Fundo, Joana

Quintas, Mafalda

Silva, Cristina L.M.

English

Repositório Institucional da Universidade Católica Portuguesa

Physical properties and stability in food systems – the relationship with molecular mobility Joana F. Fundo; Mafalda A.C. Quintas, Cristina L.M. Silva    CATÓLICA PORTO BIOTECNOLOGIA Evaluate how molecular mobility affects macroscopic properties and stability in food systems  OBJECTIVE   Model food systems - sucrose solutions           - chitosan edible films      Real food systems - fruits and vegetables CATÓLICA PORTO BIOTECNOLOGIA Framework   Food Materials Science   Tg   understand food stability   NMR measurements   solute/ solute & solute/ water interactions   the mobility and availability of water in food systems depend on the extent of interactions between the aqueous phase and the biopolymers matrix   aw CATÓLICA PORTO BIOTECNOLOGIA Chitosan Films vs Fresh-cut Pear & Melon     Good models for food systems - semicrystalline matrices  Interesting physical properties  Straightforward matrices/ Easily reproducible  Molecular mechanisms poorly understood     Real food system/ More complex system  Water can be present in both intra and extra cellular spaces - influences the behaviour of water mobility Fresh-cut Fruit  Chitosan Films  CATÓLICA PORTO BIOTECNOLOGIA  Methodology – Samples Preparation   Fresh-cut Fruit  Chitosan (1, 2 and 3% w/v)  Glycerol (10, 50 and 90% w/w) Chitosan Films  40º C until equilibrium 1%  lactic acid solution RH = 53% and T= 22ºC Solvent Casting   Stored at refrigerate temperature  -10 days CATÓLICA PORTO BIOTECNOLOGIA  Methodology - Characterisation     • Water Content • Water Activity • Chitosan and Glycerol  • Thickness  • Moisture Content • Films Solubility • Barrier Properties (Water vapour and Oxygen permeability) • Thermal Analysis   Glass  transition temperature (Tg)   Crystallinity (melting ∆h) • Mechanical Properties    Elongation at break (EB)   Tensile strength (TS)       • Water Content • Water Activity • Total Colour Difference (TCD) • Electrolyte Leakage • Scanning Electron Microscope (SEM) • Optical Microscope (MO)  • ºBrix • pH       Fresh-cut Fruit  Chitosan Films  CATÓLICA PORTO BIOTECNOLOGIA  Methodology - Characterisation   Bruker  AVANCE III 300 MHz sample relaxation time was determined (T2) : Free Induction Decay and Spin Spin Relaxation NMR Measurements  CENIMAT – I3N (Lisbon, Portugal) Y = A1 exp (-X/T2vacuole) + A2 exp (-X/T2cytoplasm) + A3 exp (-X/T2cell wall)  Y = A1 exp (-X/T2gly) + A2 exp (-X/T2water) Fresh-cut Fruit  Chitosan Films  CATÓLICA PORTO BIOTECNOLOGIA CATÓLICA PORTO BIOTECNOLOGIA Mobility vs Water Activity 90% 10% 1,E+001,E+011,E+021,E+031,E+040,48 0,50 0,52 0,54 0,56 0,58T2 Water Component (ms) Water Activity (aw) Films with the same composition – same total water content   The increase on water activity does not reflect on water mobility   Contribute to understanding differences in the stability of foods with same water activity CATÓLICA PORTO BIOTECNOLOGIA 1,E+001,E+011,E+021,E+031,E+04-100 -50 0 50T2 water component (ms) Tg (ºC) Mobility VS Glass Transition  0,26 0,055 Molecular mobility at room temperature decreases with increasing glass transition temperature   Behaviour suggests the increase of mobility with increase of free volume CATÓLICA PORTO BIOTECNOLOGIA 0,E+005,E+021,E+032,E+032,E+033,E+033,E+03-400 -300 -200 -100 0T2 water component (ms) ∆h (ºC)  Mobility vs Crystallization  0,26 0,055 For films with similar thickness, mobility increases with crystallinity Polymeric chain is organised in the crystalline lattice  Polymer binding sites are “occupied” with polymer-polymer bonds • Free volume of the system increases • Water molecules are free to move in the matrix       CATÓLICA PORTO BIOTECNOLOGIA CATÓLICA PORTO BIOTECNOLOGIA Mobility – Pear Microstructure    D0 D6 D4 D2 CATÓLICA PORTO BIOTECNOLOGIA Mobility – Pear Microstructure    D0 D10 D6 D3 CATÓLICA PORTO BIOTECNOLOGIA Mobility – Storage Time  0,00,20,40,60,81,00 2 4 6 8 10T2 water  Storage time (days) Vacuole Cytoplasm/ extracellular space Cell wall Three relaxation times (T2) can be assigned to water located in the vacuolar, cytoplasm and cell wall compartment (as is described in literature) These results will also allow to determine the distribution of water between the subcellular spaces     DATA ANALYSIS IN PROGRESS CATÓLICA PORTO BIOTECNOLOGIA  Conclusions   Water molecular mobility behaviour has no relationship with water activity Glass transition increases with decreasing mobility (relates with free volume)  Water molecular mobility increases with crystallinity of films with the same        thickness Chitosan Films Fresh-cut pear Water molecular mobility decreases with the storage time Microscope images show a structure change  that is observed in NMR measurements, with the decrease of T2 Thank you for your attention!   

Physical Properties and Stability in Food Systems – The Relationship with Molecular Mobility

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Physical Properties and Stability in Food Systems – The Relationship with Molecular Mobility

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Repositório Institucional da Universidade Católica Portuguesa