Effect of moisture and water activity on textural properties of toasted food products

Transcription

1 Effect of moisture and water activity on textural properties of toasted food products Paola Pittia and Giampiero Sacchetti Dipartimento di Scienze degli Alimenti University of Teramo Italy Euro Food s Water March 2006, Bruxelles

2 Texture It comprises all physical characteristics sensed by the feeling of touch that are related to deformation under an applied force and measured objectively in terms of force, distance and time

3 PP1 Levels of structure and mechanical properties of food matrices Scale Length Macro-structure mm Micro-structure µm Micro Meso-structure TEXTURE MECHANICAL PROPERTIES Meso Nano-structure Nano nm Molecular Molecules Micro- biopolymer, solutes, water Food composition Physical properties

4 Slide 3 PP1 Textural properties of food matrices depends on many chemical and physical properties. Composition (macromolecular components) presence and concentration of water. Physical properties related to structure Nowhere is the role of structure more apparent than in its effects on mechanical properties of foods and by extension on texture. Foods having similar composition could exert a different mechanical behaviour depending on its structure Paola Pittia, 17/03/2006

5 Structural properties of foods PP2 Structure: NATIVE BY FORMULATION PROCESSING- INDUCED

6 Slide 4 PP2 Textural properties of food matrices depends on many chemical and physical properties. Composition (macromolecular components) presence and concentration of water. Physical properties related to structure Nowhere is the role of structure more apparent than in its effects on mechanical properties of foods and by extension on texture. Foods having similar composition could exert a different mechanical behaviour depending on its structure Paola Pittia, 17/03/2006

7 Mechanical properties in cellular structures PP4 Role of: cell geometry cell size and distribution cell wall thickness and strenght porosity

8 Slide 5 PP4 Textural properties of food matrices depends on many chemical and physical properties. Composition (macromolecular components) presence and concentration of water. Physical properties related to structure Nowhere is the role of structure more apparent than in its effects on mechanical properties of foods and by extension on texture. Foods having similar composition could exert a different mechanical behaviour depending on its structure Paola Pittia, 17/03/2006

9 Roasting in food processing Intense heattreatmentathigh t em perature ( C) fora certain tim e able to induc e significantchanges on: - chem ical - physical - structuralproperties offood m atrices aimedto: increase edibilityand/orimprove nutritionalvalue determine desired sensorialproperties offoods (arom a, flavour, britleness, crispiness, crunchiness,.) Applications: co fee, m alt, breakfastcereals,

10 Coffee roasting Chemical properties Heat-induced reactions Maillard Maillard reaction, reaction, caramellisation caramellisation Water Water liquid-phase liquid-phase transition transition Moisture Weight Melanoidins + MRP products Physical properties Heat-induced reactions Colour Structure(density and porosity) Texture

11 Roasting in coffee processing Raw bean Moisture: 12%, aw: Dense structure Hard to fracture green aroma Roasted bean 0,1-0,5 % moisture Light-to-dark brown colour Characteristic aroma Porose structure Brittle, fragile

12 Structure of a cut section of raw and roasted coffee bean Structure of a cut section of a green coffee bean (left) and roasted 10 min (right) (124 x, 10kV, WD: 25 mm) (Massini et al., 1991)

13 Roasting and textural properties Force (N) raw 0 0,5 1 1,5 2 2,5 3 displacement (mm) Fracture load (N) raw Medium roasted Tostado (Robusta) Torrefado (Robusta) High Yield (Arabica) HighYield (Robusta) Force (N) roasted 0 0,5 1 1,5 2 2,5 diplacement (mm) 3 Strain at fracture (%) raw Medium Tost ado roasted (Robusta) Torrefado (Robusta) High Yield (Arabica) HighYield (Robusta) (Pittia et al., 1999; Pittia, 2005, unpublished data)

14 Roasted products and moisture adsorption: effects Product-related related Sensory quality and acceptability Shelf-life Process-related related Handling Size reduction, grinding Development of food products

15 Water and mechanical properties PLASTICISING EFFECT Stiffness Toughness hardness Moisture content, a w

16 Water and mechanical properties ANTIPLASTICISING EFFECT increased stiffness, toughness, stress at failure, upon moisture sorption Stiffness Toughness hardness glassy,amorphous matrices Moisture content, a w Cerealsnacks, gluten films, m eatproteins.

17 ANTI-PLASTICISING EFFECT Reduced free volume of the polymeric system Polymer-diluent interactions, which create steric hindrance and decrease segmental mobility Stiffening action due to the presence of rigid plasticising molecules adiacent to polar groups of the polymer Increased ability of the molecules to reorient themself, reducing the material brittleness and inhibiting the ability of cracks to propagate References: Seow et al., 1999, Moraru et al., 2002, Marzec & Lewicki, 2006

18 Effect of moisture adsorption on mechanical properties of toasted products Coffee beans various degree of roasting Raw (green) Light Medium dark RTE breakfast cereals Different formulation Different pellet moisture Corn chestnutrice toasting

19 Mechanical properties of coffee beans vs water activity Loss of brittleness and crunchiness Fracture force (N) Fracture energy (J) ,15 0,1 0, raw roasted 0 0,2 0,4 0,6 0,8 1 a w strenght 0 0,2 0,4 0,6 0,8 1 toughness a w deformability PLASTICISATION EFFECT ANTIPLASTICISATION EFFECT Fracture strain c 0 0,2 0,4 0,6 0,8 1 a w

20 Effect of water on textural properties of RTE breakfast flakes Stifness(N/m) 3,5E-03 3,0E-03 2,5E-03 2,0E-03 1,5E-03 1,0E-03 5,0E-04 0,0E+00 Frosted Toasted breakfast flakes Toasted breakfast flakes Non toasted breakfast flakes Moisturecontent(g/1 00g) Sample1 Sample2 Sample3

21 Modulusvsa w of raw and roasted coffee beans compressive modulus (N/m -2 )* raw dark 0 0,2 0,4 0,6 0,8 1 a w Fermi s equation Y ( aw) = Y 1+ e 0 aw awr b a wc : a w value at which a 50% drop of the mechanical property occurs b: index of drop steepness

22 Regression parameters of Fermi s equation applied to compressive modulus upon hydration Coffee sample Y 0 (N m -2 ) a wc b R 2 Raw **4.61a **0.770b *0.053a Light roasted **2.07b **0.834a *0.051a Medium roasted **1.90b **0.821a *0.048a Dark roasted **1.57c **0.843a *0.036a *significant at p < 0.05 level. **significant at p < 0.01 level

23 )*10 - compressive modulus (N/m raw dark 0 0,2 0,4 0,6 0,8 1 a w Coffee sample Y 0 (N m -2 ) a wc b R 2 Raw **4.61 a **0.770 b *0.053 a Light roasted Medium roasted Dark roasted **2.07 b **0.834 a *0.051 a **1.90 b **0.821 a *0.048 a **1.57 c **0.843 a *0.036 a *significant at p < 0.05 level. **significant at p < 0.01 level

24 Water-coffee matrix interactions: sorption isotherm of raw and dark roasted coffee beans 1 1 DarkroastedLineSpacing(3) Green Moisture (g/g d.w.) a w

25 Regression parameters of GAB equation applied to sorption isotherms Coffee sample X m C g K R 2 % d.b. Raw **4.34a **4.29b **0.960d Light roasted **3.58b *3.05b **0.991c Medium roasted **3.56b *6.00ab **0.998b Dark roasted **3.54b *6.76a **0.999a *significant at p < 0.05 level. **significant at p < 0.01 level Roasted samples are able to retain more water in the higher aw range (a w > 0,85) Upward concavity: aw 0,825

26 Water-coffee matrix interactions and mechanical properties Roasted coffee beans sorption isotherm: a w value where water becomes free (0,83) Mechanical properties: a wc : 0,82-0,84 Green coffee beans sorption isotherm: a w value where water becomes free (0,83) Mechanical properties a wc : 0,77 composition structure

27 DSC and NMR analysis (ongoing research) Evaluation ofthe state and m obilityofwaterin the green and roasted co fee beans m atrix Preliminary results of DSC analysis in roasted coffee: - no freezeble water in samples a w 0,82 - freezeble water in samples a w > 0,82

28 Conclusions Antiplasticising/plasticising e fectofwateron toasted food m atrices Mechanicalproperties ofco fee as a fected by waterreflect: -ce lularcharacteristicsofthe m atrix(porosity, openclosed ce ls, ce lwalsize, distribution, thickness) -mechanicalproperties ofce lwalmaterialand its moisture dependence

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30 Dipartimento di Scienze degli Alimenti University of Teramo Mosciano S.Angelo