Limits of detection for analytical methods to detect adulterants and inhibitors in milk.

Mario Noa- Pérez, Miriam Cortés- Marín, Patricia Landeros- Ramírez, Zoila Gómez- Cruz, Mario Real- Navarro, Ramón Reynoso- Orozco, Teresa de Jesús Jaime Ornelas y Carlos Juárez-Woo

Abstract

The Mexican Regulations on milk classifies a product as adulterated when it has either undergone treatment that conceals its alteration and/or defects in its process or in the sanitary quality of the raw materials, among other criteria. The principal, most widely known adulterants incorporated into milk, include those added to increase milk volume and mask acidification. Milk should also test negative for the presence of inhibitors, e.g. antibiotics or disinfectants. The objective of this work was to determine the LOD for starches, sucrose, gelatin, chlorinated disinfectants; oxidants, quaternary ammonium and 14 most widely used microbial growth inhibitors in milk. This is because although the prohibition of these substances is clearly established, the detection limits (LOD) are not declared in the current regulation. With this finality, qualitative chemical analytical methodologies for detection of adulterants described in the Mexican Standards were implemented, as well as for the Yogurt Inhibition Test. Microbiological quality skim milk powder was used as a negative control, and the commercial culture YO-MIX TM was used for the Yogurt Inhibition Test. The following LOD were obtained by chemical methods for starches (125 and 250 mg/kg), gelatin (250 mg/kg), hydrogen peroxide (6 mg/kg), sodium hypochlorite (25 mg/kg), benzalkonium chloride (12 mg/kg), N-Alkyl (C12,16) - N, N-dimethyl-N- benzylammonium (6 mg/kg). The yogurt test showed higher LOD for the disinfectants: 25,000 mg/kg for sodium hypochlorite and 60 mg/kg for the quaternary ammonium compounds. On the other hand, although oxidants were not detectable the yogurt test was sufficiently sensitive to detect the Maximum Residue Limits (MRLs) for the 14 antimicrobials tested. Carrying out both types of tests, chemical and yogurt, to determine disinfectants and inhibitors at the levels of interest in milk is recommended.