Preparing water–resistant films using partially debranched potato starch and oleic acid

Improvement in film–forming properties of starch is critical for the wide application of environmentally friendly starch film. To enhance moisture barrier and mechanical properties of starch films, the formation of starch–lipid inclusion complex was promoted by partial debranching of starch and reaction at various temperature. The partially debranched potato starch was initially prepared with pullulanase, and the starch–lipid inclusion complex was subsequently produced with oleic acid at various reaction temperatures of 30, 50, and 70 °C. The partial debranching combined with oleic acid addition induced characteristic V-type crystalline peaks in the X-ray diffraction (XRD) patterns. The highest reaction temperature, of 70 °C, induced more apparent XRD peaks and higher thermal transition temperatures and enthalpy. The partially debranched starch film with oleic acid at 70 °C showed a smooth and uniform surface with a more rigid and condensed network. The high content of starch–lipid inclusion complexes in a partially debranched starch film with oleic acid at 70 °C significantly reduced water vapor permeability (from 162.22 to 65.99 g∙mm∙m⁻²∙day⁻¹∙atm⁻¹) and increased both the contact angle (from 61.08 to 74.55°) and tensile strength (from 2.126 to 5.473 MPa) compared to a native starch film. Therefore, the formation of more abundant starch–lipid inclusion complexes at relatively high reaction temperatures with partial debranched starch can effectively enhance the moisture barrier properties of starch films for industrial application as biodegradable film.