Steam explosion treatment improves the characteristics of insoluble dietary fiber in shiitake mushroom stems: adsorption and sustained-release of flavor compounds

Using strawberry flavor as a flavor model, the selective adsorption and sustained-release mechanism of steam explosion modified shiitake mushroom stem insoluble dietary fiber (MSIDF) for different volatile substances was investigated. Results showed that the steam exploded MSIDF (S-MSIDF) exhibited a loose structure with increased surface wrinkles, higher specific surface area (SSA) and pore volume (PV), and more glycosidic bonds in hemicellulose and cellulose were disrupted, exposing more hydroxyl groups (-OH) and hydrophobic regions (C-O, C=O). The effects of steam explosion conditions on the SSA and strawberry flavor adsorption capacity of S-MSIDF were investigated. FTIR and XPS analyses indicated that the strawberry flavor molecules could bind onto S-MSIDF via non-covalent interactions (e.g., hydrogen bonding and hydrophobic interactions). DSC analyses further confirmed that the interactions between S-MSIDF and strawberry flavor molecules became stronger after steam explosion treatment, which improved the thermal stability of the flavor compounds. Adsorption kinetics, isotherm, and thermodynamics studies showed that the adsorption was a spontaneous, endothermic monolayer adsorption process controlled by a physisorption mechanism. Headspace solid-phase microextraction/gas chromatography-mass spectrometry (HS-SPME/GC-MS) analysis combined with sensory evaluation revealed that S-MSIDF exhibited superior retention capacity for esters, alcohols and aldehydes, which could combine with S-MSIDF through hydrophobic and hydrogen bonding interactions. In addition, the contents of each volatile compounds, particularly esters, alcohols, aldehydes and ketones in S-MSIDF were significantly higher than those of MSIDF during the storage period, indicating that steam explosion treatment enhanced the retention capacity of S-MISIDF for strawberry flavor compounds. This study provides scientific guidance for the development of a novel IDF-flavor powder as a functional ingredient.