Abstract
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.
Highlights
Small fruits and their juices are rich sources of polyphenols, especially anthocyanins.The anthocyanins are a sub-group of flavonoids that primarily occur in violet, blue, and red fruits.They are water-soluble plant pigments and serve as an attractant, as well as a protector against oxidative stress and excessive light
Thirty-eight fruit products derived from aronia, bilberry, blackcurrant, cranberry, elderberry, lingonberry, pomegranate, red grape, and sour cherry were extracted and investigated with regard to their inhibition of α-glucosidase and α-amylase activity, including direct juices, concentrates, and purees
The aronia juice products were richest in proanthocyanidins, anthocyanins, and phenolic acids
Summary
Small fruits and their juices are rich sources of polyphenols, especially anthocyanins. The anthocyanins are a sub-group of flavonoids that primarily occur in violet, blue, and red fruits They are water-soluble plant pigments and serve as an attractant, as well as a protector against oxidative stress and excessive light. A wide range of polyphenols reportedly inhibit α-amylase, whereas α-glucosidase appears to be primarily sensitive to anthocyanins [15] This inhibitory potential has been verified by studying polyphenol-containing extracts from various fruits, including blueberries, pomegranates, and strawberries [9,10,15]. With the help of activity-guided fractionation numerous potent inhibitors in berries could already been identified This includes besides anthocyanins mainly flavonoids, and ellagitannins. Isolated anthocyanins and copigments were investigated to create a link between the molecular structure and the inhibitory potential of individual phenolic compounds and to examine possible synergistic and antagonistic mechanism
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