Evaluation of physicochemical properties of Mucilage and comparison of extraction efficiency of two solvent and supercritical methods

The Okra belongs to the family Malvaceae with the scientific name Abelmoschus esculentus (Peyvast, 2009). The viscous property of okra is due to the thick and viscous matter in the fruit pod, called mucilage. Okra mucilage is a polysaccharide currently used in pharmaceutical industry as a hydrophilic polymer in tablet coatings (Bakre et al, 2009). Mucilage collectively contains polysaccharides, proteins, and minerals found in a plants or seeds that are more widely used in various industries, including food industry, as a stiffener in dairy products. Mucilage composed of monosaccharide polymers, amorphous and semi-transparent, and are hydrocolloids. These materials are hydrophilic molecules that can be extracted with water and form a concentrated or gel solutions. Gels are widely used in the food, pharmaceutical and non-pharmaceutical industries. The cultivation of okra in Iran is mainly occurred in tropical and subtropical regions and is found in Khuzestan, Ilam, Kermanshah, South Fars, Bushehr and Hormozgan provinces (Mozafarian, 2012). Many studies have been done on the extraction of okra mucilage and its applications in the pharmaceutical and food industries. Faroq et al. worked on the organoleptic properties of okra mucilage and concluded that okra mucilage has good flow properties and high solubility in water that can be used safely without any side effects (Farooq et al, 2013). ). Noorlaila et al studied the emulsifying property of mucilage extracted from okra (Noorlaila et al, 2014). Nazni and Vigneshwar studied the extraction and evaluation of organoleptic properties of mucilage from okra and several other plants and used ethanol and acetone to purify mucilage (Nazni et al, 2012). A study was conducted in 2018 to study the basic properties such as swelling index, emulsion stability, viscosity and antioxidant activity of okra mucilage (Fekadu Gememde et al, 2018). In a study on the use of okra mucilage in pharmacy, Ameena et al after extracting mucilage from okra and measured the physicochemical properties of mucilage, applied it in tablet formulation and many parameters such as diameter, thickness, weight change, hardness and Fragility were assessed. According to observations, low concentrations of okra mucilage can be used as a substitute for starch in tablet formulation, and also high levels of okra mucilage can be used in the drug release system as a natural substance (Ameena et al, 2010). In a study, Mishra et al presented okra mucilage as a new proposal to replace polymer materials used in various industries (Mishra et al, 2008). In 2014, the effect of okra mucilage on the release of propranolol hydrocolloid in tablets was studied. The highest hardness and lowest brittleness were observed for okra tablets (Zaharuddin et al, 2014). In this research, extraction of okra mucilage was investigated by two methods of solvent and supercritical fluid extraction. Optimization the yield and physicochemical properties of the extract obtained from both methods was also investigated.

Fresh okra obtained from local supermarket in Khuzestan province. Chemicals materials such as pure ethanol, acetone, chloroform, acetonitrile purchased from Merck and Sigma Aldrich. After transferring the okra fruit to the laboratory, the contaminants were removed from the plant and then rinsed thoroughly with water. The okra pods were dried at about 40 °C in a digital fan oven model 6882A. It was powdered by a German-made electric milling machine and then it passed through a 30-mesh sieve to be ready for extraction and it was weighted by laboratory scales (0.0001 precision manufactured by Cornell, Germany). In the solvent extraction process, the okra powder was weighed by a digital balanced (GR-200 model made in Japan) and transferred to 250 ml human. The solids stirred in distilled water and various amounts of solvent for 1 to 5 hours until the mucilage is completely released into the water. The solution was filtered and then adjacent to an organic solvent. Then, the filtrate was poured again into Petri dish and placed on a water bath at 45 °C to evaporate the residual solvent inside it. The residue inside the Petri dish was dried in a fan oven (Reyhan Teb Company) at 40 °C and powdered and kept at 20 °C until the day of analysis. In the supercritical extraction method, the supercritical fluid extraction machine which designed and manufactured in the laboratory of the Faculty of Engineering at Ferdowsi University of Mashhad was used. The carbon dioxide was supplied by Khakakan Co., Quchan Road, Iran in a 45 kg cylinder.

Generally, according to the results of both methods of solvent extraction and supercritical fluid extraction (SFE), the extraction efficiency of mucilage at the optimal point in the solvent extraction and in the supercritical methods was 5.12% and 1.58%, respectively. Due to the less use of organic solvents in the supercritical method, this method is more environmentally friendly, which is significant in converting the laboratory method to pilot or industrial scale. Physio-chemical analysis of mucilage obtained by two methods shows that the index of swelling, moisture and ash of mucilage obtained by maceration is more than that of supercritical mucilage. By comparing the obtained values at the optimal point of both methods, the solvent method has a higher total efficiency and has been more successful. However, in the supercritical fluid method, the solvent utilization is significantly reduced. The extraction time in the supercritical fluid method is also reduced by about 50%.