Stability of microencapsulated Lactobacillus acidophilus and Lactococcus lactis ssp. cremoris during storage at room temperature at low aw

Abstract

The effect of freeze drying or spray drying, the use of desiccants to maintain the low aw and the period of storage (at 25°C) of Lactobacillus acidophilus and Lactococcus lactis ssp. cremoris on survival, acid tolerance, bile tolerance, retention of surface hydrophobicity and retention of β-galactosidase was studied; an estimation of the maximum storage period was also carried out. Sodium caseinate, vegetable oil, glucose, mannitol and fructooligosaccharides were used as protectant of L. acidophilus and L. cremoris during freeze drying or spray drying and during subsequent storage. NaOH, LiCl and silica gel were used as desiccants during 10weeks of storage of microencapsulated L. acidophilus and L. cremoris kept in an aluminum foil pouch. The results showed that mainly freeze dried L. acidophilus and L. cremoris kept in foil pouch containing NaOH (aw 0.07) or LiCl (aw 0.1) showed higher survival (89–94%) than spray dried bacteria kept under the same conditions (86–90%) after 10weeks of storage (P=0.0005). Similar results were also showed by acid tolerance, bile tolerance and surface hydrophobicity of freeze-dried or spray-dried L. acidophilus and L. cremoris. Silica gel was less effective in protecting the functional properties of microencapsulated L. acidophilus or L. cremoris with percentage of survival between 81 and 87% at week 10 of the storage. However, retention of β-galactosidase was only influenced by aw adjusted by desiccators (P<0.05). Based on forecasting using linear regression, the predicted storage period for freeze dried L. acidophilus, spray dried L. acidophilus and freeze dried L. cremoris kept in foil pouch containing NaOH would be 46, 42 and 42weeks, respectively; while spray dried L. cremoris under LiCl desiccant would require 39weeks to achieve minimum required bacterial population of 107CFU/g.