| Deoxyribonucleic acid (DNA) is the fundamental hereditary material of living organisms and is widely distributed in the natural world. Studies of DNA, in which the discovery of DNA double-helical structure has established the foundation of molecular biology, have already greatly contributed to the progress of life science. DNA is a highly charged polyelectrolyte with perfectly biocompatibility, and can selectively interact with small molecules. These characteristics offer DNA excellent prospects for serving as biomaterials. It can be expected that cationic polymers such as chitosan can bind to the polyanionic backbones of DNA to form a nano-complex. Astaxanthin is a kind of carotenoids and widely distributed in nature. Astaxanthin can be synthesized in certain marine animals and plants, such as Haematococcus pluvialis, Phaffia rhodozyma. While human can only obtain astaxanthin from the food chain, as they cannot produce it in their own body. With a high antioxidant activity and other biological activities, astaxanthin is widely used in foods, drugs, cosmetics, and other industrial areas. However, as a kind of lipid-soluble pigments, it cannot solve in water and is only soluble in certain organic solvents such as chloroform, acetone. Besides, astaxanthin is sensitive to light, heat, oxygen and other factors, which makes it easily be damaged and have poor bioavailability. These problems greatly limit the application of astaxanthin.Here, we choose salmon sperm DNA and chitosan as two biomaterials and try to improve the water-solubility and stability of astaxanthin by using nanotechnology. We use these two natural nanomaterials to encapsulate astaxanthin, so as to prepare safe and edible astaxanthin nano-complex. In this paper, the main research contents are showing as follows.(1) Salmon sperm DNA and chitosan, two polyelectrolytes found in nature, were chosen for assembling water-soluble nanomaterials and further encapsulating astaxanthin. By embedding in the DNA/CS nanoparticles, astaxanthin can be easily dispersed in water and be protected from degradation of heat and oxygen. Some important factors that influencing the formation of astaxanthin-encapsulated DNA/chitosan (ADC) nanoparticles, such as the molar ratio between the amino group of chitosan and the phosphate group of DNA (N/P), the concentration of different molecules, the volume ratio between water and ethanol, etc. Above all, N/P is the most important factor. The optimal condition for preparing ADC is:when the N/P is 4:1, the concentration of DNA and chitosan is 0.2 mg/mL, respectively, and the ratio of water and ethanol is 1.5:1, we can obtain a homogeneous purple ADC nanosuspension with obvious Tyndall effect. Moreover, the ADC Nano suspension can be stablized at room temperature for 20 days.(2) The ADC nanoparticle was further characterized to evaluate its morphology, the encapsulation efficiency of astaxanthin and residual amount of ethanol, etc. The particle size and zeta potential of ADC nanoparticles are acquired by dynamic light scattering (Malvem Instruments, UK). The particle size is around 200-260 ran, and zeta potential is around+17-+30 mV, with PDI is 0.2-0.3. The maximum encapsulation efficiency is 34.96±0.19%, and the loading capacity is 40.42±0.17% assayed HPLC. The residual ethanol amount is 0.089±0.001% determined by headspace gas chromatography. The morphology of ADC nanoparticles, observed by transmission electron microscopy (TEM), was well dispersed as individual spherical nanoparticles.(3) The formation mechanism of ADC nanoparticles was studied initially. Chitosan is a natural polycationic macromolecule, and salmon sperm DNA is a biological macromolecule with the negatively charged phosphate group. DNA and chitosan mixed under a certain proportion can assemble into nanocomplex by electrostatic interaction. Chitosan can not self-assemble into nanocarriers to encapsulate astaxanthin. By inserting and embedding in the DNA strands, astaxanthin can interacted with DNA and form large aggregates. To obtain ADC nanoparticles, the three molecules should be added and mixed under certain order and proportion. So, astaxanthin can be efficiently encapsulated in the DNA/chitosan nanocarriers by non-covalent interactions and finally fonn stable ADC nanocomplex.(4) The stability of ADC nanosuspension was evaluated by testing the content changes of astaxanthin during storage. The astaxanthin concentration retention rate is 64.78±0.03% and 17.19±0.02% for 30 days’storage at 4℃ and 70℃, respectively. Acidic buffer facilitates the retention of astaxanthin in ADC nanoparticles. while alkaline buffer can decrease the stability of ADC nanosuspension. The astaxanthin concentration retention rate is up to 82.78±0.09% in acidic buffer, while down to 46.76±0.08% in alkaline buffer. It has the ability of anti-oxidation.To sum up, in this study we choose chitosan and DNA as biornaterials for encapsulating natural astaxanthin, and stable ADC nanosuspension is successfully prepared. The ADC nanoparticles have better properties than astaxanthin, such as stability, water solubility, and antioxidant activity, which makes it great value in further application. |
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