Promotion of Value-Added Uses of Soybeans
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Soybeans contain a wealth of health-promoting phytochemicals, the amounts of which are known to vary considerably across genotypes and growing conditions. The present work is dedicated to better understand these variations and to improve the methods for investigating soy phytochemicals. To address the first of these concerns, low-linolenic soybeans and colored seed coat soybeans were investigated for their health beneficial components, as well as their chemical and biological properties. A study of low-linolenic soybeans showed their similar antioxidant activity, total phenolics, and isoflavones to normal fatty acid soybeans. The potential for a different trend in tocopherols and lutein was observed between low-linolenic and regular fatty acid soybeans, but the limited study size prevented a definitive conclusion. This work was the basis for further studies on low-linolenic soybeans not included in this report. Subsequently, a study of eighteen soybeans of brown, green, yellow and black seed coat colors concluded that black seed coat soybeans had significantly higher scavenging activity against hydroxyl, peroxyl, and ABTS+ radicals. Black seed coat soybeans also contained higher total phenolic contents and isoflavones than the other colored soybeans, and were the only color to contain the anthocyanin cyanidin-3-glucoside. However, when soybean extracts were tested for their ability to prevent colon cancer cell proliferation, seed coat color and chemical composition were not necessarily predictive of an extracts' bioactivity. Lastly, a new analytical method was developed and validated for quantification of phytosterols, tocopherols and carotenoids, three separate classes of soy lipophilic phytochemicals, in a single extraction and HPLC run. A ternary, isocratic solvent system of acetonitrile, methanol and water (48:22.5:29.5, v/v/v) was used to achieve separation on a phenyl column. Evaporative light scattering detection (ELSD) was used to quantify beta-sitosterol, stigmasterol, campesterol, alpha-, delta- and gamma- tocopherols, while lutein was quantified with visible light absorption at 450 nm. This method offers a more efficient alternative to separate, individual methods for quantifying lutein, tocopherols and sterols in soybeans.