Increasing the stability of immobilized Lactococcus lactis cultures stored at 4 °C

Abstract

Immobilized cell technology was used to prepare concentrated cultures of Lactococcus lactis that lost only 22% of viability over a 30-day storage period at 4°C. Concentrated cultures of L lactis CRA-1 were immobilized in calcium alginate beads and added to glycerol, NaCl or sucrose-NaCl solutions in order to obtain aw readings ranging from 0.91 to 0.97. The suspensions were subsequently placed at 4°C and viability (CFU g-1 of bead) was followed during storage. Viability losses were high at aw readings of 0.95 and 0.97 and pH dropped significantly (up to one unit) in the unbuffered solutions. Addition of 1% soytone or glycerophosphate helphed stabilize pH, and a beneficial effect on viability during storage was observed in the glycerol-soytone mix when the beads were added to the conservation solutions immediately following immobilization. When beads were added to the conservation solution immediately following immobilization, a 70% drop in cell counts occurred during the first 5 days of incubation. Dipping the L lactis-carrying beads in milk for 2h before mixing with the glycerolsoytone 0.93 aw solution reduced this initial 5-day viability loss. Cultures grown in the alginate beads also had good stability in the 0.93 aw glycerol-soytone solution, where 78% of the population was viable after 30 days at 4°C. The process could be used to store immobilized cells at a processing plant, or by suppliers of lactic starters who wish to ship cultures without freezing or drying. © 1994 Society for Industrial Microbiology.