Preparation, Properties And Rheological Behaviors Of Chitosan Nanoparticles Encapsulating Tuberose Fragrance

Aromatic materials encapsulation, which could effectively extend the perfume retaining time, slow down the aroma releasing rate and enhance the active component stability, has been widely applied in food, tobacco, textiles and so on. Chitosan (CS) is a natural cationic polysaccharide, having huge resources, with excellent biocompatibility, biodegradability and mucoadhesive property. The nanoparticle based on CS can effectively control the rate of drugs release, reduce the toxicity and side effect, improve active components stability, and will be a kind of promising controlled-release carriers.In this paper, on the base of using chitosan and sodium tripolyphosphate (TPP) as wall materials, the CS nanoparticles encapsulating tuberose fragrance (TF-CS-Nps) were prepared in o/w emulsion using the ionic gelation method. The effects of reaction pH, wall materials mass concentration, CS molecular weight, emulsification process, fragrance amount, solid content, stirring rate, TPP drip rate and reaction time on on the size distribution and Zeta potential of TF-CS-Nps were investigated in detail. The morphological properties, molecular structure, thermal stability and fragrance encapsulation effect of TF-CS-Nps were characterized using transmission electron microscopy (TEM), fourier transformation infrared spectroscopy (FTIR), gas chromatography-mass spectrometry (GC-MS) and Thermogravimetric analysis (TGA). The steady and dynamic rheological behaviors of TF-CS-Nps aqueous suspension under different reaction pH, CS/TPP mass ratio, CS molecular weight, emulsifier content, fragrance amount and solid content were also studied.Results indicated that the size distribution and Zeta potential of TF-CS-Nps were strongly dependent on various preparation conditions. The optimal preparation conditions were obtained: reaction pH of 5.3, CS mass concentration of 1.70 mg/mL, TPP mass concentration of 1.70 mg/mL, CS molecular weight of 150 kDa, mixture of AEO9 and PEG400 as compound emulsifier, emulsifier content of 1/2 (w/w) based on fragrance, ultrasonic emulsification for 15 min, fragrance amount of 100 % (w/w) based on wall materials, solid content of 0.288 %, stirring rate of 500 r/min, TPP drip rate of 0.500 g/min and reaction time of 1 h. Under the optimal preparation conditions, TF-CS-Nps exhibited irregularity sphericity in shape and the average particle size was about 174 nm, the polydispersity (PDI) was 0.138 and the Zeta potential was 20.8 mV. In addition, the tuberose fragrance developed interactions with CS nanoparticles and more than 90 % components of the tuberose fragrance could be encapsulated in CS nanoparticles with nearly 29.5 % of the fragrance loading capacity. The thermostability of tuberose fragrance encapsulated in CS nanoparticles was improved.TF-CS-Nps aqueous suspension basically showed viscosity under low oscillation frequency, while exhibited elasticity in high oscillation frequency. The loss modulus and storage modulus of TF-CS-Nps aqueous suspension increased gradually with the increase of reaction pH, CS/TPP mass ratio, CS molecular weight and solid content, respectively. However, both loss modulus and storage modulus decreased with increasing fragrance amount, which is attributed to the reduction of crosslinking between CS and TPP resulting from the charges on tuberose fragrance. TF-CS-Nps aqueous suspension would tend to unstable under low or high emulsifier content, which led to the decrease of loss modulus and storage modulus. With increasing shear rate, shear-thinning behavior was observed in TF-CS-Nps aqueous suspension, which was the rheological property of pseudoplastic fluid. The zero-shear viscosity increased with an increase in reaction pH, CS/TPP mass ratio, CS molecular weight and fragrance amount, respectively, while the high-shear viscosity changed not obviously. The apparent viscosity had a tendency to decrease firstly and then increase with increasing emulsifier content, and sharply increased under high solid content which was attributed to the falling flowability of TF-CS-Nps aqueous suspension due to the enhancing intensity and frequency of nanoparticles interaction. Besides, The steady rheological behaviors of TF-CS-Nps aqueous suspension under different preparation conditions could be fitted with Carreau model with 4 parameters well (σ<10,R2>0.99).