TECHNOLOGIES FOR PRODUCING SOLID FATS FREE OR LOW IN TRANS FATTY ACIDS: METHODS AND COMPARATIVE ANALYSIS OF FATTY ACID COMPOSITION

ABSTRACT

This article presents the fatty acid composition of natural and modified solid fats, along with a comparative analysis thereof. Palm oil was used as a natural solid fat, while partially hydrogenated vegetable oil, interesterified fat, cottonseed palmitin, and glycerinolyzed cottonseed oil served as modified solid fats. Analysis of the fatty acid composition of the fats established that palm oil, coconut oil, cottonseed palmitin, and glycerinolyzed cottonseed oil contain no trans isomers of fatty acids, whereas the presence of trans acids was detected in all other solid fat samples. The ratio of saturated to unsaturated fatty acids in the fat samples varied within ranges from 2:3 to 3:7.

АННОТАЦИЯ

В статье представлен состав жирных кислот природных и модифицированных твердых жиров, а также проведен их сравнительный анализ. В качестве природного твердого жира использовано пальмовое масло, в качестве модифицированных твердых жиров – частично гидрогенизированное растительное масло, переэтерифицированный жир, хлопковый пальмитин и глицеринолизованное хлопковое масло. При анализе жирнокислотного состава жиров установлено, что пальмовое масло, кокосовое масло, хлопковый пальмитин и глицеринолизованное хлопковое масло не содержат трансизомеров жирных кислот, тогда как во всех остальных образцах твердых жиров обнаружено наличие транскислот. Соотношение насыщенных и ненасыщенных жирных кислот в образцах жиров варьировалось в интервалах от 2:3 до 3:7.

Keywords: cottonseed oil, fatty acid composition, hydrogenation, interesterification, glycerolysis, fractionation, trans fatty acids, solid fat content (SFC).

Ключевые слова: хлопковое масло, жирнокислотный состав, гидрогенизация, переэтерификация, глицеролиз, фракционирование, трансизомеры жирных кислот, содержание твердых триглицеридов (СТТ).

INTRODUCTION

Since the last decades of the past century, an increase in the incidence of cardiovascular diseases, overweight, diabetes mellitus, and similar pathologies has been observed among the population [1, 2, 21, 22]. Fats contained in food products, particularly solid fats, are considered one of the primary factors contributing to this trend, alongside others [3, 4]. To substantiate this factor, numerous medical professionals and researchers in the field of food technology have conducted scientific investigations [5, 6]. As a result of these studies, it was concluded that saturated fatty acids, trans isomers of fatty acids, oxidized fatty acids, and other chemically modified fatty acids pose a risk to the human organism [7, 8]. Subsequently, as the scope of research expanded, it was noted that the presence of unsaturated fatty acids alone is insufficient; it was emphasized that fatty acids must be present in specific ratios, and their optimal proportions were established [9, 10]. Despite this, no definitive consensus has been reached to date regarding the beneficial or harmful effects of particular fatty acids on the human body [11, 12]. This is attributed to the fact that each fatty acid possesses unique physical, chemical, rheological, biological, and other properties and may perform one or multiple functions in the biological processes occurring within the human organism [13, 14, 15, 16].

From a technological perspective, the degree of saturation of fatty acids determines the physical properties of lipids, particularly their melting and solidification points, hardness, and rheological characteristics [17]. As the mass fraction of saturated fatty acids in the lipid composition increases, a rise in their melting and solidification temperatures is observed. However, this is also directly dependent on the positions that the fatty acids occupy on the glycerol backbone [18]. Furthermore, the bonds between triglyceride molecules, their interaction mechanisms, crystallization state, and other factors exert an influence [19]. Taking these factors and properties into account, various methods for fat modification have been developed [20]. This article presents the results of a study investigating the fatty acid composition, melting point, and hardness of cottonseed oil modified by different methods, and outlines the conclusions drawn.

RESEARCH METHODS

First-grade cottonseed oil with the following physicochemical parameters was used as the raw material: acid value – 0.18 mg KOH/g; moisture and volatile matter content – 0.12%; color – 6 red units; peroxide value – 3.8 mmol O; iodine value – 108.9 g I₂/100g.

For the partial hydrogenation of cottonseed oil, the catalyst Nysosel 210 was used; for complete hydrogenation, Nysosel 820 was employed; and for interesterification, sodium methylate was utilized.

Conditions for the partial hydrogenation of cottonseed oil: temperature – 180°C; catalyst amount – 0.2% by weight of oil; process duration – 100 minutes; hydrogen pressure – 0.3 MPa. Conditions for the complete hydrogenation of cottonseed oil: temperature – 220°C; catalyst amount – 0.3% by weight of oil; process duration – 200 minutes; hydrogen pressure – 1.0 MPa.

Conditions for the interesterification of a blend of fully hydrogenated cottonseed oil and liquid cottonseed oil in a 20:80 ratio: temperature – 80°C; catalyst amount – 0.8% by weight of oil; process duration – 100 minutes; pressure – 0.004 MPa.

Conditions for the fractionation of cottonseed oil: temperature – 6°C; process duration – 24 hours. Conditions for the interesterification (glycerolysis) of a cottonseed oil and glycerol blend in a 10:1 ratio: temperature – 100°C; catalyst amount – 0.5% by weight of oil; process duration – 60 minutes; hydrochloric acid concentration – 20%; alkali concentration – 5%; pressure – 0.004 MPa; centrifugation speed for fat phase separation – 2000 rpm; centrifugation duration – 10 minutes.

The melting point of fats and oils was determined using the capillary method. The hardness of fats and oils was determined using a Kamensky apparatus. The fatty acid composition of fats and oils was determined by gas-liquid chromatography using a Shimadzu GC2030 gas chromatograph fitted with a 100 m x 0.25 mm x 0.2 µm column, after preparation of their methyl esters.

RESEARCH RESULTS

In the research work, cottonseed oil was fractionated to obtain cottonseed palmitin, partially hydrogenated to produce hydrogenated fat, and fully hydrogenated to obtain a solid fat, which was then subjected to interesterification with liquid cottonseed oil to obtain interesterified fat. Additionally, cottonseed oil was interesterified with glycerol to produce glycerolized fat. The obtained solid fats were analyzed for iodine value, acid value, melting point, hardness, and fatty acid composition.

During the analysis of the fat samples, the melting point was determined in accordance with GOST ISO 6321-2019. For this purpose, the fat sample to be analyzed was drawn into a glass capillary with an inner diameter of 1.0-1.2 mm, an outer diameter of 1.3-1.6 mm, and a wall thickness of 0.15-0.20 mm, to a length of 10-15 mm. The melting point was then determined by slowly changing the temperature in an aqueous medium. The acid value was determined according to GOST R 50457-92, expressed as the amount of potassium hydroxide (KOH), in milligrams, required to neutralize the free fatty acids in 1 g of the sample. During the analysis, the sample was dissolved in a solvent and examined by titration with an alkali solution. The result obtained is a crucial indicator for assessing the quality, freshness, and degree of hydrolytic deterioration of the fat.

The iodine value was determined in accordance with GOST ISO 3961-2020. The iodine value characterizes the amount of unsaturated fatty acids in the product and is expressed as the mass of iodine, in grams, that is taken up by 100 g of the product. In the test procedure, the sample is treated with a specific reagent, the excess iodine is determined by titration, and the result is calculated. The hardness of the fats was tested according to GOST 52179-2003. The hardness parameter is determined through sample preparation under specified conditions and a specific measurement method. The obtained results serve to assess the consistency, plasticity, and technological properties of the fat. This indicator is significant for determining the processability and quality of the product.

Table 1.

Physicochemical parameters of fats obtained by modification of cottonseed oil

As can be seen from the data presented in Table 1, the modification of cottonseed oil by four different methods enables the production of solid fats. It was established that the melting points of the obtained fats have similar values, with the exception of the fractionation product, whose melting point is lower compared to the samples obtained by other methods. This difference is explained by the limited possibilities for controlling the fractionation process, as well as by the fact that this method allows for the isolation of only those triglycerides that possess natural hardness, which complicates the targeted modification of the final product's melting point. In contrast to fractionation, alternative modification methods offer extensive opportunities for obtaining fats with a desired melting point by regulating technological parameters, the composition of the raw material, and other factors. Depending on their melting point, the obtained fats may be recommended for use in the production of margarines, spreads, and bakery fats.

When the hardness values of the obtained fats were analyzed, the lowest value was observed in the fat obtained by the fractionation method. As noted above, this represents the natural hardness of the extracted fat. In other modification methods, the hardness of the fats was found to be 2-3 times higher. This is explained by changes in the mass fractions of fatty acids in their composition. Therefore, in subsequent experiments, the fatty acid composition of the obtained fats was analyzed. The fatty acid composition was analyzed in accordance with GOST 31663-2012. During the experiment, analyses were carried out using a Shimadzu (Nexis GC-2030) chromatograph with an FID detector, an SP-2560 column (100 m × 0.25 mm × 0.2 μm), and Supelco 37 FAME Mix as the standard. The obtained results are presented in Table 2.

Table 2.

Fatty acid composition of modified fats

As follows from the data presented in Table 2, all studied fat samples, being derived from cottonseed oil, are characterized by an identical set of fatty acids. The differences between the samples lie exclusively in the ratio of the mass fractions of individual fatty acids. It was established that the maximum content of palmitic acid is observed in the cottonseed palmitin sample, while the highest concentration of stearic acid is recorded in the interesterified fat. This particularity accounts for the increased total content of saturated fatty acids in these two samples. The highest content of unsaturated fatty acids was noted in the samples of partially hydrogenated and glycerinolyzed fats. Meanwhile, the maximum concentration of oleic acid is characteristic of partially hydrogenated fat, whereas the highest content of linoleic acid was found in the glycerolises product.

The fatty acid composition directly influenced the iodine values of the obtained fats. However, taking into account the absence of a direct correlation between the fatty acid composition and indicators such as melting point and hardness, an additional analysis of the triglyceride composition of the studied samples was conducted.

According to the results obtained, the mass fraction of triglycerides reaches maximum values in the samples of cottonseed palmitin and partially hydrogenated fat. In the interesterified fat, a slight decrease in triglyceride content is observed, accompanied by a significant increase in the number of diglycerides. The most pronounced changes were recorded in the glycerinolyzed fat sample, where the triglyceride content sharply decreases (by approximately one third) with a corresponding increase in the proportion of di- and monoglycerides. This transformation of the molecular composition directly affects the crystallization processes, which positively influences the melting temperature characteristics and hardness indicators of the final product. When developing formulations for margarines, spreads, bakery fats, and other fatty products, along with melting point and hardness, the indicators of solid triglyceride content (SFC) are also considered as fundamental criteria. In this regard, an analysis of the solid triglyceride content in the obtained modified fats was carried out, followed by a comparison with the corresponding indicators of palm oil. The obtained results are presented in Figure 1.

As follows from the data presented in Figure 1, the solid triglyceride content (STC) indicators of modified fats derived from cottonseed oil are inferior to the corresponding values of palm oil. Palm oil is characterized by the highest STC indicators across the entire studied temperature range, which is due to the increased content of saturated fatty acids in its composition. Among the modified fats, the partially hydrogenated fat sample demonstrates the highest STC values, which is explained not only by the increased content of saturated fatty acids but also by the presence of trans isomers of fatty acids that contribute to the formation of a stable crystalline structure.

Figure 1. Solid triglyceride content (STC) indicators in modified fats and palm oil

The STC data for the selected modified fats were obtained using an NMR instrument in accordance with GOST 31757-2012 (direct method). The remaining studied samples are characterized by similar STC values, which are at a relatively low level. This particularity is due to the predominance of unsaturated fatty acids in their composition. In the case of glycerolized fat, despite the relatively high melting point and hardness indicators, resulting from the crystallization of diglycerides, the STC values are the lowest among all studied samples. This indicates that the crystallization processes of diglycerides do not significantly influence the formation of the STC indicator, which reflects the content of solid triglycerides specifically.

It is important to note that all studied modified fats are characterized by low STC values at a temperature of 35°C, which ensures their complete melting in the oral cavity and, consequently, favourable organoleptic properties. In contrast, palm oil retains a relatively high content of solid triglycerides at this temperature, which determines its lower melting ability in the oral cavity and may negatively affect the organoleptic characteristics of finished products.

CONCLUSION

As a result of the conducted research, it has been established that the modification of vegetable oils, particularly cottonseed oil, by four different methods allows for the production of fats suitable for use in the manufacture of margarines, spreads, and confectionery products. It has been shown that all studied modification methods lead to an increase in the hardness and melting point of the original oil; however, the mechanisms of these changes differ depending on the method used.

In partial hydrogenation, the increase in hardness is due to the rise in the mass fraction of saturated fatty acids, as well as the presence of trans isomers. In the case of interesterified fat, the increase in hardness is primarily associated with the increased content of saturated fatty acids. The glycerolysis product is characterized by a different mechanism: the increase in hardness is achieved by increasing the mass fraction of di- and monoglycerides, which contribute to the stabilization of the fat's crystalline structure.

The studied samples of modified fats differ in their fatty acid composition, which has a direct impact on their rheological properties and, consequently, on the quality characteristics of the products derived from them.

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