Effect of heat, pH and coating process with stearic acid using a fluidized bed granulator on viability of probiotic Lactobacillus reuteri C 10

Abstract

This study was conducted to investigate the use of a fluidized bed granulator to coat a probiotic Lactobacillus reuteri C 10 with stearic acid with a view to enhance its survival rate during storage. L reuteri C 10 cells of two treatments, namely, freeze-dried cells incorporated with trehalose and sucrose as cryoprotectants prior to freeze-drying, and freeze-dried cells without any incorporation of cryoprotectants were evaluated. Since the pH of stearic acid is 5.5 and the melting point is 57.23°C, and the inlet temperature of the fluidized bed granulator could be as high as 70°C, a preliminary study was initiated to determine the tolerance of L. reuteri C 10 cells to heat exposure from 58 to 70°C and acidic conditions of pH 4 to 6 for 60 min, during which the cell viabilities were determined every 15 min. In the coating process, 2:3 ratio of freeze-dried L. reuteri C 10 cells and stearic acid, fluidization air of 20 to 50 rpm, coating rate of 40 to 80 g/min and inlet and outlet temperatures of between 50 to 70°C were assessed for optimization of the fluidized bed granulator. Results of the  preliminary study showed that freeze-dried L. reuteri C 10 cells incorporated with cryoprotectants exhibited significantly (P < 0.05) less cell loss than cells without cryoprotectants when exposed to 62°C for 15 to 60 min, 64 °C for 15 to 30 min, 66°C for 30 min and 68°C for 15 to 30 min. Freeze-dried L. reuteri C 10 cells with cryoprotectants were also able to survive for 15 min at 70°C, but not freeze-dried L. reuteri C 10 cells without cryoprotectants. Freeze-dried L. reuteri C 10 cells with or without cryoprotectants could tolerate acidic conditions and there was growth and increase in cell viability at pH 4, 5 and 6. However, cells with cryoprotectants had significantly (P < 0.05) more growth when exposed to pH 5 for 30 to 60 min, and pH 6 for 15 to 60 min than cells without cryoprotectants. The application of a fluidized bed granulator to coat L. reuteri C 10 cells with or without cryoprotectants with melted stearic was not successful in this study because the fluidized bed granulator could not maintain the temperature of stearic acid above its melting point which led to clogging of the tube and spray nozzle of the fluidized bed granulator or resulted in the formation of a big lump of stearic acid and L. reuteri C 10 cells instead of uniform coated cell granules. Installation of a temperature jacket on the fluidized bed granulator may be necessary to control the temperature of stearic acid in the tube and spray nozzle above melting point.

Key words: Coating, fluidized bed granulator, Lactobacillus reuteri C10, stearic acid.