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<article article-type="research-article" dtd-version="1.3" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xml:lang="ru"><front><journal-meta><journal-id journal-id-type="publisher-id">mkgtu</journal-id><journal-title-group><journal-title xml:lang="ru">Новые технологии / New technologies</journal-title><trans-title-group xml:lang="en"><trans-title>New Technologies</trans-title></trans-title-group></journal-title-group><issn pub-type="ppub">2072-0920</issn><issn pub-type="epub">2713-0029</issn><publisher><publisher-name>МГТУ</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.47370/2072-0920-2024-20-1-50-62</article-id><article-id custom-type="elpub" pub-id-type="custom">mkgtu-732</article-id><article-categories><subj-group subj-group-type="heading"><subject>Research Article</subject></subj-group><subj-group subj-group-type="section-heading" xml:lang="ru"><subject>ПИЩЕВЫЕ СИСТЕМЫ И БИОТЕХНОЛОГИЯ ПРОДУКТОВ ПИТАНИЯ И БИОЛОГИЧЕСКИ АКТИВНЫХ ВЕЩЕСТВ</subject></subj-group><subj-group subj-group-type="section-heading" xml:lang="en"><subject>FOOD SYSTEMS AND BIOTECHNOLOGY OF FOOD AND BIOACTIVE SUBSTANCES</subject></subj-group></article-categories><title-group><article-title>Адаптация метода идентификации  и количественного определения моно-  и диацилглицеринов в растительных маслах</article-title><trans-title-group xml:lang="en"><trans-title>Adaptation of the method for identification  and quantification of mono- and diacylglycerols  in vegetable oils</trans-title></trans-title-group></title-group><contrib-group><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Жданов</surname><given-names>Д. Д.</given-names></name><name name-style="western" xml:lang="en"><surname>Zhdanov</surname><given-names>D. D.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Дмитрий Дмитриевич Жданов, ведущий инженер</p><p>350072, г. Краснодар, ул. Московская 2 Г</p></bio><bio xml:lang="en"><p>Dmitry D. Zhdanov, Leading engineer</p><p>350072, Krasnodar, 2 G Moskovskaya str.</p></bio><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Бутина</surname><given-names>Е. А.</given-names></name><name name-style="western" xml:lang="en"><surname>Butina</surname><given-names>E. A.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Елена Александровна  Бутина,  доктор технических наук, профессор</p><p>350072, г. Краснодар, ул. Московская 2 Г</p></bio><bio xml:lang="en"><p>Elena A. Butina , Dr Sci (Eng.), Professor</p><p>350072, Krasnodar, 2 G Moskovskaya str.</p></bio><email xlink:type="simple">butina_elena@mail.ru</email><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Дубровская</surname><given-names>И. А.</given-names></name><name name-style="western" xml:lang="en"><surname>Dubrovskaya</surname><given-names>I. A.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Ирина Александровна Дубровская, кандидат технических наук, доцент</p><p>350072, г. Краснодар, ул. Московская 2 Г</p></bio><bio xml:lang="en"><p>Irina A. Dubrovskaya, PhD (Eng.), Associate Professor</p><p>350072, Krasnodar, 2 G Moskovskaya str.</p></bio><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Герасименко</surname><given-names>Е. О.</given-names></name><name name-style="western" xml:lang="en"><surname>Gerasimenko</surname><given-names>E. O.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Евгений Олегович Герасименко , доктор технических наук, профессор</p><p>350072, г. Краснодар, ул. Московская 2 Г</p></bio><bio xml:lang="en"><p>Evgeniy O. Gerasimenko, Dr Sci (Eng.), Professor</p><p>350072, Krasnodar, 2 G Moskovskaya str.</p></bio><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Шаззо</surname><given-names>А. Ю.</given-names></name><name name-style="western" xml:lang="en"><surname>Shazzo</surname><given-names>A. Y.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Аслан Юсуфович Шаззо, доктор технических наук, профессор</p><p>350072, г. Краснодар, ул. Московская 2 Г</p></bio><bio xml:lang="en"><p>Aslan Yu. Shazzo, Dr Sci (Eng.), Professor</p><p>350072, Krasnodar, 2 G Moskovskaya str.</p></bio><xref ref-type="aff" rid="aff-1"/></contrib></contrib-group><aff-alternatives id="aff-1"><aff xml:lang="ru">ФГБОУ ВО «Кубанский государственный технологический университет»<country>Россия</country></aff><aff xml:lang="en">Federal State Budgetary Educational Institution of Higher Education «Kuban State Technological University»<country>Russian Federation</country></aff></aff-alternatives><pub-date pub-type="collection"><year>2024</year></pub-date><pub-date pub-type="epub"><day>15</day><month>04</month><year>2024</year></pub-date><volume>20</volume><issue>1</issue><fpage>50</fpage><lpage>62</lpage><permissions><copyright-statement>Copyright &amp;#x00A9; Жданов Д.Д., Бутина Е.А., Дубровская И.А., Герасименко Е.О., Шаззо А.Ю., 2024</copyright-statement><copyright-year>2024</copyright-year><copyright-holder xml:lang="ru">Жданов Д.Д., Бутина Е.А., Дубровская И.А., Герасименко Е.О., Шаззо А.Ю.</copyright-holder><copyright-holder xml:lang="en">Zhdanov D.D., Butina E.A., Dubrovskaya I.A., Gerasimenko E.O., Shazzo A.Y.</copyright-holder><license license-type="creative-commons-attribution" xlink:href="https://creativecommons.org/licenses/by/4.0/" xlink:type="simple"><license-p>This work is licensed under a Creative Commons Attribution 4.0 License.</license-p></license></permissions><self-uri xlink:href="https://newtechology.mkgtu.ru/jour/article/view/732">https://newtechology.mkgtu.ru/jour/article/view/732</self-uri><abstract><p>Работа посвящена исследованиям по адаптации и внедрению метода определения моно- и диацилглицеринов в растительных маслах. Актуальность исследований определяется введением с 2025 года нормирования монохлорпропандиолов и глицидола в растительных маслах и некоторых видах масложировой продукции. По данным научной литературы моно- и диацилглицерины, образующиеся в период созревания масличных семян под воздействием фермента – липазы, являются прекурсорами монохлорпропандиолов и глицидола, которые, в свою очередь, по данным всемирной организации здравоохранения, относятся к канцерогенным веществам. Рассмотрены некоторые наиболее вероятные механизмы образования контаминантов из моно- и диацилглицеринов, исходя из которых основным источником глицидиловых эфиров являются диацилглицерины, а источником монохлорпропандиолов – моно-ацилглицерины. Важным фактором, влияющим на скорость и полноту протекания описанных реакций, является присутствие в системе молекул воды, ионов хлора, протонов водорода, а также высокие температуры. Катализаторами таких побочных реакций являются тяжелые металлы, в том числе их соли. Таким образом, для реализации эффективных мероприятий по контролю образования контаминантов  в масле важно иметь полную картину показателей качества исходного сырья и, прежде всего, данные по содержанию моно- и диацилглицеринов, методы определения которых в лабораторной практике РФ отсутствуют.</p><p>Целью работы является разработка метода для количественного определения моно- и диацилглицеринов в растительных маслах.</p><p>В результате исследований усовершенствована методика подготовки проб, определены калибровочные зависимости с применением внутреннего стандарта, предложена методика идентификации и количественного анализа, основанная на использовании метода газовой хроматографии с пламенно-ионизационным детектором и применением высокотемпературной капиллярной колонки. Проведены работы по верификации и определены метрологические характеристики предлагаемого метода. Метод апробирован на реальных объектах – различных видах растительных масел.</p></abstract><trans-abstract xml:lang="en"><p>The article presents the research on the adaptation and implementation of a method for determining mono- and diacylglycerols in vegetable oils. The relevance of the research is determined by the introduction of standardization of monochloropropanediols and glycidol in vegetable oils and some types of fat and oil products since 2025. According to the scientific literature, mono- and diacylglycerols, formed during the ripening of oil seeds under the influence of the enzyme lipase, are precursors of monochloropropanediols and glycidol, which, in turn, according to the World Health Organization, are carcinogenic substances. Some of the most probable mechanisms for the formation of contaminants from mono- and diacylglycerols have been considered; according to them diacylglycerols are considered to be the main source of glycidyl ethers, and monoacylglycerols  are that of  monochloropropanediols. An important factor influencing the speed and completeness of the described reactions is the presence in the system of water molecules, chlorine ions, hydrogen protons, as well as high temperatures. Catalysts for such side reactions are heavy metals, including their salts. Thus, in order to implement effective measures to control the formation of contaminants in oil, it is important to have a complete picture of the quality indicators of the feedstock and, above all, data on the content of mono- and diacylglycerols, methods for determining which are not available in laboratory practice in the Russian Federation.</p><p>The goal of the research is to develop a method for the quantitative determination of mono- and diacylglycerols in vegetable oils.</p><p>As a result of the research, the sample preparation method has been improved, calibration dependencies have been determined using an internal standard, and an identification and quantitative analysis technique has been proposed, on the basis of gas chromatography with a flame ionization detector and the use of a high-temperature capillary column. Verification work has been carried out and the metrological characteristics of the proposed method have been determined. The method has been tested on real objects – various types of vegetable oils.</p></trans-abstract><kwd-group xml:lang="ru"><kwd>моноацилглицерины</kwd><kwd>диацилглицерины</kwd><kwd>растительное масло</kwd><kwd>идентификация</kwd><kwd>количественный анализ</kwd><kwd>газовая хроматография</kwd><kwd>пламенно-ионизационный детектор</kwd><kwd>пробоподготовка</kwd><kwd>адаптация методики</kwd></kwd-group><kwd-group xml:lang="en"><kwd>monoacylglycerols</kwd><kwd>diacylglycerols</kwd><kwd>vegetable oil</kwd><kwd>identification</kwd><kwd>quantitative analysis</kwd><kwd>gas chromatography</kwd><kwd>flame ionization detector</kwd><kwd>sample preparation</kwd><kwd>method adaptation</kwd></kwd-group><funding-group xml:lang="ru"><funding-statement>Исследования выполнены в рамках госзадания Минобрнауки РФ,  проект №  FZEZ-2023-0004</funding-statement></funding-group><funding-group xml:lang="en"><funding-statement>The research was carried out within the framework of the state assignment of the Ministry  of Education and Science of the Russian Federation, project No. FZEZ-2023-0004</funding-statement></funding-group></article-meta></front><back><ref-list><title>References</title><ref id="cit1"><label>1</label><citation-alternatives><mixed-citation xml:lang="ru">Моргунова Е., Бабодей В, Пчельникова А. Глицидиловые эфиры жирных кислот. Мировой тренд в безопасности продуктов питания. Наука, питание и здоровье: сборник научных трудов. Минск: Белорусская наука; 2021: 400-407.</mixed-citation><mixed-citation xml:lang="en">Morgunova E., Babodey V, Pchelnikova A. Glycidyl esters of fatty acids. Global trend in food safety. Science, nutrition and health: a collection of scientific papers. Minsk: Belarusian Science; 2021: 400-407. [in Russian]</mixed-citation></citation-alternatives></ref><ref id="cit2"><label>2</label><citation-alternatives><mixed-citation xml:lang="ru">Chen H., Tsao C.H., Chang Y.H. et al. Occurrence of thermally induced glycidyl esters and 3-monochloropropane-1,2-diol esters in refined oils and pressed oils manufactured by different processes and associated with human health risks in Taiwan. Food chemistry. 2021; 360: 130053.</mixed-citation><mixed-citation xml:lang="en">Chen H., Tsao C.H., Chang Y.H. et al. Occurrence of thermally induced glycidyl esters and 3-monochloropropane-1,2-diol esters in refined oils and pressed oils manufactured by different processes and associated with human health risks in Taiwan. Food chemistry. 2021; 360:130053.</mixed-citation></citation-alternatives></ref><ref id="cit3"><label>3</label><citation-alternatives><mixed-citation xml:lang="ru">Cheng W.W., Liu G.Q., Wang L.Q. et al. Glycidyl fatty acid esters in refined edible oils: a review on formation, occurrence, analysis, and elimination methods. Comp. Reviews in Food Sc. and, Food Saf. 2017; 16: 263-281.</mixed-citation><mixed-citation xml:lang="en">Cheng W.W., Liu G.Q., Wang L.Q. et al. Glycidyl fatty acid esters in refined edible oils: a review on formation, occurrence, analysis, and elimination methods. Comp. Reviews in Food Sc. and, Food Saf. 2017; 16: 263-281.</mixed-citation></citation-alternatives></ref><ref id="cit4"><label>4</label><citation-alternatives><mixed-citation xml:lang="ru">Далабаев А.Б., Альжаскина Н.Е. Контроль содержания глицидиловых эфиров в масложировой продукции: вызов современности. Инновационные процессы в пищевых технологиях: наука и практика: материалы Международной научно-практической конференции (Москва, 16-17 февр. 2023 г.). М.; 2023: 168.</mixed-citation><mixed-citation xml:lang="en">Dalabaev A.B., Alzhaskina N.E. Control of glycidyl ether content in fat and oil products: a modern challenge. Innovative processes in food technologies: science and practice: materials of the International Scientific and Practical Conference (Moscow, February 16-17, 2023). M.; 2023: 168. [in Russian]</mixed-citation></citation-alternatives></ref><ref id="cit5"><label>5</label><citation-alternatives><mixed-citation xml:lang="ru">Changxia Sun, Ni Wu, Shunli Kou et al. Occurrence, formation mechanism, detection methods, and removal approaches for chloropropanols and their esters in food: An updated systematic review. Food Chemistry: X 17. 2023; 100529: 1-10.</mixed-citation><mixed-citation xml:lang="en">Changxia Sun, Ni Wu, Shunli Kou et al. Occurrence, formation mechanism, detection methods, and removal approaches for chloropropanols and their esters in food: An updated systematic review. Food Chemistry: X 17. 2023; 100529: 1-10.</mixed-citation></citation-alternatives></ref><ref id="cit6"><label>6</label><citation-alternatives><mixed-citation xml:lang="ru">Wenzl T., Lachenmeier D.W., Gkmen, V. Analysis of heat-induced contaminants (acrylamide, chloropropanols and furan) in carbohydrate-rich food. Analytical and Bioanalytical Chemistry. 2007; 389(1): 119-137.</mixed-citation><mixed-citation xml:lang="en">Wenzl T., Lachenmeier D.W., Gkmen, V. Analysis of heat-induced contaminants (acrylamide, chloropropanols and furan) in carbohydrate-rich food. Analytical and Bioanalytical Chemistry. 2007; 389(1): 119-137.</mixed-citation></citation-alternatives></ref><ref id="cit7"><label>7</label><citation-alternatives><mixed-citation xml:lang="ru">Shimizu M., Vosmann K., Matthus B. Generation of 3-monochloro-1,2-propanediol and related materials from tri-, di-, and monoolein at deodorization temperature. European Journal of Lipid Science and Technology. 2012; 114(11): 1268-1273.</mixed-citation><mixed-citation xml:lang="en">Shimizu M., Vosmann K., Matthus B. Generation of 3-monochloro-1,2-propanediol and related materials from tri-, di-, and monoolein at deodorization temperature. European Journal of Lipid Science and Technology. 2012; 114(11): 1268-1273.</mixed-citation></citation-alternatives></ref><ref id="cit8"><label>8</label><citation-alternatives><mixed-citation xml:lang="ru">Smidrkal J., Tesarova M., Hradkova I. Mechanism of formation of 3-chloropropan-1,2-diol (3-MCPD) esters under conditions of the vegetable oil refining. Food Chemistry. 2016; 211: 124-129.</mixed-citation><mixed-citation xml:lang="en">Smidrkal J., Tesarova M., Hradkova I. Mechanism of formation of 3-chloropropan-1,2-diol (3-MCPD) esters under conditions of the vegetable oil refining. Food Chemistry. 2016; 211: 124-129.</mixed-citation></citation-alternatives></ref><ref id="cit9"><label>9</label><citation-alternatives><mixed-citation xml:lang="ru">Yu H.W., Muhamad H., Abas F. et al. Effects of temperature and NaCl on the formation of 3-MCPD esters and glycidyl esters in refined, bleached and deodorized palm olein during deep-fat frying of potato chips. Food Chemistry. 2017; 219: 126-130.</mixed-citation><mixed-citation xml:lang="en">Yu H.W., Muhamad H., Abas F. et al. Effects of temperature and NaCl on the formation of 3-MCPD esters and glycidyl esters in refined, bleached and deodorized palm olein during deep-fat frying of potato chips. Food Chemistry. 2017; 219: 126-130.</mixed-citation></citation-alternatives></ref><ref id="cit10"><label>10</label><citation-alternatives><mixed-citation xml:lang="ru">Rahn A., Yaylayan V.A. Thermal degradation of sucralose and its potential in generating chloropropanols in the presence of glycerol. Food Chemistry. 2010; 118(1): 56-61.</mixed-citation><mixed-citation xml:lang="en">Rahn A., Yaylayan V.A. Thermal degradation of sucralose and its potential in generating chloropropanols in the presence of glycerol. Food Chemistry. 2010; 118(1): 56-61.</mixed-citation></citation-alternatives></ref><ref id="cit11"><label>11</label><citation-alternatives><mixed-citation xml:lang="ru">Hamlet C.G., Sadd P.A., Gray D.A. Generation of monochloropropanediols (MCPDs) in model dough systems. 1. Leavened doughs. Journal of Agricultural and Food Chemistry. 2004; 52(7): 2059-2066.</mixed-citation><mixed-citation xml:lang="en">Hamlet C.G., Sadd P.A., Gray D.A. Generation of monochloropropanediols (MCPDs) in model dough systems. 1. Leavened doughs. Journal of Agricultural and Food Chemistry. 2004; 52(7): 2059-2066.</mixed-citation></citation-alternatives></ref><ref id="cit12"><label>12</label><citation-alternatives><mixed-citation xml:lang="ru">Destaillats F. et al. Glycidyl esters in refined palm (Elaeis guineensis) oil and related fractions. Part I: Formation mechanism. Food Chemistry. 2012; 131(4): 1391-1398.</mixed-citation><mixed-citation xml:lang="en">Destaillats F. et al. Glycidyl esters in refined palm (Elaeis guineensis) oil and related fractions. Part I: Formation mechanism. Food Chemistry. 2012; 131(4): 1391-1398.</mixed-citation></citation-alternatives></ref><ref id="cit13"><label>13</label><citation-alternatives><mixed-citation xml:lang="ru">IARC (World Health Organization: International Agency for Research on Cancer) Glycidol IARC monographs on the evaluation of the carcinogenic risk of chemicals to humans. 2000; 77: 469-486.</mixed-citation><mixed-citation xml:lang="en">IARC (World Health Organization: International Agency for Research on Cancer) Glycidol IARC monographs on the evaluation of the carcinogenic risk of chemicals to humans. 2000; 77: 469-486.</mixed-citation></citation-alternatives></ref><ref id="cit14"><label>14</label><citation-alternatives><mixed-citation xml:lang="ru">Sawada S. et al. Proteomic analysis of 3-MCPD and 3-MCPD dipalmitate toxicity in rat testis. Food Chem. Toxicol. 2015; 83: 84-92.</mixed-citation><mixed-citation xml:lang="en">Sawada S. et al. Proteomic analysis of 3-MCPD and 3-MCPD dipalmitate toxicity in rat testis. Food Chem. Toxicol. 2015; 83: 84-92.</mixed-citation></citation-alternatives></ref><ref id="cit15"><label>15</label><citation-alternatives><mixed-citation xml:lang="ru">Plank C., Lorbeer E. Simultaneous determination of glycerol, and mono-, di-and triglycerides in vegetable oil methyl esters by capillary gas chromatography. Journal of chromatography A. 1995; 697(1/2): 461-468.</mixed-citation><mixed-citation xml:lang="en">Plank C., Lorbeer E. Simultaneous determination of glycerol, and mono-, di-and triglycerides in vegetable oil methyl esters by capillary gas chromatography. Journal of chromatography A. 1995; 697(1/2): 461-468.</mixed-citation></citation-alternatives></ref><ref id="cit16"><label>16</label><citation-alternatives><mixed-citation xml:lang="ru">Goh E.M., Timms R.E. Determination of mono-and diglycerides in palm oil, olein and stearin. Journal of the American Oil Chemists’ Society. 1985; 62(4): 730-734.</mixed-citation><mixed-citation xml:lang="en">Goh E.M., Timms R.E. Determination of mono-and diglycerides in palm oil, olein and stearin. Journal of the American Oil Chemists' Society. 1985; 62(4): 730-734.</mixed-citation></citation-alternatives></ref><ref id="cit17"><label>17</label><citation-alternatives><mixed-citation xml:lang="ru">Соколова Е.В., Султанова Я.М., Ахметова Т.И. Определение моноглицеридов и свободного глицерина в товарном продукте «Моностеарат глицерина» [Электронный ресурс]. Вестник Казанского технологического университета. 2016; 24. URL: https://cyberleninka.ru/article/n/opredelenie-monoglitseridov-i-svobodnogo-glitserina-v-tovarnom-produkte-monostearat-glitserina (дата обращения: 12.12.2023).</mixed-citation><mixed-citation xml:lang="en">Sokolova E.V., Sultanova Y.M., Akhmetova T.I. Determination of monoglycerides and free glycerol in the commercial product «Glycerol monostearate» [Electronic resource]. Bulletin of Kazan Technological University. 2016; 24. URL: https://cyberleninka.ru/article/n/opredelenie-monoglitseridov-i-svobodnogo-glitserina-v-tovarnom-produkte-monostearat-glitserina (date of  access: 12.12.2023). [in Russian]</mixed-citation></citation-alternatives></ref><ref id="cit18"><label>18</label><citation-alternatives><mixed-citation xml:lang="ru">McNair H.M., Miller J.M., Snow N.H. Basic gas chromatography. John Wiley &amp; Sons, 2019.</mixed-citation><mixed-citation xml:lang="en">McNair H.M., Miller J.M., Snow N.H. Basic gas chromatography. John Wiley &amp; Sons, 2019.</mixed-citation></citation-alternatives></ref><ref id="cit19"><label>19</label><citation-alternatives><mixed-citation xml:lang="ru">РМГ 61-2010 Государственная система обеспечения единства измерений. Показатели точности, правильности прецизионности методик количественного химического анализа. Методы оценки. М.: Стандартинформ; 2013.</mixed-citation><mixed-citation xml:lang="en">RMG 61-2010 State system for ensuring the uniformity of measurements. Indicators of accuracy, correctness of precision of methods of quantitative chemical analysis. Assessment methods. M.: Standartinform; 2013. [in Russian]</mixed-citation></citation-alternatives></ref><ref id="cit20"><label>20</label><citation-alternatives><mixed-citation xml:lang="ru">Риски для здоровья человека, связанные с наличием 3- и 2-монохлорпропандиолов, их эфиров жирных кислот и глицедиловых эфиров жирных кислот в пищевых продуктах. Масла и жиры. 2018; 7/8: 9.</mixed-citation><mixed-citation xml:lang="en">Risks to human health associated with the presence of 3- and 2-monochloropropanediols, their fatty acid esters and fatty acid glycedyl esters in foods. Oils and fats. 2018; 7/8: 9. [in Russian]</mixed-citation></citation-alternatives></ref></ref-list><fn-group><fn fn-type="conflict"><p>The authors declare that there are no conflicts of interest present.</p></fn></fn-group></back></article>
