Effect of enzyme-assisted extraction on the physicochemical properties and bioactive potential of lotus leaf polysaccharides

Lotus leaf polysaccharides were extracted by enzyme-assisted extraction using α-amylase (LLEP-A), cellulose (LLEP-C), pectinase (LLEP-P) or protease (LLEP-PR). Their physicochemical properties and immunostimulatory activities were compared with those of hot-water extracted polysaccharides (LLWP). HPAEC-PDA and HPSEC-RI profiles indicated that variations in their molecular weight patterns and chemical compositions. Moreover, their effects on proliferation, phagocytic activity, and cytokine production in macrophages could be ordered as LLEP-P > LLEP-C > LLEP-A > LLWP > LLEP-PR, suggesting that LLEP-P by pectinase-assisted extraction was the most potent enhancer of macrophage activation. LLEP-P was further purified by gel filtration, and the main fraction (LLEP-P-І) was obtained to elucidate the structural and functional properties. LLEP-P-І (14.63 × 103 g/mol) mainly consisted of rhamnose, arabinose, galactose, and galacturonic acid at molar percentages of 15.5:15.8:20.1:32.8. FT-IR spectra indicated the predominant acidic and esterified form, suggesting the pectic-like structure. Above all, LLEP-P-І exerted greater stimulation effects on NO and cytokines production and the phagocytic activity in macrophages. Transcriptome analysis also demonstrated that LLEP-P and LLEP-P-І could upregulate macrophage immune response genes, including cytokines, chemokines, and interferon via TLR and JAK-STAT signaling. Thus, these results suggest that pectinase application is most suitable to obtain immunostimulatory polysaccharides from lotus leaves.