Production of freeze-dried kefir culture using whey

A freeze-dried kefir culture produced using whey as raw material was studied in three steps. The first step examined the effect of air flow rate and agitation in a bioreactor for the production of biomass. The highest daily biomass productivity of 14.1 g dry weight L−1 was obtained when 8.3 vvm air flow rate was used, where vvm is volume of air per unit volume of medium min−1 and is defined as the ratio of air volume fed to the volume of ungassed broth in the fermenter min−1. In the second step, production of freeze-dried cultures was studied testing various cryoprotective agents and cooling rates. Fermented whey proved to be a suitable cryoprotective medium, providing 86% survival of the kefir culture and showing satisfactory metabolic activity of freeze-dried cultures. The third step involved evaluation of the freeze-dried product in carbohydrate fermentations, showing a high operational stability during repeated batch fermentations. The use of freeze-dried kefir culture in food production as a value-added starter culture thus appears possible.