I would like to use spectrophotometric method to quantitative determination of allicin in garlic extracts.

I tried method by Han et al. (A spectrophotometric method for quantitative determination of allicin and total garlic thiosulfinates; DOI: 10.1006/abio.1995.1124) but I didn't get any difference in absorbance between control (l-cysteine only) and my sample.

I'm sure that sample contains allicin because I tried many comercially available garlic extracts.

When I add DTNB into mixture I get colour of Ellman's anion but intensity of the colour is practically the same in control and the sample so I think that reaction between allicin and l-cystein doesn't happen.

I tried time of reaction like 15 min or 2 hours (incubation at room temperature or 30 Celcius degrees) and still don't get any difference in absorbance at the end exept incubation for 2 h at 30 Celcius degrees - I got A=0,127. It gives much lower concentration of allcin then I expected. I used extract with content of allicin I know so I think that this value is incorrect too.

Have you ever had a problem with reaction between allicin and l-cysteine? What conditions should I have to make sure that reaction is done and all allicin I have react with l-cysteine?

I would be grateful for any help! Thanks!