Starch nanoparticles (SNPs) were prepared with corn starch dimethylsulfoxide (DMSO) solution through nanoprecipitation. Effects of non-solvent nature, solvent/non-solvent (S/NS) volume ratio, concentration of starch solution, and molecular weight of starch on size of the SNPs were investigated. Solubility and interaction parameters were used to describe affinity of solvent and non-solvent. It was found that the stronger the affinity, the smaller the mean size of the SNPs. Changes of S/NS volume ratio from 1:5 to 1:30 led to slight decrease in mean size of the SNPs and considerable difference in morphology of the SNPs. The size of the SNPs increased with concentration of starch solution used for precipitation. Through acid hydrolysis, molecular weight of starch was reduced, which resulted in significant decrease in mean size of the SNPs. The lyophilized SNPs could be re-dispersed in water.
Amylose nanoparticles are prepared via precipitation by dropping absolute ethanol into amylose paste. X‐ray diffraction analysis reveales that the amylose nanoparticles display V‐type crystalline structure, and crystallinity of the amylose nanoparticles is dependent upon precipitation conditions, that is, temperature of amylose paste, ethanol dropping rate, and length of amylose chains. Dropping ethanol of 20 °C into amylose paste of 90 °C at a rate of 5 mL min−1 promotes the molecular association of amylose and ethanol into a helical complex and forms more amylose single helices in the precipitated amylose nanoparticles, which results in a higher crystallinity (60.72%) after the amylose nanoparticles are dried at 4 °C for 12 h and then at 40 °C for 12 h under 11% relative humidity. Shorter amylose chains may be unfavorable to complex formation between amylose and ethanol. The findings of this study provide a guideline to prepare amylose nanoparticles with higher crystallinity via precipitation.
Starch nanocrystals (SNCs) obtained from acid hydrolysis of waxy corn starch were modified by cross-linking using either sodium hexametaphosphate or glutaraldehyde in water. The crosslinking preserved the crystalline structure of SNCs and improved the dispersion of SNCs in water. Thermoplastic starch (TPS) nanocomposite films reinforced with SNCs or the cross-linked SNCs were prepared by casting and evaporation. Compared with the SNCs/TPS film, the tensile strength and elongation at break of the cross-linked SNC-reinforced TPS films were increased and the Young's modulus was remained almost unchanged. Moreover, the moisture barrier was enhanced for TPS nanocomposite films reinforced with cross-linked SNCs. The performance improvement of the cross-linked SNC-reinforced TPS nanocomposite films was attributed to better dispersion of the cross-linked SNCs in TPS matrix and different reinforcement/matrix interactions.
Lutein is a carotenoid and has important physiological and antioxidant activity, but its poor dispersity in water and ease of oxidation impede applications. In this paper, encapsulation of lutein into starch nanoparticles is achieved by preparing starch‐lutein nanoparticles via nanoprecipitation. Lutein content in the nanoparticles reaches 13.2 mg g−1 when 90 mg lutein is added into 50 mL 1% (w/v) starch paste. Starch‐lutein nanoparticles provide preservation for lutein from chemical oxidation so that the lutein in starch‐nanoparticles oxidizes with a speed only about 25% when compared to pure lutein. In addition, the dispersity of lutein in water was considerably improved, and the aqueous dispersion of the starch‐lutein nanoparticles can remain stable for 30 days. X‐ray diffraction analysis suggests that lutein might form a complex with amylose.
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