Inactivation of Lactobacillus plantarum WCFS1 during spray drying and storage assessed with complementary viability determination methods

Survival of Lactobacillus plantarum WCFS1 spray-dried and stored under different conditions was investigated using complementary methods. One method involved a cell membrane integrity viability-based determination, the other assessed cell growth behavior in a liquid medium by means of detection time or by conventional plating. Survival decreased below 95% when spray drying was carried out at higher outlet spray drying temperatures (Tout > 70 °C). However, the membrane integrity method provided higher residual viability values compared to the detection time and conventional plating. This suggests that loss of viability may be due to a combination of damage to intracellular components and cell membrane. Also during storage viability based on growth behavior declined faster and was more temperature dependent compared to the viability as determined by the membrane integrity method. Also here additional damage to intracellular components is expected responsible to loss of viability. Major conclusion is that one should not only rely on a cell-membrane integrity based method to assess survival during spray drying and storage of bacteria. Previous studies that did so most probably underestimated viability as critical damage to intracellular components was not assessed.