Abstract

Coatings made from hydroxypropyl methylcellulose (HPMC) containing surfactant mixtures of sorbitan monostearate (SPAN 60) and sucrose palmitate (sucrose ester P-1570) in aqueous and hydroalcoholic media were developed to analyse the effect of the hydrocolloid/surfactant ratio (H/S), the hydrophilic-lipophilic balance (HLB) of the surfactant mixtures and the solvent type used as dispersing media on the water vapour barrier properties of the films and their optical effect when applied to carrot slices. The results showed that the solvent type, H/S ratio and HLB significantly affected viscosity, surface tension, and stability (particle size and flocculation rate) of the film-forming dispersions, which in turn had a great influence on the extensibility and final film structure of the coating on the carrot surface. All these aspects affected the water vapour barrier properties of the film. The best water vapour barrier properties were found in the coating made from hydroalcoholic dispersions with intermediate values of the surfactant's HLB. The colour of coated carrot slices was mainly affected by the solvent dispersion media, the induced changes being greater for aqueous dispersions. © 2008 Elsevier Ltd. All rights reserved.