Phenolic Composition and Antioxidant Activities of Soybean (Glycine max (L.) Merr.) Plant during Growth Cycle

Pier Peiretti,Francesco Gai,Ryszard Amarowicz,Michał Janiak,Magdalena Karamać,Erica Longato,Giorgia Meineri

doi:10.3390/agronomy9030153

Abstract

It is important to identify the growth stage at which the plant has the maximum antioxidant properties for the production of bioactive compounds from crops or agricultural by-products or for forage as a possible source of antioxidants in livestock. Therefore, we investigated the phenolic composition and antioxidant capacity of the aerial part of soybean at seven stages classified as vegetative stages (V5 and V6) and reproductive stages (R1, R2, R3, R4, and R5). Aqueous-methanol extracts were evaluated for their total phenolic content (TPC), ferric-reducing antioxidant power (FRAP), Trolox equivalent antioxidant capacity (TEAC), antioxidant activity as determined by photochemiluminescence assay (PCL-ACL), Fe2+ chelating ability, and antiradical activity against DPPH•. The extracts with the highest TPC content were obtained at stages V6 and R5. The phenolic compounds profile, as determined by DAD-HPLC, was characterized by 19 compounds, that differed significantly by growth stage (p < 0.05). Antioxidant tests showed significant differences among stages (p < 0.05). The lowest TEAC value was found for the R2 stage and the highest values for the R3 and R1 stages. FRAP values ranged from 623 to 780 μmol Fe2+/g extract. PCL-ACL values ranged from 516 to 560 μmol Trolox eq./g extract; Fe2+ chelation ability ranged from 36.5 to 51.7%. The highest antiradical activity against DPPH• was found in the extract from the V5 stage, which had the lowest EC50 value. The extracts of soybean plant can be used in pharmacy for the production of nutraceuticals by virtue of their good antioxidant activity and content of flavonols and other bioactive constituents.

Highlights

Soybean (Glycine max (L.) Merr.) is one of the most important plant proteins sources consumed by humans and animals
The results reported for the plants were the highest total phenolic content (TPC) for these three growth stages plus V5 (p < 0.05)
The TPC was lowest for extracts obtained from the R1–R3 stages; the lowest TPC values expressed on plant were observed for stages R2 and R3

Summary

Introduction

Soybean (Glycine max (L.) Merr.) is one of the most important plant proteins sources consumed by humans and animals. It has been demonstrated that health benefits can be derived from the antioxidant activities of some varieties of soybean, especially in their seed coat [12,13,14] or hulls, as alternative source of bioactive compounds [15]. Previous research found that the flavonoids in soy leaves are mainly kaempferol glycosides with only trace amounts of malonyl-genistin and genistin, whereas those in soybean are mainly isoflavone glycosides and derivatives with malonyl-genistin, which is the most abundant, followed by malonyl-glycitin, genistin, daidzin, daidzein, genistein, and glycitin in decreasing order [19]. Soybean seed is rich in glycosides (genistin, daidzin, glycitin) and malonyl-glycosides (malonyl-glycitin and malonyl-genistin)

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Conclusion