Adsorption, structure and surface dilational characteristics of hydroxypropylmethycellulose (HPMC) adsorbed films at the air-water interface

PÉREZ, OSCAR E; CARRERA-SÁNCHEZ, CECILIO; RODRÍGUEZ-PATINO, JUAN M; PILOSOF, ANA MR.

Valencia, Spain

Congreso; INTRAFOOD, Congress Proceedings, Innovations in Traditional Foods; 2005

EFFoST Conference

Cellulose is the most common natural plant carbohydrate in which the basic repeating structure is an anhydroglucose unit. Although it is a highly hydrophilic biopolymer it is not soluble or swellable in water due to highly crystalline nature. Solubility can be achieved altering its ordered crystallite regions by chemical substitution, generating cellulose derivatives. Among them, hidroxypropylmethylcellulose (HPMC), which has methyl and hydroxypropyl groups added at the anhydroglucose backbone, includes a family of cellulose ethers that differ principally in the molecular weight, viscosity, degree of substitution and molar substitution.  HPMC is used in the food industry, printing technology, and pharmaceutical applications because is nontoxic and possesses good mechanical properties. In the pharmaceutical industry, HPMC has acquired special interest for controlled drug-release matrices. In the food industry, HPMC is used to improve the quality of baked   products,  in gluten-free breads, for innovative battered food manufacturing, low-fat edible coatings, etc. The usefulness of HPMC is essentially based upon four key attributes: efficient thickening, surface activity, film forming ability, and the capacity to form reversible thermal gels that melt upon cooling. Surface pressure isotherms and structural and surface dilational properties of three HPMC adsorbed films at the air-water were determined. The HPMC so called E4M, E50LV and F4M display different interefacial properties. In this work we present evidence that HPMC molecules were ablle to diffuse and saturate the air-water interface at very low concentrations inthe bulk phase.As concentration increased structural changes at a molecular level occured at the interface, which corresponded to transitions from an expanded structure to a condensed one. When the surface concentration was high enough, the collapse of monolayer was the observed phenomenon. The three HPMC formed cohesive films at the air-water interface that showed a strong dependence with surface pressure. Although HPMC monolayers behaved as viscoelastic, F4M and E4M generated the more elastic films and E50LV the less ones. The observed differences in interfacial properties of these films could be attributed to the structural patterns adopted by adsorbed HPMC molecules as a consequence of the distribution of hydrophilic and hydrophobic groups along the cellulose backbone.