This study investigates the protective effects of a metabolizable and a non-metabolizable stereoisomer of glucose on encapsulated Lactobacillus rhamnosus GG (LGG) bacteria in the dry state. Separate experiments confirmed that the probiotic strain metabolizes only D-glucose. Encapsulated LGG formulations (2 wt.% LGG, dry basis) were prepared by freeze drying a mixture of the freshly cultured bacteria within various whey protein-carbohydrate matrices. The encapsulant matrices used were (i) a 1:2 mixture of protein:maltodextrin, (ii) a 1:1:1 mixture of protein:maltodextrin:D-glucose and (iii) a 1:1:1 mixture of protein:maltodextrin:L-glucose. The partial substitution of maltodextrin with either D-glucose or L-glucose in the encapsulant matrix significantly enhanced the survival of LGG powders stored at a relative humidity of 33% RH and 25 degrees C over 35 days. In comparison, there was a protective effect afforded by partial substitution of maltodextrin with either stereoisomer of glucose during storage of LGG powders at relative humidity of 70% RH and 25 degrees C over 7 days only. However, on longer term storage at relative humidity of 70% RH and 25 degrees C over 14-35 days, the viability of LGG was similar for all formulations. The results suggest that the protection afforded to LGG by the incorporation of D-glucose or L-glucose in the encapsulant matrix was primarily due to the physico-chemical effect of the glucose molecules rather than a-glucose being a metabolizable sugar. These experiments allowed discrimination between the physicochemical and nutritional roles of glucose on LGG viability. (C) 2013 Elsevier Ltd. All rights reserved.