Evolution of the microstructure of frozen foods during storage: Application on plant tissue

Transcription

1 Evolution of the microstructure of frozen foods during storage: Application on plant tissue Victor Vicent Graciela Alvarez Fatou Toutie Ndoye Prof. Bart Nicolaï Pieter Verboven

2 Outline Introduction Objectives Materials and Methods Results Future workflow plans 2

3 Cold chain for frozen foods Factory Distribution warehouse Supermarket Domestic freezer Cold chain: set of refrigeration steps in handling of foods Purposely: Preserve food quality Prolong shelf life 3

4 Quality losses in frozen foods Instability of frozen water Temperatures (fluctuations) Storage time Recrystallisation Sublimation Energy instabilities Growth of ice crystals Decrease of ice crystals number Vapour pressure Dehydration Frost formation Microstructure, textural & sensorial changes drip & weight losses Nutritional quality loss Quality loss 4

5 Recrystallisation mechanisms Ostwald ripening Growth of large ice crystals at the expenses of small ones 5 5

6 Sublimation Moisture loss from food surfaces Function of temperature gradient Freezing Frozen storage ice-sublimation frost formation freeze-burn 6

7 Quality losses in frozen foods Physical phenomena Recrystallisation Sublimation Quality indicators microstructure, drip & Microstructure weight loss, evolution WHC, freeze-burn Chemical reaction - Food microstructure: key parameter defines food quality Proteins denaturation Nutrients loss, rancidity, - 3D structure Lipid oxidation provides more insight information flavour, appearance Enzymatic reaction 7

8 Microstructure Evolution What are the effect of frozen storage on recrystallisation and sublimation? What imaging methods to investigate the microstructure of frozen foods? How can we predict the microstructure changes on frozen foods during storage? What is...? 8 8

9 Effect of temperature fluctuation on recrystallisation - Freeze-dried potato - Xradia-microCT: Pores ice crystals -80 o C -17 to -16 o C -17 to -11 o C -17 to -7 o C 1890 pores 664 pores 334 pores 302 pores 9

10 Effect of temperature on sublimation - Bread dough packed in PE bag - Frozen in air blast weight loss ice-sublimation Question: How does it related to microstructure change? 10

11 Ice-crystals imaging methods CLSM; used to visualise the freezing effect on apple tissue 3 freezing protocols -20 o C -80 o C Liquid nitrogen μm 3 μm <2 μm 11

12 Ice-crystals imaging methods Meat Carrot - Frozen foods at -5 o C -Freeze-dried -Skyscan Voids ice crystals Chicken Potato But: Shrinkage effect can blur the structure Fish Cheese 12

13 Objectives & Outline Part I: To characterise the microstructure changes during frozen storage Develop new method to study the microstructure on frozen food Extend the developed method on different storage conditions Part II: To get in depth understanding of the relationship between microstructure changes and physical phenomena Modelling of microstructure along cold chain Managing the frozen food quality along cold chain 13

14 WP I Develop new method to investigate the microstructure on frozen food Task: Use the X-ray microct on frozen sucrose solutions X-ray microct and optical microscopy on sorbet for comparison Optimize the segmentation protocol 14

15 Materials Sucrose solution Prepare sucrose solution of 13% ( apple brix) Frozen at different temperatures at -6; -12 and -20 o C 15

16 Materials Apple samples 5 repetitions (Ø = 4 mm & L = 6 mm) Freezing at different rates Fast freezing (-12 o C/min) Slow freezing (-2 o C/min) Directly on micro-ct at -6; -12 and -20 o C Thermocouples 16

17 Method μct: high resolution for 3D image of the internal structure Non-invasive Non-destructive X-rays: High energy Can be transmitted & attenuated f(x-rays energy, material properties) Can be identified by detector X-ray tube Sample rotation 17

18 3D reconstruction 3 filtered Back-projections 16 filtered Back-projections 18

19 MicroCT Vs Microscope Sucrose solution 19

20 MicroCT Vs Microscope 20

21 Results: Sucrose solution -6 o C -12 o C -20 o C Freezing 70 min 52 min 38 min time 21

22 3D model for sucrose Ice fraction -6 o C -12 o C -20 o C Unfrozen phase 22

23 Measured ice fraction 23

24 Image segmentation -6 o C -12 o C -20 o C Voids Frozen phase Unfrozen fraction 24

25 Pore size distribution -6 o C 25

26 Pore size distribution -12 o C 26

27 Pore size distribution -20 o C 27

28 Pore size distribution 28

29 Image segmentation Fast (12 o C/min) Slow (2 o C/min) 29

30 Measured ice fraction 30

31 WP II Extent the new developed method on different storage conditions Tasks: Investigate the effect of temperature fluctuations Vs constant temperature regimes Investigate the weight & drip loss and water holding capacity Tracking the 3D microstructure evolution along storage 31

32 WP III Modelling the microstructure propagation along storage Tasks: The modelling approach will be mainly built based on physical phenomena: i. Ice-crystal growth kinetics (recrystallisation) ii. As well as moisture loss kinetics (sublimation) Coupling heat and mass transfers 32

33 WP IV Managing the frozen food quality during frozen cold chain Tasks: Incorporate the models in the optimisation loops to control the cold chain for frozen food Assessing food quality evolution; weight & drip losses, water holding capacity 33

34 Publications IMa (Meeting abstracts, presented at international scientific conferences and symposia, published or not published in proceedings or journals) Vicent, V., Ndoye, F.T., Verboven, P., Nicolai, B., Alvarez, G Understanding the microstructure of frozen apple during storage using X-ray micro CT system. DOF th International Symposium on Delivery of Functionality in Complex Food Systems-Physical- Inspired Approaches from the Nanoscale to the Microscale. Paris, France, July Victor VICENT, Fatou Toutie NDOYE, Pieter VERBOVEN, Bart NICOLAI, Graciela ALVAREZ Applicability of X-ray microtomography for characterizing the microstructure of frozen apple during storage. ICCC th IIR Conference on Sustainability and the Cold Chain. Auckland, New Zealand, 7-9 April,

35 Thanks for your attention 35