Phenylalanine-Based Supramolecular Gels for Structuring Apple Juice Matrices

The development of low-molecular-weight supramolecular hydrogels based on amino acids emerges as a promising approach for food matrix structuring and functional food design. Particularly noteworthy is the ability of L-phenylalanine (PHE) to form gels in the presence of propylene glycol. Building upon previous findings where a binary water/propylene glycol system (50:50 v/v) containing 1.0% w/v PHE achieved gelation either through mechanical agitation or cold storage, this study investigates the gelation behavior and process parameters of PHE self-assembly in complex commercial or natural apple juice matrices. The incorporation of juice altered gelation kinetics, requiring adjustments in PHE concentration (1.0%–1.4% w/v), mechanical energy input (1000–2000 rpm agitation), or storage conditions. Both sucrose or sweetener-added commercial juice (1.0% or 1.2% w/v PHE) maintained a viscosity value of 72 mPa.s during 30 min of agitation at 1000 rpm, showing no gelation. However, sweetener-added commercial juice at 1.2% PHE formed a self-standing hydrogel after 1 week at 4 °C. At 1.4% w/v PHE, this system exhibited average viscosity peaks by increasing stirring speed; 126.6 mPa.s at 9.25 min (1400 rpm), 120.15 mPa.s at 10 min (1700 rpm), and 110.75 mPa.s at 15.25 min (2000 rpm). Samples containing natural squeezed juice (1.2% or 1.4% w/v PHE) displayed steady viscosities (83.8 mPa.s or 78.9 mPa.s, respectively) under 1400 rpm agitation, showing no viscosity peaks. Nevertheless, the 1.4% PHE matrix successfully formed a structured hydrogel upon cold storage.

To confirm true viscoelastic behavior, ongoing research encompasses thermal gelation kinetics (T_gel via temperature sweeps), viscoelastic moduli profiling, and yield stress determination. These findings demonstrate that PHE-based GRAS hydrogels provide a controllable, process-dependent texturizing technology for industrial unit operations, offering promising applications in the continuous processing of plant-based matrices and the scalable formulation of texture-modified foods for dysphagia management.