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lec 4 hydrocolloids Flashcards

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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
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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
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3
Q

define Emulsifier

A

surface active molecule that adsorbs at the oil-water interface and provides repulsive forces between interfaces

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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

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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)
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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).
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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.

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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
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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
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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
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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)
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12
Q

what is carboxymethyl cellulose (CMC) at intermediate ph?

A

CMC is strongly anionic at intermediate pH –> interacts strongly with cations

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13
Q

what happens to methyl cellulose (MC) solubility when heated

A

MC solubility decreases when heated
–>gelation –>precipitation

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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
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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
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16
Q

what structure does native starch have?

A

Native starch is present as semi-crystalline particles (granules)

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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

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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
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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
Q

Function/Property of Octenylsuccination?

A

surface activity –> emulsifier, encapsulation
Emulsions

26
Q

name 3 Seaweed extracts

A

Alginic acid
Carrageenan
Agar

27
Q

what properties does Alginic acid have?

A
  • 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
Q

what properties does Carrageenan have?

A
  • 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
Q

what properties does Agar have?

A
  • 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
Q

Xanthan gum

A
  • 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
Q

Gellan gum

A
  • 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
Q

Gelatin

A
  • 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
Q

do hydrocolloids reach complete dissolution?

A

not always

34
Q

what happens during Risk of lump formation

A

hydrocolloid particles stick together

35
Q

what methods are there for preventing lump formation?

A

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
Q

what are Thermo-reversible gelling agents?

A

melts on heating and gel upon cooling

37
Q

name some Thermo-reversible gelling agents

A
  • 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
Q

what are Thermo-irreversible gelling agents?

A

once formed will not melt

39
Q

name some Thermo-irreversible gelling agents

A
  • Alginic acid
  • High methoxyl pectin
  • Locust bean gum
40
Q

what is Syneresis?

A

(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
Q

describe what happens when there is Synergy between different hydrocolloids

A
  • 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
Q

What do I expect a hydrocolloid to do for my application?

A

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
Q

What is the nature of the stability problem?

A
  • 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
Q

where is it Undesirable to have crystal growth over time (typically water or sugar crystals)?

A

Examples: confectionary, frozen desserts etc.

45
Q

in what food does Syneresis (water release, “weeping”, “wheying off”) occur?

A

Examples: jams, reformed meat products, dairy-based gels, sauces etc.

46
Q

what is the role of hydrocolloids in Generic sallad dressing?

A
  • 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
Q

what is the Role of hydrocolloids in Gelatin candy (”Gummy bears”)?

A

Gelling agent

food tech (11 decks)

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