Garlic (Allium sativum)

garlic ready for drying
garlic ready for drying

Garlic is a spicy and tasty vegetable with an amazing arsenal of chemicals that has presumably evolved as a defensive mechanism against all kinds of herbivores. Obviously, this strategy has failed with many humans, at least with the alliophiles! On the other hand, it is one of the rare plants in my garden that is not devoured by slugs!

In recent years, I managed to grow enough garlic to cover our yearly consumption (which actually increased;-). Most of the time I am planting two kinds of soft-neck bulbs, but last year (2025) I tried also an Ukranian hard-neck variant that did not store well and dried up relatively early. On the surface of such a dried up clove I noticed plenty of shiny crystalline needles. 

crystals grown on the surface of a drying garlic clove
crystals viewed through a microscope under polarized light

A colleague of mine, Dr. Hartmut Schubert, put them on a single-crystal X-ray diffractometer and determined the molecular structure of this compound. It is Allixin, fully named 3-hydroxy-5-methoxy-6-methyl-2-pentyl-4H-pyran-4-one. He deposited the structure with the Cambridge Crystallographic Data Centre under deposition number 2523464, it can be accessed under DOI: 10.5517/ccdc.csd.cc2qpw2d.

The formation of allixin has been investigated in a detailed study by Japanese scientists:
Y. Kodera, M. Ayabe, K. Ogasawara, S. Yoshida, N. Hayashi, K. Ono:
Allixin Accumulation with Long-term Storage of Garlic;
Chem. Pharm. Bull. 2002, 50(3), 405-407; DOI: 10.1248/cpb.50.405

Mouse Control:

  • Left mouse button: rotate the molecule about x and y axes.
  • Right mouse button: menue.
  • Shift-Right mouse button: horizontal movement rotates about z axis.
  • Ctrl-Right mouse button: shifts the molecule.
  • Middle mouse wheel: zooms in or out.

I don't recall any other plants that produce such an amount of crystalline compounds. However, a miscroscope will reveal many instances of other amazing crystals "living" in organisms. A nice example is the video by Dr.bio4ever showing crystals of calcium oxalate (also known from rhubarb) in the skin of onions and garlic.

Some of the pharmacological effects of garlic have been summarized:
V. K. Singh, D. K. Singh:
Pharmacological Effects of Garlic (Allium sativum L.);
ARBS Annu. Rev. Biomed. Sci. 2008, 10, 6-26; DOI: 10.5016/1806-8774.2008.v10p6