An activity-guided search for compounds influencing glucose metabolism in extracts from aronia (Aronia melanocarpa, A.), pomegranate (Punica granatum L., P.), and red grape (Vitis vinifera, RG) was carried out. The three extracts were fractionated by means of membrane chromatography to separate the anthocyanins from other noncolored phenolic compounds (copigments). In addition, precipitation with hexane was performed to isolate the polymers (PF). The anthocyanin and copigment fractions (AF, CF) of aronia, pomegranate, and red grape were furthermore fractionated with high-performance countercurrent chromatography (HPCCC) and the subfractions were characterized by HPLC-PDA-MS/MS analyses. Each of the (sub-)fractions was examined by in vitro-tests, i.e., the inhibition of the activity of α-amylase and α-glucosidase. On the basis of this screening, several potent inhibitors of the two enzymes could be identified, which included flavonols (e.g., quercetin), ellagitannins (e.g., pedunculagin), and anthocyanins (e.g., delphinidin-3-glucoside and petunidin-3-glucoside). In the α-glucosidase assay all of the examined fractions and subfractions of the fruit extracts were more active than the positive control acarbose.
Time-temperature integrators (TTIs) may provide a means to monitor safety of fresh foods packaged in reduced-oxygen environments. Commercially, TTI's have not been fully realized, possibly due to confusion over selection, performance, and reliability. The purpose of this work was to develop a framework for establishing performance targets for TTI's with foods that have potential to cause foodborne botulism. An Arrhenius-type curve was developed that offers safety margins that satisfy regulatory and shelf life requirements. TTI's developed as specified should minimize "false unsafe" readings that lead to destruction of safe product. The approach could be used to establishing guidelines for application of TTI's to food safety verification.
Red fruits and their juices are rich sources of polyphenols, especially anthocyanins. Some studies have shown that such polyphenols can inhibit enzymes of the carbohydrate metabolism, such as α-amylase and α-glucosidase, that indirectly regulate blood sugar levels. The presented study examined the in vitro inhibitory activity against α-amylase and α-glucosidase of various phenolic extracts prepared from direct juices, concentrates, and purees of nine different berries which differ in their anthocyanin and copigment profile. Generally, the extracts with the highest phenolic content—aronia (67.7 ± 3.2 g GAE/100 g; cyanidin 3-galactoside; chlorogenic acid), pomegranate (65.7 ± 7.9 g GAE/100 g; cyanidin 3,5-diglucoside; punicalin), and red grape (59.6 ± 2.5 g GAE/100 g; malvidin 3-glucoside; quercetin 3-glucuronide)—showed also one of the highest inhibitory activities against α-amylase (326.9 ± 75.8 μg/mL; 789.7 ± 220.9 μg/mL; 646.1 ± 81.8 μg/mL) and α-glucosidase (115.6 ± 32.5 μg/mL; 127.8 ± 20.1 μg/mL; 160.6 ± 68.4 μg/mL) and, partially, were even more potent inhibitors than acarbose (441 ± 30 μg/mL; 1439 ± 85 μg/mL). Additionally, the investigation of single anthocyanins and glycosylated flavonoids demonstrated a structure- and size-dependent inhibitory activity. In the future in vivo studies are envisaged.
Background: The polyphenols from red fruits exhibit protective effects against degenerative diseases, including diabetes mellitus type 2, cardiovascular disease, etc. Objective: In this small pilot intervention study with only ten volunteers, we investigated the influence of phenolic extracts prepared from an Aronia juice and a red grape juice concentrate on peripheral glucose, blood glucose, and insulin after the intake of a drink containing these extracts plus maltodextrin and water. Method: Maltodextrin in water served as control; additionally, phenolic extracts from Aronia or grape juice were added. Blood samples were taken before ingestion of the bolus drink and 30, 60, 90, 120, 180, 240, and 360 min after. Additionally, continuously the peripheral glucose was measured using a commercially available sensor system. Results: In all ten volunteers, the intake of Aronia extract (100 mg) reduced both the peripheral glucose and the blood glucose levels significantly (p ≤ 0.05) in comparison to the control. Blood insulin levels were not affected. Whereas the intake of red grape extract (120 mg) did not reduce the glucose levels but increased the insulin levels significantly. Conclusion: Our pilot study showed that even low amounts of a phenolic Aronia extract could lower glucose absorption. Thus, due to the blood glucose-lowering effects of Aronia phenolics in healthy volunteers, these preliminary results warrant further investigation in the frame of a follow-up study with a larger number of volunteers.
Die Enzyme α‐Amylase und α‐Glucosidase katalysieren die Hydrolyse von Polysacchariden in resorbierbare Monosaccharide und damit die Glucosefreisetzung ins Blut. Durch Glykogenphosphorylase α wird ebenfalls Glucose ins Blut freigesetzt, hier jedoch durch die Hydrolyse von Leber‐ oder Muskelglykogen. Dipeptidylpeptidase IV spielt eine zentrale Rolle bei der Freisetzung von Insulin, indem sie das Inkretinhormon Glucagon‐like‐peptide‐1 (GLP‐1) abbaut. Hemmstoffe dieser Enzyme finden in der therapeutischen Behandlung und Prävention von Diabetes mellitus Anwendung. Neben synthetischen Inhibitoren sind bereits einige natürliche Stoffe mit hemmender Wirkung bekannt, die in unterschiedlichen Lebensmitteln vorkommen. So erwiesen sich vor allem Flavonoide als potente Hemmer. Diese Arbeit beschäftigt sich mit dem Einfluss verschiedener Extrakte aus neun roten Früchten auf die Aktivität der Enzyme α‐Amylase, α‐Glucosidase, Glykogenphosphorylase α und Dipeptidylpeptidase IV in vitro und in vivo sowie der Identifizierung der verantwortlichen Inhaltsstoffe und entstand in Kooperation mit der TU Braunschweig. Alle Saftextrakte enthielten potente Inhibitoren der untersuchten Enzyme. Zu den aktivsten Extrakten zählten die aus Aronia (Aronia melanocarpa), Granatapfel (Punica granatum) und roter Traube (Vitis vinifera). Zur Identifizierung der aktiven Inhaltsstoffe wurden diese drei Extrakte in ihre Anthocyan‐, Copigment‐ und Polymerfraktion getrennt und die ersten beiden Fraktionen in Braunschweig weiter subfraktioniert. Auch hier zeigten sich alle (Sub‐)Fraktionen als potente Inhibitoren der getesteten Enzyme. Eine Studie mit einzelnen Anthocyanen und Copigmenten belegte diese Ergebnisse und gab Hinweise auf die Strukturabhängigkeit des Inhibitionspotentials. So beeinflussen die Anwesenheit und Anzahl der Hydroxyl‐ sowie Methylgruppen, die Molekülgröße und synergistische Effekte die inhibitorische Aktivität. Um eine irreversible Inaktivierung der Enzyme auszuschließen, wurde der Hemmmechanismus der Extrakte und Fraktionen ermittelt. Hierbei zeigte sich, dass alle untersuchten Proben die Aktivität der α‐Amylase und α‐Glucosidase reversibel hemmten.Im Rahmen einer humanen Interventionsstudie wurde der Einfluss eines Extraktes aus Aroniadirektsaft sowie eines roten Traubensaftkonzentrats auf den Blut‐ und Gewebsglucosespiegel als auch auf die Blutinsulinkonzentration untersucht. Für den ersten Extrakt zeigte sich eine signifikante Reduktion der Glucosespiegel, während der zweite die Insulinkonzentration signifikant erhöhte. Für alle Parameter konnten interindividuelle Unterschiede festgestellt werden, die eine Einteilung der Probanden in „Responder” und „Nicht‐Responder” ermöglichte. In der vorliegenden Arbeit konnte das inhibitorische Potential verschiedener Extrakte aus roten Früchten sowie unterschiedlicher Polyphenole auf α‐ Amylase, α‐Glucosidase, Glykogenphosphorylase α und Dipeptidylpeptidase IV in vitro nachgewiesen sowie relevante Struktureigenschaften von Inhibitoren ermittelt werden. Im Rahmen einer humanen Interventionsstudie konnten die beobachteten Effekte auch in vivo bestätigt werden. Die Ergebnisse dieser Pilotstudie sollten zukünftig mit einer höheren Anzahl an Probanden und einer höheren Dosierung der Extrakte abgesichert werden.
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