Abstract

Hydroxypropylmethylcellulose (HPMC) films are flexible, transparent, odorless, and tasteless, with  a selective permeability to gases. However, its high water vapour permeability (WVP) makes necessary the addition of lipidic compounds (fatty acids, waxes, resins and/or surfactants) into the polymeric matrix to improve this property. Therefore, the aim of this work was to formulate and characterize composites coatings based on HPMC and different lipidic compounds (surfactants, oleic acid (OA) and ethanolic extract of propolis (EEP)). The effect of its application on the quality of strawberries and grapes throughout cold storage was also evaluated.
Results showed that the physicochemical properties of the film forming-dispersions (FFDs) were affected by the concentration of the polymer and by the added compounds (OA, surfactants, EEP), giving as a result dispersions with different particle size, ?-potential, superficial tension and rheological properties. Similarly, film properties were also affected by the incorporation of the previously cited compounds.
The greater WVP reduction was obtained increasing the HPMC, OA and EEP concentration. Among these formulations, the maximum WVP reduction was achieved by using 5% HPMC and 1.5% EEP in the film, WVP values being reduced around 88%, in comparison with pure HPMC film. Mechanical and optical properties of films changed as a function of the added compound. Incorporation of EEP into HPMC films led to an increment in the mechanical strength and stiffness of the films, which also became less glossy. Furthermore, films containing propolis showed a notable antifungal activity against the tested fungi, which was more intense against Aspergillus niger than against Penicillium italicum. 
The application of composite coatings based on HPMC and Sugin 471/PHK-40 as a surfactant to strawberry fruit (cv. Ventana) slightly modified the fruit physicochemical and sensorial properties. Coated samples showed higher resistance to water vapour transmission and respiration rate. The firmness increased and the color coordinates (luminosity, croma and hue) of these coated samples decreased through 9 days of storage at 5ºC. On the other hand, coatings caused significant changes in the sensory properties in terms of gloss, flavour, olour and firmness, more marked when using the highest hydrocolloid concentration. 
The application of HPMC coatings to grapes (cv. Muscatel) reduced their weight loss and browning rates, while improving their gloss and microbial safety.The incorporation of EEP into pure HPMC films increased the luminosity of the samples, but no other significant effect on the preservation of grape quality through out 22 days of storage at 1-2ºC and 85-90% relative humidity was observed. Again, the sensory properties of coated grapes were significantly affected by the film composition. Nevertheless, taking into account the properties of propolis, its incorporation into HPMC coatings could contribute to enhance the nutritional characteristics of the coated product. In this sense, these coatings can be considered as an efficient alternative to obtain healthier fruits.