INFLUENCE OF REFINING PROCESSES ON PHOSPHOLIPID CONTENT OF SUNFLOWER OIL

ABSTRACT

The article discusses the results of the influence of each stage of refining processes: water degumming, neutralization, bleaching, and deodorization on the phosphorus content in sunflower extracted and pressed oils. The impact of each stage of the refining process on the phosphorus content of the resulting oil was determined. It was found that water degumming reduces the phosphorus content in the oil by up to 80%, but this method is not sufficiently effective.

 The insufficient effectiveness of water degumming of sunflower oil necessitates a reduction in phosphorus content during further oil processing. It should be noted that the neutralization and bleaching processes reduce the phosphorus content to a minimum, allowing oil to be processed at high temperatures, deodorization, without the risk of darkening the color of the oil.

АННОТАЦИЯ

В статье приведены сведения о влиянии каждого этапа рафинации: процесса водной гидратации, нейтрализации, отбелки и дезодоризации на содержание фосфора в подсолнечном экстракционном и прессовом маслах.  Было определено влияние каждого этапа процесса рафинации на содержание фосфора получаемого масла. Выявлено, что водная гидратация снижает содержание фосфора в масле до 80%, но этот метод не является достаточно эффективным. Недостаточная эффективность водной гидратации подсолнечного масла, определяет необходимость снижение содержания фосфора при дальнейшей обработке масел. Следует отметить, что процессы нейтрализации и отбелки снижают содержание фосфора до минимума что, позволяет обработке масла при высоких температурах, то есть дезодоризации без риска затемнения цветности масла.

Keywords: Sunflower oil, phosphorus, refining, degumming, bleaching, neutralization, deodorization

Ключевые слова: Подсолнечное масло, фосфор, рафинация, гидратация, отбелка, нейтрализация, дезодоризация.

Introduction

Crude vegetable oils, contain different minority components such as phospholipids, tocopherols, free fatty acids (FFAs), sterols, pigments, carbohydrates, waxes, traces of metals, and others. Most of these impurities can negatively influence to the odor, taste and storage stability of refined oils and must be removed during the refining process [27,8].

The refining of vegetable oils consists of such processes as degumming, neutralization, bleaching, winterization, and deodorization. The first step in oil refining is degumming process [18]. Notably, a variety of phospholipids are present in vegetable oils, including phosphatidylethanolamine, phosphatidylcholine, phosphatidylserine, phosphatidylinositol and phosphatidic acids [29]. The phospholipid content in crude vegetable oils depends on the oil type and extraction method, with extracted oils typically containing more phospholipids than pressed oils [26].

During different processes of retreatment of vegetable oils, phospholipids negatively influence on its quality [7]. The moisture present in vegetable oils can facilitate the partial hydration of phospholipids, leading to its agglomeration and sedimentation during storage.

High phospholipid content in crude vegetable oils can lead to emulsification during the neutralization process and ultimately result in losses of neutral oil. Phospholipids also affect the color and odor of vegetable oils. Therefore, it removed during the degumming process [25,20]

Water degumming of vegetable oils is one of the oldest methods for the removal of phospholipids. This method was patented by Bollman in 1923 [17]. After mixing water or an aqueous electrolyte solution with the oil, phospholipids, proteins and mucilage coagulate. Following hydration, crude oils are separated from phospholipids and other polar components.

The amount of added water depends on the type of oils and can range from 0.5% to 6.0% of the oil mass [4, 19]. The temperature during aqueous hydration may vary between 50-70°C, and the hydration duration can be from 3 to 60 minutes [1,2,10,16,22]. Water degummed oil contains 50 - 200 mg/kg of phosphorus in the oil, depending on the content and type of phospholipids in the crude oil [20, 28].

The degumming method of vegetable oils, known as the TOP (Total Ontslijmings Process) hydration proposed by Vandermoortele [9,21,30], differs from other acid hydration processes in that it incurs minimal losses of neutral oil. During TOP degumming the phosphorus amount in the treated oil decreases by less than 10 mg/kg. With this technology, the phosphorus content in oils can be reduced to less than 10 mg/kg, and it may also lead to a decrease in the acid value of the oils (8, 21, 30).

The use of alkali (caustic soda) in oil processing was initially tested on cottonseed oil in 1842. The amount of alkali used depend on the type of oil. The neutralization process can also saponify neutral oil depending on the conditions [11].

The removal of free fatty acids from vegetable oils can be achieved through the use of aqueous caustic soda solutions (chemical refining) or through deep vacuum treatment at high temperatures (physical refining) [5, 6]. Bleaching is an important step in the refining of vegetable oils. It removes pigments, residual soaps, metals, phospholipids, and oxidation products, enhancing the quality and oxidative stability of vegetable oils [24].

The last stage of the refining is deodorization, which aims to remove odoriferous substances that influence the taste and smell of the oils. This process consists of three stages: the diffusion of aromatic substances from the liquid layer to the vapor phase, the actual vaporization of aromatic substances, and the removal of vaporized substances from the evaporation zone [14, 15, 23].

Materials and methods

Materials

Sunflower oil samples were collected from local oil factory Kattakurgan Oil Plant in Uzbekistan.

Refining process

Water degumming process. Crude extracted and pressed sunflower oils underwent a degumming process through the following steps: the oils were heated to 80°C, and water (4% by volume) was introduced. The mixture was stirred for 30 minutes using a magnetic stirrer, followed by centrifugation for 15 minutes. This procedure effectively removed impurities from the crude sunflower oils.

Neutralization process. Degummed sunflower extracted and pressed oils were heated to 80 °C. Subsequently, a water solution containing NaOH at a concentration of 15% by weight, corresponding to 4% of the oil volume, was introduced into the mixture. The resulting blend underwent 20 minutes of stirring at 80 °C the mixture underwent centrifugation for a duration of 15 minutes.

Bleaching. The neutralized oils were subjected to heating at 70 °C and were initially subjected to thorough agitation with bleaching clay, constituting 0.5% of the oil's weight. The entire reaction duration was limited to just 30 minutes. Subsequently, the mixture underwent filtration to yield the bleached oil.

Deodorization. The deodorization procedure was carried out in a laboratory apparatus at a temperature of 230°C and under a vacuum pressure of 0.2 kPa for a duration of 30 minutes, incorporating 0.2% steam.

Determination phosphorus amount in vegetable oils

The content of phospholipids was determined as the total phosphorus on a vegetable oil according to AOCS Official Method Ca 12-55 [31].

Results and discusion

Phospholipids in extracted sunflower oil typically differs from that in pressed sunflower oil. Extraction method is more efficient at removing phospholipids from the raw sunflower seeds. As a result, extracted sunflower oil generally contains significantly higher levels of phospholipids compared to pressed sunflower oil. Crude extracted sunflower oil contain 293,5 mg.kg^-1 phosphorus, pressed oil has 99,6 mg.kg¹ amounts of phosphorus, its three time lower than extracted one.

Water degumming represents a traditional technique within the oil industry employed to diminish the phospholipid content found in both extracted and pressed sunflower oil. This method encompasses the introduction of water into the crude oil, subsequently undergoing thorough mixing. The water engages with the phospholipids naturally occurring in the oil, leading to the formation of hydrated complexes that can be removed from the oil.

During the water degumming process, the phospholipids transforming into a gel-like substance, thereby decreasing their solubility in the oil. This transformation facilitates the efficient elimination of these phospholipids through procedures such as centrifugation or alternative separation methodologies. The water degumming has demonstrated noteworthy success in reducing the phosphorus content in extracted sunflower oil by approximately 80%, resulting in a phosphorus content of 57.7 mg.kg¹. In the case of pressed oil, the phosphorus content decreases to 41.3 mg.kg^-1. Consequently, the overall phospholipid concentration in the sunflower oil is substantially diminished (Tab.1.). Neutralization. During neutralization process, a caustic soda solution is added to the oil, which reacts with the free fatty acids and forms soapstock. This process also interacts with the phospholipids present in the oil. The removing of phospholipids during neutralization is achieved through several mechanisms: The addition of caustic soda creates an emulsion that helps in separating the phospholipids from the oil. The caustic soda reacts with the phospholipids, causing them to precipitate and form solid particles that can be easily separated from the oil. Centrifugation is employed to further separate the phospholipids from the oil. The phosphorus levels in the extracted oil dropped to 16.1 mg.kg^-1, and in the press oil, its decreased to 13.2 mg.kg^-1. In the neutralized oil, the phosphorus content is not sufficiently low to proceed with deodorization, as such an amount of phosphorus can lead to change color of the oil to the darker during deodorization. During the bleaching process, the removing of phospholipids takes place. This procedure is a crucial stage in oil refinement, aimed at eliminating undesirable impurities such as metals, pigments, phospholipids and others. The bleaching process  typically involves treating the oil with adsorbents, such as bleaching clay.

Table 1.

Influence of refining processes on phosphorus removal from sunflower oil

These adsorbents possess a high surface area and adsorb phospholipids and other impurities from the oil. Subsequently, the oil undergoes a filtration process to remove the adsorbents along with the adsorbed impurities. After the bleaching process, the phosphorus content in extracted oil reduced to 9.1 mg.kg^-1, while in the press oil, it was reduced to 7.1 mg.kg^-1. Removing of phospholipids during the bleaching process plays important role in enhancing the quality of vegetable oils, making its more suitable for a wide range of applications.

The deodorization process is last stage in the refining of vegetable oils, primarily aimed at eliminating undesirable aromatic compounds and other constituents that may impart unpleasant odors and tastes to the oil. Deodorization involves heating the oil to high temperatures under a vacuum, facilitating the vaporization and removal of volatile compounds, including aromatic and aldehyde compounds. However, phosphorus, present in the form of phospholipids, remains in the oil. The elevated temperature has only a minimal impact on the structure of phospholipids, resulting in a marginal decrease in the phosphorus content of the oil, typically around 0.2-0.3 mg.kg^-1.

Conclusion

The goal of this paper is analysing the effects of refining processes on phosphorus content of sunflower oils. While various refining processes contribute to reducing phospholipid amount, water degumming and bleaching appear to be the most effective methods. However, even after these processes, the phosphorus amount may still be too high for certain applications, emphasizing the need for careful monitoring and adjustment of refining processes to meet specific quality requirements.

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