Abstract

Malolactic fermentation (MLF) is an important process in wine production. To achieve successful MLF, expanding interest in ready-to-use Oenococcus oeni starter cultures has drawn greater emphasis on developing starter production and preservation methods. Growth phase, protective agents, rehydration media and stress pretreatments were the main factors to affect the survival of O. oeni SD-2a after freeze-drying. It was found thatO. oeni SD-2a cells in the early stationary phase survived better than those in the mid-log phase after freeze-drying. Protective agents play an important role in the conservation of viability. Sodium glutamate (2.5%) was the best protectant, giving the cell viability 69.5%. The addition of polysaccharides and disaccharides in suspension media also improved the cell viability significantly. Rehydration is a critical step in recovery after freeze-drying. When freeze-dried O. oeni SD-2a was rehydrated in acidic tomato broth (ATB) medium, the highest viability was obtained. Rehydration in the tested disaccharide solutions decreased the cell viability obviously. During stress treatments, O. oeni SD-2a treated with 8% ethanol resulted in the highest freeze-drying survival rate (82%), the treatment with pH 3.5 or 3.2 also notably increased freeze-drying viability.

Key words: Oenococcus oeni, malolactic fermentation and freeze-drying and viability.

Abbreviation

MLF, malolactic fermentation; LAB, lactic acid bacteria; CFU, colony-forming units; ATB, acidic tomato broth.