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Starch and its role in texture

LEARNING OUTCOMES Appreciation of what happens when starch is heated In high water environments Low water environments Understand the concept of starch conversion Recognise the techniques used to measure starch conversion and appreciate what is being assessed. Starch and its role in texture.

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Starch and its role in texture

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  1. LEARNING OUTCOMES Appreciation of what happens when starch is heated In high water environments Low water environments Understand the concept of starch conversion Recognise the techniques used to measure starch conversion and appreciate what is being assessed Starch and its role in texture Sandra Hill Nov 2005

  2. Levels of organisation sugars macromolecules assembles growth rings granules grains/ tuber

  3. Starch, Water and Heat • water associated with the crystallites • water in the amorphous phase • melting of the crystallites • hydration and swelling of the molten crystallite region and the amorphous region During this: • redistribution of water in the granule • stresses in the granule Swelling and melting are a cooperative process This is non reversible

  4. Temperature of the cooperative disassociation of the crystallites • depends on the botanical source • depends on the water (platisicer) present i.e. the water content matters Starch Gel range C Corn regular 62-80 waxy 63-74 Potato 56-69 Rice 61-80 Sago 60--74 Cassava 52-64 Wheat 53-72

  5. 62.3 64.0 59.9 58.3 66.5 70.0 68.2 71.8 Polarised Light: potato starch

  6. Measuring loss of order Polarized light microscopy X-ray order FTIR (Fourier Transform infra-red) DSC (Differential scanning calorimtery) NMR (Nuclear magnetic resonance)

  7. Starch gelatinisation and Starch pasting Native starch granules in excess water ( water 4* the amount of starch) temperatures above the cooperative disassociation of the crystallites Gelatinisation Water into the granule - granule swells -loss of some polymer PASTING If subjected to shear...

  8. The RVA

  9. Peak Set Back Final viscosity Cold water Native starches, pasted in excess water 10000 120 9000 100 8000 Potato 7000 80 6000 Wheat 5000 60 Viscosity (cP) Temperature (C) Maize 4000 WMS 40 3000 Rice Maize 2000 20 Cassava 1000 0 0 0 5 10 15 20 25 30 35 Time (min)

  10. Starch conversion Crystalline granules Non crystalline granule Some polysaccharide lost from granule Decreasing molecular weight

  11. Temperature and changes, starch in excess water 50 60 70 80 90 100 0C Disappearance of Birefringence DSC endotherm Disappearance of X-ray Swelling power Solubilisation Morphological changes Rheological behaviour

  12. Starch conversion - a continuum of changes from the native granule to dextrin! Maltese crosses DSC endotherms X-ray order water absorbance solubility enzyme digestibility alkaline viscosity RVA final viscosity ? Methods to monitor starch conversion Starch conversion

  13. Stages of granular dispersion of starch in baked goods Swollen Gelatinized Disrupted Dispersed Enzyme degraded Scottish short bread biscuits cakes bread wafers From Greenwood, 1976

  14. Heating starches in limitedwater Donovan, 1979

  15. Starch conversion Crystalline granules Non crystalline granule Some polysaccharide lost from granule Decreasing molecular weight HEAT MECHANICAL ENERGY ENZYMIC CHEMICAL ENVIRONMENT

  16. Processed samples

  17. Shearing the starch Shearing swollen granules Milling of wheat Damaged starch Thermomechanical extrusion Milling Rework Sample preparation

  18. Starch Heaters Water Die Barrel Screw Feeding Kneading Cooking What happends if low water contents and the sample is sheared? i.e. extrusion (thermalmechanical cooking) low water high mechanical energies Would seem that the mechanical input can be even more important in breaking starch than thermal energy. disassociation of the crystallites and then break down the macromolecules

  19. SME(specific mechanical energy) = (torque*screw speed* no of screws) / throughput 1Whr/kg=3.6kJ/kg

  20. SME [kJ/kg] MC [%, dwb] Crystalline pattern GE [J/g] Alk. visc. [mPas] 228 30.60 V - 1.47 276 25.55 V - 1.45 361 20.20 V/E - 1.40 433 16.89 E - 1.31 494 13.58 E - 1.23 Cold water viscosity Final viscosity SME and Starch parameters

  21. Raw maize grits Wheat ball pellets 3D pellets

  22. Impeller mill: Tecator 1093 Cyclotec mill Disc mill: Tecator 1990 Cemotec mill Perten FN mill 3303 Comparison of mills

  23. Raw maize grits RVA profiles of samples milled with two different mills 14000 120 12000 100 10000 80 8000 Viscosity (cP) 60 6000 Temperatute (C) Wheat ball pellets 40 4000 20 3000 120 2000 0 0 2500 100 0 5 10 15 20 25 30 35 2000 80 Time (min) Viscosity (cP) 1500 60 Temperature (C) 3D pellets 1000 40 500 20 1400 120 1200 0 0 100 0 5 10 15 20 25 30 35 1000 80 Time (min) 800 60 Viscosity (cP) Temperature (C) 600 Yellow disc mill Pink impeller mill 40 400 20 200 0 0 0 5 10 15 20 25 30 35 Time (min)

  24. Heating without shear Limited water

  25. Quiescent conversion of maize grits Particle structure of maize grits before and after heating (ESEM) 10mm SEM 2000x, non-heated maize endosperm particle - starch granules (10m) covered with protein matrix SEM 2000x of maize endosperm particle heated 20 min at 140°C - starch granules in place - no loss of their granular integrity

  26. Quiescent conversion of maize grits Loss of molecular order and hot water absorption and solubility indices (HWAI/HWSI) - not detectable ¹Values are mean of duplicates ²Values are mean of four repetitions

  27. Quiescent conversion of maize grits X-ray diffraction pattern

  28. Chemical dimension Redox agents affects starch depolymerisation

  29. High numbers of sulfite radicals Many superoxide radicals Some oxygen High depolymerisation Starch and Sulfite 40 Low levels of sulfite radicals Excess oxygen Low depolymerisation Excess sulfite Oxygen scavenged Low depolymerisation 35 30 25 Swelling volume (ml/100ml) 20 15 10 5 0 0.00 0.01 0.1 Sulfite concentration (%) in log scale

  30. no additive 0.01% sulfite Starch solubility when heated in excess water at 95C for 60 minutes Starch heated in excess water at 95C for 60 minutes then total material solubilised in hydroxide. 120 250 100 200 80 Solubility (%) 60 150 Intrinsic viscosity (ml/g) 40 100 20 0 50 rice sago wheat maize potato cassava 0 wheat potato cassava Paterson et al, Food Hydro. 8, 259-263

  31. 0.10 0.08 0.06 0.04 0.02 0.00 Measurement of starch pastes Starches (5%) gelatinised at 90C for 30 min in phosphate buffer. Sheared using Silverson at max speed for 2 min. Samples mixed with additives and held at 60C. Cooled to 25C before measurement at 27s-1 on Bohlin CS10. pH differences less than 0.3 units sulfite No additives Viscosity (Pa.s) 0.01% 1% 0.1% 0 2 4 6 8 10 12 Time (h) Taken from: Valles-Pamies et al, 1997

  32. with ascorbic 0.01% withoutascorbic

  33. Starch changes in processing Starch gelatinisation – disruption of the structure of the starch granules or its components as a result of heating with or without shear in an excess water environment. Starch melting – the loss of ordered regions in a granule as a result of heating and/or shear at low water contents Starch conversion- disruption of the structure of the starch granule and/or its components as a consequence of a process involving heat and/or mechanical energy. It can occur at high or low water contents

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