Polysaccharide thickeners and gels Flashcards
Cereal Structure
* ____ – rough outer covering that
protects the grain
* ____ – hard outer covering just
under the husk that protects the
soft endosperm. Makes up ~14.5%
by weight & is an excellent source
of vitamins & minerals.
* _______ _____ containing protein,
phosphorous, thiamin & other B
vit’s & some fat..
* ______ – the largest portion of
the grain, containing all of the
grain’s starch.
* _____ – smallest portion of grain,
2.5% by weight. Rich in fat,
excellent source of B vitamins and
vitamin E..
husk
bran
Aleurone layer
Endosperm
Germ
Define Starch granule
Concentric layers of amylose and
amylopectin molecules formed in the leucoplasts
and held together by hydrogen bonding
Starch Component:
Amylose
* MW ________ Da
* ~ 1000s of _____ units
* Mostly linear: ________ bonds
* No contribution to _____ structure of most
starch granules
100 000
glucose
α-1,4- glycosidic
external
Starch Component:
Amylopectin
* MW ________ to ______ Da
* ~ ______ glucose units
* Highly branched: ___________ + ___________
* Provides ______ _____ & network of branched chains
to form part of the ________ ______
10 million to 1 billion
1000 000
α-1,4-glycosidic bonds + α-1,6-glycosidic bonds
outer frame
semicrystalline matrix
Starch Granule Birefringence:
Starch granules are _________/________
* I.e. ________ _____ passing through has two _____ _____ and follows two slightly different paths
* I.e. Light is split into two different ___ of light
birefringent/birefractive
polarised light
refractive indices
rays
Starches Functions in Food
- Starches are used as:
– thickeners
– stabilisers
– texturisers
– water or fat binders
– fat substitutes
– emulsification aids - Starches contribute to:
– texture, taste & appearance
Gelatinisation
Step 1
- Starch suspended in liquid
- Granules begin to swell
Gelatinisation
Step 2
- Heat applied, granules swell further
- Starch changes from brittle to plastic
- Heat disrupts starch granules, water enters
amorphous regions - Amylose begins to dissolve
- Number & size of crystalline regions ↓
- Starch granules become disordered, loss of
birefringence
Gelatinisation
Step 3
- Heat continues to be applied
- At ~ 55-70°C sol system is formed
- Granule structure disrupted as
amylopectin loses its double helix
structure - Granules increase in size significantly
Gelatinisation
Step 4
- Paste system forms with further heating
- Amylose leaves the granules and
contributes to liquid thickening
Gelation
Step 5
- Product starts to cool
- Bonding between amylose chains,
amylopectin chains and amylose and
amylopectin entraps water → gel - Gel system forms – increased viscosity &
thickness - Higher amylose starches give a more firm,
rigid gel - Higher amylopectin starches are stable but
softer and more sticky
Retrogradation
Step 6
- Product becomes cold
- Reestablishment of an orderly starch
granule which is different from the
original - Stage 1 – water leaves granules,
amylose re-enters, rapid gelation
continues, amylose chains create
aggregating double helixes - Stage 2 – Amylopectin recrystallisation
Factors Influencing Gelatinisation
– amount of water - timing
– temperature - stirring
& the presence of:
– acid - fat
– sugar - protein
Factors Influencing
Retrogradation
- Higher amylose starches move through
stage one more quickly - Starches with high amyloses show
syneresis - Retrogradation is faster at lower
temperatures - Retrogradation occurs more in starches
with larger granules
Thickeners
* _____ – combination of butter & flour
* ______ _____ – combination of butter & flour
*___– – cornflour, arrowroot, flour (thickeners),
gravy mix
Roux
Buerre manie
Slurry
