Carbohydrates are collectively referred to as organic compounds that contain multiple hydroxyl groups and can be hydrolyzed to produce multiple hydroxyl aldehydes or ketones. There are a wide variety of carbohydrate types, including: glucose, fructose, galactose, maltose, sucrose, lactose, dextrin, starch, cellulose; nucleotides that make up human genetic material, such as ribose and deoxyribose; sugar substitutes: erythritol, alloxanose, sorbitol, mannitol, xylitol, trichlorosucrose; infant formula additives such as lactose oligosaccharides: fucosyl lactose, sialyl lactose, neotetranucleose, etc.; functional foods such as cottonseed sugar, horsetail sugar, soybean oligosaccharides, burdock polysaccharides, etc.; in the fields of medicine and cosmetics, such as lentinan polysaccharides, silver ear polysaccharides, chitosan, glucans, dextran, dextrin, cyclodextrin, acesulfame dextrin, hyaluronic acid, chondroitin sulfate, heparin sodium, aloe polysaccharides, etc.; and sugar derivatives such as 5-hydroxymethylfurfural, boswellic acid, acetylsulfaminoglucosamine, etc.; and various modified products of sugars.
The sources of sugar vary, and the types of pigments contained are extremely diverse. The extraction of sugar liquid pigments mainly includes chlorophyll, lutein, polyphenols, anthraquinones, the Maillard reaction products and degradation products of sugar liquid after heating, etc. for fermentation-based sugar liquid pigments, mainly include color-forming components of the fermentation medium, heat reaction products of sugar and nitrogen, and pigment products generated by the metabolism of microorganisms, etc. For chemical synthesis-based sugar liquid pigments, the main components are the decomposition products of sugar during the reaction process and the by-product products. The pigment components are complex and have different molecular weights. Although by controlling process conditions such as sugar liquid temperature, pH, and oxygen, the color intensity of the sugar liquid can be reduced, the decolorization process is still an indispensable process step for improving product quality.
Fat-soluble pigments are usually well-adsorbed by activated carbon or macroporous adsorption resins, but there is also a problem of low yield caused by dead adsorption of the products. For water-soluble pigments, the adsorption effect by non-polar adsorption materials is poor. Usually, ion exchange resins are used for adsorption and decolorization, as well as oxidation decolorization and membrane filtration decolorization. Each of these decolorization methods has its advantages and disadvantages.
For bulk products such as sugar solutions from sugarcane, traditional methods use clarification processes to achieve basic decolorization by adding lime milk, introducing carbon dioxide, and introducing sulfur dioxide, etc. However, there are problems such as high solid waste content, complex operation, and high color of the final product. Therefore, a recrystallization process is needed to produce refined white sugar. In modern sugar production industry, there have been many studies on membrane filtration clarification decolorization processes, and the quality of the products obtained by membrane filtration decolorization is significantly higher than that of traditional methods.
Picture above: De-colorization of a certain ribose reaction solution at Wuhan Bona
At present, fermentation-derived sugars such as human milk oligosaccharides, acetylated glycosaminoglycans, inositol, sugar alcohols, beta-cyclodextrins and intermediates, as well as chemical synthesis-derived glucose derivatives, ribose analogues, beta-cyclodextrins, etc., have all achieved large-scale production and application through membrane filtration for decolorization.
Picture above: De-colorization of a certain chondroitin fermentation clarification liquid at Wuhan Bona
Membrane filtration mainly relies on the molecular weight and charge properties of the organic membrane to achieve the separation of molecules, and utilizes the differences in molecular weight and polarity of pigment molecules to achieve the decolorization of sugar solutions. The decolorization membrane elements have the characteristics of high precision, wide pore size range, and diverse materials. The decolorization membrane filtration equipment adopts cross-flow filtration, which is unlikely to form a gel layer, can effectively avoid the phenomenon of concentration polarization, and is easy to achieve high-pressure and high-concentration operations. For different material properties, excellent decolorization membranes can always be found.
The desorption membranes usually adopt ultrafiltration membranes and nanofiltration membranes of different precisions. The selection is based on comprehensive consideration of the physicochemical properties of sugar products and pigment substances, the types and concentrations of various substances in the liquid, solvent conditions, etc. The greater the difference between sugar products and pigment substances, the easier it is to select the membrane. The fewer the types of pigments, the better the membrane filtration desorption effect. The components of sugar liquids from plant extraction and fermentation are complex. Using desorption membrane filtration can retain lipid-soluble pigments and melanin, but there are still some small molecule pigments with less difference from sugar products, which require combined use of other process methods to completely remove.
Picture above: Descoloration of the clarified liquid from a glycoside fermentation in Wuhan Bona
After the sugar solution obtained by the membrane decolorization method is concentrated and crystallized, the product has lower pigment content, low residual protein and polysaccharides, and stable product properties. The automated membrane filtration equipment significantly reduces the operational intensity, greatly reduces the amount of process additives, and alleviates the environmental pressure.
Over the years, Wuhan Bona has been client-oriented and has been dedicated to the development of application processes for membrane separation technology. By integrating processes, membranes and equipment, it has accumulated rich experience in product purification and engineering scale-up.
