Selective detection of different types of adulterants present in food items is necessary and efficient nano sensors for such applications are of vital importance. In this study, recently synthesized two-dimensional (2D) Janus monolayer of MoSSe has been explored to detect various food adulterants like formalin (CH2O), histamine (C5H9N3) and hydrogen peroxide (H2O2). By using first principles density functional theory calculations, we find that the incident adulterants weakly bind with pristine MoSSe, however the adsorption energies (Eads) are significantly improved upon vacancy defects and foreign elements substitutions. Furthermore, the sensing mechanism is studied in presence of water for the applications in practical working conditions. Energetic evaluation shows that both H2O2 and histamine result into stronger Eads as compared to formalin over defect induced MoSSe; whereas, the presence of water further enhances the adsorption of H2O2. In addition to the adsorption characteristics, charge transfer mechanism and electronic structures of pristine and defect induced MoSSe monolayers upon the exposure of studied adulterants have also been studied. Boltzmann thermochemical statistics further verified the explicabilities of pristine and defected MoSSe monolayers for in vitro test of adulterants in food products. Suitable Eads values and measurable changes in the electronic properties indicate the potential of MoSSe monolayers as efficient nano sensors towards selected adulterants for their applications in food processing, biotechnology, healthcare and medical laboratories.