Glass transition behavior of carnosine and its impact as a protectant on freeze-dried lactic acid bacteria

Glass transition behavior of carnosine (β-alanyl- L -histidine) and its impact on the storage stability of freeze-dried lactic acid bacteria (LAB) were investigated. Glass transition temperature of anhydrous carnosine was determined to be 99 ºC. From the water sorption isotherm and glass transition temperature curve, the water activity where glass transition occurs at 25 ºC (typical room temperature) was determined to be 0.28. These values for carnosine were higher than for sucrose, but lower than for trehalose. Effect of carnosine on the viability of freeze-dried LAB ( Lactobacillus acidophilus , Lactobacillus reuteri , and Lactobacillus paracasei ) before and after storage at 37 ºC for 4 weeks was compared with that of other antioxidants (cysteine, glutathione, and ascorbic acid). Carnosine and cysteine strongly ameliorated reductions in cell viability after the storage. Carnosine showed the highest number of viable cells for L. reuteri and L . paracasei . The stabilizing mechanism of carnosine is thought to be attributed to water substitution, glass transition, antioxidation, and optimum pH.