Abstract
The effect of saturated and unsaturated fatty acids on sweet potato starch and sweet potato starch-based films was studied. Three fatty acids varying in degree of unsaturation were used in the preparation of sweet potato starch-based films; i.e. stearic acid (C18:0), oleic acid (C18:1) and linoleic acid (C18:2). The stearic acid is more strongly bound with amylose than oleic acid and linoleic acid. In differential scanning calorimetry thermograms, both of the sweet potato starch-saturated fatty acid and sweet potato starch-unsaturated fatty acid composites exhibited the melting peak of amylose-lipid complex. The amylose-linoleic acid complex peak was unapparent compared with stearic acid and oleic acid. X-ray diffraction showed that the scattering intensity of amylose-lipid complex decreased with increasing unsaturation. Scanning electronic microscope indicated that the surface of the films became smooth after addition of fatty acids. The sweet potato starch-saturated fatty acid composites films exhibited higher tensile strength, lower elongation at break and lower water vapor permeability than those of the sweet potato starch-unsaturated fatty acid composite films.
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