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FOSC302 > Food extrusion > Flashcards

Food extrusion Flashcards

(67 cards)

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1
Q

define extrusion

A

combination of mixing, cooking, kneading, shearing, shaping and forming to transform raw material into a continous specific shape product

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2
Q

advantages of extrusion

A

adaptability
product characteristics
energy efficiency
use of conventional ingredients
new foods
high product quality
reduced cost
no effulent

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3
Q

explain adaptability

A

minor changes in ingredients and conditions results in a variety of products

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4
Q

explain product characteristics

A

a vairety of shapes, textues and colous can be produced

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5
Q

explain energy efficiency

A

processing of relatively dry viscous material results in less re-drying

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6
Q

explain high quality

A

good control of thermal changes of food
improved textural and flavour characteristics
minimal degradation of nutrients
destroys anti-nutritional compounds
inactivates mircroorganisms
detoxifies aflatoxin

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7
Q

what anti-nutritional compounds can extrusion inibit

A

trypsin inhibitors
undesirable enzymes(lipases and lipoxygenase)

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8
Q

explain reduced cost

A

lower processing costs
continuous high productivity

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9
Q

functions of an extruder
-name at least 4

A

agglomeration
degassing
dehydration
expansion
gelatiniation
grinding
homogenisation
mixing, shaping and shearing
texture alteration
thermal cooking

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10
Q

what is an exytruder

A

a screw that pumps continously and simultaneously transports, mixes, shears, cookes and shapes material under elevated temperatures and pressure

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11
Q

describe the mechanism of an extruder

A

-feeding of raw material
-conveying and compression using screw
-working/transformation of raw material to semi-solid using thermal and mechanical energy
-extrusion of the food through die
-release of material using rotating knives

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12
Q

classes of factors affecting extrusion (2)

A

operating parameters
rheological properties

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13
Q

explain operating parameters

A

temperature
pressure
diameter of die
shear rate

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14
Q

explain rheological properties

A

moisture
physical state of material
chemical composition

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15
Q

how are single screw extruders classified?

A

extend of shear: high, medium or low
heat generation: adiabatic, isothermal, polytropic
screw configuration: solid, interrupted flight, segmented

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16
Q

what is shear

A

how fast the screw moves

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17
Q

explain the types of heat generation

A

adiabatic: no input or extraction of heat, heat is generated through friction
isothermal: consistent temp
polytropic: heat and water transfer

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18
Q

explain solid screw configurations

A

screw itself is on the shaft

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19
Q

explain interrupted flight screw configurations

A

fabricated from different zones, flights have gaps that allow it
-increases kneading

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20
Q

explain segmented screw

A

different sections where the flights are different

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21
Q

classes of twin screw extruders

A

counterrotating: rotate in opposite directions
corotating: rotate in the same direction

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22
Q

mechanism of transportation for SSE

A

centrifugal force
-the flights push the mixture upwards
-fan/flight is not impacted by blocking discharge hole

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23
Q

mechanism of transportation for TSE

A

positive displacement pump
-what goes in must be transported
-if exit is blocked it can damage shaft.

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24
Q

three spaces in the barrell

A

feed
transition
metering

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25
describe the feed zone
deeper flights of greater pitch
26
what is a preconditioner and what happens
Chamber -can be atmospheric or pressurised - steam/moisture can be added but most often it is dry
27
the function of a preconditioner
increase residence time: mena extuder wont run out of material reduce mechanical power consumption: semi-mixing in hopper increase capacity: extruder constantly has material
28
descirbe the transition section
material is compressed and converted to a uniform plasticised dough
29
describe the metering section
shallow flights, reduced helix angle
30
what is the compression ratio
how much material is in the start comapred to metering
31
compression ratio for pressureised and non pressurised
P: 1:5 not 1:1
32
describe the flow profiles inside the barrel
drag: foreward pressure induced: backward leakage flow: backwards
33
how does low moisture and viscous material effect flow profile
increases pressure = higher output and low leakage flow
34
how does small die holes material effect flow profile
greater resistance flow = more pressure and lower output
35
how does cooling material effect flow profile
higher viscosity = higher output less leakage flow and better drag flow
36
how many ways can two parallel screws be configured
8
37
why are TSE useful
overcome the effects of slip at wall
38
key points of differientation for TSE
direction of screws rotatinf degree of intermeshing
39
describe fully intermeshign counter rotating screws
prevent cylindering effect extremely high pressure ppoor mixing no back mixing ease of moisture extraction
40
application of fully intermeshign counter roating screw
low viscosity system
41
describe intermeshing co-rotating self-wiping screw
open lengthwise, closed crosswise
42
type of flow in intermeshing co-rotating self-wiping screw
drag flow and positive displacement
43
is there cylindering effect in intermeshing co-rotating self-wiping screw
no
44
best materials for intermeshing co-rotating self-wiping screw
sticky, wet and oily materials
45
TSE vs SSE sugar content
T: 40% S: 10
46
TSE vs SSE fat content
T: 20: S: 4
47
TSE vs SSE moisture content
T: 65% S: 30%
48
advantages to intermeshing co-rotating self-wiping screw
forward or reverse conveying enhanced mixing capability increased heat transfer
49
restrictive mechanisms used to back fill twin screw extruders
die reverse pitch screws reduced pitch screws cut flight screws Dam
50
what is a dam
variable restriction which inhibits the transfer of ingredients between screws in conveying sections
51
what are reverse pitch screws
forward conveying sections fill to force material thorugh -vely pitched screw sections
52
application of cooking extrusion
ready to eat puffing at die pellets flaked or sheets
53
evaluation of extrudate properties
expansion and cellular structure water absorption index water solubility index extrudate strength
54
when does expansion occur
when internal vapour pressure forces are greater than physicla strength of product structure
55
how is expansion measured
specific volume = 1/bulk density product and die diameter ratio
56
relationship between expansion and temperature
increases
57
how to increase temp
increase mechanical energy input higher steam injections higher barrel temp
58
what is water absorption index
weight of gel per g of dried sample
59
what is water solubility index
percent of dry matter in the supertanant
60
effecct of extrusion on starch
classical gelatinisation extrusion
61
properties starches contribute to in extrudate products
puffing binding caloric value viscosity functionality
62
two protein modifications during extrusion
physico-chemical changes non-enzymatic browning
63
explain the physico-chemical changes
proteins become plasticised continous protein matrix contaiing a dispersed phase
64
what happens to solubility of proteins during extrusion
proteins denatrue and solubility is reduced
65
results of increased protein in expanded cereals
decreased expansion increased crunchiness increased firness decreased water absorption (pasta)
66
result of high levels of fat in extruded products
increased cell size smoother surface less gelatinisation lower mechanical energy dissipated as heat (slip/friction) increased chance of rancidity
67
effect of lipids in extrusion
increase palatability calcoric density cell structure surface textures

FOSC302 (14 decks)

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