Influence of transmittance and viscosity of liquid food matrices on photo-/sonodynamic sterilization efficiency

The breakout of food safety incidents poses substantial risks to public health. During food processing, a variety of foodborne pathogens (e.g., Staphylococcus aureus, Escherichia coli, Listeria monocytogenes) may frequently contaminate raw materials through compromised supply chains or inadequate hygiene practices. These microbes can survive processing stages and, upon consumption, trigger severe gastrointestinal infections, systemic illnesses, or even fatal outcomes, particularly in vulnerable populations like children and the elderly. While conventional sterilization methods are widely used, they are often associated with certain drawbacks, such as nutrient degradation and undesirable alterations in food quality. In contrast, emerging non-thermal sterilization technologies, such as photodynamic treatment (PDT) or sonodynamic treatment (SDT), can effectively inactivate foodborne pathogenic bacteria while preserving the nutritional and sensory qualities of food products. Photodynamic treatment operates via a light-activated mechanism: photosensitizers, upon absorption of specific wavelengths of light, undergo a photochemical transition to generate reactive oxygen species (ROS), primarily singlet oxygen and hydroxyl radicals, while sonodynamic treatment leverages ultrasonic waves to elicit cavitation effects and mechanical damage in pathogens. However, the inactivation efficacy of photodynamic treatment and sonodynamic treatment varies across food matrices due to the complexity and heterogeneity of food matrices, and the underlying mechanisms remain incompletely understood. Therefore, the present study employed blue pigment and guar gum to construct model food matrices with variable optical transmittance and viscosity, respectively. Then, the objective was to systematically investigate the bactericidal efficiency of curcumin-mediated PDT and SDT against Staphylococcus aureus under different food matrices conditions. Firstly, model systems with different transmittance (blue pigment gradient: 0.00625%～0.0500%) and viscosity (guar gum gradient: 0.200%～0.800%) were prepared. Absorbance was measured by spectrophotometry, and viscosity was determined by rotational viscometry. Results showed that increasing blue pigment concentration (0.00625%–0.05000%) has no significant viscosity change. Conversely, increasing guar gum concentration (0.2%～0.8%) led to nonlinear viscosity increases, while transmittance remained unchanged. Subsequent treatments involved curcumin at a concentration of 50 μmol/L as the sensitizing agent, activated by a 425 nm LED light source at an intensity of 5.3 mW/cm², combined with ultrasound at 45 kHz and 0.40 W/cm² for 30 minutes. The results show that increasing blue pigment concentrations (0.00625%～0.0500%) significantly impaired PDT efficacy due to reduced light penetration, whereas SDT was largely unaffected under the same optical conditions. In contrast, higher guar gum concentrations (0.200%～0.800%) significantly hindered SDT efficiency by impeding ultrasonic transmission, while PDT remained comparatively stable in its bactericidal performance. In addition, in the Pearson correlation analysis of light transmittance/viscosity and photo-/sonodynamic treatment, light transmittance and photodynamic treatment showed a strong correlation, while viscosity showed a strong correlation with sonodynamic treatment. In summary, optical transmittance was identified as the main factor affecting the photodynamic effect, while substrate viscosity is the key factor affecting the sonodynamic effect. These findings may contribute valuable reference data for optimizing the application of photo- and sonodynamic technologies in diverse food matrices.