The objective of this work was to assess the impact of various NaCl concentrations on Lactobacillus rhamnosus OXY viability after freeze-drying. Osmotic stress was applied during the exponential growth phase of bacterial culture. At salt concentrations between 0.2–0.5 M, a high biomass concentration and a significant increase in cell viability after lyophilisation was observed. An analysis of two-dimensional protein gels indicated the presence of shock proteins, for example, GroEL, ClpB, DnaK, TF, which provide resistance during freeze-drying and subsequent storage. On the basis of these results, it is recommended that lactic acid bacteria cultures be sub-lethally treated with 0.5 M NaCl before freeze-drying.
Authors:B. Wróblewska, L. Jędrychowski, E. Szabó, and Gy. Hajós
Commercial sodium caseinate isolate (SCI) was hydrolysed with either protease Subtilisina carlsberg - Alcalase 2.4 FG (purchased from Novo Nordisk), pronase from Streptomyces griseus, and papain EC 18.104.22.168 (both from Sigma) in a two-step process to determine the changes in the immunoreactivity of a-, ß- and ?-casein. Enzymatic hydrolysis of SCI was performed by pH-stat method. Hydrolysates were analysed using IEF, SDS-PAGE, 2D electrophoresis, FPLC-gel permeation chromatography. Immunoreactive properties of peptide fractions separated from the hydrolysates by FPLC were determined using dot-immunobinding and ELISA methods. The two-step process was observed to be effective in reduction of casein fractions immunoreactivity, however, allergenic epitopes were still present in all peptide fractions.