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Sci Pharm. 2006; 74: 137–149

Effect of protective agents on the viability of Lactococcus lactis subjected to freeze-thawing and freeze-drying

Diana Berner, Helmut Viernstein

Department of Pharmaceutical Technology and Biopharmaceutics, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria

Abstract

The effect of different protectants and the impact of the initial cell density on the viability of Lactococcus lactis Sr. 3.54 subjected to freeze-thawing and freezedrying was studied. Several additives were tested as protective agents against freezing and drying injuries. Maximum viability of the cells after freeze-thawing was obtained with sucrose and skim milk mixtures as protective agents (78% viability). Freeze-drying with protectants based on skim milk or MRS-broth were most effective (survival levels >60%). The effect of the initial cell load on the final recovery was dependent on the protectant. Every sample showed an increase in viability when a high initial cell concentration (1010cfu ml-1) was used. The blank showed a 1500 fold increase, skim milk/sucrose based lyophilisates an 1,7 fold increase in viability when the initial cell load was changed from 1009 to 1010cfu ml-1. The use of 1010cfu ml-1 as initial cell concentration and sucrose/skim milk as protectant yielded a lyophilisate with 71% viability. Results suggest the possibility of producing freeze dried powders of Lactococcus lactis with high viability for the food industry.

Keywords

Lactococcus lactis, freeze-drying, freeze-thawing, lactic acid bacteria, initial cell concentration

Received July 2nd, 2006 | Accepted September 3rd, 2006

doi:10.3797/scipharm.2006.74.137