Why did hydrolyzed wheat starch not taste as sweet as sugar?

[banaji727]

I missed this question on a test recently and our teacher isn't that interested in telling us what me missed. Can you guys help me out? I'd really like to know what the answer is.

Because of a sugar shortage, German scientists hydrolyzed wheat starch by adding HCl to heated starch solutions, breaking some of the glycosidic linkages between the glucose monomers. Why do you think the consumers found the sweetener to be less sweet than sugar? Why do you think the acid broke only 50% of the linkages in the wheat starch?

At first I thought it had to be related to the fact that the heating may have denaturation but I just lost it after that.

[canalon]

Yep, haeating denaturate some of the starch, but look at the structure of starch, and you might find the answer.

[JackBean]

Yep, haeating denaturate some of the starch, but look at the structure of starch, and you might find the answer.

Just a little question? How can be starch denatured?

BTW wasn't here this topic just a while ago?

[david23]

yeah jack didnt you have the same question minus the heating and taste

[JackBean]

sorry?

[MJD]

Theoretically speaking, if the starch was completely hydrolyzed to yield only monomers of glucose, then glucose would not be a sweet as would sucrose (table sugar). This is a subtle point, but is still valid.

http://www.healthyeatingclub.com/info/b ... ata2f.html

[jwalin]

this seems a good point.
but then why do you think the question asks why 50% of the bonds were only broken?
and about denaturation.
starch cannot be denatured by temperature

[HArak24270]

Okay, think I finally got this. Please let me know if I missed something.

Why did the process break only 50% of the glycosidic linkages in wheat starch?

the HCl was able to partially hydrolized the starch by donating H+ atoms to the solution. The glucose monomers of starch are linked by single O atoms (left behind by dehydration synthesis); thus, adding 2 H atoms from HCl hydrolized some of the starch. However, the starch was only partially hydrolyzed. Why? Because no enzyme was present to complete the chemical reaction. For the complete hydrolysis of starch to take place, the enzyme amylase must be present. This is what happens in animal digestion (the combined effort of HCl and amylase to completely break down starch.)

Why did consumers complain of slight bitterness?

The leftover Cl caused the bitter taste.

This question comes from the Campbell Reece textbook Biology, page 91 in the 7th edition. And eff any teacher who can't take the time to answer students' questions properly, particularly when those questions are used in a test.

[JackBean]

I think second question could be right, but isn't Cl- salty?

You are not donating any protons from HCl, these work only as catalyst, but both hydrogen comes from water (together with the oxygen needed), so I would guess equilibrium, insufficient time or something.