Thermal inactivation of Bacillus cereus spores in infant formula under shear conditions

Abstract

International audienceDuring production of spray-dried infant formulas, spores of Bacillus cereus have to be inactivated in order to assure product safety. The heating step which aims at the inactivation of bacterial spores can be conducted either before concentration of the product or afterwards. However, spores tend to show increased heat resistance in concentrated products. The aim of this study was therefore to determine the inactivation kinetic parameters for the inactivation of B. cereus spores in concentrated infant formula as well as in non-concentrated infant food. Spores of B. cereus IP5832 were suspended in reconstituted infant formula (10 and 50% total solids) and heat-treated at temperatures from 90 to 110 °C under shearing at $$ \mathop{\gamma}\limits^{\bullet }=500\,{s^{-1 }} $$. Additionally, experiments at 95 °C were performed in tubes without shearing in phosphate buffer and non-concentrated infant formula. In tubes, the inactivation curves exhibited tailing. When applying heat and shear stress, linear inactivation curves were observed in both the concentrated and the non-concentrated infant formula. The kinetic parameters E a and k ref (ϑ ref = 100 °C) based on the employed Arrhenius model were 201 kJ.mol−1 and 0.011 s−1 and 201 kJ.mol−1 and 0.021 s−1 for the concentrated and the non-concentrated medium, respectively. The D values in the concentrated product at the examined temperatures were twofold higher. The heat sensitivity (z value) of the spores was not altered by concentrating the medium. The data from this study can be used to design or evaluate heating processes for concentrated products aiming at the inactivation of B. cereus spores

Thermal inactivation of Bacillus cereus spores in micellar casein concentrates–effect of protein content and pH development

“…The addition of casein in a concentration of 2.5% to the heating medium phosphate buffer did not change the heat resistance of Clostridium sporogenes spores (Amaha and Sakaguchi 1954). This is in contrast to studies on the heat resistance of mesophilic Bacillus spores performed in milk (9.4%-40.0% dry matter) and infant formula (9.8%-49.5% dry matter) concentrates where an increased heat resistance was observed at higher dry matter contents (Behringer and Kessler 1992;Stoeckel et al 2013). The increased heat resistance of the spores in concentrates was explained with the lower water activity of the heating media at the high dry matter contents ) caused by high lactose and mineral salt contents.…”

“…The production of the spores was performed as described in Stoeckel et al (2013). Briefly, spores were produced from growing cells on sporulation medium agar containing manganese.…”

Inactivation of Bacillus spores in batch vs continuous heating systems at sterilisation temperatures

“…In a recent study with spores of B. cereus , we showed that tailing only appeared in nonsheared batch heating experiments (Stoeckel et al . ). Tailing in the batch system, but not in the continuous system, was also observed by Wescott et al .…”

Bacterial spores isolated from ingredients, intermediate and final products obtained from dairies: thermal resistance in milk

“…The preparation of the spore suspensions was performed as described in Stoeckel et al (2013), except that the sporulation medium from Iciek et al (2006) was used for thermophilic strains. Briefly, spores were produced from growing cells on sporulation medium agar containing manganese.…”

“…The composition of dairy products influences the heat resistance of spores. Spores are protected from heat at lowered water activities produced by high solute concentrations as, e.g., in milk concentrates (Kessler 2002;Stoeckel et al 2013). Also other intrinsic properties of heating media such as pH changes during heating influence the heat resistance (Mathys et al 2008;Reineke et al 2011).…”