Kjeldahl or Combustion for testing protein levels of a soy isolate
In testing protien levels of a soy isolate does anyone have opinion on the accuracy between these methods?
Due to the wide acceptance of combustion method in the industry, and the quicker and safer alternative combustion offers over kjeldahl we are considering moving to a combustion unit.
Thanks,
CB
Dear CraigL,
An official answer to yr query will usually depend on whether the methods for yr application are "approved", eg by AOAC. If so data will usually hv been published, eg in JAOAC.
So are they ? (KJ certainly is for a range of food products, combustion no idea.)
Previously I hv used Kjeldahl for several years (not yr situation) and I agree it can be somewhat precarious to operators. Didn't even know there was a combustion method, offhand this sounds potentially more empirical although Kj can certainly be sensitive to the type of food matrix IMEX.
Rgds / Charles.C
There are plenty of studies comparing combustion method to the Kjeldahl method going right back to the 80s (Search the AOAC journal), and the combustion method compares very well.
Having used both methods in my murky past I can say that I would never want to use the kjeldahl method again!
I was using a LECO machine latterly and it was faster and more accurate, as well as a lot safer to work with. It was heavy on consumables - gas, filters, etc but still the better way to go I thought.
Note: It's been a while since I did much food chemistry so maybe the more automated kjeldahl machines are better to work with now!
Dear Dr.Des.
Thks for the input.
The links (abstracts) / pdf below (not particularly recent) give a little info. on the options. The JAOAC is undoubtedly a better source but would appear to require money.
https://www.iso.org/...4:-2:ed-1:v1:en
http://en.wikipedia....ki/Dumas_method
http://www.ncbi.nlm..../pubmed/8374325
Dumas-keldahl methods.pdf 541.94KB 12 downloads
Rgds / Charles.C
Used both methods. My understanding is the kjeldahl method involves measuring the nitrogen group which chemically characterises protein. Can't say which is best, more reliable etc. I can say I disliked the kjeldahl method purely as a lab technician. Hated working with acids... :(
do you ever try biuret methods. That method based on spectrophotometry
rgds
AS Nur
Combustion method is Dumas method, which is when compared to Kjeldahl method, gives higher values for nitrogen content - may be due to release of bound nitrogen in the molecules.
Automated Kjeldahl machine's are available, which have proven to be easy to operate and deliver reproducible, consistent results.
Since DUMAS also calls for automation, so it would be good for you to compare auotmated versions of both the procedures and take a final decision. You can also ask them to arrange a demonstration for you on your product.