity of unknown compounds. Under the guidance of the polarity, an efficient enrichment and separation approach was established through liquid-liquid extraction and high-speed counter-current chromatography with solvent systems composed of n-hexane-ethyl acetate-acetonitrile-water (5:3:5:7, v/v), n-hexane-ethyl acetate-methanol-water (1:2:1:2, v/v), respectively. Thus, the total content of minor compounds was increased from 2.6% to 17.2%, and two novel compounds (6´´-O-coumaroyl-2´-O-glucopyranosylphloretin and 3´´´-methoxy-6´´-O-feruloy-2´-glucopyranosylphloretin) were obtained. The discovery of the new dihydrochalcones expanded the structural diversity of compounds produced by the genus Malus. The experimental results demonstrated that compound polarity can be described by the polarity parameter model and is an important reference for investigating optimum solvent systems for liquid-liquid extraction with a three-phase solvent system and high-speed counter-current chromatography.

Extraction and separation of flavonoids from Malus hupehensis using high-speed countercurrent chromatography based on deep eutectic solvent

In the present experiment, a green and highly efficient extraction method for flavonoids established on deep eutectic solvents (DESs) was investigated by using the response surface methodology. The DES-based high-speed countercurrent chromatography (HSCCC) solvent systems were developed for the separation of high purity compounds from the DES extract of Malus hupehensis for the first time. Under the optimal conditions (liquid-to-solid ratio of 26.3 mL/g, water content of 25.5%, and extraction temperature of 77.5°C), the yield of flavonoids was 15.3 ± 0.1%, which was superior to that of the methanol extraction method. In accordance with the physical property of DES-based HSCCC solvent systems and K values of target compounds, DES-based HSCCC solvent systems composed of choline chloride/glucose-water-ethyl acetate (ChCl/Glu-H₂O-EAC, 1:1:2, v/v) was selected for the HSCCC separation. Thus, five flavonoids (two novel compounds 1-2, 6´´-O-coumaroyl-2´-O-glucopyranosylphloretin and 3´´´-methoxy-6´´-O-feruloy-2´-O-glucopyranosylphloretin; three know compounds 3-5, namely, avicularin, phloridzin, and sieboldin) were efficiently separated from Malus hupehensis. DESs are the environment friendly and highly efficient solvents as the components of extraction solvent and HSCCC solvent system, and can be re-utilized many times. However, ethyl acetate can be soluble with a few hydrogen bond donors, such as urea, carboxylic acid and polyol, through the shake flask test. It is the great difficulty for the efficient and rapid separation of target compounds from the DESs extract because of the DESs residual in the HSCCC fractions. ChCl and Glu are the great choices of DESs without this problem. In addition, K values increased with the increase of the molar ratio of ChCl/Glu and the content of water, which could effectively guide us to choose the suitable DES-based HSCCC solvent system. The twice HSCCC separation results indicated that DES was the valuable and green solvent for the HSCCC separation of pure compounds from the extract for the first time, and showed the recycle superiority of DES-based HSCCC solvent system.

Comprehensive evaluation of the antioxidant capacity of Sceptridium ternatum using multiple colorimetric methods and 1,1-diphenyl-2-picrylhydrazyl-high-performance liquid chromatography analysis

Sceptridium ternatum is a medicinal herb with multiple health benefits. However, its antioxidant activity and active components have not been clarified. In this study, the antioxidant capacity of S. ternatum was comprehensively investigated using multiple colorimetric methods and 1,1-diphenyl-2-picrylhydrazyl-high-performance liquid chromatography analysis. First, the phenolic content, flavonoid content, and radical scavenging ability of S. ternatum were parallelly determined using colorimetric methods performed in 96-well microplates. The flavonoid content, rather than the phenolic content, was highly correlated with its antioxidant activity. Sceptridium ternatum was shown to be a rich source of flavonoids, with a highest flavonoid yield of 3.44 ± 0.11 mg/g. Subsequently, 1,1-diphenyl-2-picrylhydrazyl-high-performance liquid chromatography experiment and quadrupole time-of-flight mass spectrometry analyses were carried out for rapid screening of the individual antioxidants. A total of 14 O-glycosyl flavonoids with quercetin or kaempferol aglycone have been characterized. Particularly, quercetin 3-O-rhamnoside-7-O-glucoside exhibited the most potent antioxidant ability. Its half-maximal effective concentrations for scavenging 1,1-diphenyl-2-picrylhydrazyl and 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) radicals were 70.55 ± 2.69 and 106.90 ± 1.76 µg/mL, respectively, which were comparable with those of l-ascorbic acid. Our results indicated that the combined colorimetric and chromatographic methods provided a practical strategy for the discovery of bioactive compounds from natural products.

Chemical composition, anti-inflammatory and antinociceptive effects of the butanolic fraction of Annona nutans (Annonaceae) leaves

The species Annona nutans (R. E. Fries) is a plant found in Bolivia, Paraguay, Argentina and the Brazilian cerrado. Considering the anti-inflammatory and antinociceptive activities of the hydrometanolic fraction (FHMeOH) of A. nutans leaves previously reported, the present study aimed to evaluate in vivo anti-inflammatory and antinociceptive activities of a subfraction obtained from FHMeOH, the butanolic fraction (FBuOH_f). Intraperitoneal (i.p.) treatment with FBuOH_f (50 and 100 mg · kg^-1) inhibited paw edema induced by carrageenan. Moreover, FBuOH_f (100 mg · kg^-1, i.p.) also suppressed polymorphonuclear (PMN) leukocyte migration in the footpad. Regarding the antinociceptive activity, FBuOH_f (50, 100, and 200 mg · kg^-1, i.p.) inhibited acetic acid-induced abdominal writhing. In the formalin test, this fraction (200 mg · kg^-1, i.p.) reduced licking time only in the inflammatory phase. The FBuOH_f contents flavonoids and cinnamic acid derivatives, such as quercetin-3-O-galactoside, quercetin-3-O-glucoside, isorhamnetin-3-O-galactoside, quercetin-3-O-β-D-apio-furanosyl-(1→2)-galactopyranoside and chlorogenic acid, identified and quantified by LC-MS. The FBuOH_f possesses anti-inflammatory and peripheral antinociceptive activities.

Vibrational (FT-IR, Raman) analysis of tea catechins based on both theoretical calculations and experiments

Structural investigations, based on density functional theory (DFT) calculations, are performed on tea catechins, including 4-aminobutyric acid (GABA), L-theanine (Thea), caffeine (CAF), theobromine (TB), theophylline (TP), catechin (C), epicatechin (EC), gallocatechin (GC), epigallocatechin (EGC), catechin gallate (CG), epicatechin gallate (ECG), gallocatechin gallate (GCG) and epigallocatechin gallate (EGCG). With an identified lowest energy conformer of investigated molecules, FTIR and FT-Raman spectra have been assigned according to DFT calculations in the way of B3LYP/6-31 + G (d, p). Normal spectra of these catechin powders are also measured by Raman spectrometers. There is a kind of everlasting correlation between experimental results and theoretical data. And our research has also obtained a clear evidence for reliable assignments of vibrational bands, bringing great feasibility to the rapid tea catechin detection.

Dihydrochalcone-derived polyphenols from tea crab apple (Malus hupehensis) and their inhibitory effects on α-glucosidase in vitro

Three dihydrochalcone-derived polyphenols, huperolides A-C (1-3), along with thirteen known compounds (4-16) were isolated from the leaves of Malus hupehensis, the well-known tea crab apple in China. Their chemical structures were elucidated by extensive spectroscopic analysis including NMR (HSQC, HMBC, 1H-1H COSY and ROESY), HRMS and CD spectra. Huperolide A is a polyphenol with a new type of carbon skeleton, while huperolides B and C are a couple of atropisomers, which were isolated from natural sources for the first time. The antihyperglycemic effects of the isolated compounds were evaluated based on assaying their inhibitory activities against α-glucosidase. As a result, phlorizin (4), 3-hydroxyphloridzin (5), 3-O-coumaroylquinic acid (12) and β-hydroxypropiovanillone (15) showed significant concentration-dependent inhibitory effects on α-glucosidase. Therefore, those compounds might be responsible for the antihyperglycemic effect of this herb, and are the most promising compounds to lead discovery of drugs against diabetes.