The effects of steam explosion pretreatment on the content, composition, surface structure and antioxidant activity of polyphenols in apple pomace were studied. The contents of total phenols, free phenols and bound phenols in the samples before and after the steam explosion were determined by the Folin Ciocalteu method. The free phenols were analyzed qualitatively and quantitatively by HPLC. The antioxidant capacity of the sample powder and simulated digestive juice in vitro was determined by DPPH and ABTS radical scavenging methods. Finally, the surface structure of the samples was characterized by a color difference meter and scanning electron microscope. The results showed that the content of polyphenols in apple pomace had no significant change at 1.0 MPa, but the content of bound phenols decreased significantly at 1.5 and 2.0 MPa. However, the content of free phenols and total phenols increased significantly with the increase of pressure. The results of qualitative analysis of free phenols showed that there was no significant change in the types of free phenols in apple pomace before and after steam explosion treatment, mainly phenolic acids and flavonoids. The results of the quantitative analysis showed that the content of free phenols except hyperoside and quercitrin increased significantly under the condition of 2.0 MPa treatment, and the other pressure had no significant change. After steam explosion treatment, the antioxidant capacity of apple pomace powder and in vitro digestion supernatant were improved to vary degrees, and the overall pressure was 2.0 MPa. The results of color difference analysis and scanning electron microscope showed that the color of apple pomace after steam explosion treatment became darker, and the surface was porous. With the increase of pressure, the wall-breaking effect was more obvious. Therefore, steam explosion treatment can destroy the dense structure of apple pomace, promote the release of free polyphenols from apple pomace, and improve the antioxidant activity of apple pomace to a certain extent.
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