Effects of sun-drying and steaming on Ehretia macrophylla Wall. (EMW) fruit polysaccharides: structure, physicochemical properties and gut-related functions

Abstract

Pectin-like polysaccharides from Ehretia macrophylla Wall. fruit (EMWFP) remains scarcely explored; their macromolecular structures are highly responsive to traditional post-harvest processing. Using in vitro digestion-fermentation models and structural analyses, this study provides a comprehensive evaluation of the processing-structure-function relationships of EMWFP subjected to conventional sun-drying (F-EMWFP) versus steaming followed by sun-drying (S-EMWFP). Initial steaming preserved the native high-molecular-weight architecture of S-EMWFP (~750.01 kDa) with a high degree of esterification, consistent with the inactivation of native degrading enzymes during steaming. In contrast, sun-drying alone led to extensive depolymerization, yielding low-molecular-weight F-EMWFP (~15.34 kDa). These profound structural divergences translated into markedly distinct functionalities. The preserved integrity of S-EMWFP is formed of a robust porous micro-network, conferring superior hydration properties (WHC of 7.063 g/g) and potent in vitro sequestration of cholesterol (26.55%) and bile acids. Conversely, the degraded form F-EMWFP acted as a superior in vitro prebiotic candidate, significantly enriching beneficial Lactiplantibacillus , Bifidobacterium , and Segatella while suppressing Escherichia-Shigella and exhibiting notable antioxidant activity (ABTS of 74.05%). Overall, this study highlights that targeted thermal pre-treatments can strategically tailor this underexplored fruit polysaccharide toward either functional food matrices for lipid management (S-EMWFP) or gut-targeted nutraceutical formulations (F-EMWFP).