Chapter 9: Complex Carbohydrates: Starches, Cellulose, Gums, Pectins Flashcards
What are complex carbohydrates also called?
polysaccharides
How many glucose molecules make up starches?
100 to several thousand glucose units linked in chains
Name examples of polymers of sugar.
wheat, flour, rice, corn
Define amylose.
The linear structure of starches
Define amylopectin.
The branched structure of starches
What are starch pockets called?
Granules
How do starches perform differently in food mixtures?
The ratios of amylose to amylopectin within granules
What are waxy structures made of?
Mostly amylopectin
What is cellulose made of?
Polysaccharide made from large amounts of beta-glucose
Why can’t we digest cellulose
We lack the enzyme to digest it
What is cellulose known as in the diet?
Fibre
Give characteristics of gums.
Soluble in H2O, extracted from plants
Name 2 functions of gums.
- Thickens and stabilizes mixtures
- Traps colour and flavour
Give 2 examples that use gums.
Salad dressings and gummy candies
Where are pectins found? What are they made of?
- Found in plant cells (naturally occur in fruit)
- Made of sugar acids
What are pectins used for?
Jams/Jellies
Name the 3 functions of complex carbs in food preparation.
1) They provide structure
2) They act as binding agents
3) They thicken liquids
Name 3 examples in which complex carbs provide structure.
- Flour = structure of baked goods
- Cellulose = structure of fruits and veg
- Pectins = structure of jams/jellies
What happens when starches are heated? Cooled?
Heated: thickens
Cooled: gels
What do amylose molecules bind best for?
Binding batters to meat, fruit and vegetable pieces for deep frying
Name 3 examples of carbs as binding agents.
- Amylose to bind batters and produce for deep-frying
- Carageenan (gum) stabilizes cocoa in milk, dairy products, ice cream
- Guar gum and xanthan gums improve consistency of gluten free baked products
How do complex carbs react when heated with H2O? What happens?
Starch pockets open, allowing H2O molecules to slide into spaces in the starch molecules -> H-bonds with sugar OH groups (thickens)
When complex carbs are heated with H2O, what happens when there’s too much heat?
starch molecules break apart (hydrolyze)
Define gelatinization.
Thickening liquid with starch
Define gelatinization point.
Temp at which max swelling occurs - point at which the starch will hold the most water and have the greatest thickening power
What interferes with gelling? Why?
Salt and sugar compete for water (because polar) so large amounts interfere with gelling.
Name the 4 types of combinations of complex carbs.
- Slurries
- Sols
- Pastes
- Gels
Define slurries.
Uncooked mixtures of starch and water (acids and bases are added to the mixture to chemically alter the structure of the starch molecules)
Define sols
Pourable thickened liquids (pancake, waffle, muffin batter and white sauce, gravy)
Define pastes.
Thickened starch/liquid mixtures with very little flow
Define gels.
Rigid starch mixtures in which molecules of hydrogen bonds together and form a junction
What is retrogradation?
Firming of a gel during cooling and standing
When is retrogradation desirable? What can it form if it continues for too long?
When it causes thickening during cooling, it can form cracks if it continues
Define syneresis.
Condition of water leaking from a gel over time
Define viscosity.
The resistance of a mixture to flow or a measure of starch’s thickening ability.
What makes you more resistance to flow?
The more solid you are
What does viscosity change with?
With temperature
How does cornstarch’s viscosity change?
When pressure is applied
Which is more viscous: amylose or amylopectin?
Amylose
Define stability.
The ability of a thickened mixture to remain constant over time and temperature
What can stable sauces do?
They can be frozen and reheated with very little change in appearance or taste
How do cornstarch and flour compare in terms of stability and thickening?
Cornstarch has more thickening power, but flour is more stable over time and temp
Define opacity.
The degree of light blockage
Define translucency.
The degree of how much light passes through objects
Define texture.
The feel of graininess or smoothness of a mixture on the tongue and palate
Why is cornmeal not used for gravy?
Since it has a grainy mouthfeel
How are modified starched changed?
Structurally by chemical or mechanical means
What are modified starches often made from?
Wheat, corn, soy
What can you change when you modify a starch?
Sweetness, viscosity, mouthfeel and appearance
How are cross-linked starches made?
Cross-linked starch is changed chemically so bonding takes place between starch molecules
What do cross-linked starches form? When are they most stable?
a molecular network, more resistant to acids and more stable during freezing/thawing, will not lead water on standing, and do not continue to thicken during food storage
What are cross-linked starches more resistant to?
Acids
In what are cross-linked starches used?
baby foods, salad dressings, cream-style corn, fruit pie fillings
Name the 3 basic methods to thicken sauces with starch.
1) Cold Water Paste
2) Starch and Fat
3) Starch and Sugar
How is cold water paste made? How much starch to water?
Made by quickly stirring the starch while adding at least an equal amount of cold water
Must be heated while stirring
Give examples of cold water paste.
Gravy, soups
How do starch and fat thicken sauces?
Separates starch granules with melted fat, uses equal amounts of fat and starch
Give examples of starch and fats used to thicken sauces.
White sauce and gravy
What is roux?
Gravy made from starch heated in fat until the starch turns a reddish brown
Mixture of equal amounts by weight of flour and fat that is cooked to varying degrees of doneness.
What does roux add? What does it require?
Adds distinctive flavours to gravies and sauces
Requires low heat and constant stirring
How can starch and sugar thicken sauces?
Sugar helps separate starch granules and prevents them from sticking
Why are digestible starches needed?
- Abundant and economical source of E
- Needed in the diet to allow fat to be used for E and prevent ketosis
Why is glucose needed?
The brain’s only E source
What is fibre also called?
Fibre, bran, bulk on food labels
What does fibre provide for food texture?
Crispiness/Mouthfeel
Why is fibre added to bread products?
Slow staling and improve loaf volume
Name 2 functions of indigestible fibre.
Aids in digestion/elimination of waste
Helps maintain a feeling of fullness
Name 4 functions of fibre in the body.
- Provides bulk for digestive processes
- Decreases bile reabsorption
- Lowers cholesterol levels in blood
- Promotes the utilization of fats
What is the ratio of natural sources of starch?
Amylose: 15-35%
Amylopectin: 65-85%
Which polysaccharides are not generally available to the home cook?
Gums and pectins
Which gum is the most common and widely used? What does it do?
Gum arabic: surrounds flavour particles, protecting them from moisture absorption, evaporation, or chemical oxidation.
What happens to pectin molecules in the presence of sugar?
Pectin molecules will dehydrate, then acid will cause hydrogen bonding to occur between negatively charged molecules, thus creating a thickened structure
Why must starch first be heated in order to act as a thickener?
To break intermolecular bonds. Starch molecules relax and expose polar structures to water, which allows H-bonds to form between the starch molecules and water. It increases the amount of water the molecule can trap.
How does the starch differ in instant puddings?
Pregelatinized: allows it to gel, or set, at the T of cold milk. The starch in regular pudding mixes will not gelatinize until the mixture is hot enough to boil. Then it will not gel until it is chilled
What happens when sugar is combined with flour or any other starch in a gel?
It will decrease the strength and viscosity of the gel and increase the translucency of the paste
What is the pH of jams and jellies?
2.0 to 3.5
List four physical properties food scientists evaluate before selecting a starch for thickening.
Retrogradation, viscosity, stability, opacity versus translucency and texture
How are molecules bonded in a gel?
In a three-dimensional network which keeps the molecules from shifting positions.
Two Hs bond together: junction
Long starch chains form firmer gels that are more stable in heat
How do amylose and amylopectin molecules form gels?
Amylose: set rapidly and form firm gels upon cooling (elastic)
Amylopectin: forms thinner gels or no gels at all (rigid)
What is a main cause of bread becoming stale?
Tendency of amylopectin starches to become rigid (combined with moisture loss)
List the four types of starch and liquid mixtures from least to most viscous.
Least – Sols, Pastes, Gels - Most
Why does lemon pie filling call for more starch than coconut cream or chocolate pie filling?
Since acids hydrolyze starch, which will weaken or break down gels. Lemon juice is added after the starch has thickened the lemon pie’s filling. The filling is then cooled rapidly to minimize the thinning effect of acid in lemon.
What makes viscosity vary?
Molecular size, shape, and charge
Are linear or branched molecules more viscous?
Linear are more viscous because they will not roll over easily unless they are parallel to the direction of flow.
How can pure wheat starch help achieve evenly shaped cookies?
Substituting 30% of the flour in cookies with pure wheat starch (protein removed) will increase the spreading action of the batter
Give an example of a starch that is stable when frozen or heated.
Waxy maize starch
Which starch would you use to make a translucent sauce? To make an opaque sauce?
Translucent sauce: cornstarch, potato starch, and arrowroot
Opaque: wheat flour
Define beurre manie.
Mixture of equal amounts by weight of butter and flour. The mixture can be added to hot soups to thicken the broth. The heat of the broth melts the fat. This allows the starch from the flour granules to disperse into the broth with little risk of lumping.
Describe the structure of glycogen.
Large, heavy and branched
The more branched the glycogen is, the more glucose units the body can release at a time
What does the size of the glycogen store depend on?
The amount of carbohydrates consumed and how frequently the individual exercises. The more you exercise, the more energy the muscles will store
Why do beans make you gassy?
The fibre tetrasaccharide stachyose -> gas
Minimize by taking a special digestive enzyme, but less positive fibre effects
So, eat high fibre foods and eat yogurt -> growth of beneficial bacteria
