shows the viability of W. confusa strain grown in MRS and MYEG fermentation substrates and preserved by refrigeration and lyophilization during six weeks. Significant interaction effect (p < 0.05) was found among factors fermentation substrate, method of conservation and storage time, suggesting that the effect of each factor on the viability of W. confusa strain depended on the levels of the other two factors. After 4 hrs of fermentation, cell concentration was higher in strain grown in MRS (2.1 x 1010 cfu/mL) than MYEG (1.4 x 109 cfu/mL). The survival of W. confusa strain was significantly reduced due to lyophilization, with final counts immediately after lyophilization of 3.3 x 109 cfu/mL for strain grown in MRS and 5.4 x 107 cfu/mL for strain grown in MYEG. No further significant loss in cell viability was observed up to the 5th week of storage of lyophilized strain grown in MRS.
The method of conservation significantly affected (p < 0.05) the viability of W. confusa strain grown in MRS and MYEG substrates. The survival of refrigerated W. confusa strain grown in MRS declined progressively until the 6th week of storage. In the case of lyophilized strain, the viability remained essentially unchanged during the study period (six weeks), with an average of 1.9 x 109 cfu/mL. A very different pattern was found for the case of strain grown in MYEG substrate, where strain preserved by lyophilization exhibited less viability than strain preserved by refrigeration.
The observed reduction in viable strain after lyophilization was consistent with results by Zarate and Nader-Macias (2006), who reported a 0.05 to 2 reduction in viable Log cfu/mL after the lyophilization of L. acidophilus, L. paracasei, and L. salivarius. These authors reported that the viability in lyophilized strain stored in lactose or skim milk, strongly declined during the first months of storage. According to Carvalho et al. (2004), the different growth kinetics corresponding to different fermentation substrates, are due to the degree of stress affecting the cell membrane fatty acid composition. The loss of viability during the lyophilization process has been also linked to physical changes in the cell membrane (Koch et al. 2008).