Beer Forum

There's an interesting article on electrochemical detection of hop alpha acids by Javor Kac and Tomaz Vovk in J. Chromatogr B: vol 850 issues 1-2, pages 531-537. Unfortunately my library does not have an electronic subscription to that (Elsevier) journal.

Anybody got that journal? Can you send me the PDF?

Thanks,
Charlie

Sent! I love the university!

I wouldn't mind a copy of that PDF myself if one of you guys feels so inclined. I was wondering the other day if there were any LC methods to measure alpha acids.

mattturner wrote:Sent! I love the university!

Got it!

Thanks!
Charlie

BrewChemistinCO wrote:I wouldn't mind a copy of that PDF myself if one of you guys feels so inclined. I was wondering the other day if there were any LC methods to measure alpha acids.

There are oodles of methods for alpha acids by HPLC. Mostly C18, methanol:water:H3PO4 85:17:0.25, and UV/Vis at 314 nm. You can see the standard ASBC method here http://maltmunchingmashmonsters.com/tech/hopanal.html (it incorrectly references "HPO4", not H3PO4, and I'll fix that PDQ).

The J. Chromatogr B method I was looking for (Thanks again Matt!) was interesting to me because it claims 50x greater sensitivity than the ASBC method, and I happen to have a spare electrochemical detector. I ran across it today while I was looking for a gradient method to shorten run time (found that info too!).

Let me know what you need, or google [Alpha and Beta Acids in Hops by HPLC].

Charlie

I've got this method up and running. I'm seeing xanthohumol, humulone, co-humulone, lupulone and co-lupulone in acetonitrile extracts of whole hops, but not in methanol extracts. I'm using my "B" grade cascade for method development, so it might be sampling error.

No quantitation because I don't have any standards. I'll try to post a chromatogram tomorrow.

Charlie

Pardon my crappy scanner, but this is what I'm seeing.



Chromatogram from Shimadzu SPD-10A uv/vis detector at 314 nm.



Chromatogram from an ESA Coulochem III electrochemical detector.

Xan = xanthohumol
CoH = cohumulone
H = ad- and n-humulone
CoL = colupulone
L = lupulone
? = unknown

Notice the unknown compounds in the ECD trace.

The following two papers are said to report information on phenolic compounds, flavones and glycosides in beer. If you have access to them I would very much like for you to send me a copy.

Floridi S. et al. J. Agric. Food Chem. Vol 51, p1548 - (2003)
Rehova, L. et al. J. Sep. Sci. Vol 27, p 1345 - (2004)

Charlie