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I was wondering if starch can be broken up into individual glucose units. Because on a site I saw, it said that through acid hydrolysis starch can be broken up into amylose and amylopectin. However, as I researched amylopectin I found out it is branched and had a different bond than amylose so just to simplify everything:

Can starch be broken up into individual glucose units and through what processes?

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Starch is what plants primarily use as a glucose storage. As such, it is essential that they can break it back down into glucose otherwise it would defeat its own purpose and be removed by evolution very quickly. Think about it: Requiring a lot of energy to build up something that serves no further purpose — not exactly giving a plant an advantage in survival.

There are different methods how to break it down. Plants, of course, use enzymes. Humans can also break down starch with the help of enzymes (which is why potatoes give us energy), much like most other animals, fungi and many single-cell organisms.

The first amylose-breaking enzyme is present in saliva, so it’s that early that the breakdown begins. However, distinct glucose usually isn’t liberated until the gut.

Chemically, the easiest method would be acidic hydrolysis, i.e. use hydrochloric acid and heat. The downside is, that this method might destroy the individual glucose units, too; so using enzymes is preferred if you want glucose.

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Yes, you can. In fact you do it every time you eat a piece of bread or a potato; of course, when I say you, I mean the enzymes in your body.

But I am guessing you wish to break it down in vitro instead of in vivo. Well you can do that too.

Here's a simple experiment: just filter an collect some saliva from your mouth, and get a hold of some starch solution. Add a few drops of Iodine to the starch solution, and it will indicate the presence of starch by turning bluish-black. Now add some of your saliva to it, and wait for a bit and the colour begins to fade away.

What's happening here is an enzyme called $\alpha$-amylase in you saliva is hard at working breaking the bonds in the starch chain. It acts at random locations along the starch chain, $\alpha$-amylase breaks down long-chain carbohydrates, ultimately yielding maltotriose and maltose from amylose, or maltose, glucose and "limit dextrin" from amylopectin.

Do note that salivary amylase doesn't bring about complete breakdown to glucose, instead you have some glucose but mostly di- and trisaccharides which are further worked upon by more enzymes from the pancreas further down your digestive tract.

There are different kinds of amylase proteins out there, but all of them are glycoside hydrolases and act on $\alpha$-1,4-glycosidic bonds.

Now, you're not wrong to think acid hydrolsis would work, but that's a more inelegant solution in my opinion. Moreover, as @Jan pointed out, it's also likely to cause breakdown of individual glucose units.

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  • $\begingroup$ so how would you go about using enzymes to create chemically pure glucose then? $\endgroup$ – Zackkenyon Feb 27 '18 at 17:07

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