Abstract
Introduction. Soy pulp, or okara, is a soy milk by-product. It contains a complex of valuable macro- and micronutrients, including fat-soluble vitamins. Recently, there has been a growing interest in replacing synthetic antioxidants with a mix of natural tocopherols. Soy beans and their by-products contain vitamin E and therefore can be used in food production, cosmetic, etc. 
 Study objects and methods. The present research featured soy pulp. The content of tocopherols in the soy product was determined by high performance liquid chromatography using Sigma Aldrich standards and corresponding calibration dependencies. The research also involved spectrophotometry for determining tocopherols in standard solutions followed by chromatographic separation using fluorimetric detection. 
 Results and discussion. To determine tocopherols in the okara, the test samples were treated with hexane. The filtered solution was exposed to low temperatures, after which the phases formed by centrifugation were separated. The samples were tested for all forms of tocopherols with the exception of β- and γ-forms. The chromatographic separation of the peaks of these forms was difficult due to the fact that their structural formulas were similar and differed only in the arrangement of methyl groups, i.e. the ortho- and paraposition. As a result, it was decided to determine the sum of the β- and γ-forms, which did not affect the objectivity of the analysis, since, according to published data, the content of β-tocopherol in soy products stays within 5%. 
 Conclusion. The proposed method for sample preparation made it possible to improve the separation of the lipid fraction, which had a positive effect on the results of the analysis. The method also determined not only the quantitative, but also the qualitative content of tocopherols in the product. This reduced the risk of malfunctioning chromatographic equipment: the method proved more economical in terms of labor and reagent use. The obtained results corresponded to the existing scientific data on the content of tocopherols in soy products. The content of tocopherols in soy okara was 109 mg%.
Highlights
Soy pulp, or okara, is a soy milk by-product
Conflict of interest The authors declare that there is no conflict of interest regarding the publication of this article
Maksimova Undergraduate of the Department of Food Technology and Biotechnology, Ivanovo State University of Chemistry and Technology, 7, Sheremetievskiy Ave., Ivanovo, 153000, Russia
Summary
Первоначально исследовали растворы стандартов (рис. 1) изомеров токоферола в гексане (регистрировали не менее 5 хроматограмм каждого раствора). 1) изомеров токоферола в гексане (регистрировали не менее 5 хроматограмм каждого раствора). Время выхода изомеров β- и γ-форм в данных условиях хроматографического анализа совпадало. Что β-форма содержится в сое в количестве до 5 % от суммы токоферолов, то было решено вести расчет суммарного количества β- и γ-форм в образце [28, 29]. Время удержания (Rt, мин) стандартов токоферолов представлено в таблице 4. Для других форм изомеров токоферола калибровочные зависимости идентичны. Поскольку температура замерзания гексана составляет –95 °С, а температуры застывания большинства триглицеридов – до –20 °С, то ожидали, что после выдержки гексанового раствора пробы соевого продукта на холоде (при –70 °С) омыляемая фракция липидной составляющей будет находиться в кристаллическом состоянии. При проведении подготовки пробы соевого образца для анализа выдерживанием измельченного материала в гексане с последующей фильтрацией и низкотемпературной выдержкой наблюдали четкое разделение фаз, образование дискретной жировой фазы.
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