Exam Flashcards
Give 4 causes of protein denaturation
Heat
Shear
pH
interfacial forces
What sugar gives the most sweetness?
Fructose
What sugar should be added for spread ability?
Low methoxy pectin
What sugar should be added for thickening? (give 2)
Alginate
Locust Bean Gum
What are the major changes the occur in malting?
-Softening of grain
-Activation of enzymes
-Some formation of starch and soluble carbohydrates
What are the major changes the occur in kilning?
-dehydration
-prevents further germination and enzyme activity
What are the major changes the occur in milling?
-Physical breakdown of grain
-Increased starch/enzyme contact
-Increased surface area
What are the major changes the occur in mashing?
-enzymatic starch hydrolysis
-formation of glucose and maltose
-separation of sugars from husks
What are the major changes the occur in brewing?
-hop addition
-alpha acid extraction
-isomerisation to iso alpha acids
-enzyme denaturation
What factors favour yeast growth over bacterial growth in beer fermentation?
-ethanol
-low pH
-low temp
-some antibacterial compounds extracted from hops
What is the Crabtree effect?
Yeast produce ethanol preferentially in high glucose concentrations.
What are the implications of the crabtree effect for yeast production.
Fed batch required to achieve higher productivity.
What are the 8 stages in a polymeric membrane cleaning cycle?
-Product drainage
-Pre rinse
-alkali recirculation
-rinse
-acid recirculation
-rinse
-alkali + chlorine recirculation
-rinse
What are the conditions for the alkali and acid rinses in polymeric membrane cleaning?
-50 C
-alkali pH 10.8-11
-acid pH 2.0-2.2
what is the purpose of acid cleaning step in polymeric membrane cleaning?
-mineral/salt removal
what is the purpose of alkali cleaning step in polymeric membrane cleaning?
-fat/protein removal
what is the purpose of the alkali/chorine step in polymeric membrane cleaning?
disinfection, alkali moves equilibrium to free chlorine
what chemical is used to disinfect in membrane cleaning?
Sodium hypochlorite NaOCL
What chemical class is used for removal of insoluble metals in membrane cleaning?
Sequestrants
What chemical class is used for the removal of hydrophobic species in membrane cleaning?
Surfactants
Why must casein microfiltration be conducted below a critical flux?
Excessive flux causes formation of a “dynamic membrane” of foulants, which will have a reduced size cut and retain whey protein.
What causes the transition from the constant rate drying step to falling rate drying step? What is this point called?
Loss of continuous film of water at solid surface. Critical moisture content.
give 2 causes of surface enrichment
-large slowly diffusing molecules
-fast evaporation (high temperature)
What are the physical changes caused by extrusion (6)?
-mixing
-kneading
-agglomeration
-shearing
-shaping
-dehydration
What are the chemical changes caused by extrusion (4)?
-cooking
-pasteurisation
-protein denaturation
-starch gelatinisation
What are the steps of starch gelatinisation?
-disintegration and hydration
-viscosity increase due to starch untangling
-breaking of untangled starch clusters reducing viscosity
-thermal and enzymatic degradation of starch
What are some reducing monosaccharides?
All
What is a common non reducing disaccharide?
Sucrose
What thermodynamic property is responsible for emulsion instability?
Interfacial tension
What is responsible for interfacial tension?
Net attractive force towards the bulk of a fluid
What is the mechanism for pH based casein coagulation?
Lowering of pH reduces charge on casein micelles, causing the hairy layer to collapse
What is the mechanism for rennet based coagulation?
Cleavage of the kappa casein chain removes the hairy layer from micelles.
What roles do additional cultures play in cheese making?
-add flavour
-promote ripening through proteolytic and lipolytic enzymes
-form holes
give 4 ways caramelisation and mailard browning differ.
-mailard requires protein + reducing sugar
-mailard is fast at high temp
-caramelisation requires temps greater than 150 C
-caramelisation requires very low water content
-mailard is acid inhibited
-produce different flavours
how to identify constant pressure filtration equation?
V/2
how to identify constant rate filtration equation?
not constant 2
What are the major steps in white wine production?
- Destemming
- Crushing
- Maceration
- Pressing
- Fermentation
- Maturation and Clarification
- Stabilising and Finishing
What are the major steps in red wine production?
- Destemming
- Crushing
- Fermentation and maceration
- Pressing
- Malolactic Fermentation
- Maturation and Clarification
- Stabilising and Finishing
What changes occur in maceration?
-Agitation of Skins
-Sugars and enzymes released from skins
-Phenolics released from skins and seeds
What changes occur in pressing?
-separation of skins from juice
What changes occur in malolactic fermentation?
-conversion of malic acid to lactic acid by lactic acid bacteria
-increase in pH
What common preservative is added to wines? In what production stage is it added?
Sulphur Dioxide, crushing
What changes occur in fining?
Absorbsion and precipitation of suspended material
What are the two major acids present in grapes?
Tartaric acid, malic acid
What water activity is required for bacterial growth?
0.9
What water activity is required for mould growth?
0.6
What water activity is required for yeast growth?
0.8
draw the curves for non log linear cell death
check slides
give a common cause of non log linear survival?
mixed strains with thermal resistant microbes
give a common type of homogeniser?
rotor-stator mixer
What are the 3 regions of current density vs voltage called?
ohmic region, plateau region, overlimiting region.
What is a cause of the increase in current density in the overlimiting region?
Water splitting
Give the most likely cause of poor current efficiency in electrodialysis?
Water splitting
Give 2 minor potential causes of poor current efficiency in electrodialysis?
Poor membrane selectivity
Back diffusion of ions
Which stream is the product in electrodialysis?
Diluate
Which stream is the waste (salt solution) in electrodialysis?
Concentrate
