Food chem 19

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Food chem 19
2012-04-22 16:27:40
Food chem 19

Food chem 19
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  1. How do sugars affect gel formation?
    Sugars tend to retard gel formation and retrogradation
  2. How do sugars retard gel formationa and retrogradation?
    They compete for available water and interfere with starch-starch hydrogen bonding
  3. How do surface active agents affect gel formation?
    Surface active agents tend to inhibit retrogradation and gelation
  4. How do molecular inclusions affect gelation?
    It has been suggested that molecular inclusions similar to iodine within the polymer helix are formed with surfactants and that this affects the ability of amylose to associate with its comanio macromolecules
  5. What is the pH of most foods?
    The pH of most foods lie in the range of 4-7
  6. Why does pH have only minor effects on starches?
    pH has only minor effects on starches as they are uncharged polymers
  7. What happens to highly acidic foods when heated or storef dor etensive periods of time?
    In highly acidic foods, particulary when heated or stored for extensive periods of time there can be reduction in viscosity due to acid hydrolysis of starch
  8. How does thermal processing affect the final viscosity?
    Thermal processing can affect the final viscosity (hydrolysis) by magnifying the effects of pH
  9. Why does ionic strength have only a minor effect on gelation?
    Like pH, ionic strength has only minor effects as most starch have no ionizable groups
  10. How do proteins affect gelation?
    Proteins are capable of dramatically changing how a starch behaves in terms of gelation and viscosity
  11. What reaction involving proteins and starch is well known?
    The interaction of starch with milk proteins is well known, producing a smooth gel known as pudding
  12. Which properties of starch can be significantly changed in the presence of protein?
    The viscometric behavior of starch and end product texture and organoleptic properties can be changed significantly in the presence of proteins
  13. Why is the specific behavior of starch in food systems hard to predict?
    The specific beavior of starch is hard to predicvt in complex food systems as it depends on many factors- usually determined out by product formulation testing
  14. At which temperature do most starches gelatinize?
    Most starch gelatinize around 60°-70°C
  15. At which temperatures do high amylose starches (>55%) gelatinize?
    High amylose starchses may take temperatures of 100-110°C to gelatinize
  16. What is a desirable property of high amylose starches?
    Such starches have good film forming properties and can be used to prodeuce biodegradable packaging materials or packages which are readily water soluble
  17. Where is most of our starch in North America drived from?
    In North America most of our starch is derived from corn (some wheat, little pea)
  18. Why are starches modified?
    Starches can be modified to provide very specific properties which provide unique functionalities that food processor require
  19. What are preglatinized starches?
    Starch granules are heated just below their gelatinization temperature causing them to swell- they are then drum dried
  20. What does pregelatinization of starches cause?
    • Cuases some disorganization of the starch granule
    • Makes it cold water dispersible
    • Allows the developement of viscosity without requiring as much heating or time
  21. What is the downside of pregelatinized starches
    One requries more pregelatinized starch than regular sarch to attains imilar viscosity effects
  22. What is one application of pregelatinized starches?
    Instant gravy mix
  23. What is another term for acid modified starches?
    Commonly termed 'thin boiling starches'
  24. How is acid modified starch formed?
    Holding starch just below its gelatinization temperature in an acidic medium
  25. What is the acid used for in acid modified starches?
    Acid is used to partially and randomly hydrolysed the glycosidic linkages within the starch granule without destroying the integrity of the granule per se- neutralize and dry
  26. Where are thin boiling starches used?
    Thin boiling starches are used in candy manugfacture- are easy to handle, low viscosity fluids which set into a firm gel upon cooling (starch gum candies- turkish delight, jujubes)
  27. What do cross-linked starches result in?
    Maximym viscosity is normally reached when the starch granules are swollen extensively but still intact-- however, normally they rbeak down with subsequent shear
  28. How are starch granules held together?
    One can hold starch granules together by crosslinking starch chemically so that the swollen granule retains its integrity rather than disintegrating into a colloidal solution
  29. What are typically used as crosslinking agents?
    Acetic, citric or adipic anhydrides
  30. What is the net result of crosslinking starches?
    The net result is a starch granule which will swell somewhat less, but will mainain its structural integrity
  31. What are crosslinked starches less susceptible to?
    Cross-linked starches are less susceptible to acid hydrolysis as the crosslinks make up for some of the bonds broken by the action of acid
  32. What are starch derivatives used to control?
    • Retrogradation/staling
    • Improve freeze/thaw stability
    • Reduce textural and opacity changes
  33. What is the overall objective of starch derivatives?
    To reduce inter polymer hydrogen bonding via introduction of charged groups or by bulky groups to cause steric hinderance
  34. How are orthophosphate groups used to creat starch derivatives?
    These are charged and will repel like charged polymers as long as the pH is not too close to the polymer isoelectric point
  35. What are some common derivatizations?
    • Esterification
    • Acylation
    • Etherification
  36. What is etherification?
    Introduction of hydroxylpropyl groups into the starch granule
  37. How does steric hinderance effect starch derivatives?
    Steric hindernce prevents the polymers from associating as readily as in natural starch
  38. What is an examply of a specialty derivative of starch?
    Starch can have substantive hydrophobic side chains (C16-C18) introduced to enable them to be used as emulsifiers and/or emulsion stabilizers
  39. How are starches oxidized?
    • Can use sodium hypochlorite (NaOCl) to oxidize a portion of the hydroxyl groups into carboxyl groups
    • Some aldehyde and ketone groups may also be introduced
  40. What happens when starches are oxidized?
    Starch becomesx a charged molecule and its solubility is pH dependent like phosphorylated starches
  41. What happens when COOH is introduced onto a starch molecule?
    COOH introduction stabilizes the molecule to retrogradatio but it now becomes susceptible ot pHa nd ionic variations in food products
  42. What are the 2 basic starch conversion categories?
    • Dry starch pyroconversio- roasting
    • Wet starch conversion- acid and enzymativ hydorlysis of starch
  43. What is dry starch pyroconversion?
    • Roasting
    • For the proeduction of cold water soluble starchs- also known as 'roasted' starches
  44. What is wet starch conersion?
    • Acid and enzymatic hydrolysis of starh
    • Wet conversion for the production of dextrins or as a perliminary step to the production of sweeteners from starch
  45. What is the general concept of pyroconversion?
    Starch granules are sprayed with dilute HCl and subjected to a relatively high temperatures
  46. What are the key reactions in pyroconversion?
    • Random hydrolysis of the alpha 1,4 and 1,6 linkages
    • Transglucosidation
    • Repolymerization- any free sugars produced can repolymerize
    • Caramellization reactions can take place with free sugars formed with color development ensuing
  47. What is transglucosidation?
    The breaking of alpha 1,4 and the reformation of other linkages, generally random in nature ix. 1,3 or 1,5 etc
  48. What are the three general types of roasted starch products?
    • White dextrins
    • Yellow dextrins
    • British gums
  49. How are white dextrins produced?
    Produced under conditions of high moisture, high acid and relatively low temperature- hydrolysis reaction predominates
  50. What is the main property of white dextrins?
    Cold water soluble
  51. How are yellow dextrins produced?
    The conditions are lower mositure, moderate levels of acid and higher temperatures
  52. How does the yellow color in yellow dextrins develop?
    Yellow color develops due to non-enzymatic browning (caramellization) as a result of free sugars released and reacting at higher temperatures
  53. How are british gums produced?
    Low moisture- little or no acid used with higher temperatures
  54. Why are british gums dark in color?
    Acid is a catalyst and high temperatures promote extensive more caramellization- gums are dark in color with little hydrolysis and much more transglucosidation (crosslinking)
  55. When are british gums used an why?
    Used extensively in candy manufacutre- this type of product is much more viscous and capable of forming a stiff gel
  56. What is starch an indirect source of?
  57. How is wet starch conversion done?
    • The starting point gelatinizing the starch, followed by hydrolysis using a combination of high pressure steam and hydrochloric acid
    • Under these conditions hydrolysis is extensive and random producing both dextrins and sugars
  58. What is gained from controlling wet starch conversions?
    By controlling this process, the extent of hydrolysis can be manipulated to produce syrups having a range of viscosities and sweetnesses (inversely proportional to each other)
  59. Why are there limitations on the degree of starch conversion?
    Acid hydrolysis can come to equilibrium and there are limits on the degree of starch conversion attainable and hence a limit to the sweetness attainable
  60. How can the degree of starch breakdown be followed?
    The degree of starch breakdown can be followed by measuring the reducing sugar content of the hydrolysate (Fehling's test)
  61. How is reducing sugar content expressed?
    Reducing sugar content is expressed in terms of dextrose equivalents or DE
  62. What makes reducing sugar content increase?
    Reducing sugar content increases with hydrolysis as mono, di and oligosaccharides are produced
  63. What is dextrose equivalents?
    The DE is the ratio of the reducing power (RP) per gram of the converted syrup relative to an equivalent weight of pure dextrose

    DE = [(RP/g of syrup)/(RP/g Dextrose)]*(100)
  64. What does a DE of 100 mean?
    The hydrolysis of starch is 100% complete
  65. Why can acid hydrolysis generally not reach beyond a DE of 50?
    Acid hydrolysis generally cannot yield dfextrose equivalents much beyond DE=50 as equilibrium is reached, leading to re-polymerization
  66. How does one attain syrups with a DE>50?
    To obtain syrups which are >50% glucose, enzymatic conversion is required
  67. Why does gelatinization precede any enzymatic conversion?
    Starch gelatinization precedes any enzymatic conversion process to facilitate enzymativ access to the substrate
  68. Which enzymes are capable of hydrolyzing starch?
    The enzymes which are capable of hydrolyzing starch are commonly termed 'amylases' and these enzymes are found in most living systems
  69. How do we attain amylases commercially?
    Commercially we now tend to obtain these enzymes from microorganisms
  70. What is alpha-amylase?
    An endoenzyme- can attack alpha-1,4 glycosidic linkages anywhere within the starch molecule but not the alpha-1,6 branch point
  71. What is alpha-amylase also known as?
    alpha-amylase is also known as a liquifying enzyme- characteristically adding this emzyme causes a rapid loss in viscosity in a gelatinized starcch solution
  72. Why does alpha-amylase result in a rapid loss in viscosity in a gelatinized starch solution?
    This is due to the random internal bond breakage rapidly reducing the overall molecular weight of starch
  73. What is the end product after adding alpha-amylase to a gelatinized starch solution?
    End products- largely oligosaccharides, some glucose, maltose and pannose (a trisaccharide contain the alpha 1.6 branching linkage)
  74. What is beta-amylase?
    Exoenzyme which attacks the non-reducing end of the starch chain knocking off 2 glucose units at a time
  75. What does beta-amylase produce?
    Produces maltose by hydrolysing the alpha-1,4 glycosidic bond every two glcose units over
  76. What is beta-emylase commonly known as?
    Commonly knwon as saccarifying enzyme as its use only develops sweetness rapidly, but viscosity does not change significantly
  77. What are glucoamylases?
    Can remove single glucose units from the non-reducing end of starch as weel as split maltose into two glucose units
  78. What is the end product of glucoamylases?
    Produces glucose, which is much sweeter than maltose
  79. What is the result of the combined action of alpha and beta amylase as well as glucoamylase?
    Combined action of alpha and beta amylase as well as glucoamylase leaves mainly 'limit dextrins'- largely made up of the trisaccharide- pannose
  80. What is pullulanase?
    This enzyme specifically hydrolysise alpha-1,6 glycosidic linkages
  81. How does pullulanase work?
    Attacks the branch points so that the trisaccharide pannose can be broken down to glucose plus maltose
  82. What is the combination of the 4 basic enyzmes used for? (alpha-amylase, beta-amylase, glucoamylase, pullulanase)
    The combination of these four basic enzyme provides a means of converting starch to predominantly D-glucose (dextrose)
  83. What is the net result of using all four enzymes?
    Net result one can produce syrups which have a DE>90 (predominantly glucose)
  84. What is a benefit of obtaining a DE>90?
    At DE>90, glucose can be crystallized out of solution and obtained in pure form in a manner very similar to sucrose refining