HPLC Analysis of Garlic Clove Homogenates (continued)

Results

The method employed provided optimum separation of thiosulphinates with a short analysis time and avoided peak-broadening of late peaks. The HPLC contours indicate ten peaks (in agreement with Naganathan although the separation of methyl 2-propenethiosulphinate and (Z)-1-propenyl methanethiosulphinate is inadequate principally due to the trace amounts of (Z)-1-propenyl methanethiosulphinate present in the sample - see Figure 1.

Each sample clone was the subject of three separate extractions. Individual peak analysis is given in Appendix 1 and HPLC contours are shown in Appendix 2.
In his study of Allium extracts, Naganathan prepared synthetic thiosulphinate standards and his published data has been used in this study for tentative identification (Fig 2).

Further identification was afforded by comparison of UV spectra with published data (Figure 2) and examples are shown in Appendix 3.

Data Analysis

The coefficient of variation for total thiosulphinate averaged 3.1% for all eighteen analyses and this level of accuracy is reflected in the values for the major components - 2-propenyl methanethiosulphinate (4.2%) and diallyl thiosulphinate (3.4%) (Appendix 1). Where thiosulphinates were present in very small amounts the coefficient of variation was often higher (>10.0%) and this was most likely due to the unstable nature of the extracted compounds in organic solvents.
The results obtained from the HPLC analyses (Appendix 1) are summarised below.

Summary of thiosulphinate content of garlic clones
(Concentration of thiosulphinates in Mole % of total)