D-mannose is widely distributed in nature. D-mannose can be prepared by extracting, separating and purifying plant polysaccharides to obtain pure products. In addition, D-mannose can be obtained by chemical method and biological transformation method.

1. Extraction method

Coffee grounds were used as raw materials for extraction

Coffee grounds is the waste of instant coffee production, which contains rich polysaccharides, and the main polysaccharide is mannan, mannan hydrolysis can obtain D-mannose. Under the conditions of sulfuric acid concentration of 1.5mol/L~3.0mol/L, temperature of 100℃~130℃ and reaction time of 80min~120min, the yield of D-mannose in hydrolysate was 28%~30%. Then, pure D-mannose was obtained through a series of steps such as decolorization, evaporation concentration, crystallization separation and drying.

The seed of palm tree was used as raw material for extraction

The palm tree is rich in the southern provinces of China. It belongs to the palm family. The leaves, flowers, roots and bark of the palm tree can be used as medicine. The liquid containing D-mannose was extracted from palm tree seeds by acid hydrolysis, alkali neutralization and enzyme reaction. The liquid containing D-mannose was concentrated and separated by silica gel after decolorization on activated carbon. The liquid ion-exchange resin containing D-mannose was desalted and D-mannose crystals were crystallized at last with crystallization yield of 86.7% and total yield of 48.4%.

2. Chemical synthesis

The chemical synthesis method used to prepare D-mannose is the differential isomerization of glucose by chemical reagent, but the processing concentration and temperature of acid must be strictly controlled. By hydrolyzing sucrose (T=100℃, pH=2.0) for 2 h, 50% D-glucose and 50% D-fructose were obtained. Then, the mixture was heated at 100℃ for 2 h with 0.15%(NH4)2MoO4(pH=3.0). The yield of D-mannose was 30%. The highest glucose conversion rate was 32.3% when catalyzed by 1%(NH4)2MoO4(pH=3.0) at 150℃ for 2 h. The yield of D-mannose prepared by chemical synthesis method is not high, and the operation is complicated, so it is only suitable for small-scale preparation in laboratory.

3. Biological law

Biological fermentation

Biological fermentation uses microorganisms to ferment polysaccharides or monosaccharides to obtain D-mannose. Mannose protein is easily obtained from yeast by enzymatic hydrolysis or heating to high temperatures. In addition, EPS is hydrolyzed by the M. chitosanitabida bacterial strain, which can produce high levels of extracellular polysaccharide (ESP). It is composed of glucose, mannose and galactose (molar ratio 18:6:1). It is not easy to obtain free D-mannose by microbial fermentation.

Biological transformation method

Biological conversion method is to convert fructose or glucose into D-mannose at mild temperature, pressure and pH level through enzymatic reaction. The enzymes in enzymatic reaction include D-mannose isomerase, fibrodisaccharide differential isomerase and D-lyserose isomerase, and the sources are wide. D-mannose isomerase is suitable for large-scale production, while cellulose differential isomerase is the only isomerase that converts glucose into D-mannose. However, this enzyme has a low conversion rate and generates a large number of by-products (D-fructose) during the conversion process, so it is not suitable for large-scale industrial production.