ABSTRACT
The aim of this study was to prepare alginate-immobilized freeze-dried cultures of Streptococcus thermophilus and to compare the acidifying activities of these rehydrated cultures with classical free cell liquid inoculants. Streptococcus thermophilus BT1 grew in alginate beads and the population reached 10(10) cfu g(-1) after 6 h incubation. Re-inoculation of the beads in fresh medium with a further 6 h incubation did not improve the biomass level, but extending the incubation at 42 degrees C to 24 h caused significant death. The rehydrated immobilized cell technology (ICT) starter contained 13% free cells. In acidifying activity tests, the ICT culture had a similar acidification curve to that of a classical milk-grown free cell culture, except that it reached lower final pH values. Although the differences between the ICT and liquid cultures were not important, there were significant effects of inoculation level on lag time, maximum acidification rate and on the pH and time at which the acidification rate was at its highest.
Subject(s)
Milk/microbiology , Streptococcus/growth & development , Alginates , Animals , Biomass , Colony Count, Microbial , Culture Media , Fermentation/physiology , Freeze Drying , Glucuronic Acid , Heating , Hexuronic Acids , Hydrogen-Ion Concentration , Microspheres , Milk/chemistry , Milk/metabolism , Streptococcus/metabolism , Streptococcus/physiologyABSTRACT
1. During multiplication of irradiated cells, a segregation may take place between bleached cells, whose progeny is unable to green, and green ones. Some of the green cells give progenies exclusively made of green cells; the progeny of others is partly composed of bleached cells. 2. If one assumes that greening results from the activity of functional units endowed with genetic continuity (Plastidial Segregating Units = PSU), segregation of these units seems to occur according to a model involving random sorting out during the three first divisions. During the following divisions, functional units seem to multiply faster than those impaired by irradiation. 3. The greening rate of colonies issued from irradiated cells seems to be conditioned mostly by the number of functional PSU remaining in the mother cell of the colony.
