Evaluation of the effects of glycerol and sorbitol concentration and water activity on the water barrier properties of cassava starch films through a solubility approach

• Published in: Carbohydrate polymers 2008-04, Vol.72 (1), p.82-87
• Main Authors: Müller, Carmen M.O., Yamashita, Fabio, Laurindo, João Borges
• Format: Article
• Language: English
• Subjects: Solubility approach; Starch films; Water permeability
• ISSN: 0144-8617; 1879-1344
• DOI: 10.1016/j.carbpol.2007.07.026

The effects of glycerol and sorbitol on the water sorption isotherms and water vapor permeability ( K w ) of cassava starch films prepared by casting were investigated. K w values were determined in three ranges of relative humidity, RH, (2–33%, 33–64% and 64–90%) and the GAB model was used to fit experimental water sorption isotherms. These data were used to determine the relative influence of the diffusion coefficient of water ( D w ) and the average solubility coefficient ( β ¯ ) of water in the films on the K w value. In all cases, an increase in K w values were observed with increasing plasticizer concentration and RH. The D w , β ¯ and K w values of films prepared with glycerol were greater than those of films prepared with sorbitol. For high RH, the β ¯ values increased 6-fold for films with glycerol and 7-fold for films with sorbitol, while D w values did not change significantly. These results indicate that K w values are dependent on the solubility coefficient ( β ¯ ) of water in the film, which is not consistent with the proposal that an opening of polymer chains promoted by plasticizers leads to an increase in D w and K w .