NMR measurement of bacteria death kinetics during heat stress

- 1H NMR method found to rapidly quantify the heat stress death kinetics.
- Ratio of methylene and methyl peaks directly proportional to death percentage.
- Method rapid, in situ, minimal preparation and no chemical agents required.

Modelling the thermal processing of food matrices incorporating microorganisms requires heat stress death kinetics. It is demonstrated that proton nuclear magnetic resonance (1H NMR) is a rapid means of quantifying the heat stress death kinetics of a human probiotic bacterium (Bifidobacterium animalis subsp. lactis DR10™ or strain HN019). It was found that the ratio of the methylene (CH2) resonance at 1.2 ppm to the methyl (CH3) resonance at 0.9 ppm signal intensity as observed by 1H NMR was directly proportional to the percentage of death of a population of cells during heat stress. The derived death kinetic rate constants for a series of heating temperatures showed excellent correlation to the Arrhenius equation. The method has several advantages over existing methods for measuring bacterial death kinetics, as it can be carried out in situ with minimal preparation and without the addition of chemical agents.