ABSTRACT
Lactobacillus acidophilus cells surviving freeze drying and vacuum drying became sensitive to oxgall and lysozyme probably from damage to the cell wall. The dried cells also became sensitive to NaCl and permeable to orthonitrophenol ß-galactoside from damage to the cytoplasmic membrane. Scanning electron microscopy indicated loss of some surface material from the damaged cells. Transmission electron microscopy (TEM) revealed partial loss of wall and membrane material, but these losses seemed to have resulted from the treatments given during fixation of cells for TEM and as a consequence of damage to the wall and membrane that occurred during drying. A surface protein of 46-kilodalton molecular weight, that is bound to the wall by hydrogen bonding, was also lost from the dried cells. It is postulated that drying adversely affects some weak bonds of the cellular macromolecules probably from the loss of bound water.
ABSTRACT
Samples of 27 dried acidophilus products used as dietary adjuncts for Lactobacillus acidophilus in humans, were enumerated for viable cells on plate count agar (PCA), MRS broth plus 1.5% agar (MRSA) and MRSA plus 0.15 % oxgall (MRSOA). Colony-forming units did not differ greatly on plating media because most viable cells formed colonies aerobically, anaerobically or in the presence of bile salts. Health food samples had very low numbers of viable cells and counts varied between samples from different lots. Only one of four brands from the health food group had viable L. acidophilus cells. Samples from this group had organisms other than lactobacilli, including coliforms and gram-negative, lactose-negative, motile rods. Most pharmaceutical and milk culture samples had high numbers of viable cells, but only two brands from pharmaceutical samples had viable cells of L. acidophilus . L. acidophilus strains were susceptible to drying, with vacuum drying being more lethal than freeze drying.
