BLEACHING OF COTTONSEED OIL USING A FIBROUS SORBENT DERIVED FROM SILK FIBER WASTE

УДК: 547.962.94

Abstract

Various sorbents, mainly soil-based sorbents, are used in the purification of vegetable oils. We obtained a multifunctional sorbent from silk fiber waste by various methods of purification of vegetable oils. Silk factories produce a large amount of fibrous waste from natural silk at different stages. A fibroin-based sorbent from silk waste was obtained by alkaline hydrolysis and activation under the influence of ultrahigh-frequency rays, and the sorbent was used to purify cottonseed oil. As a result of purifying cottonseed oil using sorbent samples from silk fiber waste, we were able to reduce the peroxide value from 10.58 mmol/L to 5.81 mmol/L. Reducing the peroxide value of vegetable oils increases the shelf life of vegetable oils. The sorbent does not affect the oil composition, even if it is in an oil environment for a long time. In addition, the obtained fibrous sorbent sample reduces the acid number of the oil to 0.15 mmol/L KOH. The sorbent derived from silk fiber waste that we recommend is also important because it reduces waste from silk factories and is easy to separate from oil.

Аннотация

Для очистки растительных масел используются различные сорбенты, в основном почвенные. Мы получили многофункциональный сорбент из отходов шелкового волокна различными методами очистки растительных масел. Шелковые фабрики производят большое количество волокнистых отходов натурального шелка на разных этапах. Сорбент на основе фиброина из отходов шелка был получен путем щелочного гидролиза и активации под воздействием ультравысокочастотных лучей, и этот сорбент был использован для очистки хлопкового масла. В результате очистки хлопкового масла с использованием образцов сорбента из отходов шелкового волокна нам удалось снизить перекисное число с 10,58 ммоль/л до 5,81 ммоль/л. Снижение перекисного числа растительных масел увеличивает срок их хранения. Сорбент не влияет на состав масла, даже если он находится в масляной среде в течение длительного времени. Кроме того, полученный образец волокнистого сорбента снижает кислотное число масла до 0,15 ммоль/л KOH. Рекомендуемый нами сорбент, полученный из отходов шелкового волокна, также важен, поскольку он уменьшает количество отходов шелковых фабрик и легко отделяется от масла.

Ключевые слова: фиброин шелка, ультравысокочастотное излучение, хлопковое масло, перекисное число, кислотное число.

Keywords: Silk fibroin, ultra high frequency radiation, cottonseed oil, peroxide value, acid number.

Introduction

One of the most important sectors of the food industry is the vegetable oil sector. A large part of the food produced worldwide comes from the vegetable oil sector. Cottonseed, linseed, sunflower, soybean oil , etc., are the main products of the industry. The production of competitive, high-quality, and environmentally responsible products is the main goal of the vegetable oil industry. Vegetable oils are currently purified using various adsorbents, mainly silicates and clays[1,2]. They consume a lot of money and energy to purify vegetable oils. Bentonites are activated with acids at high temperatures (250–300ºC) to purify vegetable oils. However, if the oil remains with the adsorbent for a longer period of time, it oxidizes and releases a vegetable odor, which changes the structure of the oil . Sorbents used in the cottonseed oil refining process mainly need to bind impurities such as phospholipids, free fatty acids, pigments, various oxidation products, and gossypol. In modern refining processes, the capacity of sorbents is not only determined by adsorption capacity, but also by selectivity, regeneration, and food safety requirements [2,3]. Solving this problem is one of the most urgent problems. To solve this problem, we used sorbents obtained from silk fiber waste.

It is very important to study the mechanical, physical and chemical properties and applications of natural silk fibroin. Currently, various preparations based on natural silk fibroin have been created and are used in many areas [4–8]. Based on the research, the sorption processes of heavy metals in silk fibroin, the adsorption conditions, and the mechanism of various dyes were studied[9,10], and the high sorption capacity of silk fibroin was once again demonstrated. The sorbent properties of natural silk fibroin have been studied. Hydrolyzed fibroin ("HF") from waste natural silk fibers can be used to refine vegetable oils, prepare food products, and study medicines.

Up to ten to twenty-eight percent of silk fibers extracted from the cocoon become waste. Depending on the production capacity of the business, one silk spinning factory in Uzbekistan produces an average of 60 tons of silk waste annually. The separation of waste fibers from additives and silk fibers requires a large amount of energy. Finding ways to reuse this fiber waste is one of the most pressing problems. Silk fiber waste is considered unsuitable for the textile industry due to its mechanical and qualitative properties.

Nevertheless, silk waste and silk fibers have the same physicochemical properties and the same chemical composition. This allows the production of hydrolyzed fibroin from waste silk fibers with strong sorption properties and solves some problems in its practical application [11]. The amount of fibroin and sericin proteins in silk depends on the nutrition and living conditions of the silkworms. Our research has shown that silkworm cocoons grown in the Khorezm region of Uzbekistan contain 67.5% fibroin, 32.5% sericin, and other chemicals. During the production process, 28% is converted into fiber residues. It is very important to study the sorbent properties of fibrous waste

Materials and methods

Required materials and equipment. Fibrous waste of silk (Cleaned of additives. Urganch Bahmal, LLC, Urgench, Uzbekistan), Sodium carbonate (purity 99,9%), KOH (purity 99,9%) was purchased from Chimreaktivinvest (Uzbekistan), unrefined oil obtained from cotton Seeds. Bidistilled water is obtained from the “GFL 2104 Double distillation water still” device (Germany). Optical microscope ("Optika_B-150 DBR"), Lovibond® Tintometer Model F. Ultra-high frequency radiation was performed on a ME81ARW (Samsung) device at a frequency of 2450 MHz. ATR-IR Fourier spectroscopy analyses were performed on a “FTIR 4600 JASCO” (Japan) spectrophotometer.

Obtaining fibroin fiber from fibrous wastes of natural silk . Studies have focused on the use of silkworm waste as a sorbent in the purification of vegetable oils. The fibrous waste of silk was found to contain up to 88% fibroin, up to 12% sericin, and other substances. Conditions were selected for the obtaining of fibroin from the fibrous waste of silk: sericin was dissolved in a NaHCO₃ solution at 90ºC for 40 minutes [12]. Fibroin fibers were obtained from the solution and washed with distilled water.

Obtaining “HF” from silk fibroin. Further studies were conducted on the hydrolysis of fibroin fibers from silk fibers and their sorbent properties. Silk fiber fibroin was hydrolyzed under alkaline conditions and with ultrahigh-frequency radiation (510 W) to obtain “HF” in the form of fibers[13]. The extraction of “HF” in an alkaline medium was carried out by immersion in a 3% KOH solution. In this case, it took 60 minutes to obtain “HF” in a 3% KOH solution. The formation of cracks and pores on the surface of “HF” fibers was studied. The fact that “HF” has ampholytic properties and the presence of polyfunctional groups allow it to be used in various environmental conditions. To further increase the cracks and porosity in “HF” particles, “HF” powder was exposed to ultrahigh-frequency radiation for 5 minutes after immersion in an alkaline medium and in a wet state. After the procedure, the sample was neutralized and washed with hot distilled water until the salt remained. As the cracks and pores in the "HF" increase, its sorption properties also increase.

Purification of cottonseed oil with “HF” . Cottonseed oil was purified to test the sorption properties of the obtained "HF" samples.100 g of purified vegetable oil was poured into numbered flasks and immersed in a water bath. When the temperature reached 70ºC, 1.0 g of hydrolyzed fibroin ("HF") sample was added to the flask and mixed at a speed of 250 rpm. Continue mixing for 30 minutes, bringing the oil temperature to 90ºC. At the end of the process, the oil was filtered. The color level of the filtered oil was measured on a Lovibond device. The peroxide value and acid content were measured by the method of [14].

Result and discussion

The surface and sizes of GF samples obtained from silk fiber waste were studied using optical microscopy. Optical images of the samples were obtained using a digital - “Optika_B-150 DBR” -USB optical microscope [15]. The length values of HF 52 particles were determined using an optical microscope, and the average fiber length was calculated based on this. Among the particles, the smallest particle was 20 μm and the largest particle was 193 μm. The average fiber length is 100 μm (Table 1).

Table 1. Length of KOH-treated HF fibers

1-A. Image of HF particles                             1-B. Image of cracks formed on

    treated   with KOH (100x)                               the surface of the hydrolized fiber