Study On Extraction Technology And Physicochemical Properties Of Lac Dye

Lac dye was a mixture of anthraquinone carboxylic acids which were extracted from lac secreted by lac insect. Because of its good capability of coloring, bright color, good stability and characteristics of pure natural, non-toxic, it was widely used in food, medicine, cosmetics, printing and dyeing industries. Extraction and refining of lac dye, physicochemical properties, development of detection methods, determination of composition and identification of molecular structure, evaluation of stability and antioxidant performance were studied in this paper. The concrete contents included: ultrasonic assisted extraction, salting-out extraction, purified method of macroporous adsorption resin, detection of the content of total anthraquinone, detection of relative content of component and structural identification, study of stability and antioxidant performance, the main research results were as follows:（1） The total anthraquinone content in the UV spectrophotometer lac red pigment was established, 0.5% Mg（Ac）2-CH3 OH solution as chromogenic reagent, with the detection wavelength of 540 nm, carminic acid concentration of 5⁵0μg/mL within the determination of total anthraquinone content in lac red pigment, the total anthraquinone content of lac red pigment measured 82.13%, and the average recovery was 97.80%, RSD was 1.31%.（2） The optimal extraction conditions of lac red pigment under the assistance of ultrasonic were determined as follows: frequency, 20 kHz; pulse-on time, 9 s, pulse-off time, 12 s; extraction duration, 18 min; material/liquid ratio, 1:5; ultrasonic power, 1400 W; and extraction number, 5. The extraction efficiency was up to 85.15% and the yield of lac red pigment was 0.44% under the optimal extraction conditions. The primary and secondary factors that effect the extraction of lac red pigment were material-liquid ratio, pulse time, extraction duration, ultrasonic power.（3） The optimum conditions of lac red pigment extracted from the shellac solution precipitation method: the amount of sodium chloride added to 9.6364 g, speed of revolution was 800 rpm, salting temperature of 34.5℃, precipitation time 25 min, lye concentration of 0.188mol/L, with good fitting degree, R2=0.9862 and R2Adj=0.9612. For the shellac pigment precipitation solution, the effect of the acidification settlement and calcium salts settlement method of lac red pigment precipitation studied, the results showed that: the pH value of acid deposition <3.119, lac red pigment is precipitated completely, the extraction rate reached 94.47%, and the anthraquinone content precipitated pigment product as 12.72%, pH value of 3.761; For the sedimentation of calcium salts, the amount of calcium in 3g/L, the extraction rate reached 95.42%, anthraquinone content reached 31.28 %, pH value of 3.633.（4） Through the study of the static adsorption/desorption properties of 7 kinds of macroporous adsorption resin, the results showed that the adsorption capacity of and the desorption rate of AB-8 macroporous resin lac red pigment was higher. Appropriately increasing the temperature, AB-8 macroporous resin adsorption of lac red pigment; 20% aqueous ethanol with pH7 the lac red pigment desorption best. Studies have shown that when the flow rate was 0.5mL/min, AB-8 macroporous resin dynamic adsorption/desorption was the highest rate of the lac red pigment; When 0.01% aqueous solution of HCl elution in addition to miscellaneous, and the flow 3mL/min 20% aqueous ethanol with pH7, use the AB-8 macroporous adsorption resin desorption, the effect is good, and the desorption rate is greater than 90%.（5） The purificatory lac dye was detected by LC-MS, and 8 kinds of anthraquinones carboxylic acids were found, in addition to lac acid A, B, C, E, four kinds of new anthraquinones carboxylic acids were found, and respectively named lac acid F, G, H, I, lac acid D mentioned in some papers was not found. Combined with secondary mass spectrometry and nuclear magnetic resonance（NMR）, the structure of lac acid A, C were confirmed, the structure of lac acid G, H were identified and the structure of lac acid F, I were just be speculated. The relative contents of lac acid A, B, C, E, F, G, H and I were 63.09%, 23.51%, 8.76%, 0.50%, 2.15%, 0.61%, 0.49% and 0.90% detected by HPLC. The lac acid A and B were detected to be the main components of lac dye.（6） The lac dye was stable to light. It was stable to outdoor sunlight with over 95% preservation rate after 28 days. It was also stable to heat, either low temperature or high temperature. The lac dye had high antioxidant ability, but the ability could be slightly reduced when the concentration of reductants was higher than 2%. It was improved and preserved on color with daily used food additives. Except damaged by ions such as Fe3+, Fe2+, Ca2+, Sn2+ in water solution, its stability was not easy to interrupt with other metal ions. The colour of lac dye solution was from orange to aubergine with the increase of pH value and the optimum range was under 6.（7） The lac dye had strong scavenging activity on ABTS+?, when the concentration of lac dye reached to 3.75μg/mL, its scavenging rate on ABTS+? could exceed to 87%, with the antioxidant activity 4.17 times of that of the ascorbic acid. The lac dye also had scavenging activity on DPPH·, when the concentration of lac dye reached to 25.00μg/mL, its scavenging rate on DPPH· could be as high as 68%, its scavenging activity on DPPH· was quarter of ascorbic acid. But it had no scavenging activity on O₂ˉ?.