In order to improve the acidification activity of frozen suspensions of Lactobacillus delbrueckii subsp. bulgaricus CFL1, the protective effect of nine additives, in binary and multicomponent solutions, was quantified during freezing and storage at -20degreesC. The best protective media were those containing sodium ascorbate and betaine or sodium glutamate, greatly improving the acidification activity recovery after freezing (+ 70%) and frozen storage (+ 90%) when compared to a control medium. However, the effect of each additive was different before than after freezing or during frozen storage. The presence of an antioxidant in the protective media appeared essential to maintain the acidification activity of L. bulgaricus during the cryoprotection stage and frozen storage. Betaine and sodium glutamate provided the highest resistance to freezing, while leading to the greatest reduction of the cryoscopic point of the medium. Their cryoprotective effect was explained by a decrease in the number of ice crystals formed during freezing and frozen storage.