Effect of drying methods of microencapsulated Lactobacillus acidophilus and Lactococcus lactis ssp. cremoris on secondary protein structure and glass transition temperature as studied by Fourier transform infrared and differential scanning calorimetry

Abstract

Protective mechanisms of casein-based microcapsules containing mannitol on Lactobacillus acidophilus and Lactococcus lactis ssp. cremoris, changes in their secondary protein structures, and glass transition of the microcapsules were studied after spray-or freeze-drying and after 10 wk of storage in aluminum foil pouches containing different desiccants (NaOH, LiCl, or silica gel) at 25°C. An in situ Fourier transform infrared analysis was carried out to recognize any changes in fatty acids (FA) of bacterial cell envelopes, interaction between polar site of cell envelopes and microcapsules, and alteration of their secondary protein structures. Differential scanning calorimetry was used to determine glass transition of microcapsules based on glass transition temperature (T g ) values. Hierarchical cluster analysis based on functional groups of cell envelopes and secondary protein structures was also carried out to classify the microencapsulated bacteria due to the effects of spray-or freeze-drying and storage for 10 wk. The results showed that drying process did not affect FA and secondary protein structures of bacteria; however, those structures were affected during storage depending upon the type of desiccant used. Interaction between exterior of bacterial cell envelopes and microencapsulant occurred after spray-or freeze-drying; however, these structures were maintained after storage in foil pouch containing sodium hydroxide. Method of drying and type of desiccants influenced the level of similarities of microencapsulated bacteria. Desiccants and method of drying affected glass transition, yet no T g ≤25°C was detected. This study demonstrated that the changes in FA and secondary structures of the microencapsulated bacteria still occurred during storage at T g above room temperature, indicating that the glassy state did not completely prevent chemical activities.

Viability, Acid and Bile Tolerance of Spray Dried Probiotic Bacteria and Some Commercial Probiotic Supplement Products Kept at Room Temperature

“…In addition to low water activity, the high viability of Bifidobacterium and L. acidophilus of SD GM product could also be due to the protection effect of the components of microencapsulating materials consisting of casein and glucose which had been heated to create Maillard substances (Crittenden and others ), mannitol and FOS. Since glucose, via its carbonyl group, interacted with primary amino group of caseins (Blei and Odian ), the chance of mannitol to interact with P = O of lipid head groups of bacterial cell envelopes through mannitol's capacity as donor of proton might increase when moisture was removed during spray drying, as indicated by our FTIR study (Dianawati and others ). This phenomenon might provide protection effect on the cells therein during spray drying and during storage.…”

Pre-cold stress increases acid stress resistance and induces amino acid homeostasis in <i>Lactococcus lactis</i> NZ9000

“…Thus, preadaptation to cold stress led to the activation of specific metabolic pathways to protect the bacteria from the adverse effects of high-acid conditions and associated secondary effects [15][16][17][18]. These results suggest that pre-cold stress may activate intracellular metabolic pathways that enhance stress tolerance and survival of L. lactis subjected to subsequent acid stress.…”

Research into probiotic properties of cultured butter during storing

“…[15] proved the possibility and feasibility of combined cultivation of mesophilic lactic acid lactococci and acidophilus bacillus, which enables obtaining a product with fairly high concentration of viable cells of the both groups of microorganisms.…”