● Galla chinensis is a cystic worm that is formed by gallnut mistletoe on the lacquer tree "salt wood" and its young leaves or petioles. Tannic acid is also listed as the main component of gallnut, which has many physiological functions such as scavenging free radicals, inhibiting lipid peroxidation, anti-cancer, anti-mutation, anti-aging and anti-cataract.
● The extraction methods of gallnut tannins mainly include traditional water extraction and solvent extraction methods. These methods are simple to operate, but the extraction rate is low. The new methods include ultrasonic extraction, supercritical CO2, and negative pressure cavitation. Although these methods improve the extraction rate to some extent, they are less used in production due to the disadvantages of expensive equipment and small batch production. Irradiation degradation technology is characterized by safety, low energy consumption, and no toxic and harmful by-products. Ionizing radiation is a commonly used irradiation technology at home and abroad. The basic principle is to make use of the strong penetrating power of cobalt 60-γ rays, and the large amount of energy carried by it to cause the ionization effect of the substance to degrade or crosslink.
(1) According to the single factor test, the optimal extraction temperature for the extraction of gallnut tannic acid by irradiation pretreatment is 80 °C, the optimum ratio of material to liquid is 1:40, and the optimal irradiation dose is 400 kGy. It is better to use 4 h.
(2) According to the optimal conditions of each factor, orthogonal test was carried out, and the test results were analyzed by variance. The results showed that the extraction temperature was 90 °C, the ratio of material to liquid was 1:35, and the irradiation dose was 800 kGy. The tannic acid yield was highest at 4.5 h.
(3) A confirmatory test was carried out on the analysis results. The yield and purity of tannic acid under optimal conditions were investigated, which were 65.13% and 81.36%, respectively. The relative standard deviation (RSD=1.25%) was less than 2.0%. The combination of process technology has good stability and repeatability.
(4) Compared with the conventional water extraction method and industrial acid hydrolysis method, the extraction time used in this experiment is less, and the yield of tannic acid extraction is higher, which is increased by 15.13% and 20.13%, respectively.
● Among the gallnuts, the yield and quality of the horn and the doubling are the best, but these horns have a porphyry wall of 1~3 mm thick, which is difficult to decompose. The main component contains more resin than tannic acid. Starch, wax, protein and sugar. High temperature is conducive to the extraction of tannic acid, but the gallnut is easy to soften and rot after being soaked in water, even more so at high temperature, so the direct extraction with water needs to control the extraction temperature, so that the tannic acid extraction rate is lower. Irradiation pretreatment can destroy the structure between molecules, so that the physical and chemical properties of the substance are changed and degraded, which has a good degradation effect on macromolecular substances. The extraction of tannic acid by water extraction can save energy and is easy to operate. Even if the liquid is relatively large, the cost is low, and there is no need to worry about solvent residue. In the choice of irradiation dose, the high-dose is more likely to destroy the internal structure of potato starch molecules in the range of 50~400 kGy. The degradation effect of lycium polysaccharide is the most significant at 1000 kGy dose. Abu found that irradiation had a degrading effect on the tannin contained in some plants, but had no significant effect on the tannins of other plants. Garcia also found that the irradiation dose has no obvious effect on hydrolyzed tannin in the range of 5~35 kGy, while gallnut tannin is a hydrolyzed tannic acid with a small molecular weight (less than 2000), so choose 0~ Irradiation dose range of 1200 kGy.
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