Natural pigments are mainly extracted from animal and plant tissues and microorganisms. They not only have the function of coloring food, but also, most of them, have physiological activities.
In the extraction of natural pigments, many plant extraction methods are often used in the production process. Because the extract contains a large amount of soluble macromolecular impurities, such as macromolecular proteins, tannins, polysaccharides, traditional special concentration and separation methods can only achieve temporary clarification of the extract. And these soluble impurities will still precipitate out during the long-term storage process, resulting in delamination and becoming muddy in the finished product, which greatly affects the product quality.
The traditional extraction methods of natural pigments generally use supercritical extraction, organic solvent extraction, microwave extraction and other methods. The products obtained in these ways have low yield, low purity, and high process energy consumption, which are not conducive to the competitive development of enterprises. According to the characteristics of natural pigment extract, combined with the characteristics of membrane separation technology, the extract is pretreated to remove some solid impurities (commonly used filtration methods include plate and frame filtration/centrifugation), and then through membrane filtration, soluble macromolecular impurities are removed, and the pigment liquid is completely clarified, and then enters the concentrated membrane to trap the pigment, so that ash and other small molecular impurities can pass through, achieving the dual purpose of concentration and dehydration and impurity removal.
The application of membrane separation technology in the production of natural pigments improves the production yield of natural pigments, removes secondary dyes and small molecular impurities, and reduces production costs. Undoubtedly, membrane technology has played an important role in consolidating its position in the natural pigment industry.
The membrane filtration system used in the natural pigment industry mainly include ultrafiltration and nanofiltration:
(1) Ultrafiltration is used for the clarification of pigments produced by fermentation, which replaces the traditional clarification method. It can effectively intercept macromolecular suspended solids and proteins and allow the clarified pigment extract to penetrate through the membrane and enter the permeate side.
(2) Nanofiltration membrane technology is used for the concentration/dewatering of pigments at room temperature, usually combined with evaporator or in place of evaporator. During filtration, water and some small molecular impurities (such as citrinin in Monascus Red) pass through the membrane while the pigment components are retained and concentrated.
The natural pigment combined with membrane separation process can recover the remaining pigment in the supernatant and increase the yield by more than 20%. At the same time, the filtrate of the centrifugal separation liquid is clear and transparent after ultrafiltration, with few impurities; the nanofiltration membrane is pre-concentrated at room temperature to avoid The damage to the pigment by heating and evaporation improves the quality of the finished product. The concentration of the concentrated solution can reach 20-30%, saving the cost of spray drying (the cost of water removal for nanofiltration concentration is 20-30 yuan/ton of water, and the cost of spray drying is 80-100 yuan/ton of water). The titer extraction yield of the applied pigment of this process will be close to 100%, and the color gradation of the finished product will be 15-30% higher than the original process.
(1)High filtration precision. Because it can completely remove the macromolecular protein, tannin, starch, plant fiber, etc. in the solution, improve the clarity of the extract, avoid precipitation of the finished product for a long time, extend the shelf life, and improve the clarity of the product;
(2) Long service life and low operating cost;
(3) Easy cleanout and recycling, low maintenance cost;
(4)The cost of membrane concentration is only about 1/5 of thermal concentration, which greatly saves the cost of enterprises;
(5)Through sieving and filtering, the molecular mass in the extract is more concentrated, and no stratification will occur after long-term storage;
(6)While concentrating, it removes small molecule impurities and inorganic salts to improve product quality.
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