Chemistry Reference
In-Depth Information
Table 4.1
Hydrocolloid gums applied to affect rheology/texture of foods
Hydrocolloid
Molecular structure
Thickening conditions Gelling conditions
Pectin
Polygalacturonic acid. Varying
amounts of methyl-substituted
carboxyl groups (Low M or
High M).
Lower
with increased
ionic strength.
η
Divalent ions, low pH (LM),
high soluble solids and low
temperature (HM).
Guar Gum
Mannose backbone with single
galactose side chain. Typical
M:G
Random coil.
η
determined by Mw.
Non-gelling. Viscosity
enhancement with xanthan.
=
2:1.
Locust Bean
Gum (LBG)
Mannose backbone with single
galactose side chain. Typical
M:G
Random coil.
η
determined by Mw.
Gels when mixed with
xanthan.
=
4:1.
Carrageenan
Repeating units of galactose
and 3,6-anhydrogalactose. Iota
carrageenan: 2 sulphates per
repeat. Kappa carrageenan:
1 sulphate per repeat.
Viscosify as fluid gel
particles at low polymer
concentration.
Sodium/potassium/
calcium ions
Potassium ions
Gellan gum
Repeat uniting of glucose,
glucuronic acid, glucose and
rhamnose. The first glucose can
have glycerate and acetate
groups attached.
Viscosify as fluid gel
particles at low polymer
concentration.
gel with mono- and divalent
ions.
Alginate
Guluronic and mannuronic
acid in different content and
distribution.
Lower
with increased
ionic strength.
η
Divalent ions, low pH
Xanthan
Glucose backbone with three
sugar unit side chain (mannose,
glucuronic acid, mannose)
every second glucose. Internal
mannose may be acetylated
external mannose may be
pyruvylated.
Weak gel formation
providing suspending
properties, but flows
when sheared.
Gels with the addition of
LBG or konjac
glucomannan.
Agar
Repeating units of galactose
and 3,6-anhydrogalactose.
Viscosify as fluid gel
particles at low polymer
concentration.
Thermoreversible gels
Cellulosics
Cellulose backbone derivatised
to different extents with methyl
(MC), hydroxypropyl methyl
(HPMC) or carboxymethyl
(CMC) substituents.
MC/HPMC:
η
determined by Mw; CMC
degree of substitution
determines decrease in
MC and HPMC gel upon
heating and revert to the
solution state upon cooling.
η
with increased ionic
strength.
Starch
Linear (amylose) or branched
(amylopectin) polymer of
glucose.
Starch granules swell
upon heating and
provide space fillings.
Retrogradation produces
gels whose textures are
determined by the
amylose/amylopectin ratio.
