I've was making tofu from soy-milk, but noticed this disagreeable odor produced during the process.

I conducted a string of internet searches in an attempt to find a method to eliminate this odor.

I learnt that the enzyme lipoxygenase is primarily responsible for this odor, and is activated upon grinding soy beans in water. Additionally, it appears that lipoxygenase is inactivated in the presence of D-glucose and the enzyme glucose oxidase.

Obtaining D-glucose is fairly simple, but I'm at odds as to where I can find glucose oxidase.

Further investigation suggests that commonly available honey contains glucose oxidase.

Armed with this knowledge, I want to know:

Can I add a measured quantity of dilute honey, along with some D-glucose, to the soy milk and inactivate the lipoxygenase enzyme this way?

One more query... I found somewhere that glucose and glucose oxidase in water, makes hydrogen peroxide and this H2O2 inhibit the lipoxygenase enzyme... So my query is.... What, if add hydrogen peroxide directly, in a measured quantity, in water and grind the soybeans with this solution.


A few things first:

Enzymes are proteins (usually) that promote or accelerate a biochemical reaction. The enzyme lipoxygenase in particular, promotes the dioxygenation of some lipids called Polyunsaturated Fatty Acids (PUFAs); for this, the enzyme requires molecular oxygen (which is present in the air, and gets dissolved in the soy milk) . You can think of this as, "it makes the soy milk go bad". The oxidation of the PUFAs in the soy milk doesn't need lipoxygenase...but having lipoxygenase around makes things faster ; if the oxidation of over 90% of the PUFAs in a bowl of soy milk takes (say) 10 days without the lipoxygenase...then it would take (say) a day with lipoxygenase present . As to what specific substance(s) is responsible for the smell, I don't really know yet.

The enzyme glucose oxidase promotes the breakdown of D-glucose. Once again, it too requires molecular oxygen.

Now the basis of that patent you cited (I haven't actually read the thing) is apparently along the lines of:

If you dump in glucose and (a small amount of) glucose oxidase into the soy milk, the reaction that follows (oxidation of glucose) should hopefully decrease the molecular oxygen content on the soy milk. This should decrease the activity (not complete inactivation though) of lipoxygenase and hence should reduce the intensity of the odor (not complete removal of the odor)

Now you suggest using dilute honey in place of pure glucose oxidase (since the former's easy to get). But that would barely work.

The composition of honey depends on multiple factors; type of bee, region, season, etc. But from looking up the composition of various kinds of honey (courtesy: Google), apparently glucose oxidase constitutes a fraction of honey. So diluting honey here would make things worse (lower concentration of glucose oxidase). Obviously, adding concentrated honey is also out of question...since that would alter the flavor of the tofu altogether.

As @airhuff mentioned in the comments below: Use of honey is still an option...but a poor option, nonetheless. Why you ask? Because there are no simple means for one to go about quantifying the glucose oxidase content in some random honey-sample. The process(es) are time-consuming, pricey and hence, (probably) impractical for your needs. Additionally, even if it contains the "right" amount of glucose oxidase, I fear that even dilute honey would still alter the taste of the tofu (there's a reason why honey is the popular epitome for "sweetness").

What can you do now?

1) You can buy glucose oxidase online at Sigma-Aldrich. But if your tofu-making session is a one-time thing (i.e- You don't run a tofu-making factory) then this is a bit impractical.

2) Minimize contact with air! The primary reason the soy milk reeks is because the lipoxygenase is breaking down PUFAs using molecular oxygen. So if you want to limit the enzyme's activity, you must keep contact between the soy milk and air to a minimum.

Some ways you can do this:

a) As soon as your done grinding the soy beans with water, transfer it to an air-tight container (fill it all the way to the brim) until you need it.

b) When you're transferring the soy milk from one vessel to another, be sure to avoid air-bubbles. This answer by @Buttonwood may prove useful in that regard.

On a side note:

I'm genuinely pleased to see that you've gone to great lengths to find a solution to your problem before you approached us at Chemistry.SE. For someone who probably doesn't have much of a background in Chemistry (In the original post, you mentioned you were a "commerce student"), this post came as a pleasant surprise. I myself am only student, and I'm relatively new to Chemistry.SE (been here for under a year)... and you'd be surprised to know how so very few users (from a "non-Chemistry" background such as yours) proactively attempt to resolve their problems before resorting to Chem.SE; so kudos to you! We look forward to your future contributions on Chem.SE. Cheers!

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    $\begingroup$ I might not write off the use of honey. One statement from the link in the OP reads "During ripening of honey, glucose oxidase is inactivated but it regains its activity on dilution of honey". And it seems from the patent that pretty low levels of glucose oxidase were used (sorry, I'm not a biochem guy and had a tough time quantifying from "units" of the enzyme). Still, you are probably right that the dilution of honey would be too much, it just might be a possibility though. Also, I wonder if heating would significantly reduce O2 content w/o destroying product? Anyway, nice +1 answer :) $\endgroup$
    – airhuff
    Jul 3 '17 at 18:50
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    $\begingroup$ What is your opinion for: 1) blanching soybean in water with sodium bicarbonate... 2) Other Heat treatment like deep fat-fry, steam heating 3) using vacuum deodoriser.............. These are another methods for removing/reducing unpleasant odor (I am searching evryday more and more and more for solving my) :) Good Night :) It is 12:24 am in india :) $\endgroup$ Jul 3 '17 at 18:53
  • $\begingroup$ @air Whup! Thanks for the pointer, I've "fine-tuned" the post in light of your comment. As for heating the stuff to drive out most of the oxygen... I honestly don't know if it would do more harm than good(I've never made tofu before...wouldn't touch soy milk with a meter-long stick anyways). It's an idea, but not one I'm keen on :P $\endgroup$ Jul 3 '17 at 19:06
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    $\begingroup$ @ManojVerma , note that your original question was "Can I add a measured quantity of dilute honey, along with some D-glucose, to the soy milk and inactivate the lipoxygenase enzyme this way?" I think paracetamol answered this very nicely. Your comment above constitutes a new question altogether. I would suggest accepting this answer as you seem to like it, then posting the above comment as a new question. Your call though. $\endgroup$
    – airhuff
    Jul 3 '17 at 19:09
  • $\begingroup$ @Manoj As with your main post...it'd be a great help if you could cite sources for these methods. I've never made tofu before, but: Option (1) doesn't look like it'll help; option (2) might probably help [but I don't know if it'll affect the taste], and option (3) isn't a lasting solution, neither is is very practical (to do at home). ;) $\endgroup$ Jul 3 '17 at 19:10

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