Changes in Nutrient Components and Digestive Enzymatic Inhibition Activities in Soy Leaves by Ethephon Treatment

Abstract

In this study, the high isoflavone-enriched soy leaves (IESLs) were manufactured by treating with the chemical inducer ethephon, a plant growth regulator, to confirm changes in the properties of soy leaves (SLs), which are underutilized. Ethephon treatment concentrations consisted of 0 (SL1), 150 (SL2), and 300 (SL3) μg/mL. The composition analysis and physiological activity were conducted according to the ethephon treatment concentration of SLs. There was no significant difference in the proximate composition and fatty acids, except for an increase with increasing ethephon treatment concentrations. Depending on the ethephon treatment concentration, free amino acids increased to 1413.0, 1569.8, and 2100.4 mg/100 g, and water-soluble vitamins increased to 246.7, 244.7, and 501.6 mg/100 g. In particular, the functional substance isoflavone increased significantly to 1430.11, 7806.42, and 14,968.00 μg/g. Through this study, it was confirmed that the nutritional components and isoflavones of SLs increased according to the ethephon treatment concentration, a chemical inducer treatment agent. This can be used as a high-value-added biosubstance for raw materials for functional foods, cosmetics, and for natural drugs.

Keywords: digestive enzymatic inhibition activity; ethephon; isoflavone; soybean leaf; water-soluble vitamin.

Figure 1

Heatmap for analysis of fatty acids in soy leaves by ethephon treatment. (A) Saturated fatty acid; and (B) unsaturated fatty acid. Ethephon treatments at 0 μg/mL, SL1; ethephon treatments at 150 μg/mL, SL2; ethephon treatments at 300 μg/mL, SL3.

Figure 2

Heatmap for analysis of free amino acids in soybean leaves by ethephon treatment. (A) non-essential amino acid; and (B) essential amino acid. Ethephon treatments at 0 μg/mL, SL1; ethephon treatments at 150 μg/mL, SL2; ethephon treatments at 300 μg/mL, SL3.

Figure 3

Heatmap for analysis of water-soluble vitamins in soy leaves by ethephon treatment. Ethephon treatments at 0 μg/mL, SL1; ethephon treatments at 150 μg/mL, SL2; ethephon treatments at 300 μg/mL, SL3.

Figure 4

Comparison of total phenolic and total flavonoid contents in soy leaves by ethephon treatment. (A) Total phenolic contents; and (B) total flavonoid contents. All values are means of determination in three independent experiments. Different small letters correspond to the significant differences relating to the treatment concentration using Tukey’s multiple test (p < 0.05). Ethephon treatments at 0 μg/mL, SL1; ethephon treatments at 150 μg/mL, SL2; ethephon treatments at 300 μg/mL, SL3.

Figure 5

Typical isoflavone HPLC chromatogram of the 50% methanol extracts in soy leaves by ethephon treatment. (A) Standard; (B) treatment concentration of ethephon: 0 μg/mL; (C) treatment concentration of ethephon: 150 μg/mL; and (D) treatment concentration of ethephon: 300 μg/mL. One, Daidzin; 2, Genistin; 3, Manloyldaidzin; 4, Manloylgenistin; 5, Daidzein; and 6, Genistein.

Figure 6

Heatmap for analysis of isoflavones in soy leaves by ethephon treatment. Ethephon treatments at 0 μg/mL, SL1; ethephon treatments at 150 μg/mL, SL2; ethephon treatments at 300 μg/mL, SL3.

Figure 7

Comparison of the antioxidant activities in soy leaves by ethephon treatment. (A) DPPH radical scavenging activity; (B) ABTS radical scavenging activity; (C) hydroxyl radical scavenging activity; and (D) ferric reducing/antioxidant power. All values are present as the mean ± SD of pentaplicate determination. Different small letters correspond to the significant differences relating to the treatment concentration using Tukey’s multiple test (p < 0.05). Ethephon treatments at 0 μg/mL, SL1; ethephon treatments at 150 μg/mL, SL2; ethephon treatments at 300 μg/mL, SL3.

Figure 8

Comparison of the antioxidant and digestive enzymatic inhibition activities in soy leaves by ethephon treatment. (A) α–glucosidase inhibition activity; and (B) pancreatic lipase inhibition activity. All values are present as the mean ± SD of pentaplicate determination. Different small letters correspond to the significant differences relating to the treatment concentration using Tukey’s multiple test (p < 0.05). Ethephon treatments at 0 μg/mL, SL1; ethephon treatments at 150 μg/mL, SL2; ethephon treatments at 300 μg/mL, SL3.