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Hiya,

if you want to end the stinky egg cube digestion pracs once & for all, tofu works a treat.
Firm tofu well drained & blotted dry cuts into nice cubes, the results are good & you don't feel like gagging when you uncork the test tubes!
The prep room will never stink of hard boiled eggs again!

Which practical is that?
Lada

It's an enzyme activity prac...the digestion of egg white by pepsin & trypsin.
1cm cubes of hard boiled egg white are weighed then put in 0.5% pepsin & trypsin solutions in 37 degree water baths.
The next day they're drained & re-weighed.....& the entire building ends up smelling like the sulfurous pits of hell ....or like everyone did eggy farts
At low pH the protein's digested, mass decreases at pH 1-4, not much change at 7, & mass increases at 10-14
I've just discovered that the results are actually better substituting the egg with tofu.....& I there's not a whiff of sulfur in here

never thought of Tofu - thanks for sharing - will try it out next year casue i too hate that prac

Hi Bindibadgi,

I just told our Bio teacher about you using the tofu, she is impressed and said we will def use that next time . We have just done the egg white and it is very whiffy here to say the least
Thanks for your suggestion

Cheers
Lisa

H-E-L-P
Brain not functioning Friday afternoon and this is the first time I have done this prac.

Have dissolved 1tsp pepsin in 200 mls distilled water and need to adjust from pH2 to pH8

other than acid and base for pH2 and pH8...what other solutions can I use from pH3 to pH 7 ??

Thanks in anticipation...needed for P1 Monday

Think I'm still operating on UK tme...so tired now

Probably not a helpful suggestion at this point in time, but when we have done that experiment, we have used pre-purchased "buffer solutions" you can buy them ready made, or buy tablets which you dissolve in water, and they stay at the stated pH. Have a check. You may have some in your store room. (I have half a shelf full in mine!)

cheers
Ian

Hi Smee,
We've just done this prac. With catalase and hydrogen peroxide this year. Every year we try something different!!! For the pH part, what I did this time was give them buffered enzyme solutions, and to do this I made up the solution of catalase (which is pH7), then to some I added drops of 0.1M HCl until ph reached 5 (keep testing with Universal indicator), put some in a dropper bottle, then add more HCl until it reaches pH 3. To some of the original solution I added 0.1M NaOH until it became pH9, put some aside, then added more alkali to pH11. Could you do something similar with your pepsin?
Have you seen the thread on pepsin and tofu? Just went up today. I'm going to try it on Monday.
Don't worry too much. This is a real bitch of a prac. Everyone seems to do it differently.
Good luck

Here's the method for the tofu pepsin prac we just did if anyone wants it.....& a couple of graphs showing the basic trends we got.

The student prac tested pH levels of 1, 4, 7, 10 & 13, but the tofu completely disappeared at pH 13 (destroyed rather than digested at that caustic pH), & the kids got confused by that so I played around with a narrower pH range closer to the optimum for pepsin of around 1.5-2.5, & got a clearer trend, so we might switch to the narrower pH range next time we do the prac.

The best bit though is the clean up.....easy, odour free & no cooking of eggs required

Just found this and now going to try tofu instead of egg white tomorrow, any tips?

Hope it works as I just told the teacher I have found a better way to do it, with no smell.

Oh! Nice find. You must tell us how it goes. That sulfurous smell lingers so, and a working alternative would be appreciated.

I like the gelatin-in-a-measuring-cylinder enzyme prac.

Make up clear gelatin, and pour 90mL into a 100mL measuring cylinder. Blend fresh ripe pineapple, not green horrible pineapple, (there now, lost half of you haven't I? ) and pour 10 mls of juice (DON'T strain it) on top of the gelatin. Add one glass marble.

The enzyme in the fresh juice digests the protein in the gelatin, and by the end of a day, the marble had made it to the bottom of the cylinder. Easy peasy.

Here's the method for the tofu pepsin prac.....& a couple of graphs showing the basic trends we got.
We did the tofu version twice, but our head teacher didn't like it, even though I thought the results were good, once we switched to the narrow pH range.....but she winged so it got dropped Give it a trial first & show your teachers your results.....just in case they have lingering doubts. It doesn't work quite as well as the egg white, but I thought it was a good little prac if they wanted a protein based prac using pepsin or trypsin. The student prac tested pH levels of 1, 4, 7, 10 & 13, but the tofu completely disappeared at pH 13 (destroyed rather than digested at that caustic pH), & the kids got confused,so I played around with a narrower pH range closer to the optimum for pepsin of around 1.5-2.5, & got a clearer trend, so we might switch to the narrower pH range next time we do the prac.

The best bit though is the clean up.....easy, odour free & no cooking of eggs required.

For the last couple of years though, we've happily done the capsicum catalase prac (thanks to the lovely Sassi for the prac ) & had great results & labs that smell like salad This week our Yr 12 IB classes have been doing individual enzyme pracs.....each kid's teasting different catalase sources, so I've raided the local fruit & veg shop, & today the labs smell like fruit salad....yum!

Another enzyme prac alternative it using pectinase & tinned apple or tomato.

I couldn't figure out how to link from another thread, so I've updated my old post with all the tofu prac details in a new post in the thread about the effect of pH on enzyme activity.

Cheers,

Kiah

bindibadgi wrote:I couldn't figure out how to link from another thread, so I've updated my old post with all the tofu prac details in a new post in the thread about the effect of pH on enzyme activity.

The tiny white "note page" image () before the poster's name marks a link to that very post. Just copy the url into a URL tag and post it:

Link: [ url=http://chemtalk.com.au/viewtopic.php?p=28827#p28827 ]Just a demo: remove the spaces.[ /url ]

The tofu worked quite fine, no smell, easy to set up (no cooking!). The results were more than adequate for our grade 8's.