Milk hydrogels as nutrient media and survival rate enhancer under cryogenic conditions for different microorganisms

Milk-containing hydrogels from 2-hydroxyethylmethacrylate (HEMA) and acrylamide (AAm) as p(HEMA)/whole milk, p(HEMA)/semi-skimmed milk, p(HEMA)/skimmed milk, p(AAm)/whole milk, p(AAm)/semi-skimmed milk, p(AAm)/skimmed milk were synthesized by conventional redox polymerization technique using corresponding monomers and milk as solvents. The aim of this study was to investigate the use of milk-containing hydrogels as a nutritional medium, e.g., up 124 days for enhanced or longer cryostorage media for various microorganisms such as Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus subtilis, and fungi, Aspergillus niger, Aspergillus fumigates, and a yeast Candida albicans. It was shown that milk hydrogels can be used as nutritional media for the growth of these microorganisms, whereas the control hydrogels cannot be used for the same purpose. The survival rates of p(HEMA)/whole milk and p(AAm)/whole milk hydrogels for E. coli after 124 days were found to exceed those of the control p(HEMA) and p(AAm) hydrogels by 109- and 56-fold, respectively. Moreover, the survival rates for S. aureus were calculated to be 42 and 24 times longer than the controls, as the hydrogels containing whole milk were used as storage media in comparison with the bare hydrogels. Furthermore, the cryogenic survival rates of p(HEMA)/whole milk and p(AAM)/whole milk were compared with whole milk and nutrient broth used as a control, and calculated to be 67-, 171-, 35-, and 89-fold greater, respectively, than those of the control samples for E. coli.