Water activity in dry foods containing live probiotic bacteria should be carefully considered: A case study with Lactobacillus rhamnosus GG in flaxseed

This study evaluated the effect of water activity on the long-term storage stability of the probiotic Lactobacillus rhamnosus GG (LGG) in a dry food matrix. Viability of LGG was further studied in a crushed flaxseed matrix – a new possible product matrix to deliver probiotics – as well as in reference matrices as maltodextrin. Three different water activities (aw=0.11, 0.22 and 0.43) were used, and preparations were stored at room temperature for up to 14months. The viability of LGG was less dependent on the matrix used, but strongly dependent on the water activity. Viability in flaxseed was lost rapidly with aw 0.43: with aw 0.22 the reduction was 2.4 log10 units and with aw 0.11 the reduction of viability was only 0.29 log10 units during the entire storage time. Taken together, regulating water activity to a low value may offer possibilities for extending the shelf life of dry probiotic products. ► Long-time storage stability of Lactobacillus rhamnosus GG was followed in dry food. ► Test matrices had water activity (Aw) values: 0.11, 0.22 and 0.43. ► Viability was less dependent on the matrix used but strongly dependent on the Aw. ► Best stability was obtained with Aw 0.11.