AbstractBACKGROUNDCatechins, a member of the flavonoids, exist widely in teas, and have health benefits. However, catechins have poor stability, which greatly limits their application. In order to improve the stability of catechins, different catechins including (−)‐epicatechin (EC), (−)‐epicatechin gallate (ECG), (−)‐epigallocatechin (EGC) and (−)‐epigallocatechin gallate (EGCG) were conjugated onto dialdehyde starch by acid‐mediated coupling method. The structure, stability and antioxidant activity of dialdehyde starch–catechin conjugates were determined.RESULTSThin‐layer chromatography and ultraviolet–visible spectroscopy, fluorescence, nuclear magnetic resonance and infrared spectra revealed that catechins were successfully conjugated onto dialdehyde starch, coupling between 6−H/8−H of catechins’ A ring and dialdehyde starch's aldehyde groups. The conjugates presented an amorphous structure and sheet‐like and/or blocky morphologies. As compared to dialdehyde starch, the conjugates showed enhanced thermal stability. Furthermore, the stability of catechins in pH 7.4 phosphate‐buffered saline was improved after conjugating onto dialdehyde starch. The conjugates exhibited significantly higher antioxidant activities than dialdehyde starch, decreasing in the following order: dialdehyde starch–ECG, dialdehyde starch–EGCG, dialdehyde starch–EC, dialdehyde starch–EGC and dialdehyde starch.CONCLUSIONDialdehyde starch–catechin conjugates have great potential as stable antioxidant agents. © 2022 Society of Chemical Industry.