Non-Thermal Treatments and Lactic Acid Bacteria Fermentation for Reducing Chlorpyrifos and Phoxim Residues in Buffalo Milk: A Comparative Approach

Background: Organophosphorus pesticides (OPPs), particularly chlorpyrifos and phoxim, are lipophilic contaminants of environmental and food-safety concern in dairy systems. These OPPs exhibit sufficient chemical stability to persist through milk processing and storage even though neither compound is classified as a Persistent Organic Pollutant (POP) under the Stockholm Convention. Moreover, these OPPs pose public health risks through neurotoxicity, endocrine disruption, and bioaccumulation in high-fat matrices such as buffalo milk. Objective: Thus, this study aimed to compare and evaluate ultrasonication, ultraviolet (UV)/titanium dioxide (TiO2) photocatalysis, and lactic acid bacteria (LAB) fermentation to reduce chlorpyrifos and phoxim concentrations in artificially spiked buffalo milk. Methods: Residues were quantified by Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) extraction coupled with gas chromatography–mass spectrometry (GC-MS). Sonication (100 W, 37 kHz) was applied for up to 20 min; UV/TiO2 (254 nm; 50–200 mg TiO2/100 mL) for up to 60 min; and three LAB preparations were individually inoculated into spiked pasteurized milk and incubated for 24 h (n = 3; p < 0.05). Results: Sonication achieved removal efficiencies of up to 66.81% and 97.52% for chlorpyrifos and phoxim, respectively. UV/TiO2 (200 mg/100 mL, 60 min) achieved 57.31% removal of chlorpyrifos and 98.63% removal of phoxim; because TiO2-dark-adsorption controls were not included in this study, these values reflect combined adsorption and reactive oxygen species-mediated processes rather than photocatalysis specifically. Lactiplantibacillus plantarum CICC20261 achieved the greatest LAB-mediated reduction (49.61% chlorpyrifos; 43.28% phoxim) while maintaining robust viability under pesticide exposure (7.79 ± 0.51 log CFU/mL after 24 h under chlorpyrifos; 7.40 ± 0.84 log CFU/mL under phoxim), compared with 9.23 ± 0.42 log CFU/mL in the pesticide-free control at 24 h. Conclusion: Under the specific, non-equivalent reference conditions used for each method (Section 3.3), UV/TiO2 numerically achieved the highest phoxim removal and a moderate chlorpyrifos removal, while sonication was highly effective for phoxim specifically. Together, sonication and LAB fermentation offer rapid, complementary non-thermal approaches to pesticide reduction. Claims of sustainability, eco-friendliness, or industrial applicability are not yet supported by direct measurements of milk quality, sensory attributes, or (for UV/TiO2) nanoparticle safety; thus, such claims should be regarded as provisional until such data are available. However, as currently configured, UV/TiO2 photocatalysis should be regarded as a proof-of-concept degradation method rather than an immediately deployable process, because the protocol did not include a nanoparticle recovery step (e.g., filtration, centrifugation, or catalyst immobilization) or confirmatory quantification of titanium. Residual nano-TiO2 in treated milk therefore represents an unresolved food-safety consideration that requires evaluation before industrial adoption.