Inhibitory effects of Ligustrum robustum (Rxob.) Blume extract on α-amylase and α-glucosidase

Potential of polyphenols from Ligustrum robustum (Rxob.) Blume on enhancing the quality of starchy food during frying

The increasing concerns about health have led to a growing demand for high-quality fried foods. The potential uses of Ligustrum robustum (Rxob.) Blume, a traditional tea in China, as natural additives to enhance the quality of starchy food during frying was studied. Results indicated that L. robustum polyphenols extract (LREs) could improve the quality of fried starchy food, according to the tests of color, moisture content, oil content, texture property, and volatile flavor. The in vitro digestion results demonstrated that LRE reduced the final glucose content from 11.35 ± 0.17 to 10.80 ± 0.70 mmol/L and increased the phenolic content of fried starch foods from 1.23 ± 0.04 to 3.76 ± 0.14 mg/g. The appearance and polarizing microscopy results showed that LRE promoted large starch bulges on the surface of fried starchy foods. Meanwhile, X-ray diffraction results showed that LRE increased the intensity of characteristic diffraction peak of fried starch with a range of 21.8%-28%, and Fourier transform infrared results showed that LRE reduced the damage to short-range order structure of starch caused by the frying process. In addition, LRE increased the aggregation of starch granules according to the SEM observation and decreased the enthalpy of starch gelatinization based on the differential scanning calorimetry results. The present results suggest that LREs have the potential to be utilized as a natural additive for regulating the quality of fried starchy food in food industries. PRACTICAL APPLICATION: The enhancement of L. robustum polyphenols on the quality of starchy food during frying was found, and its mechanisms were also explored. This work indicated that L. robustum might be used as a novel economic natural additive for producing high-quality fried foods.

Ultrasound-assisted complex enzyme extraction, structural characterization, and biological activity of polysaccharides from Ligustrum robustum

Ligustrum robustum is one of the traditional teas in China with a long history of drinking and medicinal use. Through Response surface optimization, the yield of polysaccharides extracted by ultrasonic-assisted complex enzyme (UAE-EN) method was increased to 14.10 ± 0.56 %. Neutral homogeneous polysaccharide (LRNP) and acidic homogeneous polysaccharide (LRAP-1, LRAP-2, LRAP-3) from L. robustum were purified. The molecular weights of them were 5894, 4256, 4621 and 3915 Da. LRNP was composed of glucose (Glc), galactose (Gal), arabinose (Ara) with molar percentage of 24.97, 42.38 and 30.80. Structure analysis revealed that the backbone of LRNP consisted of 1,5-linked α-Araf, 1,4-linked β-Galp, 1,6-linked β-Galp, and 1,4-linked β-Glcp with the branches of 1,2-linked α-Araf, 1,3-linked α-Araf, 1,3-linked β-Glcp and 1,6-linked β-Galp residues, some terminal residues of α-Araf, β-Glcp and α-Galp were also included. In vitro experiments showed that the four polysaccharides possessed excellent antioxidant, antitumor and hypoglycemic activities. LRNP possessed the protective effect against oxidative stress. The studies provide a basis for further exploitation of L. robustum.

Monoterpenoid Glycosides from the Leaves of Ligustrum robustum and Their Bioactivities (II)

Ligustrum robustum has been not only used as a heat-clearing and detoxicating functional tea (Ku-Ding-Cha) but also consumed as a hypotensive, anti-diabetic, and weight-reducing folk medicine. From the leaves of L. robustum, ten new monoterpenoid glycosides named ligurobustosides T10 (1a), T11 (1b), T12 (2a), T13 (2b), T14 (3a), T15 (3b), F1 (4b), T16 (5a), T17 (5b), and E1 (6b), together with five known ones (4a, 6a, 7, 8a, 8b), were separated and identified using the spectroscopic method and chemical method in this research. The results of biological tests exhibited that the fatty acid synthase (FAS) inhibitory action of compound 5 (IC50: 4.38 ± 0.11 μM) was as strong as orlistat (IC50: 4.46 ± 0.13 μM), a positive control; the α-glucosidase inhibitory actions of compounds 1-4 and 7-8, and the α-amylase inhibitory actions of compounds 1-8 were medium; the ABTS radical scavenging capacities of compounds 1-3 and 5-8 (IC50: 6.27 ± 0.23 ~ 8.59 ± 0.09 μM) were stronger than l-(+)-ascorbic acid (IC50: 10.06 ± 0.19 μM) served as a positive control. This research offered a theoretical foundation for the leaves of L. robustum to prevent diabetes and its complications.

A New HPLC-UV Method Using Hydrolyzation with Sodium Hydroxide for Quantitation of Trans-p-Hydroxycinnamic Acid and Total Trans-p-Hydroxycinnamic Acid Esters in the Leaves of Ligustrum robustum

Trans-p-hydroxycinnamic acid and its esters in the leaves of Ligustrum robustum might be a new resource to prevent diabetes and its complications. In the present study, a new HPLC-UV method using hydrolyzation with sodium hydroxide for quantitation of trans-p-hydroxycinnamic acid and total trans-p-hydroxycinnamic acid esters in the leaves of L. robustum was developed, since it was difficult and troublesome to analyze no less than 34 trans-p-hydroxycinnamic acid esters by usual HPLC. The extract of L. robustum was hydrolyzed with sodium hydroxide at 80 °C for 2 h, and then, hydrochloride was added. HPLC analysis was performed in reverse phase mode using a C-18 column, eluting with methanol-0.1% acetic acid aqueous solution (40:60, v/v) in isocratic mode at a flow rate of 1.0 mL·min^-1 and detecting at 310 nm. The linear range for trans-p-hydroxycinnamic acid was 11.0-352.0 μg·mL^-1 (r² = 1.000). The limit of detection and limit of quantification were 2.00 and 6.07 μg·mL^-1, respectively. The relative standard deviations of intra-day and inter-day variabilities for trans-p-hydroxycinnamic acid were less than 2%. The percentage recovery of trans-p-hydroxycinnamic acid was 103.3% ± 1.1%. It is the first HPLC method using hydrolyzation for quantification of many carboxylic esters. Finally, the method was used successfully to determine trans-p-hydroxycinnamic acid and total trans-p-hydroxycinnamic acid esters in various extracts of the leaves of L. robustum. The 60-70% ethanol extracts of L. robustum showed the highest contents of free trans-p-hydroxycinnamic acid (3.96-3.99 mg·g^-1), and the 50-80% ethanol extracts of L. robustum displayed the highest contents of total trans-p-hydroxycinnamic acid esters (202.6-210.6 mg·g^-1). The method can be applied also to the quality control of the products of L. robustum.

Chemical Constituents from the Leaves of Ligustrum robustum and Their Bioactivities

The leaves of Ligustrum robustum have been consumed as Ku-Ding-Cha for clearing heat and removing toxins, and they have been used as a folk medicine for curing hypertension, diabetes, and obesity in China. The phytochemical research on the leaves of L. robustum led to the isolation and identification of two new hexenol glycosides, two new butenol glycosides, and five new sugar esters, named ligurobustosides X (1a), X₁ (1b), Y (2a), and Y₁ (2b) and ligurobustates A (3a), B (3b), C (4b), D (5a), and E (5b), along with seven known compounds (4a and 6-10). Compounds 1-10 were tested for their inhibitory effects on fatty acid synthase (FAS), α-glucosidase, and α-amylase, as well as their antioxidant activities. Compound 2 showed strong FAS inhibitory activity (IC₅₀ 4.10 ± 0.12 μM) close to that of the positive control orlistat (IC₅₀ 4.46 ± 0.13 μM); compounds 7 and 9 revealed moderate α-glucosidase inhibitory activities; compounds 1-10 showed moderate α-amylase inhibitory activities; and compounds 1 and 10 displayed stronger 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) ammonium salt (ABTS) radical scavenging effects (IC₅₀ 3.41 ± 0.08~5.65 ± 0.19 μM) than the positive control l-(+)-ascorbic acid (IC₅₀ 10.06 ± 0.19 μM). This study provides a theoretical foundation for the leaves of L. robustum as a functional tea to prevent diabetes and its complications.

Phenylethanoid and Phenylmethanoid Glycosides from the Leaves of Ligustrum robustum and Their Bioactivities

The phytochemical study on the leaves of Ligustrum robustum, which have been used as Ku-Ding-Cha, led to the isolation and identification of three new phenylethanoid glycosides and three new phenylmethanoid glycosides, named ligurobustosides R₁ (1b), R_2-3 (2), R₄ (3), S₁ (4b), S₂ (5), and S₃ (6), and five reported phenylethanoid glycosides (7-11). In the bioactivity test, (Z)-osmanthuside B₆ (11) displayed strong fatty acid synthase (FAS) inhibitory activity (IC₅₀: 4.55 ± 0.35 μM) as the positive control orlistat (IC₅₀: 4.46 ± 0.13 μM), while ligurobustosides R₄ (3) and S₂ (5), ligupurpuroside B (7), cis-ligupurpuroside B (8), ligurobustoside N (9), osmanthuside D (10), and (Z)-osmanthuside B₆ (11) showed stronger ABTS radical scavenging activity (IC₅₀: 2.68 ± 0.05~4.86 ± 0.06 μM) than the positive control L-(+)-ascorbic acid (IC₅₀: 10.06 ± 0.19 μM). This research provided a theoretical basis for the leaves of L. robustum as a tea with function in treating obesity and diabetes.

Wheat Starch Modified with Ligustrum robustum (Rxob.) Blume Extract and Its Action Mechanism

We investigated the modification of wheat starch with Ligustrum robustum (Rxob.) Blume extract (LRE) and determined the action mechanism. Based on differential scanning calorimetry, LRE decreased the gelatinization enthalpy of wheat starch from 19.14 to 7.15 J/g and changed gelatinization temperatures (including the variation in gelatinization onset temperature, peak temperature and conclusion temperature in different degrees). Moreover, LRE affected the pasting viscosity curve of wheat starch, and changed its rheological parameters (including the decrease in storage modulus and loss modulus, as well as the increase in loss tangent). Based on the analysis of scanning electron microscopy and wide-angle X-ray diffraction, LRE increased the hole size and the roughness of the gel microstructure, and decreased the crystallinity of wheat starch. Meanwhile, the evaluation results of the texture analyzer and the colorimeter showed that LRE could change the quality properties (including decrease hardness, fracturability and L* values, as well as increase a* and b* values) of wheat starch biscuits after hot air baking (170 °C). Furthermore, with molecular dynamics simulation analysis, phenolic compounds of LRE combined with starch molecules via H-bonds and affected the formation of molecular bonds (including intra- and intermolecular hydrogen bonds), so as to change the spatial conformation and properties of wheat starch during gelatinization and retrogradation. The present results suggest that LRE can modify the physicochemical properties of wheat starch and further improve its processing properties, indicating its potential in the design and development of starch foods (such as steamed buns, bread, biscuits, etc.).

Effects of Ligustrum robustum (Rxob.) Blume extract on the quality of peanut and palm oils during storage and frying process

The potential uses of Ligustrum robustum (Rxob.) Blume extract as a natural antioxidant to protect the quality of different oils during storage and frying process were studied. The results showed that L. robustum extract has been shown to retard the decline in the quality of both oils based on the tests of acid value, peroxide value, p-anisidine value, color, volatile flavor, and fatty acid compositions, and the protective effect of L. robustum extract on the quality of peanut oil was better than that of palm oil. By the component analysis, L. robustum extract was found to have a total phenols content of 140.75 ± 1.52 mg/g, and ligurobustoside C was identified as the main phenolic compound. The thermogravimetric and differential scanning calorimetry results showed that L. robustum extract enhanced the oxidative stability of peanut and palm oils. In addition, Fourier transform infrared results indicated that L. robustum extract had protective effects on the C=C bond and ester bond of oil molecule. Moreover, by using electron spin resonance technique, L. robustum extract showed the ability to inhibit and scavenge alkyl-free radicals in both oils. The present results suggested that L. robustum extract may protect the quality of oils during the storage and frying process by inhibiting the oxidation of unsaturated fatty acids and might be a potential natural antioxidant in the food industry. PRACTICAL APPLICATIONS: The excellent antioxidant ability of Ligustrum robustum (Rxob.) Blume extract on the oxidation of different oils and its low price indicated that it could be used as a new low-cost natural antioxidant in oil processing.

Monoterpenoid Glycosides from the Leaves of Ligustrum robustum and Their Bioactivities

The leaves of Ligustrum robustum have been applied as Ku-Ding-Cha, a functional tea to clear heat, remove toxins, and treat obesity and diabetes, in Southwest China. The phytochemical research on the leaves of L. robustum led to the isolation and identification of eight new monoterpenoid glycosides (1–8) and three known monoterpenoid glycosides (9–11). Compounds 1–11 were tested for the inhibitory activities on fatty acid synthase (FAS), α-glucosidase, α-amylase, and the antioxidant effects. Compound 2 showed stronger FAS inhibitory activity (IC₅₀: 2.36 ± 0.10 μM) than the positive control orlistat (IC₅₀: 4.46 ± 0.13 μM), while compounds 1, 2, 5 and 11 displayed more potent ABTS radical scavenging activity (IC₅₀: 6.91 ± 0.10~9.41 ± 0.22 μM) than the positive control L-(+)-ascorbic acid (IC₅₀: 10.06 ± 0.19 μM). This study provided a theoretical basis for the leaves of L. robustum as a functional tea to treat obesity.

The Occurrence and Biological Activity of Tormentic Acid-A Review

This review focuses on the natural sources and pharmacological activity of tormentic acid (TA; 2α,3β,19α-trihydroxyurs-2-en-28-oic acid). The current knowledge of its occurrence in various plant species and families is summarized. Biological activity (e.g., anti-inflammatory, antidiabetic, antihyperlipidemic, hepatoprotective, cardioprotective, neuroprotective, anti-cancer, anti-osteoarthritic, antinociceptive, antioxidative, anti-melanogenic, cytotoxic, antimicrobial, and antiparasitic) confirmed in in vitro and in vivo studies is compiled and described. Biochemical mechanisms affected by TA are indicated. Moreover, issues related to the biotechnological methods of production, effective eluents, and TA derivatives are presented.

The ameliorative effect of the Pyracantha fortuneana (Maxim.) H. L. Li extract on intestinal barrier dysfunction through modulating glycolipid digestion and gut microbiota in high fat diet-fed rats

Pyracantha fortuneana fruits are consumed as a dietary supplement in China and attenuate obesity and metabolic disorders. Obesity is known to be associated with intestinal barrier dysfunction driven by hyperglycemia and gut dysbiosis. However, whether the health benefits of P. fortuneana fruits are linked with the intestinal barrier function (IBF) remains unknown. This study aimed to evaluate the restorative effects of P. fortuneana fruit extract (PFE) on the IBF. Sprague Dawley rats were fed with a chow, a high-fat diet (HFD), or a PFE-supplemented diet for 8 weeks. Results showed that PFE intervention ameliorated HFD-induced intestinal barrier dysfunction by attenuating impaired structural integrity, reducing the elevated lactulose/mannitol ratio, and improving the mRNA and protein expression levels of tight junction proteins in HFD-fed rats. The ameliorations were associated with a beneficial effect on glycolipid homeostasis, as evidenced from the PFE decreasing intestinal absorptive capacity based on the d-xylose excretory rate, lowering the expression of GLUT2 and inhibiting digestive enzyme activities. The proanthocyanidins in the PFE showed greater in vitro inhibition on α-amylase, α-glucosidase, and lipase compared with triterpenoid saponins. Furthermore, the ameliorations on the IBF were also associated with effects on the microbial composition based on 16S rRNA gene sequence analysis. Several bacterial groups, which were linked with gut barrier integrity, were modulated after PFE administration, that is, Actinobacteria, Bacteroidaceae, Corynebacteriaceae, Lactobacillaceae, and S24-7 were elevated and the HFD-induced increase in Clostridia, Ruminococcaceae, Oscillospira, and Flexispira was restored. These data provide evidence for the ameliorative effect of the PFE on diet-induced intestinal barrier functional alternations in association with its capacity to modulate glycolipid digestion and gut microbiota in HFD-fed obese rats.

Ligustrum robustum Intake, Weight Loss, and Gut Microbiota: An Intervention Trial

Ligustrum robustum (LR) shows antiobesity effects in animal studies. However, little is known about the effect on human. The present study aimed to investigate the effect of LR intake on weight change in obese women and the role of gut microbiota. Thirty overweight and obese female participants (BMI ≥24 kg/m²) were recruited in the current study. The participants drank LR 10g/d for 12 wks. Their body composition and related biomarkers were assessed. Alterations of the gut microbiota were analyzed using 16S rRNA sequencing. The primary outcome was the change in body weight. LR intake resulted in 2.5% weight loss over 12 wks (P<0.01). Change in body fat at 12 wk was -1.77 ± 1.19 kg (P<0.01). In addition, decreased Firmicutes-to-Bacteroidetes ratio (P=0.03), increased richness (the ACE estimator, P<0.01; the Chao1 estimator, P<0.01), and altered representative taxa of the gut microbiota were observed. Bacteroidaceae, Bacteroides, Bacilli, and Lactobacillales were higher while Ruminococcaceae, Enterobacteriaceae, Enterobacteriales, Lachnospiraceae, Clostridia, and Clostridiales were lower at 12 wk. Moreover, LR intervention decreased fasting glucose (P<0.01), serum leptin (P<0.01), and IL8 (P=0.02) and increased HOMA-β (P<0.01). LR intervention moderately decreased the body weight in overweight and obese women and such effect might be due to modulation of gut microbiota.

Dietary polyphenols modulate starch digestion and glycaemic level: a review

Polyphenols, as one group of secondary metabolite, are widely distributed in plants and have been reported to show various bioactivities in recent year. Starch digestion not only is related with food industrial applications such as brewing but also plays an important role in postprandial blood glucose level, and therefore insulin resistance. Many studies have shown that dietary phenolic extracts and pure polyphenols can retard starch digestion in vitro, and the retarding effect depends on the phenolic composition and molecular structure. Besides, dietary polyphenols have also been reported to alleviate elevation of blood glucose level after meal, indicating the inhibition of starch digestion in vivo. This review aims to analyze how dietary polyphenols affect starch digestion both in vitro and in vivo. We can conclude that the retarded starch digestion in vitro by polyphenols results from inhibition of key digestive enzymes, including α-amylase and α-glucosidase, as well as from interactions between polyphenols and starch. The alleviation of postprandial hyperglycemia by polyphenols might be caused by both the inhibited starch digestion in vivo and the influenced glucose transport. Therefore, phenolic extracts or pure polyphenols may be alternatives for preventing and treating type II diabetes disease.

Investigating inhibitory activity of novel synthetic sericin peptide on α-D-glucosidase: kinetics and interaction mechanism study using a docking simulation

BACKGROUND

We synthesised a novel sericin peptide (SP-GI) with α-d-glucosidase inhibitory activity, which has a sequence of SEDSSEVDIDLGN. The kinetics of its peptide-induced inhibition on α-d-glucosidase activity and its interaction mechanism merging with molecular docking were both investigated.

RESULTS

SP-GI exhibited significant inhibitory activity with an IC₅₀ of 2.9 ± 0.1 µmol L^-1 and this inhibition was reversible and non-competitive with a K_i value of 1.0 ± 0.1 µmol L^-1 . An interaction study with SP-GI revealed it bound to α-d-glucosidase at a single binding site, resulting in alterations in α-d-glucosidase secondary structure. This led to quenching of intrinsic α-d-glucosidase fluorescence by a static quenching mechanism. Molecular docking results showed that the SP-GI binding site on α-d-glucosidase differed from acarbose, with hydrogen bonding and van der Waals forces being the main binding drivers.

CONCLUSION

These findings suggest the potential use for SP-GI or other natural sericin peptides as dietary supplements for the treatment of type 2 diabetes. © 2017 Society of Chemical Industry.

Antioxidant Capacity and Phenolic Contents of Three Quercus Species

The antioxidant capability and phenolic contents of ethanol extracts (free phenolics) and ethyl acetate extracts (bound phenolics) of three Quercus species were estimated in this work. The antioxidant activities were examined by 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) free radical, reducing power and b-carotene bleaching methods. HPLC was employed to detect major phenolic acids. The leaf extract of Q. salicina contained maximum total phenolics while the highest total flavonoid content was found in the leaf extract of Q. serrata. The antioxidant activities varied among three species. Bark extract of Q. salicina was the most potential and it was closed to levels of the standard antioxidative dibutyl hydroxytoluene (BHT). The bark extract of Q. serrata also showed promising antioxidant activities despite their eminence was negligibly lower than Q. salicina. Stronger antioxidant activities of free phenolics than those of the bound phenolics may be attributed to higher quantities of free phenolics in the barks of Quercus species, however total flavonoids may not contribute a critical role. By HPLC analysis, thirteen phenolic acids were detected in the leaf and bark extracts. Of them, Q. salicina showed maximum in number (ten compounds) and quantities of detected phenolic acids. Ellagic, chlorogenic and benzoic acids were dominant in Quercus species. Findings of this study revealed that leaves and barks of three Quercus species are rich source of antioxidants, and Q.salicina is the most promising and should be elaborated to exploit its pharmaceutical properties.