Bacillus spp. thermal resistance and validation in soups

The purpose of this work was to obtain heat resistance data relevant to pasteurisation regimes and to model the effects of a range of temperatures (93 to 107°C) and pH (3.6 to 6.4) on the survival of the several Bacillus spp. spores that have been associated with spoilage of foods (Bacillus pumilus, B. licheniformis, B. subtilis, and B. megaterium), and to validate the results obtained by heating the spores in soups at selected temperatures. The thermal resistance observed in soups for 3 out of the 4 Bacillus spp. tested were higher than predicted. This may be due to the viscosity of the soup offering protection to the test organisms during the heat treatment; alternatively other ingredients in the soup recipes may cause this effect. This work will assist in the better design of thermal processing for the elimination of bacilli in soups.