Encapsulation of polyphenol-rich black raspberry in sodium alginate gel: a natural antimicrobial and antioxidant approach against dental pathogens

This study evaluates the antibacterial and antioxidant properties of sodium alginate (SA) gels loaded with polyphenol-rich extracts from Rubus occidentalis (black raspberry) leaves, targeting Streptococcus mutans and Lactobacillus acidophilus, two primary pathogens involved in dental caries. Extracts prepared using acetone, chloroform, and methanol were analyzed using HPLC and GC–MS, revealing that the methanol extract contained the highest levels of gallic acid (5.62 µg/mL), chlorogenic acid (17.24 µg/mL), and catechin (47.83 µg/mL). Antioxidant activity, assessed via DPPH assay, showed the methanol extract achieved the lowest IC₅₀ value (110.5 µg/mL), compared to acetone (400.5 µg/mL) and chloroform (238.0 µg/mL). The methanol extract showed the strongest effect in antibacterial assays, with minimum inhibitory concentrations (MICs) of 32 µg/mL for L. acidophilus and 125 µg/mL for S. mutans. When encapsulated in SA gel, the methanol extract formulation demonstrated the largest zones of inhibition (23 ± 2.14 mm for S. mutans and 25 ± 3.01 mm for L. acidophilus), along with superior antioxidant values (ABTS: 251.3 ± 4.32 µmol Trolox/g; FRAP: 118.62 ± 1.68 µmol Fe(II)/g). Results of confocal laser scanning microscopy examination confirmed a significant biofilm disruption. These findings highlight the potential of methanol-extracted polyphenols from R. occidentalis leaves, particularly when delivered via SA gel, as a natural therapeutic for oral infection control and dental biofilm inhibition.