Effects of Pseudomonas syringae as bacterial ice nucleator on freezing of model food

For industrial application of ice-nucleation active bacteria, the quantity of bacterial cells that should be added and can be added is very important. There exists an appropriate range for the concentration of bacterial cells that is effective, economical and safe. This article investigates quantitatively the impacts of the cell concentration. Pseudomonas syringae pv. panici, was cultured at 26 °C with media of nutrient broth and harvested at late log phase. The ice-nucleation activity unit per unit volume was 6.9 × 105 INA/mL measured with the droplet method proposed by Vali. Freezing experiments carried out with deionized water showed that the bacteria exhibited better activity in the cases of high cooling temperature and/or small sample size. Freezing experiments carried out with 10% sucrose solution and 0.9% NaCl solution showed that the stable freezing point was independent of the concentration of ice-nucleation active bacteria. The quantitative relationship between the degree of supercooling and the concentration of ice-nucleation active bacteria is proposed to be expressed as ΔT = a − bCexp(kC), where C is the concentration of ice-nucleation active bacteria, a, b and k are empirical parameters. It can be concluded that adding ice-nucleation bacteria is of economical efficiency for applications which have higher cooling temperatures.