Meat, is a highly structured product consisting of muscle fibres, lipids and connective tissue sheaths. These differents compounds are suspected of modulating the diffusion of digestive enzymes in meat during its gastric digestion. To follow the pepsin diffusion in digested meat and better understand the role of meat structure organization we investigated the use of high resolution time of flight secondary-ion mass spectrometry (Tof-SIMS) imaging to detect pepsin in food. Two beef muscle samples (1.5 X 1.5 X 2.5 cm) were incubated in a pepsin solution at pH 2. After 2 hours incubation at 37°C under agitation, the samples were cryofixed, histological sections were collected on glass slides and used for chemical imaging. The entire surface area of the sections (1.5 X 1.5 cm) was mapped by ToF-SIMS imaging (ToF-SIMS V; ION-TOF GmbH, Münster,Germany). Mass spectra of commercial pepsin powder and aqueous solution were acquired using the same tool.Pepsin powder analyzes revealed signals of nitrogen species that seems to be characteristic of pepsin.Lipids and connective tissue were revealed by the map which also exhibit large amounts of chlorine on the periphery of the section associated with a depletion of phosphorus species. This result reflects the penetration of the digestion solution which is rich in HCl, and that probably extract the soluble endogenous phosphorus compounds.Finally, an enrichment in nitrogen species CxHyN, assigned to pepsin, was observed in the penetration zone of the digestive solution, but also along the connective tissue layers.The use of ToF SIMS allowed the visualization of pepsin in a food. This result opens great perspectives to understanding the mechanisms of digestion of solid foods
