Pinto bean protein-based acid-induced cold-set gels as carriers for curcumin delivery: Fabrication and characterization

Abstract

In this study, a new acid-induced cold-set gel based on pinto bean protein isolate (PBI) was developed, and then its textural, morphological, rheological, and physical properties were evaluated. Textural and rheological properties of the gels improved when protein and glucono-delta-lactone (GDL) concentrations were increased. Acid-induced gels showed a disordered structure of aggregates. The water holding capacity (WHC) of the gels increased significantly (p<0.05) from 85 to 86% to 92–96% when the protein concentration increased from 5% to 7%. The gel fabricated with 7% protein and 15% GDL indicated better mechanical and rheological properties; hence it was selected for curcumin entrapment and further evaluations. According to circular dichroism (CD) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results, the pre-heating process at pH ∼ 7.3 ± 0.08 allowed to fabricate thermally aggregated PBI (TA-PBI). The pre-heating process caused a significant increase in particles diameter (p<0.05), but surface hydrophobicity decreased (p<0.05). PBI cold-set gel presented an excellent embedding potential (98.54%) at a curcumin concentration of 0.7 mg/mL. Fluorescence spectroscopy indicated that curcumin was attached to PBI. The results of confocal laser scanning microscopy (CLSM) revealed a homogeneous distribution of curcumin in TA-PBI gels. The thermal analysis confirmed the presence of curcumin in an amorphous form within the cold-set gel. PBI gels could effectively inhibit curcumin's immediate release in a simulated gastric medium (22.6% after 2 h) and led to its sustained release in a simulated intestinal condition (61.68% after 4 h). Release test results were aligned with the protein digestibility pattern. Peppas model could predict the release of curcumin from hydrogel in the gastrointestinal tract. In conclusion, TA-PBI gels can be introduced as promising delivery vehicles for the sustained release of curcumin in food and pharmaceutical systems.