Carbohydrates 2
No description yet. This curated deck is ready for daily study.
Card preview (24)
what are homopolysaccharides?
PS consisting of only one type of monosaccharide
what are the functions of polysaccharides in plants?
energy storage (starch), structure (cellulose)
what are the functions of polysaccharides in humans?
energy (glycogen), colon health (fibre)
what are the functions of polysaccharides in foods?
texture and stability (starch, gums, pectin)
what is DP, degre of polymerization?
the number of monosaccharide units in a polysaccharide
what is the general scientific term for polysaccharides?
glycans
what is non-freezable or plasticizing water?
water naturally hydrogen-bonded to polysaccharide molecules. it will not freeze. they can exchange freely and rapidly with bulk water molecules.
what happens when a polysaccharide solution is frozen?
a two-phase system of ice and a glass consisting of about 70% PS molecules and 30% nonfreezable water.
the viscosity of a polymer solution is a function of
the size and shape of its molecules and the conformations they adopt in the solvent
the shapes of polysaccharide molecules in solution are a function of
the allowable rotations about the bonds of glycosidic linkages
which polysaccharides produce the greatest viscosity?
longer, linear, more extended, more rigid
why does a highly branched PS give lower viscosity?
it occupies less volume and collides less often in solution
why can unbranched glycans with regular repeating unit structures precipitate or gel rapidly?
segments of the long molecules associate in a zipper-like fashion. more molecules associate and form a crystallite, which may precipitate. amylose retrogradation is and example of this
what are the two general kinds of rheological flow?
pseudoplastic and thixotropic
what is pseudoplastic flow?
the greater the applied force, the less viscous it becomes. upon removal of the applied force, the solution regains its initial viscosity instantaneously
what is thixotropic flow?
the viscosity reduction that results from an increase in the rate of flow does not occur instantaneously. the viscosity decreases under a constant rate of shear in a time-dependent manner, and regains the original viscosity after cessation of shear.
what is a gel?
a continuous, three-dimensional network of connected molecules or particles entrapping a large volume of a continuous liquid phase
in many food products, the gel network consists of…
PS or protein molecules or fibrils formed from polymer molecules joined in junction zones by hydrogen bonding, hydrophobic associations, ionic cross bridges, entanglements and/or covalent bonds over small segments of their lengths, while the liquid phase is an aqueous solution/dispersion of low-molecular weight solutes and segments of the polymer chain not involved in junction zones
a gel can be described as a viscoelastic…
semisolid, partly that of an elastic solid and partly viscous liquid
what is syneresis?
the expulsion of liquid from a gel
what is amylose?
a linear chain of alpha-1-4 linked glucose units
what is the shape of amylose?
the linkage gives the molecule a helical shape. the interior of the helix contains a predominance of hydrogen atoms and is hydrophobic
what is amylopectin?
alpha-1-4 linked glucose units with branching alpha-1-6 linked chains
how is the amylopectin molecule shaped?
longer, unbranched sections (C chain, only reducing end) that carry B chains, which in turn carry A chains of which two adjacent chains form a double helix. “backbone model”