September 15, 2019, 06:17:19 AM
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Topic: What does recrystallizing (partially) inverted sugar syrup yelds?  (Read 258 times)

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Offline guferr

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To be more specific: By boiling a saturated sucrose and distilled water solution (without doing anything to avoid sucrose hydrolysis and the transformation in inverted sugar syrup) and then letting it cool down to crystallize, what is obtained?

The crystals formed are pure sucrose? Or does fructose and D-glucose monohydrate crystallize from it too? Does that differ from the results obtained by using the two-solvent recrystallization method?

The reason why i'm asking this is because I was intended to let it crystallize in water alone, but it was taking too long, so I washed and filtered it 3x with pure ethanol, removing the syrup and making a great portion of the sugar to crystallize (much more than what was already crystallized when I began washing). I them made a last wash with isopropanol and put it to dry.

But now I'm thinking: Are those crystals pure sucrose? Should I have made something to avoid the hydrolysis of sucrose from the beggining? Or isn't it necessary?

Thanks!

Offline jeffmoonchop

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Re: What does recrystallizing (partially) inverted sugar syrup yelds?
« Reply #1 on: June 03, 2019, 11:58:34 AM »
Not too clear what you're asking here but sucrose is highly soluble in water and has very long induction times so it takes a long time to crystallise especially if you've boiled too much water off because the solution becomes very viscous which reduces nucleation rate.

Adding ethanol to the solution is a good tactic to crystallise because sucrose is less soluble in ethanol than it is in water so it acts as an antisolvent and lubricator, a large effect of the increased nucleation rate is the lower viscosity. the metastable band width will be shorter and you'll see more crystals come out.

Offline guferr

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Re: What does recrystallizing (partially) inverted sugar syrup yelds?
« Reply #2 on: June 03, 2019, 02:31:22 PM »
Not too clear what you're asking here but sucrose is highly soluble in water and has very long induction times so it takes a long time to crystallise especially if you've boiled too much water off because the solution becomes very viscous which reduces nucleation rate.

Adding ethanol to the solution is a good tactic to crystallise because sucrose is less soluble in ethanol than it is in water so it acts as an antisolvent and lubricator, a large effect of the increased nucleation rate is the lower viscosity. the metastable band width will be shorter and you'll see more crystals come out.

My main question is if the fructose and glucose in the syrup will also crystallize together with sucrose, because I didn't make anything to avoid the hydrolysis of sucrose, so the syrup probably contain a mix of sucrose, glucose and fructose. But I don't want to have fructose and glucose in the formed crystals, I just want sucrose.

Offline jeffmoonchop

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Re: What does recrystallizing (partially) inverted sugar syrup yelds?
« Reply #3 on: June 03, 2019, 03:37:01 PM »
If you're worried about impurities you can do the experiment in more mild conditions. Saturate sucrose in a solution at say 80 or even 50C. You'd dissolve less but still a lot. Then you can be more confident that only sucrose is crystallising.

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