In an attempt to introduce probiotic functionalities to breakfast cereals and similar food products, the technique of solid-state fermentation (SSF) was applied to cultivate Lactobacillus plantarum (NCIMB 8826) on oat bran and spent oats after lipid extraction by supercritical CO(2) extraction. When compared to the frequently favored submerged processes for bacterium incubation, SSF presents not only the potential of simple downstream processing but also a more natural growth environment for the target bacterium. Preliminary studies confirmed that oat bran contained balanced nutrients to support a 25-fold bacterium propagation within a range of moisture content from 50% to 58% after a 36-h cultivation. Limited hydrolysis of the raw materials by the enzyme complex from submerged incubation of Aspergillus awamori and A. oryzae to increase nutrient accessibility extended the exponential growth phase and enhanced bacterial growth by over 183-fold. The process with the most potential, however, was to simultaneously grow both fungi aerobically on the raw materials in solid state to achieve sufficient hydrolysis, followed by controlled fungal autolysis at 65 degrees C prior to anaerobic bacterium incubation. Following this process bacterium population reached a maximum of 7.3 x 10(9) cells in each gram of the fermented solids, corresponding to a 1653-fold increase from the point of inoculation.