Abstract:Octenyl succinic tapioca starch（OSTS） was synthesized from tapioca starch through a subtractive pretreatment involving octenyl succinic anhydride （OSA） esterification. The degree of substitution was used as a criterion to optimize the OSTS preparation process through single factor experiments and orthogonal tests and to analyze the properties of OSTS. The findings indicated that the optimal conditions for OSTS synthesis included a 35% starch concentration，a pH of 8.5，a temperature of 35 ℃，and a duration of 4 h. The degree of substitution for OSTS prepared under these conditions was 0.015 1±0.000 3. The presence of characteristic peaks at 1 740 cm-1 and 1 572 cm-1 on the infrared spectrum confirmed the successful esterification of the starch，indicating that OSA esterification did not alter the crystalline structure of the starch，and esterification occurred solely on the starch surface. The emulsifying activity and stability of the starch were significantly enhanced （P＜0.05），with an increase in hydrophobicity and a rise in the contact angle from 20.5° to 58.3°.