Characterization of Immobilized Endo-Polygalacturonase PGC-AN64 from Aspergillus niger HO32 with Potential Biotechnological Interest

Abstract

This study focuses on the characterization and application of an immobilized purified endo-polygalacturonase PGC-AN64 from Aspergillus niger HO32 using sodium alginate (SA), and its combinations with guar gum (SA-Gu) or chitosan (SA-Ch) as supports. Immobilization efficiencies were 75%, 83%, and 77% for PGC-AN64-SA, PGC-AN64-SA-Ch, and PGC-AN64-SA-Gu, respectively. Immobilized enzymes showed enhanced thermostability and pH stability. At 80°C, the half-lives reached 8, 11, and 16 h, and residual activity at pH 5 after extended incubation (12–24 h) was maintained at approximately 56–58%, depending on the matrix. Reusability tests showed activity retention of ~50% for PGC-AN64-SA after 4 cycles, and ~64% and 51% for PGC-AN64-SA-Ch and PGC-AN64-SA-Gu, respectively, after 6 cycles. Orange juice clarification efficiency was reflected by transmittance values of 85.20±1.68% for free PGC-AN64, and ~84% for all immobilized forms. XRD, FTIR-ATR, and FE-SEM analyses confirmed structural changes upon immobilization. In addition, orange juice clarification resulted in a decrease in total soluble solids and color modifications: reduced a* values, and increased L* and b* values. These findings highlight that immobilizing PGC-AN64 on SA-based matrices improves enzyme stability, operational reusability, and retains orange juice clarification performance. The approach offers an efficient and safe enzymatic solution for agro-industrial applications, particularly in juice processing.