Effects of different ratios of mannitol to sorbitol on the functional properties of sweet potato starch films

Abstract

Sorbitol as a plasticizer is easily crystallized from starch film, resulting in the reduction in plasticizing effect. To improve the plasticizing performance of sorbitol in starch films, mannitol, an acyclic hexahydroxy sugar alcohol, was used to cooperate with sorbitol. The effects of different ratios of mannitol (M) to sorbitol (S) as a plasticizer on mechanical properties, thermal properties, water resistance and surface roughness of sweet potato starch films were investigated. The results showed that the surface roughness of starch film with M:S (60:40) was the smallest. The number of hydrogen bonds between plasticizer and starch molecule was proportional to the mannitol content starch film. With the decrease of mannitol contents, the tensile strength of starch films gradually decreased except for M:S (60:40). Moreover, the transverse relaxation time value of starch film with M:S (100:0) was the lowest, indicating that it had the lowest degree of freedom of water molecules. Starch film with M:S (60:40) is the most effective in delaying the retrogradation of starch film. This study offered a new theoretical basis that different ratios of mannitol to sorbitol improve different performances of starch films.