Effects of octenylsuccination on physical, mechanical and moisture-proof properties of stretchable sweet potato starch film

The high humidity sensitivity of glycerol plasticized starch films badly limited their applications for various foods. Stretchable sweet potato starch films with improved moisture-proof property were successfully obtained by using equivalently mixed octenylsuccinated/native starches (OSS/NS). FT-IR analysis evidenced the successful synthesis of OSS and its presence in OSS/NS blend films. The effects of the degree of substitution (DS) of OSS on the properties of the resulting blend films were evaluated. The incorporation and DS of OSS were of much importance in determining the properties of the blend films. In contrast with the control film, OSS/NS blend films presented significantly improved moisture-proof property as indicated by the lower values in water solubility and water vapor permeability, and the higher values in contact angle and oil permeability. The amplitudes of these improvements varied with the increasing DS of OSS. Meanwhile, the stretchability, elongation at break and transparency of OSS/NS blend films were higher than those of the control film and increased with the increasing DS of OSS. Oppositely, the results of XRD showed that OSS/NS blend films owned lower crystallinity compared with the control film. These variations were virtually ascribed to the hydrophobicity of OSS and the plasticization of octenyl groups in film formation. Frankly speaking, incorporating OSS into sweet potato starch film is a double-edged sword, providing positive effects by enhancing moisture-proof property, stretchability, elongation at break and transparency while simultaneously triggering deterioration in tensile strength and/or structural homogeneity. (C) 2014 Elsevier Ltd. All rights reserved.