Freeze-Dried Preservation of Carnobacterium maltaromaticum CNCM I-3298 and Investigation of the Underlying Mechanisms

Carnobacterium maltaromaticum is a lactic acid bacterium with growing applications in food biopreservation, probiotics, and microbial time-temperature integrators for tracking food quality throughout the cold chain. To develop efficient, ready-to-use dried concentrates for these applications, this study evaluated the impact of different protective formulations on the freeze-drying and storage stability of C. maltaromaticum CNCM I-3298 and explored the underlying molecular mechanisms. The formulations included sucrose, trehalose, and trehalose combined with maltodextrins. Sodium ascorbate was added to the most promising formulations for its potential antioxidant effect. Specific acidifying activity measurements before and after freezing, after freeze-drying and during storage at 25 °C revealed a gradual loss of bacterial activity following freeze-drying and storage. Sucrose, and trehalose with sodium ascorbate provided the best and outstanding protection. Increasing the glass transition temperature using trehalose or trehalose–maltodextrin matrices did not improve stability at 25 °C. Based on prior studies of proteins, we hypothesized that fast relaxation dynamics contribute to the degradation of cells in the glassy state. Fourier transform infrared micro-spectroscopy revealed that freeze-drying primarily affected nucleic acids, proteins (amide I and II), and cell wall components. Storage caused minor additional changes. First results relating to sodium ascorbate’s positive effect when added to trehalose and some spectral features in the fingerprint region need further investigation.