Thermal Stabilization and Kinetic Modeling of an Enriched Hydrophilic Extract from Grape Pomace Using Alginate-Carboxymethyl Cellulose Blended Hydrogels

Introduction: This study investigated binary biopolymer matrix engineering to preserve fragile anthocyanins and phenolic acids in encapsulated aqueous grape pomace extracts under thermal stress.

Methods: An enriched hydrophilic aqueous phase stripped of lipophilic interferences was encapsulated in 2% pure sodium alginate (SA) or a 1.5% SA and 0.5% carboxymethyl cellulose (CMC) blend. Beads were stored for 27 days at 30°C, 40°C, and 50°C. Total Phenolic Content (TPC) and DPPH activity were monitored following complete matrix dissolution. Data were modelled using Three-Way Mixed ANOVA and Principal Component Analysis (PCA).

Results: A highly significant three-way interaction (P<0.001) confirmed undulating, non-monotonic profiles for both parameters, invalidating linear degradation models. For DPPH, the formulation effect was exceptionally robust (F(1, 6) = 1668.07, P<0.001); pure SA suffered an abrupt loss of radical scavenging activity by Day 7, whereas the CMC blend significantly stabilized and enhanced radical scavenging activity, uniquely peaking at 40°C on Day 7, hypothetically due to the matrix-promoted formation of acid-stable pyranoanthocyanins and highly structured intermolecular copigmentation complexes. Conversely, TPC showed a non-significant overall formulation effect (p=0.360). Heat degrades complex compounds in pure SA. This artificially raised the TPC scores even though the actual antioxidant power had crashed. In contrast, the CMC blend protected the extract and maintained close links between phenolic levels and antioxidant activity. PCA components of eigenvalues greater than 1.0 captured 82.6% of the variance. Variable contribution analysis confirmed PC1 mapped overall phenolic concentration, while PC2 and PC3 tracked proposed functional degradation and transient molecular association phases, respectively.

Conclusions: Standard linear modeling fails to capture the complex, multi-phasic kinetics of encapsulated grape pigments. Blending 0.5% CMC creates a dynamic molecular shield that prevents unchecked thermal cleavage, potentially redirecting degradation pathways toward highly stable, functional anthocyanin networks under thermal stress.