the On ultimate composition of simple alimentary substances; with some preliminary remarks on the analysis of organised bodies in general Philosophical Transactions of the Royal Society 355 (1827)
The subject of digestion, however, had for a long time occupied my particular attention: and by degrees I had come to the conclusion, that the principal alimentary matters employed by man, and the more perfect animals, might be reduced to three great classes, namely, the saccharine, the oily, and the albuminous William Prout (1785-1850)
CarbohydratesinFoods
Chemicalstructureofcarbohydrates
Generalcharacteristics: ComposedofC,H,O Polar(OHandotherpolarfunctionalgroups) Hydrophilic(highwaterbindingcapacity) Simplecarbohydrates Sugars Othersmallcarbohydrates(e.g.ethanol) Complexcarbohydrates Digestible Nondigestible(fiber)
Simple carbohydrates
Monosaccharides(5carbon,6carbonsugars)
ribose
glucose
fructose
galactose
A few foods are rich sources of monosaccharides; most foods contain low concentrations
Simple carbohydrates (cont) Disaccharides : 2 monosaccharide units connected by ether bond
(common table sugar)
(milk sugar)
Maltose (starch hydrolysis product)
Q: what monosaccharide(s) comprise maltose?
Invert sugar
Viscous liquid (a syrup) Hydrolysis product of sucrose
sucrose
acid hydrolysis H20 (incomplete)
enzyme hydrolysis Invertase, -fructofuranosidase (complete)
+
glucose fructose
Simple carbohydrates (cont)
Oligosaccharides: 3-5 monosaccharide units
commonly found in beans and other legumes Stachyose and other oligosaccharides are often poorly hydrolyzed to mono- and disaccharides in the small intestine, and pass into the large intestine where they are fermented by bacteria to methane gas
Foodsourcesofsimplecarbohydrates:
Mostfruits(glucose,fructose) Somevegetables beets(upto8%sucrosebywt) sweetpotato(glucose) Honey(fructose) Maplesyrup,sugarcane(sucrose) Brownsugar(mixtureofcanesugarandmolasses) Milk(lactose) Drybeans(oligosaccharides) Cornsyrup,conventional(glucose,fructose) Cornsyruphighfructose softdrinks
Functionsofsimplecarbohydrates
Caloriesource 4kcal/gram
Sweetenerssweetnessdependsonstructure Wateradsorbents e.g.lactoseinbakingpowders Crystallinematrixcandies Foamingaids icecream
Minor differences in structure can have dramatic effects on taste
Sweetness values of various simple carbohydrates in solution (equal concentration)
Sucrose Glucose Fructose Invert sugar Maltose Lactose High fructose corn syrup
fructose concentration)
100 (arbitrary reference value) 60 70 130 180 ~125 43- 50 15 40 100 160 (depending on
(hydrolyzed sucrose)
Aspartame (Equal)
20,000 - 30,000
Synthetic sweeteners
Functionsofsimplecarbohydrates(cont)
Sweetenerssweetnessdependsonstructure Wateradsorbents e.g.lactoseinbakingpowders
Crystallinematrixcandies Foamingaids icecream
Hydrogen bonds and water-binding by carbohydrates
O H H
O H H
O H H
H
O
O HH
H
Functionsofsimplecarbohydrates(cont)
Sweetenerssweetnessdependsonstructure Wateradsorbents e.g.lactoseinbakingpowders Crystallinematrixcandies Foamingaids icecream(4050%air)
Physical formulations of simple carbohydrates
Coarse crystalline sucrose
table sugar brown sugar: sucrose + molasses
Fine crystalline sucrose
powdered sugar contains usually starch (dessicant)
Concentrated solutions (syrups)
cane syrup maple syrup corn syrup high-fructose corn syrup
Complex carbohydrates
Polymers of monosaccarides (simple sugars) Almost entirely of plant origin
Digestible complex carbohydrates Absorbed as mono- & di-saccharides Significant source of calories Non-digestible complex carbohydrates (fiber) Poorly digested Partially fermented in the large bowel (bacteria) Not a significant source of calories
Digestible complex carbohydrates: Starches
Most common digestible complex CHO
Polymer
A naturally occurring or synthetic compound consisting of large molecules made up of a linked series of (repeated) simple monomers
Stucture of starches:
Two forms, both polymers of glucose:
linear branched amylose amylopectin
1. Amylose
linear polymer of glucose -1-4 ether bonds 300 - 1200 glucose molecules per amylose molecule ["Degree of polymerization (DP) " = 300 1200]
.. ..
2. Amylopectin
branched polymer of glucose * 1-4 bonds * 1-6 bonds at branch points * usually larger (more total glucose units, higher DP) than amylose
1
6
Starch Granules
In plant tissue, starch molecules are packaged in dense particles called granules
Constituent amylose or amylopectin molecules are inter- mixed in concentric layers within the granules (see next slide)
Most starches:
Important Exceptions: Arrowroot starch: " Waxy " starches :
20 - 30 % amylose 70 - 80 % amylopectin
> 95% amylopectin 100 % amylopectin 65 - 85 % amylose
High amylose corn starch:
Structure of starch granules
(non-hydrated state)
* Composition and structure of granules
determines functionality of starches
Starch Funtionality
Major function as ingredient :
Thickening of aqueous solutions Gelling "Gelation"
Texture modification
"Gelatinization"
Gelatinization:
Process of absorption of water by starch granules when heated in water Gelatinization temperature: 60 90 C If granules sufficiently concentrated (4 - 6 grams per 100 ml w ater), the solution will become viscous (thick) A heated solution of hydrated and swollen starch granules is called a starch paste
Unheated starch granules dispersed in cold water (viewed in plane polarized light; cross pattern indicates crystallinity)
Gelatinized starch granules dispersed in hot water (a starch paste)
hydrated, amorphous granules
Excessive heating or agitation (stirring, boiling) can cause granule breakage, resulting in loss of viscosity (thinning of the solution)
Gelation of starch:
Formation of a 3-dimensional, cross-linked network of solublized amylose molecules (a "gel"), resulting from the cooling of a hot starch paste
regions of hydrogen bonding between adjacent amylose molecules (inside or outside of hydrated starch granules) (artist rendition)
*
Starches containing only amylopectin will NOT gel !
Hydrogen bonding between adjacent (linear) amylose molecules in the formation of a starch gel
Digestion of starches by pancreatic, salivary amylases
amylose amylopectin
-amylase
+
glucose
maltose
amylase, maltase glucose (absorbed)
Notes:
-Amylase occurs in plants and bacteria but not in animal tissues Amylase action generates sweetness in ripening fruits