Fig. 1. Response surface representation of the effect of cooling temperature (T) and duration (D) on the rate of loss in acidification activity during frozen storage (k) and on the residual acidification activity after 180 days of frozen storage at −20 °C (t180) of Lb. acidophilus RD758.

Fig. 2. Response surface representation of the effect of cooling temperature (T) and duration (D) on the unsaturated to saturated fatty acid ratio (U/S), and on the relative percentage of the cycC19:0 fatty acid of Lb. acidophilus RD758.

Fig. 3. 2-D electrophoresis gel of cytosolic proteins of Lb. acidophilus RD758 grown at 37 °C and pH 6 with intermediate cooling at 26 °C for 8 h. Three hundred micrograms of protein extract was loaded in the first dimension. Gels were stained with colloidal Coomassie blue. Four induced proteins are encircled with a continuous line and one repressed protein is encircled with a dotted line.

Experimental design used to study the effects of the cooling conditions on cryotolerance of Lb. acidophilus RD758

Tc: coded value of cooling temperature; Dc: coded value of cooling duration; T: cooling temperature (in °C); D: cooling duration (in h).

Coefficients of the polynomials describing the acidification activity and the membrane fatty acid composition of Lb. acidophilus RD758

T, cooling temperature (in °C); D, cooling duration (in h); k, rate of loss in acidification activity during frozen storage (in min day⁻¹); t180, residual acidification activity after 180 days of frozen storage (in min); U/S, ratio between unsaturated and saturated fatty acid relative concentrations; cycC19:0, relative percentage of the cycC19:0 fatty acid; Rm, multiple correlation coefficient; ns, not significant at 90% level.

Characteristics of five proteins showing different intensity levels (greater than 2 or less than 0.5) after an intermediate cooling at 26 °C for 8 h of Lb. acidophilus RD758

MW, molecular weight; pI, isoelectric point; ni, not identified.