Preferential localization of Lactococcus lactis cells entrapped in a caseinate/alginate phase separated system

• Lactococcus lactis cells were added in alginate/caseinate aqueous two-phase system.
• Alginate/caseinate aqueous two-phase system was studied at three different pHs: 7.0, 6.0, and 5.5.
• Epifluorescence microscopy showed cells preferential localization in caseinate.
• Zeta potential and MATS were used to substantiate this preferential localization.

This study aimed to entrap bioprotective lactic acid bacteria in a sodium caseinate/sodium alginate aqueous two-phase system. Phase diagram at pH = 7 showed that sodium alginate and sodium caseinate were not miscible when their concentrations exceeded 1% (w/w) and 6% (w/w), respectively. The stability of the caseinate/alginate two-phase system was also checked at pH values of 6.0 and 5.5. Lactococcus lactis subsp. lactis LAB3 cells were added in a 4% (w/w) caseinate/1.5% (w/w) alginate two-phase system at pH = 7. Fluorescence microscopy allowed to observe that the caseinate-rich phase formed droplets dispersed in a continuous alginate-rich phase. The distribution of bacteria in such a system was observed by epifluorescence microscopy: Lc. lactis LAB3 cells stained with Live/Dead® Baclight kit™ were located exclusively in the protein phase. Since zeta-potential measurements indicated that alginate, caseinate and bacterial cells all had an overall negative charge at pH 7, the preferential adhesion of LAB cells was assumed to be driven by hydrophobic effect or by depletion phenomena in such biopolymeric systems. Moreover, LAB cells viability was significantly higher in the ternary mixture obtained in the presence of both caseinate and alginate than in single alginate solution. Caseinate/alginate phase separated systems appeared thus well suited for Lc. lactis LAB3 cells entrapment.

Localization of cells in the 1.5% (w/w) alginate/4% (w/w) caseinate (w/w) emulsions at pH 7 – microscopic observations (filter 00 and 09) (100×) with LAB3 cells labeling with Live/Dead® Baclight™ kit and caseinate phase labeling with Rhodamine B.Figure optionsDownload as PowerPoint slide