Ok.. I need a scientist here....

SerifSansSerif · Dec 24, 2015

First time posting in the gluten free section.

I don't have any problems with gluten, and, oddly enough, I'm not a beer aficionado either.

But playing around with unusual brews or unusual processes interests the hell out of me.

So that leads me here:

I've been toying with the idea of sweet potato as a main fermentable in a brew. I know there's some problems with converting the starches and sweet potato might cause issues. (or at least it seems that way from looking around).

Randomly enough, I thought maybe freezing starches might have an unusual effect on them.

So some internet searching ensued. Strangely enough, "freezing starches" turned up a few results talking about the effects that freezing has on potatoes (different species, I know).

The use of unmodified starches in frozen foods is severely limited by the undesirable textural changes that occur after freezing and thawing. Retrogradation of glucan chains leads to syneresis, a separation of the starch gel and water phases. Stabilization of the starch structure is normally achieved by chemical modification to prevent these changes from occurring. We have now created a freezethaw-stable potato starch by alteration of starch composition and structure by genetic modification. An amylose-free starch with short-chain amylopectin was produced by simultaneous antisense downregulation of three starch synthase genes. This starch is extremely freezethaw stable and shows no syneresis even after five freezethaw cycles. The use of this starch has potential for environmental and consumer benefits because its production requires no chemical modification.

Which has lead me to something that hit upon this:

http://onlinelibrary.wiley.com/doi/10.1111/1541-4337.12143/pdf

And now I'm getting a bit lost...

My GUESS here is that by freezing and thawing starches, the starches seem to lose water and compact, and then, when brought back to room temp, tend to regain the water. All this restructuring apparently, seems to have some affects on the enzymes present in these starches (if, in fact, they are present), and can cause some form of degradation of the starches (possibly causing them to break down into sugars???)

It's just got my mind reeling in a few different directions. Perhaps a few hours in a freezer might help my sweet potatoes to get sweeter?

No clue here, but that's why I'm asking if anyone with a science background might be able to explain some of this as though I was a five year old.

Thanks!

SerifSansSerif · Dec 25, 2015

Ok. a bit further research seems to be tossing me in two directions here:

According to this, storing potatoes (and assuming sweet potatoes) at sub 40F temps (but above freezing I assume) causes potatoes to undergo changes that create sugars from breaking down the starches. (potatoes of all sorts are still alive after all). and this is sort of backed up with studies on other vegetables that are cold tolerant and studies that are researching if cold tolerance is related to this starch to sugar conversion that the plants start to undergo (while still alive) at these temperatures.

http://extension.psu.edu/food/preservation/news/2012/potatoes-fresh-and-frozen

On the other hand, there's also some sort of studies saying that the freezing and reheating of starches may break down the starches and cause them to rearrange their structures into more "undigestable" forms. But then, this is where the studies start getting hard to read, and it seems to focus on corn starches..

It probably won't work, but figuring this research may still help someone at some date, so leaving it up here. Will edit this portion as I find more info.

Of more interest on sweet potatoes:

https://fbns.ncsu.edu/USDAARS/Acrobatpubs/S114-150/S141.pdf

An exerpt:

The recrystallization of dispersed starches results in
stronger hydrogen bonds [25]. The cook-cool-re-warming of
the potatoes affected about 7% of the starch and allowed it to
escape digestion in the small intestine compared to about 3%
in freshly cooked potato [26]. Earlier studies on potatoes in
vitro showed cooling, freezing, or drying produces starches
partially resistant to -amylase. Digestibility of starch made
resistant to -amylase by cooling improves on reheating. The
increased resistance to amylase on cooling appeared to relate
to changes in crystalline structure of starch rather than overall
physical form [26]. The resistant starches do significantly
affect the glycemic index.
Protein within sweet potato also exhibited high amylase
activity with an average of 480 units/mg protein and a range
of 274-758 units/mg protein [27]. After heating the extract
for 10 minutes at 80°C to destroy native amylase activity,
amylase inhibitory activity was assayed via the dinitrosalycylic
acid method. No amylase inhibitors were found in the
sweetpotato extract. Rekha, et al., [28] found that native
amylase activity remained after heating for 10 minutes at
80°C and thus used trichloroacetic acid to selectively precipitate
the amylases before assaying the extract for amylase
inhibitory activity via the iodine binding method. Of the 100
cultivars studied, amylase inhibitors were found in 79.
Cultivar also can play a significant role in the stability of
the amylase inhibitors [29]. Boiling sweetpotato pieces in
water for 30 minutes resulted in residual amylase inhibitor
activities of 29.3 ± 1.1% (cultivar RS III), 29.1 ± 1.1% (cultivar
S 62), 44.6 ± 1.9% (cultivar S 56-2), and 58.9 ± 0.7%
(cultivar S 1195). Microwave baking resulted in complete
amylase inhibitor inactivation in the S 62 cultivar after 120
seconds and the S 1195 cultivar after 180 seconds. Residual
amylase inhibitor activities of 29.1 ± 1.1% and 19.2 ± 0.6%
remained after 180 seconds in the cultivars RS III and S 56-
2, respectively. Grating or blending, oven drying at 70°C for
24 hours, and then powdering to obtain flour resulted in
complete inactivation of amylase inhibitors in all cultivars
tested [29].

brwmistr · Dec 25, 2015

Not a scientist by profession but a scientist at heart. I have tried the sweet potato thing trying to use its natural enzymes to assist the break down of starch in the grain I use, not much extra enzymes to share with non-potato friends apparently. The natural enzymes in the potato at a 40 -80Cel range will activate on the starch in the potato and will turn those into sugar thus the "Sweet Potato" claim, much like the Sweet Squash as well. To increase flavor you can toast the potato in the oven which will not only convert the starch to sugar as it moves thru the temp range but dry out the liquid and increase the Sweet Taste due to sugar concentration. Plus you get that toasty flavor as the sugar crystallizes. As someone told me a starch molecule absorbs water only when supplied the right temperature to do so, thus, we use starch to make thick gravy, as it holds the water. If you then Freeze it you do two things, 1)Suspend the liquid in the starch molecules while damaging the membrane, and 2)Lose the heat required to suspend/take-up that liquid in the molecule.
You may have heard people using the freezing method to increase sugar content and this was done to remove the water that froze first thus concentrating the sugar but freezing in itself doesn't do this.

Others might have a more in depth view of this then I do but it's a start.

Ok.. I need a scientist here....

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Ok.. I need a scientist here....

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