Freeze-dried Starter Production and Viability Measurements with Bacillus and Lactic Acid Bacteria

Abstract

Freeze-drying, or lyophilization, is a preservation technique that removes water content from microbial cultures under low temperature and vacuum conditions. This process not only maintains the viability of bacillus and LAB but also retains their functional properties, making them suitable for various culinary applications. The aim of this study is produce freeze-dried starter cultures and assess their viability. Two microbial strains, previously, Bacillus proteolyticus and Lactobacillus plantarum was isoled from african locus bean were used. To the mixture of these strains, protective agents and carrier has been added at a ratio of 1 : 1. The mixtures were freeze-dried. The lyophilized starters were stored at -20 °C, 4 °C, and at room temperature (29 ± 0.67 °C). The viability rate was determined every 14 days for 3 months. The results show that cassava powder and starch allow for better viability of microbial strains. The best storage time is -20°C. For good viability of microbial strains during the production of freeze-dried starters, starch must be used as a protective agent, cassava powder as a carrier and everything must be kept at -20 °C. The viability of strains generally decreases over time, even under optimal conditions. Cumulative damage to cellular structures and nucleic acids would lead to cell death. Exposure to oxygen would cause oxidative stress, particularly for anaerobic microorganisms such as lactic acid bacteria. During the storage of the lyophilised products at −20°C, 4°C, and room temperature, the starch–cassava powder formulation used as a protective agent and carrier support demonstrated the highest viability rate for the multiple starter cultures. This finding suggests that the starch–cassava powder matrix was more effective in preserving microbial cell viability across different storage conditions, thereby enhancing the stability and survivability of the starter cultures during storage.