Phenolic Compounds of Soybean Seeds from Two European Countries and Their Antioxidant Properties

Abstract

There is only a small acreage of planted soybeans in northern Europe, as the global production of this crop is mainly dictated by the warmer temperatures needed for bountiful yields. The defense response of soybean plants to a cold climate entails the secretion of specific compounds which help mitigate oxidative stress, i.e., antioxidants, including phenolic compounds. The objective of this study was to examine differences in the concentrations of phenolic compounds, their antioxidant properties, and the concentration of key isoflavones (namely genistein, daidzein, malonyl daidzein, malonyl genistein, and daidzin) in the seeds of six soybean cultivars from two different regions of Europe, namely Poland and France. The total phenolic contents, isoflavone levels, and in vitro antioxidant capacities of soybean seeds from most of the investigated cultivars of northeast Europe were found to be greater than those from southwest Europe. The phenolic compounds of seed extracts are primarily responsible for the free-radical scavenging of soybeans. Factors regulating the production of phenolic compounds in the seeds have not been thoroughly elucidated. Hence, the results presented in this paper can be useful in the selection of soybean cultivars with higher levels of seed phenolics, because of their beneficial impact on human health and on the soybean's defense mechanism against plant stresses.

Keywords: antioxinants; isoflavones; phenolic compounds; seeds; soybean.

Figure 1

The capability to scavenge the free radical DPPH^• by extracts from soybean seeds (A). Half-maximal effective concentration (EC₅₀) of extracts from soybean seeds to scavenge DPPH^• (B). Means with the same letters (a,b,c,d,e,f) are not significantly different (p < 0.05). Data represent the mean ± SD of four replicates. Varieties from France are marked with an asterisk (*), while the other varieties come from Poland.

Figure 2

Chromatogram of resolved isoflavones in seed extracts of the soybean cultivar Aldana. The retention times of identified compounds were as follows: 1-daidzein-26 min; 2-genistein-33 min; 3-malonyldaidzein-34 min; 4-malonylgenistein-39 min; 5-daidzin-42 min; and 6-genistin-48 min.