In this study, oil-free (F1) and direct-contact oil-containing (F2) astaxanthin microcapsules were prepared by wet milling followed by spray drying, and indirect-contact astaxanthin microcapsules (F3) with excipient-emulsified oil were produced by high-pressure homogenization followed by spray drying. The microcapsules were characterized for their physicochemical properties, morphological characteristics, encapsulation efficiency, and apparent solubility. Their stability was evaluated under thermal and long-term storage conditions, and bioaccessibility was determined using an in vitro simulated digestion model. Results demonstrated that among the three types of microcapsules, F1 exhibited the highest astaxanthin payload (10.12%), middle moisture content (3.23%), favorable flowability, and a high encapsulation efficiency of 98.36%. Under scanning electron microscopy (SEM), F1 exhibited smooth and intact surfaces, and differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) confirmed the formation of a densely encapsulated structure. The apparent solubility of F1 was 6.41-, 2.30-, and 2.32-fold greater than those of free astaxanthin, F2, and F3, respectively. After rehydration, the particle size of F1 was the smallest (420.83 nm), and F2 was in the middle (441.28 nm), indicating that F1 had the best dispersion stability. After thermal treatment at 100 ℃, F1 and its redispersed solution showed 1.62- and 2.04-fold higher astaxanthin retention than free astaxanthin, respectively. Following 210 days of storage at 4 ℃ or ambient temperature, F1 retained more than 81% of its initial astaxanthin content, 1.04 to 1.08 times that of F2 and F3, respectively. After being stored for 70 days, the redispersed solutions of F1 and F2 showed higher (more than 85% and 80%) astaxanthin retention than that of F3. The bioaccessibility of F1 was 19.95 and 1.17 times those of free astaxanthin and F3, respectively, and the bioaccessibility of F2 was 1.30 times that of F3. In summary, the oil-free astaxanthin microcapsules prepared by wet milling and spray drying offer distinct advantages in terms of physicochemical properties, stability, and bioaccessibility, thereby being promising for applications in functional foods, pharmaceuticals, and related industries.

Purpose: To investigate the binding interaction of astaxanthin with the transmembrane transporter protein cluster determinant 36 (CD36). Methods: Molecular docking was used to simulate the binding interaction between astaxanthin and CD36, the interaction parameters were obtained using an algorithm, the number of binding sites was determined, and the best matching model was established. Moreover, surface plasmon resonance (SPR) was used to measure the binding and dissociation constants of intermolecular interactions. Results: Astaxanthin entered the hydrophobic cavity inside CD36, and the docking binding energy was −11.70 kcal/mol, suggesting a dose-dependent effect. Besides, the equilibrium dissociation constant K_D was 1.00 × 10^-6 mol/L, indicating that astaxanthin bound to CD36 with high affinity, and the kinetic curves showed that the binding mode of astaxanthin and CD36 was slow binding and slow dissociation. Astaxanthin bound to more amino acids of CD36 through hydrophobic interaction. Unlike lutein and β-carotene, which formed weak van der Waals force with the polar amino acid Asn53 of CD36, astaxanthin formed hydrogen bonding with Asn53, which may be partly responsible for the high-affinity binding between astaxanthin and CD36. Furthermore, it was inferred that the ketone group on the terminal ring of astaxanthin or α-hydroxy ketone formed by hydroxyl and ketone groups played a certain role in the formation of hydrogen bonds. Conclusion: Astaxanthin interacts spontaneously with CD36 with high affinity, and the binding mode is slow binding and slow dissociation, contributing to efficient transmembrane transport.

Carotenoids and fat-soluble vitamins (C&FSV) belong to the group of highly lipophilic food components that have important effects on the body’s health, which are ingested mainly through consumption of foods. The knowledge about the intestinal absorption mechanism of dietary C&FSV has been developed from partial C&FSV absorption through simple diffusion to specific transporter-mediated absorption of dietary C&FSV. This paper reviews the latest research progress in the process of digestion and absorption of C&FSV with special focus on, transporter-mediated apical transport, cytosolic transport and intracellular metabolism in enterocytes, and secretion from the basolateral membrane of enterocytes for the entire absorption process, and it provides a comprehensive summary of the regulation of C&FSV transporters. This review is expected to drive the understanding of the intestinal absorption mechanism of lipid-soluble bioactives so that they can better exert their beneficial health effects.

In order to achieve high-valued utilization of algal residue, the present study investigated the preparation and activity of antioxidant peptides from Haematococcus pluvialis. Antioxidant peptides were prepared through 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation scavenging activity-guided fractionation of an enzymatic protein hydrolysate from H. pluvialis by using ultrafiltration, preparative high performance liquid chromatography (HPLC) and analytical HPLC. Amino acid sequence was identified by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The antioxidant peptides were screened and confirmed by molecular docking, and the mechanism of action of the antioxidant peptides was clarified. Furthermore, the in vivo antioxidant activity of the antioxidant peptides was evaluated by using Caenorhabditis elegans. The results showed that the antioxidant capacity of the protein hydrolysate from H. pluvialis was enhanced by 2.96-fold after purification, and fraction i, with the strongest free radical scavenging ability (which scavenged (96.97±2.00)% of ABTS radical cation at 0.25 mg/mL) was selected for structural identification. Ten peptide sequences i-1 to i-10 were obtained. The molecular docking results showed that the minimum binding free energy between i-1 and ABTS radical cation was lowest, indicating that i-1 had the strongest antioxidantcapacity. Furthermore, the novel antioxidant peptide was identified as KFTPAP. In vivo experiments showed that the peptide significantly improved antioxidant capacity in C. elegans (P < 0.05) in terms of the activities of superoxide dismutase (SOD) and catalase (CAT) and malondialdehyde (MDA) content, the effect being most pronounced at a concentration of 100 μmol/L. The potent antioxidant activity of this peptide may be due to the fact that hydrophobic amino acid residues concentrate at the C-terminus, and it contains phenylalanine residues and derives from chlorophyll proteins. This study provides a reference for the high value-added utilization of H. pluvialis residues and the development of food-derived antioxidants.

Z-Isomerization of carotenoids usually change their properties, so it is necessary to comprehensively analyze the physicochemical properties of all-E and Z-astaxanthin (AST). AST with high proportions of Z-isomer were prepared by illumination followed by silica gel column chromatography, and the physicochemical properties of all-E- and Z-AST were measured and compared using an X-ray diffractometer, a differential scanning calorimeter, a scanning electron microscope and a colorimeter, and their in vitro antioxidant activity and in vivo antioxidant activity in Caenorhabditis elegans were evaluated. Meanwhile, the mechanisms underlying the differences in color and antioxidant activity between the two isomers of AST were revealed using quantum chemistry. The results showed that as the proportion of Z-isomer rose, the crystallinity of AST declined, its morphology changed from regular to amorphous, and its solubility in organic solvents and vegetable oils increased. The solubility of 96% Z-AST was 491.2 and 59.9 times as high as that of all-E AST in ethanol and olive oil, respectively. Moreover, the scavenging effect of Z-AST on hydroxyl radical and superoxide anion radical and its capacity to enhance resistance to oxidative stress in C. elegans were significantly higher than those of all-E-AST (P < 0.05). Furthermore, the results of quantum chemistry showed that after Z-isomerization of AST, the absorption intensity at the maximum absorption wavelength (λ_max) attenuated significantly, and the molar absorption coefficient decreased, and the red value of AST dropped significantly. The antioxidant capacity of AST was improved by an increase in the length of hydroxyl bonds in the terminal rings and changes in the ionization potential and electron affinity. These results provide a theoretical basis for revealing the differences between all-E and Z-AST and guiding the application of AST in health field.