Differences in structure, antioxidant capacity and gut microbiota modulation of red raspberry pectic polysaccharides extracted by different methods

Abstract

Red raspberries are associated with various health benefits, with pectic polysaccharides as their primary component and potential key contributor to these effects. This study aimed to evaluate the antioxidant and prebiotic potential of four red raspberry pectic polysaccharides (RP)—EN-RP (enzyme-assisted extraction), AC-RP (acid-assisted extraction), AL-RP (alkali-assisted extraction), and US-RP (ultrasound-assisted extraction)—and to elucidate the relationship between their structure and function. AC-RP and US-RP contained higher proportions of homogalacturonan (HG) at 50.92 % and 53.10 %, respectively, while EN-RP and AL-RP exhibited higher proportions of rhamnogalacturonan-I (RG-I) at 63.89 % and 43.37 %, respectively. All four polysaccharides demonstrated significant antioxidant and prebiotic properties. AL-RP exhibited the strongest DPPH radical scavenging activity, while US-RP showed the highest hydroxyl radical scavenging ability. These pectic polysaccharides were highly fermentable, significantly modulating gut microbiota composition and promoting the production of propionic acid, particularly EN-RP and AL-RP. Compared to the blank group, RP intervention significantly enriched Bacteroides, Phocaeicola, Bifidobacterium, Limosilactobacillus, and Paraprevotella. Carbohydrate-active enzyme genes in metagenomes revealed that glycoside hydrolases played a vital role in the degradation and utilization of red raspberry polysaccharides. Furthermore, correlation analysis indicated that a higher RG-I proportion and an elevated Rha/GalA ratio enhanced the abundance of certain beneficial microbial species and increased propionic acid production. These findings advance the understanding of the structure-function relationship of natural pectic polysaccharides and highlight their potential for tailoring gut microbiota and promoting health through precise dietary interventions.