Papers by Author: Alberto M. Sereno

Abstract: Gracilaria is a red algal genus that biosynthesizes a polymer called agar that is extensively used in the food and pharmaceutical industries as gelling and stabilizing agent. In the last years, many studies have focused on gel properties of this biopolymer; but the agar films and coatings still have few studies reported. The edible film and coating have a protective function, preventing moisture, oxygen and flavour transfers between food and surroundings. The objectives of this work are the production of biodegradable agar films from Gracilaria vermiculophylla, collected in Ria de Aveiro, Portugal, and the study of the effect of glycerol, an hydrophilic plasticizer, on the properties of the films and on subsequent application in edible coating of fresh fruits and vegetables. The agar extraction was carried out at specific optimum parameters determined in previous work (3.5 h pre-treatment duration, 6% NaOH concentration and 2 h extraction time). Agar films were made using the knife coating technique and compared with commercial agar. The physical properties of films such as hygroscopicity, mechanical resistance (Young’s modulus, tensile strength and elongation), and permeability to water vapour and oxygen were characterized. As expected, the plasticizer addition revealed and increase on elongation and decrease on tensile strength. The films were transparent and optically clear, showing good properties similar to the commercial agar films. The potential application of the agar/glycerol solution to fresh vegetable preservation was tested. Model fruits and vegetables were coated with the biopolymer/plasticizer solution and compared with a control sample in terms of colour, firmness, weight loss and shelf life. Considering on one hand the abundance of the raw algal material which is actually an invasive species, and the properties of the agar films and coatings obtained on the other hand, commercial use of G.vermiculophylla from Ria de Aveiro is well justified.

Abstract: “Sargaço” is the name given to a mixture of dead seaweeds collected on Portuguese beaches. “Sargaço” is composed of algae containing biopolymers such as carrageenan, alginate and agar which are extensively used in food and pharmaceutical industries as gelling and stabilizing agents. The objective of this work was the biopolymers extraction from “Sargaço”, collected at Leça da Palmeira-Portugal, for production of biodegradable films and subsequent application in edible coatings for food. A mixture of biopolymers was hot-extracted from alkali treated “Sargaço”. Films were made from an optimized extract, using the knife coating technique. Films physical properties were characterized and results show that biodegradable films from “Sargaço” are more hygroscopic, less elastic, more deformable, and more permeable to water than films obtained from a commercial alginate and a domestic κ/ ι-hybrid carrageenan developed during previous studies. As such, this mixture of biopolymers is an interesting cheap alternative to produce biodegradable materials and a potential application to fresh fruit preservation has been tested.

Abstract: Osmotic dehydration of pumpkin (Cucurbita pepo, L.) fruits was carried out with binary solutions of sucrose and NaCl at different temperatures and solute concentrations. Water loss and solids gain kinetics were experimentally determined and fitted using a diffusional model. Pumpkins samples were considered as finite cylinders and the analytical solution of the unsteady diffusion equation was used considering the external resistance to the mass transfer negligible. The influence of shrinkage and temperature on the effective diffusion coefficients was also assessed in this work.

Abstract: Chesnut and pumpkin fruits were dehydrated with osmotic solutions of sucrose and NaCl at 25°C. These food materials have different structure, composition and porosity. Water loss and solids gain kinetics were experimentally determined and modeled using a diffusional model. In spite of the several mass transfer mechanisms taking place along with diffusion during osmotic dehydration, the modeling was satisfactory and involved effective coefficients of diffusion useful to quantify the different mass transfer fluxes. Water and sucrose transfer rates during osmotic dehydration with sucrose solutions are independent on the initial food material characteristics; however they seem to be related with the permeability of these components to a sucrose layer formed in the surface of the samples. In the case of osmotic dehydration with sodium chloride solutions, the coefficients of diffusion show a dependence on food material characteristic and higher values of these coefficients for pumpkin (more porous material) were found.

Abstract: Osmotic dehydration experiments of pumpkin with binary aqueous solutions of sucrose, sodium chloride and ternary solutions with both solutes at 298 K were carried out. Weight reduction, water loss and solute acquisition kinetics were determined. Experimental data were fitted employing a diffusional model considering samples as spheres and the external resistance to the mass transfer negligible. The model gave as parameter of fitting an effective diffusion coefficient for each component transferred (water, sucrose and sodium chloride) for each experimental condition assayed. Correlations between the effective diffusivity and solute concentration were established for binary and ternary systems.