P toluene sulfonic acid tsa

Urea (CH₄N₂O, Proquimsa, Coahuila, Mexico), phosphorus pentoxide (P₂O₅, Sigma-Aldrich, St. Louis, MO, USA), zinc powder (Chemical Dynamics, Florida, USA), ethanol (C₂H₆O, Sigma-Aldrich, St. Louis, MO, USA), methanol (CH₄O, Sigma-Aldrich, St. Louis, MO, USA), acetone (C₃H₆O, Sigma-Aldrich, St. Louis, MO, USA), Toluene (C₇H₈, Sigma-Aldrich, St. Louis, MO, USA), Hexane (Sigma-Aldrich, St. Louis, MO, USA), Phosphoric Acid (H₃PO₄, Fermont, Nuevo León, Mexico), Ammonium Hydroxide 30% (NH₄OH, Fermont, Nuevo León, Mexico), Hydrochloric Acid 30% (HCl, Fermont, Nuevo León, Mexico), porcine hematin (Sigma-Aldrich, St. Louis, MO, USA), aniline (Sigma-Aldrich, St. Louis, MO, USA), sodium carbonate (Na₂CO₃, Sigma-Aldrich, St. Louis, MO, USA), sodium bicarbonate (NaHCO₃, Sigma-Aldrich St. Louis, MO, USA), p-toluene sulfonic acid (TSA, Sigma-Aldrich, St. Louis, MO, USA), hydrogen peroxide (H₂O₂, Sigma-Aldrich, St. Louis, MO, USA), Dimethyl sulfoxide (DMSO, Sigma-Aldrich, St. Louis, MO, USA), N-Methyl-2-pyrrolidone (NMP, Sigma-Aldrich, St. Louis, MO, USA), deuterated sulfuric acid (D₂SO₄, Sigma-Aldrich, St. Louis, MO, USA), deuterated DMSO (Sigma-Aldrich, St. Louis, MO, USA), deuterated acetone (Sigma-Aldrich, St. Louis, MO, USA) and deuterated water (D₂O, Sigma-Aldrich, St. Louis, MO, USA).

Chitosan was obtained by heterogeneous deacetylation of chitin extracted from the lactic acid fermentation (LAF) of shrimp (Litopenaeus vanameii) wastes and purified as reported elsewhere [10 (link)]. LA (85% aqueous solution) was acquired from J.T. Baker (Toluca, Mexico). Triethanolamine (TEA) and p-toluenesulfonic acid (TSA) was supplied by Sigma-Aldrich (Saint Louis, MO, USA). Low-density polyethylene (LDPE) film samples were kindly donated by Casa Miyako (Mexico City, Mexico). The L. monocytogenes strain was a kind gift of Dr. Rigoberto Hernández-Castro from the culture collection of Hospital General Dr. Manuel Gea González (Mexico City, Mexico) and in trypticaseine soy broth (TSB) at 37 °C for 24 h to attain 10⁷ colony-forming units (CFU) per mL. Inoculum was prepared by dilution in sterile saline solution (0.9 NaCl wt/v% (weight/volume)) up to 10⁴ CFU/mL. Soy protein isolate (SPI) was purchased to Sigma Aldrich. Fresh cheeses were provided by a farm (Celaya Guanajuato, Mexico).