Survivability of alginate-microencapsulated Lactobacillus plantarum during storage, simulated food processing and gastrointestinal conditions

Abstract

A comparison between the most investigated alginate-based encapsulating agents was performed in the current study. Here, the survivability of Lactobacillus plantarum microencapsulated with alginate (Alg) combined with skim milk (Sm), dextrin (Dex), denatured whey protein (DWP) or coated with chitosan (Ch) was evaluated after exposure to different heat treatments and in presence of some food additives, during storage and under simulated gastrointestinal condition. In addition, the encapsulated cells were evaluated for production of different bioactive compounds such as exopolysacchar. ides and antimicrobial substances compared with the unencapsulated cells. The results showed that only Alg-Sm maintained the viability of the cells >10⁶ cfu/g at the pasteurization temperature (65 °C for 30 min). Interestingly, storage under refrigeration conditions increased the viability of L. plantarum entrapped within all the tested encapsulating agents for 4 weeks. However, under freezing condition, only Alg-DWP and Alg-Sm enhanced the survival of the entrapped cells for 3 months. All the microencapsulated cells were capable of growing at the different NaCl concentrations (1%-5%) except for cells encapsulated with Alg-Dex, showed viability loss at 3% and 5% NaCl concentrations. Tolerance of the microencapsulated cells toward organic acids was varied depending on the type of organic acid. Alg-Ch and Alg-Sm provide better survival for the cells under simulated gastric juice; however, all offer a good survival for the cells under simulated intestinal condition. Our findings indicated that Alg-Sm proved to be the most promising encapsulating combination that maintains the survivability of L. plantarum to the recommended dose level under almost all the stress conditions adopted in the current study. Interestingly, the results also revealed that microencapsulation does not affect the metabolic activity of the entrapped cells and there was no significant difference in production of bioactive compounds between the encapsulated and the unencapsulated cells.

Keywords: Antimicrobial; Extrusion; Food science; Lactobacillus plantarum; Materials science; Microbiology; Microencapsulation; Sodium alginate.

Figure 1

Schematic representation of the encapsulation system and the adopted stress conditions.

Figure 2

Scanning electron micrograph of (a) Alg-Sm; (b) Alg-Dex; (c) Alg-Ch, and (d) Alg-DWP capsules loaded with L. plantarum.

Figure 3

Microscopic images of (a) Alg-Sm; (b) Alg-Dex; (c) Alg-Ch, and (d) Alg-DWP capsules loaded with L. plantarum.

Figure 4

Particle size distribution of the microcapsules in dry state.

Figure 5

Survivability of microencapsulated L. plantarum after different heat treatments at 40 °C for 24 h; 45 °C for 30 min; 65 °C for 30 min (initial cell count: ≈10⁸ cfu/g), during refrigerated storage at 6 ± 2 ᵒC for one month (initial cell count: ≈10⁹ cfu/g) and freezing storage at -18 ± 2 °C for three months (initial cell count: ≈10⁸ cfu/g). Error bars represent the standard error of the mean.

Figure 6

Survivability of the microencapsulated L. plantarum (A) after incubation at 37 °C for 24 h in different NaCl concentrations (B) during refrigerated storage at 6 ± 2 °C for one month in different NaCl concentrations. (C) after incubation at 37 °C for 24 h in different concentrations of food-applied organic acids. (D) after incubation at 37 °C for 24 h with the metabolites of the other LAB. Error bars represent the standard error of the mean. Error bars represent the standard error of the mean. Initial cell count: ≈10⁹ cfu.

Figure 7

Survivability of the microencapsulated cells after exposure to simulated gastric juice (SGJ) (a) and simulated intestinal juice (SIJ) (b). Error bars represent the standard error of the mean. Initial cell count: ≈10⁸ cfu/g.

Figure 8

Antimicrobial activity of cell free supernatant of free and microencapsulated L. plantarum.