κ-Carrageenan/konjac glucomannan composite hydrogel filled with rhamnolipid-stabilized nanostructured lipid carrier: Improvement of structure and properties

Abstract

This study investigated the feasibility of applying rhamnolipid-stabilized nanostructured lipid carrier (RNLC) as a novel type of particulate filler and its impact on the structure and properties of κ-carrageenan/konjac glucomannan (KC-KGM) composite hydrogel. RNLC particles (204.87 ± 3.50 nm) were fabricated by high-pressure homogenization method. X-ray diffraction and differential scanning calorimetry results suggested that KC-KGM could regulate the crystallinity and polymorphism of RNLC. Fourier transform infrared spectroscopy analysis verified the presence of hydrogen bond and electrostatic interaction between RNLC and KC-KGM. Cryo-scanning electron microscopy and magnetic resonance imaging observation revealed that the increase of RNLC (0–0.25 wt%) led to a denser network structure with good uniformity, improving the texture profiles (hardness and cohesiveness) and rheological properties (moduli, critical strain and thermal stability) of composite hydrogels. RNLC at higher filling levels (0.5–2 wt%) made composite hydrogels more rigid and brittle. Low field-nuclear magnetic resonance analysis confirmed the decreased mobility of immobilized/free hydrogen protons in RNLC-filled composite hydrogels, and their water synthesis rates could be reduced by up to 12.26% after freeze-thawing for five repetitions. The fitting of Korsmeyer-Peppas model (R2 > 0.992) unraveled that the swelling mechanism of composite hydrogels belonged to pseudo-Fickian diffusion, and the swelling behavior could be altered by adjusting the particle filling level. Overall, the optimal synergistic effect between structure and properties could be achieved when the mass ratio of KC-KGM to RNLC reached 4:1. These findings would bring more potential for applying RNLC as a functional filler in gel foods.