Optimization of extraction process of aloe-emodin

- Sep 16, 2019-

Aloe emodin and aloin are effective active ingredients of aloe, which are widely used in medicine and health care. Ultrasound-assisted extraction technology is mainly applied to the extraction of plant active ingredients, which can effectively shorten the extraction time and improve the extraction efficiency. Aloe vera dry powder was used as raw material, and ethanol and ethyl acetate were used as extracting agents respectively. The optimal conditions were obtained by comparing the reaction conditions. Aloe-emodin is obtained by oxidizing aloe vera in a dry powder of aloe vera using iron oxide as an oxidant after extracting aloin.

 

● Aloe vera is a perennial evergreen and succulent herb, which is a common medicinal plant in China. Aloe vera is known to contain more than 160 chemical components, including more than 80 active ingredients. Due to the variety, origin and season, the chemical composition of aloe vera is not the same [4]. Among them, aloin is one of the main active substances of aloe vera, the chemical formula is C21H22O9, and the appearance is yellow or light yellow crystalline powder. The melting point is 148-149 ° C, the boiling point is 752.602 ° C, soluble in pyridine, soluble in glacial acetic acid, formic acid, acetone, ethanol and so on. Aloin has thermal instability. As the temperature increases, the content of aloin decreases gradually and should be stored at low temperature during storage. Aloe-emodin (structure shown in Figure 1), usually in the presence of orange needle crystals (from toluene) or khaki powder. The chemical formula is C15H10O5, melting point 223-224 ° C, soluble in acetaldehyde, benzene (yellow), ammonia (magenta), sodium carbonate aqueous solution. Soluble in hot ethanol. Anthrone which is reduced to indophenol and its tautomers in an acidic solution. The preparation of aloe emodin at the current stage mainly starts from two aspects: natural plant extraction and artificial synthesis. Generally, we extract aloe-emodin from two natural plants, rhubarb and aloe, or artificially synthesize from other components of aloe.

aloe emodin chemical structure

● In this experiment, we extracted aloe-emodin with rhubarb dry powder as the starting material, extracted aloin from aloe vera dry powder and prepared aloe-emodin. The experimental conditions were optimized and the extraction results were compared for different solvents and under different conditions. At the same time, ultrasonic assisted extraction technology was used to compare the yield of aloe-emodin under different experimental conditions, and it is expected to provide better conditions for the preparation of aloe-emodin.


1 Materials and methods

1.1 Materials

Aloe dry powder, Yunnan Wanlv Biotechnology Co., Ltd.; aloe emodin standard, Shanghai Yuanye Biotechnology Co., Ltd.; rhubarb dry powder, purchased from the network; other reagents are of analytical grade or chemical purity. Ultrasonic cell pulverizer (JY92-II), low speed benchtop large capacity centrifuge (TDL-50B).

1.2 Methods

1.2.1 Extraction of aloe-emodin from rhubarb powder

The rhubarb powder (25 g) was subjected to Soxhlet extraction under the conditions of 90 ° C using absolute ethanol (125 mL) as a solvent, and the extract was stopped after extraction with substantially no color. The extract was concentrated and dissolved in ethyl acetate. The organic layer was extracted by 5% NaHCO3 solution and 5% Na2CO3 solution. An additional 5% NaOH solution was added for extraction and the aqueous layer was taken. The aqueous layer was acidified by adding 15% hydrochloric acid, and then hot isobutanol was added for the last extraction. The organic layer was taken and recrystallized from chloroform to obtain aloe-emodin (0.2021 g, extraction rate: 0.81%).

1.2.2 Extraction of aloe-emodin from aloe vera powder

Aloe vera dry powder (10g) was placed in a 500mL round bottom flask, 4M HCl (150mL) was added, and after reacting at 110oC for 30 minutes, it was filtered while hot, and the filter residue was washed with deionized water. The filtrate was combined and re-calculated to 300 mL. , heated to boiling. After FeCl3 (25 g) was added to deionized water (15 mL), the solution was slowly added to the above reaction solution. After the reaction was continued for 8 hours, it was filtered while hot and washed with deionized water to give a crude material. Toluene (400 mL) was added to the crude product, connected to a Soxhlet extractor, and the reaction was continued at 140 °C for 8 h. After the reaction was completed, the mixture was filtered while hot, cooled to room temperature, and placed in a refrigerator to recrystallize. After filtration and drying, aloe emodin pure product 1.0687 g was obtained, and the extraction rate was 10.69%.

 

1.2.3 Ultrasound-assisted extraction of aloe-emodin from aloe vera dry powder

Aloe dry powder (12.8 g) was added to a round bottom flask, 300 mL of 4 mol/L hydrochloric acid was added, and a power of 300 W was set in a sonicator, and the reaction time was 40 min. After the reaction was heated to 110 ° C for 30 min, filtered while hot, the filter residue was washed with deionized water, and the filtrate was combined to obtain a crude aloe extract. Aloe-emodin oxidized by aloin by oxidation (as shown in Figure 2). The crude aloe extract was made up to 300 ml of L, reheated to boiling, and slowly added to the FeCl3 solution (50 g), and the reaction was continued for 8 h. After hot filtration, the crude material was dissolved in toluene (400 mL) and extracted with a Soxhlet apparatus at 140 ° C for 8 h. After the completion, the mixture was filtered while hot, and the filtrate was cooled and cooled in a refrigerator at -5 ° C overnight, and filtered to obtain 1.5130 g of aloe-emodin pure product, and the extraction rate was 11.82%.

ALoin to Aloe emodin

● In the extraction of aloe-emodin, the yield of oxidized aloin was higher than that of traditional Soxhlet extraction. Soxhlet extraction of rhubarb dry powder takes completely 40 hours, and the method of oxidizing aloin takes less than 20 hours. Ultrasonic extraction of aloe vera has an absolute advantage in both yield and efficiency (see Table 1). The experimental results show that the ultrasonication of the dried aloe vera powder as raw material for the oxidation reaction, the yield of aloe-emodin is increased by 10%, greatly improving the extraction efficiency, thus realizing high yield extraction.



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