Lectures 6&7: Carbohydrates
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Why do mono- and di-saccharides have high solubility in water?
They are hydrophilic and can form H-bonds easily because of all of the OH groups they contain
What is the chemical composition of sucrose?
glucose + fructose
What is the chemical composition of maltose?
glucose + glucose
What is the chemical composition of lactose?
glucose + galactose
Why can sugar be used as a natural preservative? In high concentration, in low concentration
• Water will be drawn to sugar molecules before it is drawn to bacteria because of ease of hydrogen bonding. This locks the water around it, making the water activity really low and killing off bacteria • Keeps product moist • Higher levels of sugar- slows growth of bacteria and mold, maintains and stabilizes water content, reduces water activity making it a natural preservative
What are the natural sources of monosaccharides?
• Fructose - honey and a lot of fruits; Sweetest tasting • Glucose - grapes, corn (especially young kernels) • Galactose - milk, dairy (is a component of lactose); not found in plants, only in animal products
What determines the sweetness of mono- and di-saccharides? How do they rank?
Smaller molecule = sweeter (small ring structure binds easier to receptors) longer the molecule = less sweet b/c harder to access receptors Fructose>sucrose>glucose> sugar alcohols>galactose>maltose>lactose
Describe and name some sugar alcohols. What are the benefits?
• Sorbitol, mannitol, and xylitol • Come from plant products (fruits and berries) • Similar sweetness to sucrose • “Sugar free” since they are not well absorbed • Structure = bunch of carbon with -OH groups attached to each • Provide less calories • Help manage blood sugar • Prevent tooth decay (in gum and toothpaste) - bacteria absorb the sugar alcohol but can’t process it, so kills/diminishes bacteria on teeth
What types of bonds do amylose have? Draw the structure.
a-1,4-glycosidic bonds
What types of bonds do amylopectin have? Draw the structure.
two amylose chains linked together by a-1,6-glycosidic bonds
What types of bonds does cellulose have? Draw the structure.
Not branched; straight, linear structure so doesn’t form a helix like amylose and amylopectin Made from large amounts of b-D-glucose
Briefly describe the process of how starch reaches the retrogradation point.
Granules are heated → swelling → holding water → retrogradation
Describe the gelatinization process of starch
H-bonding in starch make it water insoluble. These bonds break with heat allowing water in and thus the granules swell and become larger. Once they get large enough the granule breaks and dissolves releasing amylose/pectin into water where they tangle together in a large network, allowing water to now form H-bonds with amylose/amylopectin, locking water so it no longer moves freely. Mixture becomes thickened due to this.
Describe retrogradation
After heating and binding with water, the room-temp amylose and amylopectin want to form H-bonds to each other again.Water is then squeezed out Eg: leaving gravy in fridge overnight and having liquid on top
Name four functions of complex carbohydrates
• Provide structure • Bind ingredients together (eg: breading when deep frying foods) • Thickeners • Stabilizers
Describe dietary fiber and its benefits
Dietary fiber are CHOs that cannot be digested by our body’s enzymes • Insoluble fiber - Do not dissolve in water Promotes movement of food in gut and stimulates bowel movements • Soluble fiber Dissolves in water Health benefits - • Help keep the gut healthy • Help reduce risk of diseases like diabetes, coronary heart disease and bowel cancer