1. How would the thickening power of starch when added with sugar, acid and fat effect their chemistry?.
2. How would these results be different when we use pure starches instead of flours?
SOLUTION This solution is FREE courtesy of BrainMass!
1. Sugar competes with starch for water by dissolving in water. The less water available for starch, the less gelatinization, so less thickening. Acid breaks down starch molecules. Less starch available, less gelanization, so less thickening power. Adding fat decreases viscosity which then decreases gelatinization and hence less thickening.
2. Flour has less amylopectin than pure starch. When less amylopectin is present, the gel formed is stronger and the thickening power is lessened.
http://food.oregonstate.edu/learn/starch.html (Look under subtopic 'ingredients added' as well as to the right of this)
For the 2nd question reference: http://indianapublicmedia.org/amomentofscience/the-rest-is-gravy/
Here's a more detailed explanation:
Starch contains molecules called amylopectin and amylose. The amylopectin molecules are bonded to amylose molecules by hydrogen bonds commonly known as H-bonding. When they bond like this, they form granule-like shapes. When dissolved in water, water molecules can break the H-bonds. If H-bonds break, amylose is no longer bonded to amylopectin and hence amylose leaves but is replaced by water molecules. This insertion of water is what results in thickening. So the more water there is, the more thickening is possible. Similarly, the more amylopectin there is, the more thickening is possible.
When sugar is added, the sugar molecules like to dissolve in water. So some water is now used to dissolve sugar. This means a lesser amount of water is available for insertion into starch. The lesser water that inserts, the lesser thickening possible.
When acid is added, they break certain bonds in amylopectin specifically O-H and C-O bonds. So the amount of amylopectin is less. The less amylopectin, the less is available for thickening, hence thickening is less.
When fat is added, it forms new bonds with amylopectin and hence there is less free amylopectin available for thickening. Some parts of fat can also bond with water and hence less water is available for thickening.
Pure starch contains amylopectin and amylose. Flours contain added compounds called proteins. So 100g of flour will contain less amylopectin than 100g of pure starch. So less thickening is possible for flour when the same amounts of flour and pure starch are compared.© BrainMass Inc. brainmass.com December 24, 2021, 10:47 pm ad1c9bdddf>