Metal-Phenolic Network-Directed Coating of Lactobacillus plantarum: A Promising Strategy to Increase Stability

Abstract

Lactobacillus plantarum exhibits probiotic effects, including regulating the balance of the intestinal microbiota and enhancing immune function. However, this strain often experiences viability loss upon ingestion due to harsh conditions within the human digestive tract. This study aimed to evaluate the efficacy of metal-phenol networks (MPNs) fabricated via three polyphenols-tannic acid (TA), tea polyphenol (TP), and anthocyanin (ACN)-combined with Fe(III) coatings in protecting Lactobacillus plantarum during simulated digestion and storage. The results demonstrated that MPNs formed a protective film on the bacterial surface. While TA and ACN inhibited the growth of Lactobacillus plantarum YJ7, TP stimulated proliferation. Within the MPNs system, only Fe(III)-TA exhibited growth-inhibitory effects. Notably, ACN displayed the highest proliferation rate during the initial 2 h, followed by TP between 3 and 4 h. All MPN-coated groups maintained high bacterial viability at 25 °C and -20 °C, with TP-coated bacteria showing the highest viable cell count, followed by TA and ACN. In vitro digestion experiments further revealed that the Fe(III)-ACN group exhibited the strongest resistance to artificial gastric juice. In conclusion, tea polyphenol and anthocyanin demonstrate superior potential for probiotic encapsulation, offering both protective stability during digestion and enhanced viability under storage conditions.

Keywords: Lactobacillus plantarum YJ7; metal–phenol networks; single-cell encapsulation; stability.

Figure 1

Electron micrographs of single-cell delivery carriers in three MPN systems under TEM. (A) Control group; (B) Fe(III)-TA group, (C) Fe(III)-TP group, and (D) Fe(III)-ACN group.

Figure 2

CLSM electron micrographs of single-cell delivery carriers in three MPN systems. (A) Fe(III)-TA group, (B) Fe(III)-TP group, and (C) Fe(III)-ACN group.

Figure 3

Determination of particle size and zeta potential of single-cell delivery carriers in three MPN systems. (A) Particle size, (B) zeta potential. * p < 0.05, ** p < 0.01.

Figure 4

The effects of single-cell encapsulation on the growth of Lactobacillus plantarum. (A) Effects of three polyphenol materials on the growth curve of Lactobacillus plantarum YJ7, (B) the growth curve of Lactobacillus plantarum YJ7 in the encapsulated single-cell carriers, and (C) proliferation activity of single-cell delivery carriers in three MPN systems determined by CCK-8. ** p < 0.01, *** p < 0.001.

Figure 5

In vitro storage experiments of single-cell encapsulation carriers. (A) The number of remaining viable bacteria in each group after 7 days of storage at −20 °C. (B) The number of remaining viable bacteria in each group after 7 days of storage at 4 °C. (C) The number of remaining viable bacteria in each group after 7 days of storage at 25 °C. * p < 0.05, ** p < 0.01, *** p < 0.001.

Figure 6

Viable bacteria count of single-cell delivery carriers in vitro test with simulated gastric fluid. * p < 0.05, ** p < 0.01.