Microstructure changes during baking

Transcription

1 Microstructure changes during baking Advances in Molecular Structuring of Food Materials Prof. Carmen Tadini University of São Paulo NAPAN Food and Nutrition Research Center 1

2 1. Importance and general aspects Bread in its many forms is one of the most staple foods consumed. 2

3 1. Importance and general aspects It is important to understand about the unique properties presented by the wheat proteins, namely their ability to form a cohesive mass of dough. 3

4 2. Breadmaking process To convert wheat flour into an aerated and palatable food 4

5 2. Breadmaking process: largely common steps Mixing of the ingredients according to the formulation Salt Yeast Flour Other ingredients Water Spiral dough mixer 5

6 2. Breadmaking process: mixing Mixing of the ingredients according to the formulation to disperse uniformly the ingredients; to dissolve and hydrate the ingredients; to contribute energy to the gluten development; to incorporate air bubbles within the dough. 6

7 2. Breadmaking process: development of the gluten structure The gluten structure (hydrated proteins) is developed in the dough through the application of energy during mixing, often referred to as kneading ; This step is responsible for the transformation wheat flour and water into a cohesive dough with viscoelastic properties; 7

8 3. Principles of dough formation: development of the gluten structure Random orientation (b) (c) (a) If As At the mixing early mixing stage proceeds, time of mixing, pass more the the protein optimum gluten fibrils becomes development, are hydrated in contact the and the cross-links with glutenins the mixer begin tend blade, to to break; align, bowl the gluten sides and networks other flour are developed by particles; the cross-linking of protein with disulphide bonds; Molecular interpretation of gluten development (Zaidel et al., 2010) 8

9 3. Principles of dough formation: development of the gluten structure Wheat storage protein has unique properties; No other cereal storage protein possesses the ability to form a viscoelastic dough when wetted and kneaded. In studying dough formation, it is common to observe the physical events on a macro scale, at the supramolecular level; The macro scale properties of dough change with time and our knowledge about these modifications in rudimentary, at best. 9

10 3. Principles of dough formation: development of the gluten structure The real reason for understanding the dough formation is the final product a good loaf of bread! The two characteristics that define good dough are: The ability to retain gas (CO 2 ); A proper balance of viscous flow and elastic strength. Gluten is the component of the dough that determines how well these requirements are met. 10

11 3. Principles of dough formation: flour and dough components Wheat flour components (dry basis) can be classified into six groups: Starch; Storage (gluten) proteins; Non-starch polysaccharides (pentosans); Lipids; Water-soluble proteins; Inorganic compounds (ash). 11

12 3. Principles of dough formation: Starch The largest portion of flour (76 g/100g d.b.) Starch; 17 % (d.b.) amylose -1,4 linked glucose units M W =100,000 Da 58 % (d.b.) amylopectin -1,4 and -1,6 linked glucose units M W =20,000,000 Da 12

13 3. Principles of dough formation: Starch Protein-protein interaction Starch granules SEM mag 5000 x Protein phase 13

14 3. Principles of dough formation: Protein - flour having 12 % protein contains about 10 % of gluten Gliadin single-chain polypeptides < M W < Glutenin Mixing multiple-chain polymeric proteins Disulphide bond formation 14

15 4. Rheology and bread quality Within the cereal science community: Rheological properties of dough are related to the bread quality; Gluten proteins are responsible for variations in baking quality; In particular, the insoluble fraction of HMW glutenin polymer is related in dough strength; the exact molecular mechanisms responsible for this variation still remain unclear; 15

16 4. Rheology and bread quality Challenges: In polymer physics, it is widely accepted that molecular size, structure and MWD are linked to their rheological properties; Since gluten can be viewed as a polymer, an understanding of its rheological properties in relation to the molecular structure and its functional behavior during the breadmaking process is highly desirable; 16

17 4. Rheology and bread quality Challenges: However, many of the rheological tests on dough are inappropriate, because they do not use deformation conditions appropriate to baking, and are quite often insensitive to changes in molecular weight and structure; 17

18 4. Rheology and bread quality Rheology is the study of the flow and deformation of materials. Mixing behavior Product quality Rheology Baking performance Mouthfeel and texture 18

19 4. Rheology and bread quality The general aims of rheological measurements are: To obtain a quantitative description of the materials' mechanical properties; To obtain information related to the molecular structure and composition of the material; To characterize and simulate the material's performance during processing and for quality control. 19

20 F [mn] 4. Rheology and bread quality Rheological tests attempt to measure the forces required to produce given controlled deformations, such as: Compression Uniaxial extension Biaxial extension t [s] Force-displacement curve 20

21 4. Rheology and bread quality m = 3000 kg = 30 kpa A = 1 m 2 21

22 4. Rheology and bread quality There are many tests methods according to the type of strain imposed: Compression; Extension; Shear; Torsion; Or depending of the magnitude of the imposed deformation: Small; Large; 22

23 4. Rheology and bread quality For measuring cereal products, the main techniques have been divided in: Descriptive empirical methods; Fundamentals measurement; Descriptive empirical techniques: There are a lot used mainly by cereal industry in evaluating performance during processing and for quality control; 23

24 4. Empirical methods Farinograph Dough Mixing time, torque, apparent viscosity Extensograph Dough Extensibility Rapid visco amylograph (RVA) Pastes, suspensions Apparent viscosity, gelatinization temperature Though these techniques do not provide data in fundamental units, important information on the quality and performance on cereal products are obtained. 24

25 4. Empirical methods However, these measurements are not strictly rheological tests since: the sample geometry is variable and not well defined; the stress and strain are uncontrolled, complex and non-uniform; and it is not possible to define any rheological parameters such as stress, strain, strain rate, modulus or viscosity. 25

26 4. Empirical methods Therefore, these tests are purely descriptive and dependent on: the type of instrument; size and geometry of the test sample; and the specific conditions. 26

27 4. Fundamental methods Oscillatory tests Fluids, pastes, batters, dough Dynamic shear moduli, dynamic viscosity Uniaxial extension Dough Extensional viscosity Dough inflation system Dough Strain hardening These techniques measure well-defined physical properties in fundamental units. 27

28 4. Fundamental methods However, these measurements have many problems since: Complex instrumentation which is expensive, time consuming and requires high level of technical skill; Often inappropriate deformation conditions; Difficulty in interpretation of results; and Slip and edge effects during testing. Therefore, these tests are independent on: The type of instrument; Size and geometry of the test sample; and The specific conditions. 28

29 5. Uniaxial extension empirical method The required force to deform the dough is expressed in Extensograph Units (EU); From the extensograph loadextension curve, several parameters can be derived; R max Disadvantage: The rate of deformation under fermentation is three orders of magnitude smaller than the measured maximum rate. A tot E max 29

30 5. Uniaxial extension fundamental method Kieffer dough and gluten extensibility rig The dough is stretched in one direction; Again from force-extension curve you can obtain parameters as stress and strain: L F L L ; ln A L L L 0 0 Disadvantage: F R max [N] Maximum point at fracture For the tests, the original sample dimensions are considered; But their dimensions change extensively E 1 and non-uniformly during testing. E max E tot d [mm] 30

31 5. Uniaxial extension theory Samples preparation in a mould: ten pieces 5 cm long wherein: y 0 : specific point where the deformation is zero [mm] L 0 : initial length [mm] L t : length at the time t [mm] w: width of the gap [mm] v L L t 2 w y0 2 w = 2 + y + y 2 2 t 0 2 L t /2 b 1 b 2 h y 0 L 0 /2 w 31

32 5. Uniaxial extension theory 2 2 w L 2 yt y0 t H ln ln L 2 0 w 2 y 2 0 d 2 4 H 1 dl 1 y y dy y y dt L dt L 2 w dt L 2 yt y0 t 0 t t 0 2 t t 2 t v v L t /2 b 1 h b 2 w y 0 L 0 /2 32

33 H [dimensionless] 5. Uniaxial extension comparison of micro-extensograph with a extensograph 4 3 micro-extensograph 2 1 extensograph d [mm] Hencky strain ( H ) as a function of the hook displacement (d). 33

34 5. Uniaxial extension force balance F m y t F d L t / 2 y 0 Forces acting on the dough piece 34

35 5. Uniaxial extension Stress calculation F m y t F d L t / 2 y 0 Forces acting on the dough piece 35

36 TG 1 [g/100g] Effect of maize resistance starch (MRS) and transglutaminase (TG) on rheological properties of pan bread dough Central Composite Design(2 2 ) base on 100 % mixture MRS 1 [g/100g] 36

37 max [kpa] Effect of MRS and TG on rheological properties of pan bread dough uniaxial extension max [kpa] 37

38 P [mmh 2 O] 6. Biaxial extension empirical method During proof and baking the growth and stability of gas bubbles within the dough determines the expansion of the dough and therefore the ultimate bread volume and texture; Rupture point wherein: P: maximum pressure [mmh 2 O] L: extensibility at rupture [mm] W: deformation energy 10-4 [J] Bubble pressure Bubble height t [s] 38

39 6. Biaxial extension fundamental method Dough inflation system (DIS) The deformation closely resembles practical conditions experienced by the cell walls around the expanding gas cells within the dough; Researchers advise that these tests are more relevant for bread making quality than small strain dynamic measurements. Parameters Conventional tests DIS Air flow rate ( ) mlmin -1 Baking/proofing conditions Strain rate ( ) s -1 ( ) s -1 ( ) s -1 Strain (0.1 1) % > 100 % Shear, dynamic oscillation Biaxial extension 39

40 6. Biaxial extension theory Samples preparation in a mould: five circular samples 55 mm diameter with 8 mm thickness R P h r 0 a 40

41 6. Biaxial extension force balance thin shell of dough 2 The internal pressure on a local thickness is: P r r And for a near-spherical bubble: 1 1 = 2 = ; r 1 = r 2 = R; P R R r 1 wherein: r 2 P r h P: internal pressure [mmh 2 O] : stress [kpa] 0 a 41

42 6. Biaxial extension force balance The estimate thickness () is: 1 h a R P h r That was directly measured by optical technique. Therefore: P R Pa h Pa h 2 2 Pa h h h h0 a 4h a A L 2 dl L h H ln ln ln ln 1 2 L0 L0 A 2 a L dv 4h dh dt 2 2 dt h a 2 a 42 0

43 [mm] 6. Biaxial extension h [mm] Spherical bubble crown thickness () as a function of the bubble height (h), (measured); (calculated). (Tanner et al., 2008) 43

44 P [mmh 2 O] 6. Biaxial extension If the pressure and bubble height versus time data is transformed into a stress-strain curve: Rupture point Bubble pressure Bubble height t [s] 44

45 P [mmh 2 O] 6. Biaxial extension During large stretching of materials, the cross-sectional area changes in a non-uniform way. If the pressure and bubble height versus time data is transformed into a stress-strain curve: Rupture point Bubble pressure Bubble height t [s] Tension extension curve for the polar region of a bubble 45

46 [kpa] 6. Biaxial extension During large stretching of materials, the cross-sectional area changes in a non-uniform way. If the pressure and bubble height versus time data is transformed into a stress-strain curve: L df d L 0 Bubble rupture [-] Tension extension curve for the polar region of a bubble 46

47 [kpa] 6. Biaxial extension criterion for instability in tension The condition of necking instability is: F A 0 ; df da Ad 0 and since: d d da d d A at df 0 L df d L 0 k n Bubble rupture [-] 47

48 TG 1 [g/100g] Effect of maize resistance starch (MRS) and transglutaminase (TG) on rheological properties of pan bread dough Central Composite Design(2 2 ) base on 100 % mixture MRS 1 [g/100g] 48

49 [kpa] Effect of MRS and TG on rheological properties of pan bread dough biaxial extension [kpa] MRS 0.18 TG 0.34 TG

50 P [mmh 2 O] Strain - hardening From stress-strain data: k exp n H wherein: : stress [MPa]; H : Hencky strain [-]; exp 2.21 H k: coefficient related to the dough viscosity [MPa]; n: strain hardening index [-]. Rupture point Values of n greater than 1, indicate strain hardening Bubble pressure Greater strain hardening Bubble height Greater bubble failure Greater loaf volume t [s] 50

51 7. Our approach Dynamic rheometer large deformation Measured parameters in real time: c: current [ma]; V red : reducer speed [rpm]. Calculated parameters: v kc wherein: 2 : torque [Nm]; v: blade speed [rpm]; k 1 : constant [24.91 NmmA -1 ]; k 2 : constant [3.96]. v 1 red k 51

52 7. Our approach Dynamic rheometer large deformation The instantaneous specific power (P o ) can be calculated: P P E 2v rad min N m 60 m min s kg red o v W 30 m kg red o t Po dt 0 wherein: m: dough mass [kg]; t: total mixing time [s]; E: specific energy [kj/kg]. 52

53 Effect of three enzymes: transglutaminase (TG), glucoxidase (Gox) and xylanase (He) on rheological properties of pan bread dough Mixture Design of three components The dough was prepared with a blend of 12.5 g of MRS plus 87.5 g/100g of wheat flour. From each run, a dough sample was also submitted to rheofermentometer tests: 53

54 Parameters obtained by development curve and gas release curve Maximum height Maximum pressure The dough strength is not only dependent on the total work input, but also on aeration during the mixing and produced gas bubbles during fermentation. 54

55 Parameters obtained by development curve and gas release curve H z A new parameter: m V tz H z ; m z V t t0 0 0 t0 wherein: z: normalized gas flow rate [-]; V t : total gas volume [ml]; subscript 0 indicates control 55

56 Effect of three enzymes: transglutaminase (TG), glucoxidase (Gox) and xylanase (He) on rheological properties of pan bread dough Results: The new parameter, corrected maximum height ( ) indicated that dough prepared with higher concentrations of Gox and TG, presented better baking performance. H m TG [4 g/100g] H m Gox [4 g/100g] TG [0 g/100g] He [4 g/100g] 56

57 8. Rheology and bread quality Gluten and dough are most unique from the point of material science as they have complex behavior: Rheological properties measured to accuracy are important for product development both in research or industry; The correlation studies on these properties of the dough with baking performance of the end product is an example of such appliance; 57

58 References BLOKSMA, A. H. A Calculation Of The Alveograms Of Some Rheological Model Substances. Cereal Chemistry, n. 34, p , CAUVAIN, Stanley P. ; YOUNG, Linda S. Technology of Breadmaking. 2 nd ed.. New York: Springer, LLC, CHIN, N. L. ; CAMPBELL, G. M. Dough aeration and rheology: Part 1. Effects of mixing speed and headspace pressure on mechanical development of bread dough. Journal of the Science of Food and Agriculture, n. 85, p , 2005a. CHIN, N. L. ; CAMPBELL, G. M. Dough aeration and rheology: Part 2. Effects of flour type, mixing speed and total work input on aeration and rheology of bread dough. Journal of the Science of Food and Agriculture, n. 85, p , 2005b. DUNNEWIND, B. ; SLIWINSKI, E. L. ; GROLLE, K. ; VAN VLIET, T. The Kieffer Dough and Gluten Extensibility Rig An experimental evaluation. Journal of Texture Studies, n. 34, p , LAUNAY, B. ; BURÉ, J. ; PRADEN, J. Use of the Chopin Alveographe as a rheological toll I. Dough Deformation Measurements. Cereal Chemistry, n. 54, p , LAUNAY, B. ; BURÉ, J. Use Of The Chopin Alveographe As A Rheological Toll II. Properties In Biaxial Extension. Cereal Chemistry, n. 54, p , SANCHEZ, Diana Buchner de Oliveira. Desempenho Reológico e Entálpico da Massa de Pão com Amido Resistente de Milho e Transglutaminase. SP: USP, 2009, Dissertação (Mestrado). 58

59 Prof. Carmen Tadini 59