Effects of sucrose and vegetable oil on properties of native cassava (Manihot esculenta Crantz) starch-based edible films
Biopolymer films and coatings from polysaccharides, proteins and lipids, formulated either with one or more components have the potential to control mass transfer and thus extend food shelf life. Due to the increase in the price of starches from traditional sources (such as corn), native or modified cassava starch has been recently considered as an economic alternative for the food industry. In this study, the effects of sucrose and vegetable oil as natural, cheaper and available plasticizer and moisture barrier material, on optical, mechanical and water barrier properties of cassava starch-based films were analyzed. Visual appearance and the polarized light microscopy data revealed that oil made the film opaque, and larger oil droplets were formed as sucrose content increased. The modification of the starch network, when sucrose was used at higher concentrations (15-20%), in combination with oil, weakened mechanical and water barrier properties. The behaviour of sucrose added to aqueous starch solution, in combination with oil, favored a development of larger droplets observed by polar microscopy, and which made the film matrix discontinuous and irregular. The heterogeneity of the film structure made the composite films fragile and facilitated water vapor diffusion. However, the film formulations containing low sucrose concentration (≤ 10 %) and an oil content of 10%, significantly reduced water vapor permeability, in comparison to film without oil. The formulations of composite film with low content of sucrose (≤ 10 %) showed smaller lipidic droplets and a structure more homogeneous by polar microscopy. Film thickness increased with total solid content in film matrix, and this effect was significantly pronounced as higher sucrose content (15-20%) was present with added vegetable oil. In addition to the linking with total solid content, this study revealed that, the thickness of films depends on reordering of molecular chains to form a more compact matrix in composite starch films, and this results in further increase film thickness. The composite films, thicker than the film control, were less cohesive due to less affinity between matrix components, and this resulted in anti-plastifiant behaviour of sucrose. Thus, sucrose used at higher levels, in combination with oil, induced negative effects on mechanical and water barrier properties of polysaccharide film. This study revealed the impact of the nature of molecular interactions on the structural characteristics and functional properties of composite matrix.
Keywords: cassava, biofilm, starch, sucrose, lipid
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