Inactivation Efficacy of Combination Treatment of Propyl Gallate and UVA LED for <i>Escherichia coli</i> O157:H7 in Apple Juice

The objectives of this research were to analyze the synergistic antimicrobial effects of food-grade antioxidant propyl gallate (PG) and ultraviolet A (UVA) irradiation to inactivate Escherichia coli O157:H7 in peptone water (PW) and apple juice. Samples were treated with a final concentration of 2 mM PG and varying doses of UVA irradiation (0, 5, 10, 15, and 20 J/cm²), both individually and in combination. The combined 2 mM PG and UVA (20 J/cm²) treatment demonstrated significant microbial reductions of 3.12 log CFU/mL in PW and 2.95 log CFU/mL in apple juice. Mathematical modeling provided the D_3d and D_5d values, representing the doses required to achieve 3-log and 5-log reductions, respectively. In apple juice, the D_3d and D_5d values for the PG+UVA combination treatment were approximately 2 times smaller than those for UVA treatment alone, highlighting the enhanced efficacy of the combined approach. The PG+UVA treatment generated various reactive oxygen species (ROS), as PG acted as a photosensitizer under UVA exposure. These ROS led to cell membrane damage and enzyme inactivation, which ultimately resulted in microbial inactivation. Additionally, this approach maintained the quality of apple juice, preserving its pH, color, cloud value, total phenolic content, and total flavonoid content. The results demonstrate that the PG+UVA treatment is a promising non-thermal pasteurization technology for microbial control in apple juice, effectively maintaining product quality while enhancing food safety and its potential for broader application in the food industry.