Joana F. Fundo

Molecular mobility, composition and structure analysis in glycerol plasticised chitosan films

This study was developed with the purpose to investigate the effect of polysaccharide/plasticiser concentration on the microstructure and molecular dynamics of polymeric film systems, using transmission electron microscope imaging (TEM) and nuclear magnetic resonance (NMR) techniques. Experiments were carried out in chitosan/glycerol films prepared with solutions of different composition. The films obtained after drying and equilibration were characterised in terms of composition, thickness and water activity. Results show that glycerol quantities used in film forming solutions were responsible for films composition; while polymer/total plasticiser ratio in the solution determined the thickness (and thus structure) of the films. These results were confirmed by TEM. NMR allowed understanding the films molecular rearrangement. Two different behaviours for the two components analysed, water and glycerol were observed: the first is predominantly moving free in the matrix, while glycerol is mainly bounded to the chitosan chain.

The Effect of Polymer/ Plasticiser Ratio in Film Forming Solutions on the Properties of Chitosan Films

In this work physical-chemical properties of chitosan/ glycerol film forming solutions (FFS) and the resulting films were analysed. Solutions were prepared using different concentrations of plasticising agent (glycerol) and chitosan. Films were produced by solvent casting and equilibrated in a controlled atmosphere. FFS water activity and rheological behaviour were determined. Films water content, solubility, water vapour and oxygen permeabilities, thickness, and mechanical and thermal properties were determined. Fourier transform infrared (FTIR) spectroscopy was also used to study the chitosan/glycerol interactions.Results demonstrate that FFS chitosan concentration influenced solutions consistency coefficient and this was related with differences in films water retention and structure. Plasticiser addition led to an increase in films moisture content, solubility and water vapour permeability, water affinity and structural changes. Films thermo-mechanical properties are significantly affected by both chitosan and glycerol addition. FTIR experiments confirm these results.This work highlights the importance of glycerol and water plasticisation in films properties.

Molecular Dynamics and Structure in Physical Properties and Stability of Food Systems

Physical properties and stability are critical for delivering safe and healthy food to the consumers and thus is a theme that attracts food scientists for a long time. Recently, literature suggests that stability can be fully grasped only if food molecular dynamics and structure are taken into consideration, i.e. an appropriate understanding of the behaviour of food products requires knowledge of its composition, structure and molecular dynamics, through the three-dimensional arrangement of the various structural elements and their interactions. Food systems behaviour is strongly dependent on the water molecular dynamics. Understanding changes in location and mobility of water represents a significant step in food stability knowledge, since water “availability” profoundly influences the chemical, physical and microbiological quality of foods. Nuclear magnetic resonance has been presented as a powerful technique to investigate water dynamics and physical structures of foods through analysis of nuclear magnetisation relaxation times, because it provides information on molecular dynamics of different components in dense complex systems. The application of this technique may be very useful in predicting food systems physicochemical changes, namely texture, viscosity or water migration. This paper aims at reviewing some of the main aspects related to food physical properties and stability, and the role of water in these properties. More specifically, this paper intends to contribute to a deeper understanding of the relationship of molecular constituents–structure–function of food systems, contributing to the development of foods with improved functionality.

Physicochemical and bioactive compounds of ‘Cantaloupe’ melon: effect of ozone processing on pulp and seeds

ABSTRACT Melon seeds are an important source of bioactive compounds, which are considered to be health beneficial. Therefore, the objective of this work was to assess the impact of gaseous ozone treatments (30 and 60 min) on melon seeds paste (nonedible part) and compare with the effect on pulp (edible part). Ozone treatments were evaluated in terms of physicochemical (color, pH, and soluble solids content) and nutritional profiles (total phenolics, total carotenoids, and total antioxidant capacity) of processed material. Results indicate that ozone has a different impact on the two fruit matrices, being seeds less affected by this preservation treatment.

2 – Microstructure, composition and their relationship with molecular mobility, food quality and stability

Abstract Food stability is a critical parameter for both consumers and producers, since it assures safety, nutritional, and sensorial quality of foodstuffs, and at the same time maximizes shelf-life. For a long time, water activity, aw, was considered a determinant parameter in food stability and physical properties. This concept was challenged with the revolutionary approach to the study of food systems using the glass transition concept. Recently, scientific research suggests that molecular mobility is a fundamental approach to fully attain food physical properties and stability. Current literature suggests that stability can only be fully grasped if molecular mobility and structure are taken into consideration; that is, an appropriate understanding of the behavior of food products requires knowledge of its composition, structure, and molecular dynamics, through the three-dimensional arrangement of the various structural elements and their interactions. Food systems are complex mixtures of water, biopolymers, low-molecular weight ingredients, and colloid particles, and the molecular mobility between these different components reflects on the stability of such systems, determining the physical state, microstructure, and composition, which impacts food characteristics. Particularly, food water content, location, and interactions with other components are critical in microbial growth, degradation reactions, and sensorial aspects. Understanding changes in water location and mobility represents a significant step in food stability knowledge, once that water availability profoundly affects chemical, physical, and microbiological quality of foods.