Optimization of Active Filtration to Reduce Gluten Cross-contact in Reused Frying Oil

Justification: Food manufacturers often use the same frying oil to prepare several foods for economic reasons, raising concerns about allergen and/or gluten cross-contact. Active filtration, which employs one or more adsorbents, is designed to remove oil-soluble impurities. However, the effectiveness of this treatment in the removal of proteins remains unreported. 
Objective: This study aimed to (1) optimize the working conditions for filter aids using response surface methodology, and (2) evaluate their effectiveness in reducing gluten content in reused frying oil. 
Methods: Frying oil spiked with 5,000 ppm of wheat gluten underwent a frying process (175 °C for 3 min) followed by cooling to 105 °C. Diatomaceous earth was added at varying concentrations (0-1%) and mixed for different durations (5-30 min). The oil was then filtered through metal sieves of varying pore sizes (150-1000 µm). Optimized conditions were subsequently applied to oil used to fry breaded shrimp.
Results: Addition of filter aid significantly reduced the gluten concentration in the wheat gluten-spiked oil compared to sieving alone. Treatment with 0.05% (w/w) reduced the residual gluten concentration by 48% compared to sieving alone. The optimal condition was achieved at a filter aid concentration of 0.525%. In addition, increasing the incubation time from 5 min to 30 min further decreased the residual gluten concentration. When 10 batches of breaded shrimp (12 g/batch) were fried in 120 mL frying oil, gluten levels in the oil reached approximately 79 ppm. Adding filtration aids significantly reduced gluten content in reused oil, with residual gluten levels decreasing by 79% to 99% compared to sieving alone.
Significance: This study highlights the potential of active filtration as an effective strategy to minimize residual gluten in reused frying oil, providing a practical approach for preventing allergen cross-contact during frying operations.