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DavidHawman 04-20-2010 07:38 PM

Mash temperatures
 
This question has been bugging me ever since I started reading about mashing. The amylases in the seed become most active at ~150F and denature around ~160F hence brewers aim to mash at temperatures around that. Enzymes, for the most part, function in a narrow band of temperatures. Below which they are sluggish and above which they denature, sometimes irreversibly.

My question is: Why is that temperature for the amylases so high? Most enzymes in the human body are most active at 98.6F since that is the environmental temperature they operate in the most.

So it stands to reason that the seed enzymes would be most active around 60-70F or the temperature of the ground when they germinate but instead they are double that. I doubt you would find a single enzyme in the human body that would be more than barely functional at 180F let alone in its most active state.

Conversely, if an enzyme is most active around 150F then what use is that for the seed if it never reaches anywhere near that temperature while germinating since the enzyme will be incredibly sluggish?

What am I missing? :confused:

Rick500 04-20-2010 07:52 PM

Interesting question.

This might shed some light:

Quote:

Since a wide variety of organisms, including humans, can digest starch, alpha-amylase is obviously widely synthesized in nature, as opposed to cellulase. For example, human saliva and pancreatic secretion contain a large amount of alpha-amylase for starch digestion. The specificity of the bond attacked by alpha-amylases depends on the sources of the enzymes. Currently, two major classes of alpha-amylases are commercially produced through microbial fermentation. Based on the points of attack in the glucose polymer chain, they can be classified into two categories, liquefying and saccharifying.

Because the bacterial alpha-amylase to be used in this experiment randomly attacks only the alpha-1,4 bonds, it belongs to the liquefying category. The hydrolysis reaction catalyzed by this class of enzymes is usually carried out only to the extent that, for example, the starch is rendered soluble enough to allow easy removal from starch-sized fabrics in the textile industry. The paper industry also uses liquefying amylases on the starch used in paper coating where breakage into the smallest glucose subunits is actually undesirable. (One cannot bind cellulose fibers together with sugar!)

On the other hand, the fungal alpha-amylase belongs to the saccharifying category and attacks the second linkage from the nonreducing terminals (i.e. C4 end) of the straight segment, resulting in the splitting off of two glucose units at a time. Of course, the product is a disaccharide called maltose. The bond breakage is thus more extensive in saccharifying enzymes than in liquefying enzymes. The starch chains are literally chopped into small bits and pieces. Finally, the amyloglucosidase (also called glucoamylase) component of an amylase preparation selectively attacks the last bond on the nonreducing terminals. The type to be used in this experiment can act on both the alpha-1,4 and the alpha-1,6 glucosidic linkages at a relative rate of 1:20, resulting in the splitting off of simple glucose units into the solution. Fungal amylase and amyloglucosidase may be used together to convert starch to simple sugars. The practical applications of this type of enzyme mixture include the production of corn syrup and the conversion of cereal mashes to sugars in brewing.

Thus, it is important to specify the source of enzymes when the actions and kinetics of the enzymes are compared. [...]
http://www.eng.umd.edu/~nsw/ench485/lab5.htm

Anyway, what I took from that is that the source of the alpha-amylase determines in part how it behaves. So maybe the alpha-amylase used by the human digestive system works best at ~98.6F, but the alpha-amylase in grain works best at ~150F.

pkeeler 04-20-2010 08:03 PM

Sounds like you are angling for proof that the Gods love us and have stuck this enzyme in barley so we could make beer. ;)

It is a good question, are these enzymes active at lower temps at higher pH's? Are they active in the plant (as opposed to the seed) at lower temps? Possibly, when the plant is growing, there are other chemicals that make the enzymes active at lower temps. I think you would need a degree in botany to answer this one.

david_42 04-20-2010 09:33 PM

It's more complicated than that. Beta amylase is most active between 130-150F, alpha doesn't de-nature rapidly until 165F. The main starch enzyme in your body is alpha amylase. Nature has a lot of "good enough" processes. If it all made sense, we would be producing Beano in our guts. It can breakdown almost any complex sugar at body temps.

DavidHawman 04-20-2010 10:31 PM

I guess my question is that biologically speaking, enzymes in organisms are tightly bound to the environmental conditions the organism grows in. Why are the amylase enzymes of barley so outside the temperature ranges of a seed?

Evolution has tailored the enzymes of living organisms to operate at peak efficiency at the conditions of the enzyme's environment. Human stomach enzymes work at a pH of 2 or 3, those in the blood at a pH of about 7. Enzymes that operate outside normal parameters are sometimes reporting enzymes that act to trigger mechanisms to bring the organism back to normal but I don't see amylase doing this.

The amylase enzymes of barley seems to violate this close tailoring. I doubt very much that if you plant a barley seed in soil at 150F it would grow because nearly all its enzymes would denature. Yet, the seed contains amylase enzymes that are highly active at this temperature.

pkeeler's suggestion of pH and cofactors could explain this but it seems quite a stretch that a simple pH change could allow an enzyme to function at twice its normal temps...

Ah the wonders of science.

nicoharris 04-21-2010 02:40 AM

There are ideal temperatures for enzymes to work, however at the same time life is about trade-offs. Even though a-amylase may work best at higher temperatures, 150 to 160 degrees would be too high for many other biological processes. So body temperature may be contained within a certain boundary in order to maximize total body function rather than benefiting solely the function of a-amylase.

Brewster2256 04-21-2010 05:08 PM

From an evolutionary standpoint, perhaps the rate at which the enzymes function under typical plant conditions, is sufficient and more beneficial than at a greater rate.

For example, in our own bodies, we benefit from complex starches because they provide a more sustainable source of energy, and in the same way, perhaps the slower rate of conversion of polysaccharides to mono/di-saccharides provides an energy source, while holding starches whole for later use. After all while we store energy as fat, plants store it as starch.

Scimmia 04-21-2010 06:03 PM

Quote:

Originally Posted by DavidHawman (Post 2016204)
So it stands to reason that the seed enzymes would be most active around 60-70F or the temperature of the ground when they germinate but instead they are double that. I doubt you would find a single enzyme in the human body that would be more than barely functional at 180F let alone in its most active state.

Conversely, if an enzyme is most active around 150F then what use is that for the seed if it never reaches anywhere near that temperature while germinating since the enzyme will be incredibly sluggish?

We need the starch to convert in an hour, the seed doesn't. What does it matter if it's sluggish if it's got days to get it done?

I don't have any data to back that up, just makes sense to me.

ajf 04-22-2010 01:27 AM

Does unmalted barley contain amylase enzymes? If so, why do we use malted barley, rather than unmalted?
If the enzymes are produced as a by-product of the malting process, isn't it reasonable to assume that those enzymes are going to be active at something similar to the kilning temperatures experienced during the malting?

-a.

Brewster2256 04-22-2010 03:09 PM

Kilning is not exactly a natural part of the barley life-cycle, considering it's the arrest of development which stops further growth of the sprouting grain, before it can utilize more starch for growth. The enzymes are produced via germination, which is mostly at room temperature.


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