Preparation, Characterization, and pH-Responsive Intestinal Release Properties of Gel Beads Encapsulating Sea Cucumber Mouthpart Peptides

Sea cucumber mouthpart peptides (SCPs) are marine bioactive peptides with considerable application potential. However, their oral delivery remains challenging because of their poor stability and low intestinal bioavailability. To develop a delivery system for SCPs with gastric protection and pH-responsive intestinal sustained-release properties, double-layer gel beads (SCP-BMs) were fabricated through ionic gelation, with SCPs as the core material and sodium alginate (SA) and chitosan (CS) as the wall materials. The preparation conditions of the gel beads were optimized using single-factor experiments and response surface methodology (RSM). The optimized gel beads were then characterized for their morphology, thermal stability, in vitro gastrointestinal release behavior, and antioxidant activity. The results showed that the optimal preparation conditions were 1.67% (w/v) sodium alginate, 0.96% (w/v) chitosan, and 2.16% (w/v) CaCl2. Under the optimized conditions, the encapsulation efficiency (EE) reached 94.33%, significantly higher than that of the single-layer gel beads (SCP-SMs, 58.61%). Structural characterization showed that SCP-BMs exhibited a more compact structure than SCP-SMs, along with improved thermal stability. In vitro release and antioxidant assays demonstrated that SCP-BMs exhibited better gastric protection, pH-responsive intestinal release, and higher 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS) radical scavenging activity compared with SCP-SMs. This study demonstrated that the SA/CS double-layer wall material system effectively improved the encapsulation efficiency, structural stability, and intestinal release behavior of SCP gel beads. These findings provide a feasible strategy for the development of SCP delivery systems and offer a theoretical basis for the high-value utilization of sea cucumber byproducts.