Phenolic Profile, Antioxidant, and Antidiabetic Potential Exerted by Millet Grain Varieties

Abstract

This study evaluated the potential antioxidant and antidiabetic properties in vitro of four millet grain varieties cultivated in South Korea. The free fractions were tested for their total antioxidant capacity using 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS⁺) and 2,2'-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays, followed by α-glucosidase, α-amylase, and advanced glycation endproducts (AGEs) formation inhibition assays. The total phenolics, flavonoids, and condensed tannins in the free fractions ranged from 107.8 to 136.4 mg ferulic acid equivalent (FAE)/100 g, 101.3 to 115.8 mg catechin equivalent (CE)/100 g, and 17.65 to 59.54 mg catechin equivalent (CE)/100 g, respectively. Finger Italian millet had the highest total phenolic content (136.4 mg FAE/100 g) and flavonoid content (115.8 mg CE/100 g). Barnyard and finger Italian millet showed the highest DPPH (IC₅₀ = 359.6 µg/mL and 436.25 µg/mL, respectively) and ABTS radical scavenging activity (IC₅₀ = 362.40 µg/mL and 381.65 µg/mL, respectively). Similarly, finger Italian millet also exhibited significantly lower IC₅₀ values for the percentage inhibition of α-glucosidase (18.07 µg/mL) and α-amylase (10.56 µg/mL) as compared with acarbose (IC₅₀ = 59.34 µg/mL and 27.73 µg/mL, respectively) and AGEs formation (33.68 µg/mL) as compared with aminoguanidine (AG) (52.30 µg/mL). All eight phenolic compounds identified in finger Italian millet were flavonoids, with flavanols being the predominant subclass. Taken together, millet flavonoids play important roles in the prevention and management of type 2 diabetes, and hence finger Italian millet has the potential to be developed as a functional food.

Keywords: advanced glycation endproducts; antioxidant activities; digestive enzymes inhibitors; flavonoids; functional food; millet grains; phenolic compounds.

Figure 1

Pictures of millet grains used in the present study.

Figure 2

Antioxidant capacities of ethanol extracts of millet varieties. (A) 2,2′-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity IC₅₀ values; (B) 2,2′-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) radical scavenging activity IC₅₀ values. FIM, finger Italian millet; BM, barnyard millet; M, millet; IM, Italian millet. Different lower case letters denote significant difference (p < 0.05).

Figure 3

Digestive enzymes and advanced glycation endproducts inhibitory activities from ethanol extracts of millet varieties. (A) α-glucosidase inhibitory activity IC₅₀ values; (B) α-amylase inhibitory activity IC₅₀ values; (C) and advanced glycation endproducts (AGEs) inhibitory activity IC₅₀ values. FIM, finger Italian millet; BM, barnyard millet; M, millet; IM, Italian millet. Different lower case letters denote significant difference (p < 0.05).