Decontamination of dehydrated food products

Seeds, powders and powdered products are widely used in the food industry. Indeed, 80% of the ingredients used are in dehydrated form, which is why their microbiological stability has long been studied. The ever-increasing demands for quality on the part of consumers mean that the safety of products such as milk powder, flour, spices, egg products, dehydrated mushrooms, seaweed powders and carrageenans is the focus of a great deal of attention on the part of manufacturers. What's more, new food trends, and in particular the craze for ethnic dishes with spicy flavours, have contributed to an explosion in the spice and aromatics market over the last decade.

Variable in composition, the microflora of these products is known to be present in large quantities, due to the traditional production conditions (harvesting, drying, storage...). The presence of this microflora, adapted to low water content, makes it difficult to decontaminate food powders. Two types of micro-organisms are present in powdered products: vegetative and spore-forming forms. Many authors have reported that the thermal resistance of spores and vegetative forms is greater in water-poor environments. In fact, the osmotic stress undergone by micro-organisms during contamination of powdered products increases the thermotolerance of yeasts and bacteria.

Although feasible, the process of destroying micro-organisms in solid products is fraught with difficulties on several levels. These are reduced when solid products are contained in an aqueous phase, and new treatments such as ohmic heating or microwaves enable effective decontamination. In the case of divided solids processed in bulk, such as spices and aromatic herbs, the problem arises in terms of treatment homogeneity and heat penetration power.

The aim of this dossier is to review the main physico-chemical characteristics of powders, characterize the microflora encountered on powdered products, present the various principles of dry microorganism destruction, and provide a bibliographical summary of all thermal and athermal techniques for decontaminating food powders. Finally, the last part of the document will be devoted to the presentation of the principles of new innovative processes currently under development, in particular controlled instantaneous expansion (CIE), pulsed light and the FHT system (fluidization at high temperatures), patented by the University of Burgundy's Food and Biotechnology Process Engineering Laboratory.