Effects of Proanthocyanidin-Iron Network-Coated Lactic Acid Bacteria on Blackberry Juice Fermentation

This study aimed to investigate the effects of proanthocyanidin-iron network-coated lactic acid bacteria on blackberry juice fermentation. Through the reaction between iron ions and proanthocyanidins (Pc) to generate a metal-phenol network, Lactobacillus plantarum BC17 was encapsulated by it to create a protective structure named BC17@Pc-Fe, and then this structure was applied in the fermentation of blackberry juice. The effects of proanthocyanidin-iron-encapsulated lactic acid bacteria on the viable count, total sugar, reducing sugar, total phenols, anthocyanins, pH, total acidity, and antioxidant capacity during the fermentation process of blackberry juice were studied. Results showed that the particle size of BC17 increased from 1990±156 nm to 5560±901 nm, and the charge carried by it increased from −13.77±1.44 mV to −4.05±1.48 mV. The results of scanning electron microscopy results confirmed that the metal-phenol network, effectively encapsulated BC17. During the fermentation process of blackberry juice, the viable count in the BC17@Pc-Fe group reached 7.59±0.03 lg CFU/mL, which was significantly higher than that in the BC17 group (6.64±0.03 lg CFU/mL) (P<0.05). Moreover, the respective total sugar, and reducing sugar, total phenols, and anthocyanin contents increased by 13.29%±2.81% and 6.49%±1.01%, and 4.47%±2.02%, and 33.96%±4.26%, compared to the BC17 group. Additionally, compared to the BC17 group, the BC17@Pc-Fe group showed a 2.72%±0.01% decrease in pH and a 4.60%±0.03% increase in total acidity. Antioxidant capacity assessments showed that the DPPH radical scavenging rate, ABTS⁺ radical scavenging rate, OH scavenging rate, and ferrous ion reducing power in the BC17@Pc-Fe group increased by 19.33%±2.94%, 29.17%±2.82%, 12.31%±7.22%, and 11.31%±0.03%, respectively, compared to those of the BC17 group. The metal-polyphenol network coated BC17 effectively enhanced the antioxidant capacity of fermented blackberry juice. This study presents a method for enhancing fermented blackberry juice quality by improving the growth and fermentation performance of lactic acid bacteria, offering a new approach for the production of lactic acid bacteria-fermented fruit juice products.