Three different encapsulation systems were developed in the form of oil-in-water acidic emulsions (pH 3.0) with the oil phase in the form of microdroplets in which Pediococcus acidilactici cells were enclosed. The first emulsion contained corn oil microdroplets (mean diameter 1.5 mu m) emulsified with peptides and stabilized with SDS. The other two, were food grade systems with microdroplets of corn or olive oil (m.d. 2.1 and 2.2 mu m, respectively) emulsified with peptides and stabilized with xanthan. In all systems, meat peptone. a rich source of peptides and amino acids. was provided in aqueous solution in which the cultures were Suspended. Peptone derived peptides acted as emulsifiers and at the same time as nutrient substrates and osmoprotectants for cells. Emulsions were stored for 30 days at 4 C. During this period, samples were examined for physical stability and viability of the encapsulated and freely suspended microorganisms present in the emulsions. Examinations were made through phase contrast microscopy and subsequent image Capture and analysis with an automatic image analysis system. Viable and nonviable cells were discriminated oil the basis of color differences produced through staining with trypan blue. The method permitted extraction of a large amount of information and produced large amounts of data through automated measurements on images. Emulsion characteristics and cell viabilities were also examined under conditions simulating the gastro-intestinal environment. Encapsulation proved to be critical since, following successive treatments of samples with simulated gastric juice (pH 2.0) and intestinal juice (pH 7.4). it ensured viability rates of encapsulated cells as high as 85% and delivered as much as 92% of the initially encapsulated cells to the target point. The formulated emulsion systems may have a large number of applications in the food sector provided further studies on engineering properties and improvements of stability over a wide pH range are carried out. (C) 2009 Elsevier Inc. All rights reserved.