Process Optimization of Fish Gelatin Edible Films Production Using Red Pitaya Peel RSM Modeling of Homogenization and Drying Effects

The purpose of this study was to optimize the processing conditions for the production of edible films from a mixture of fish gelatin (6% w/v), red pitaya peel powder (0.5% w/v), and glycerol (2% w/v) using Response Surface Methodology (RSM) with a Central Composite Design (CCD). The process factors evaluated were homogenization speed (A), drying time (B), and drying temperature (C). The responses measured were tensile strength (TS), elongation at break (EAB), thickness (T), moisture content (MC), and solubility (S). TS decreases with higher A (–0.0007A) but increases with C (+0.0025C). EAB is optimal at high A (+1.50A) but decreased with B (–0.1866B) and C (–9.65C). T was influencedby AB,AC,and BC interactions as well as the quadratic effects of A, B, and C. MC increased with A (+0.2318A) and B (+0.0725B) due to the high hygroscopicity of the film but decreased with C (–0.5497C). S decreases with all factors (–0.0643A, –0.2738B, –2.36C).The optimum conditions (A = 9000 rpm, B = 19 h, C = 50°C) yielded TS = 0.0221 MPa, EAB = 125.25%, T = 0.209 mm, MC = 12.46%, S = 46.70%. The resulting film exhibited natural color characteristics (L* = 75.07, a* = 9.2, b* = 5.8), WVTR (345 g/m²/24 h), moderate antioxidant activity (38.47-48.85% DPPH inhibition), and bactericidal effect vs. E. coli and S. aureus (MBC/MIC ratios 1.12 and 1.81, respectively), meeting CLSI criteria (MBC/MIC ≤ 4). FTIR analysis was used to strengthen the presence of functional group interactions within the film matrix, while SEM observations were conducted to assess the uniformity and surface density.