Efficient Spray-Drying of Lactobacillus rhamnosus PTCC 1637 Using Total CFU yield as the decision factor

A major challenge for functional foods containing probiotics is to provide a sufficient number of probiotic microorganisms to survive the harsh environments during processing and storage so that they can confer their health benefits. Extensive studies have been carried out on the spray-drying of probiotics based on enhancing their survivability after drying and during storage. However, in this study, the production of spray-dried powder of L. rhamnosus was investigated based on maximizing the total CFU yield, which is a combination of the yields of survivability, powder production, and stability. The results suggested that although enhancing additives such as tragacanth to skim milk could significantly increase the survival of the cells during drying, it may significantly decrease the powder yield which could result in a low total CFU yield. Furthermore, good stability of cells micro-encapsulated in skim milk + sucrose could not compensate for their low survival during the drying. It was determined that bacterial adaptation to sodium chloride, micro-encapsulation of cells in 20% skim milk, and suitable spray-drying conditions (inlet air temperature of 150 °C and feed flow rate of 8 ml/min) could lead to the highest total CFU yield compared to other conditions. Using the micro-encapsulated cells in yogurt showed a 5-fold stability enhancement in the viable cells compared to the fresh cells without excessive acid production during 20 days of storage. These results confirmed the positive effects of micro-encapsulation on the shelf-life of probiotics.