lec 4 hydrocolloids Flashcards
1
Q
What is a hydrocolloid (gum)?
A
- Long chain and high molecular weight polysaccharides
- Some proteins can be considered as hydrocolloids (e.g. gelatin, caseinates, vegetable protein isolates etc.)
- Natural or chemically modified
- Molar mass: commonly 105-107 g/mol
- Linear or branched chains
- Hydrophilic
- Can be dissolved but can also be colloidal (supra-molecular aggregates or particles)
- Increases viscosity and/or forms gels
- Texture
- Mouthfeel
- Handling
- Stability
2
Q
define Hydrophilicity and water-holding
A
- Interaction between water molecules and hydrophilic groups (primarily –OH groups)
- Hydrocolloids occupy a large volume –> viscosity increase
- Network formation of hydrocolloid chains –> gel formation
3
Q
define Emulsifier
A
surface active molecule that adsorbs at the oil-water interface and provides repulsive forces between interfaces
4
Q
define Stabilizer (thickener)
A
increases viscosity of the continuous phase (most of the time water) and gives stability by slowing down or preventing creaming/
sedimentation and/or flocculation
5
Q
what are Galactomannans
A
- Mannose backbone with galactose sidegroups
- Extracted from beans
- Non-ionic polymers –>salt tolerance
- Examples: Guar gum and locust bean gum (carob gum)
- Differences in sidegroup pattern –> different thickening properties and solubility
- Example applications: Liquid foods, ice cream (prevent crystal growth)
6
Q
what are Exudate gums
A
- Sap from various trees and shrubs
- Complex chemical structure, mixture of different polymers
- Principal structure: arabinogalactan
- Contains proteinaceous chains–>surface active–> emulsifier
- Example gums: Gum arabic (acacia) and tragacanth (slightly acidic).
7
Q
Gum Arabic
A
- Properties vary
- Ages –> properties change over time
- Gives Newtonian solutions even at high concentrations!
- Gels “dissolve pleasantly” without glue-like character (example: “Läkerol”)
Example applications: candies,
chewing gum, soft drinks (flavour
emulsion), encapsulation.
8
Q
what is pectin?
A
- Major cell wall polysaccharide in plants
- Most common sources: citrus peel and apple pomace
- Polymer consisting of > 65 wt % galacturonic acid + other sugar monomers
- Galacturonic acid is to ̴ 80% present as a methylester in the plant
- Pectin is processed to reduce the degree of esterification
- Low methoxyl (LM) and high methoxyl (HM) pectin
- LM and HM pectin have different properties
9
Q
what is high methoxyl (HM) pectin
A
- Gels form when sugar or other co-solutes are present –>low aw (water activity) favours polymer association (local crystallization)
- Gels more efficiently at low pH – less charged polymer chains
10
Q
what is Low methoxyl (LM) pectin
A
- Mainly gels through Ca2+ bridging of galacturonic acid between polymer chains
- Less efficient gelation at low pH
11
Q
what are Cellulose derivatives?
A
- Chemically modified cellulose polymers: β(1-4) linked glucose monomers
- Modification –> water solubility
- Most common derivatives for food use: carboxymethyl cellulose (CMC) and
methyl cellulose (MC)
12
Q
what is carboxymethyl cellulose (CMC) at intermediate ph?
A
CMC is strongly anionic at intermediate pH –> interacts strongly with cations
13
Q
what happens to methyl cellulose (MC) solubility when heated
A
MC solubility decreases when heated
–>gelation –>precipitation
14
Q
what is a Cereal β-glucan?
A
- Cell wall polysaccharide – mainly from oats and barley
- Some similarity to cellulose in structure
- But water soluble/dispersable due to “kink in polymer chain” (1->3 segments)
- Forms large aggregated structures In solution through partial crystallization (1->4 segments) –> gel formation
- Associated with beneficial health effects
Cereal β-glucan
15
Q
define starch
A
- α(1->4) polymer of glucose:
- amylopectin (AP) highly branched and ultra-high molar mass
- amylose (AM) mainly linear and lower molar mass
- Properties depend on botanical source
16
Q
what structure does native starch have?
A
Native starch is present as semi-crystalline particles (granules)
17
Q
what happens when starch is heated in the prescence of water?
A
Gelatinize and swell upon heating in the presence of water –> recrystallizes
(retrogrades) upon cooling
* Swelling of granules increase the viscosity as a larger volume is occupied
* Recrystallization leads to syneresis i.e. water release
* Opaque gels
18
Q
what is the point of Chemically (and sometimes enzymatically) modified starch?
A
- Improve technical functionality
- Avoid syneresis
- Improved stability towards chemical or enzymatic degradation
- Typically lower price compared to cellulose derivatives
19
Q
what types of modifications can be done to starch?
A
phosphorylation
hydroxypropylation
acetylation
octenyl succination
oxidation
cross-linking
20
Q
Funtion/Property of Hydrolysis
(degradation)?
A
Viscosity lowering, bulking agent,
water holding
Application : Candies, confectionary,
formulated liquid foods etc
21
Q
Function/Property of Oxidation?
A
Reduces gelling and stickiness.
Improves gel clarity.
Application : Formulated foods,
confectionary, batters
22
Q
Function/Property of Crosslinking?
A
Thickening, texturizing
Application : Pie fillings, bread, infant
foods, soups, dressings etc.
23
Q
Function/Property of Acetylation/
Phosphorylation?
A
Thickening, improves gel clarity
Application : Candies
24
Q
Function/Property of Hydroxypropylation?
A
Thickening, freeze stability
Application : Soups, puddings, frozen
foods
25
Function/Property of Octenylsuccination?
surface activity --> emulsifier, encapsulation
Emulsions
26
name 3 Seaweed extracts
Alginic acid
Carrageenan
Agar
27
what properties does Alginic acid have?
* comes From cell walls of brown algae
* Block co-polymer of D-mannuronic acid and L-guluronic acid
* Often used as the acid salt – sodium alginate
* Strongly anionic polymer
* Forms gels with Ca 2+
28
what properties does Carrageenan have?
* Structural material from red seaweeds
* Linear polymer of sulphated galactopyranose that forms helices in solution
* Anionic polymer --> forms gels with cations (and partial crystallization)
* Chemical structure depends somewhat on the source
* Most common: κ, ι, λ (increasing no. of sulphate groups -> increasing solubility)
* κ-carrageenan -> rigid and brittle gel
* ι-carrageenan -> elastic and shear-reversible gel
* λ-carrageenan -> weak gel with low yield point
* Interacts strongly with proteins (in particular milk proteins) –often used in dairy applications
29
what properties does Agar have?
* Extracted from various species of red seaweed
* Main component is agarose - Linear polymer of galactopyranose
* Can be thought of as a carrageenan with very few sulphonate groups
* Unusual gelation behaviour (temperature hysteresis)
* Gelation temperature: 30-35 °C
* Gel melting temperature: 90-95 °C
* Helix formation is important for gelling
30
Xanthan gum
* Microbial polysaccharide
* Branched anionic polymer
* Forms stiff helix in solution
* Strongly shear thinning flow behaviour
* Unusual feature: Maintains high visc. over a wide T-range
* Stable in pH = 1-9
* The presence of salts enhances viscosity
* Large range of applications in formulated foods
31
Gellan gum
* Microbial polysaccharide
* Processed to yield high or low acyl gellan
* High acyl (native) --> elastic gel
* Low acyl --> firm/brittle gel
* Needs cations to form gels
* Viscosity decreases strongly with T
* Wide range of applications
32
Gelatin
* Polymeric protein produced from animal (predominantly porcine) collagen
* Type A: Acidic extraction--> pI = 7-9 (higher gel strength “bloom”)
* Type B: Alkaline extraction--> pI = 4.6-5.2 (lower gel strength, more degraded, less common as food ingredient)
* Behaves as a random coil (disordered polymer chain) at T > 35-40 °C
* Gelation upon cooling by coil-to-helix transition (if conc. > approx. 1%)
* Gives clear gels with a “short” and “non-ropy” texture that “melts” in the mouth
33
do hydrocolloids reach complete dissolution?
not always
34
what happens during Risk of lump formation
hydrocolloid particles stick together
35
what methods are there for preventing lump formation?
Polymer disperser (aspirator) -Separates particles with air
Dry blend (5 parts sugar with 1 part hydrocolloid) -Separates particles with sugar
Non-solvents -Separates particles with vegetable oil or corn syrup
High-shear mixing equipment- Separates particles with flow and breaks up lumps
36
what are Thermo-reversible gelling agents?
melts on heating and gel upon cooling
37
name some Thermo-reversible gelling agents
* Gelatin
* Agar
* κ-Carrageenan
* ι-Carrageenan
* Low methoxyl pectin
* Gellan gum
* Methyl cellulose
* Hydroxypropyl cellulose
* Xanthan gum
* Alginic acid
* High methoxyl pectin
* Locust bean gum
38
what are Thermo-irreversible gelling agents?
once formed will not melt
39
name some Thermo-irreversible gelling agents
* Alginic acid
* High methoxyl pectin
* Locust bean gum
40
what is Syneresis?
(weeping) – expulsion of liquid from a gel
* Mainly time dependent – crystallization or precipitation of
hydrocolloids
* Very common in gels including native starch
* Freezing tends to cause syneresis
* Firm gels tend to weep more than soft gels
Syneresis
From: T. E. Kodger, Wageningen University
41
describe what happens when there is Synergy between different hydrocolloids
* Combination of hydrocolloids sometimes show synergistic effects on viscosity – gives more viscosity than predicted
* Related to specific inter-molecular interactions
* Economic benefits – decreased dosage
* Cost-in-use: The price of an ingredient x its percentage in a formulation
* Well-known example: mixture of xanthan and LBG
* Combinations may also influence gel strength
* Example: Reduced gel strength of agar gels with addition of alginate.
42
What do I expect a hydrocolloid to do for my application?
One or several answers possible:
* Increase stability (shelf-life)
* Increase stability under specific conditions (such as high temperature, freezing etc.)
* Create, improve or modify the texture of the finished product (thickening or gel formation)?
* Improve both texture and stability
* Provide nutritional benefits (e.g. dietary fiber)
Formulating with hydrocolloids
43
What is the nature of the stability problem?
* Instability upon heating (viscosity decrease, “melting”, separation etc.)?
Examples: bakery fillings, batter for deep frying, reformed
meat products etc.
* Instability over time (creaming, sedimentation, phase separation etc.)?
Examples: fruit pulp sedimentation or flavour oil creaming in beverages, foamed products e.g. whipped toppings or mousse, salad dressing-type products, frozen desserts etc.
44
where is it Undesirable to have crystal growth over time (typically water or sugar crystals)?
Examples: confectionary, frozen desserts etc.
45
in what food does Syneresis (water release, “weeping”, “wheying off”) occur?
Examples: jams, reformed meat products, dairy-based gels, sauces etc.
46
what is the role of hydrocolloids in Generic sallad dressing?
* Poorly emulsified oil – no emulsifier, dressing will have to be shaken just before use
* Increased viscosity ->transiently dispersed oil
* Dressing should cling to salad ->needs yield point
* Microcrystalline cellulose and maltodextrin used as oil replacement -> “short” texture
* Increasing xanthan and or guar gum -> “snotty” texture
* Decreasing oil content influences flavour of other components -> vinegar and sugar needs to be adjusted
47
what is the Role of hydrocolloids in Gelatin candy (”Gummy bears”)?
Gelling agent
