The following was written by Donald D. Kasarda who is a research chemist in the Crop Improvement and Utilization Research Unit of the United States Department of Agriculture. If you have any questions or comments regarding the piece, you can address them to Don at: firstname.lastname@example.org.
Because barley malt is made from barley grain that has been germinated it is reasonably certain to be less toxic than barley itself. The hordein proteins and starch in the endosperm of barley grains, like the equivalent gluten proteins and starch in wheat, are there for storage purposes. In a sense, they provide food for the new plant upon germination. In order to use the hordein proteins, the grain releases and generates enzymes upon germination that break down the storage proteins into their constituent amino acids. The problem is that the process is not complete during a short germination, so some peptides (short pieces of the proteins) remain intact in malted barley. There is experimental evidence for this. The resulting mix of peptides is highly complex.
We know from work described in the scientific literature that relatively small polypeptide chains can still retain activity in celiac disease and we know something about a few sequences that seem to be harmful. But we probably dont know all the sequences that are harmful and we havent put our fingers on the common theme that gives rise to the activity in celiac disease. So the question arises as to whether or not the remaining sequences in malted barley are harmful.
The possibilities that come to my mind are:
- There are sufficient remaining harmful peptides (with sizes including approximately 12 or more amino acid residues) to give a significant activity in celiac disease to barley malt (remember though that barley malt is usually a minor component of most foods in which it is used and processing might decrease the amount of harmful peptides in a malt product);
- There are traces of these peptides, but they are sufficiently minimal so as to cause no discernible harm; or
- The key harmful amino acid sequences are completely destroyed by the enzymes during germination (I can speculate that there might be an important enzyme, very active, in germination that clips a key bond in active sequences, thus reducing the concentration of those active sequences to almost nil while still allowing non-harmful peptides to exist; no evidence exists for this speculation, but it could be used as a working hypothesis for experimentation).
There is no completely solid evidence for or against there being a threshold of gluten consumption below which no harm, or at least no lasting harm, occurs and above which definite harm occurs (but see my previous post to the list on starch/malt question). This is a difficult area to study where zero consumption is being approached and the arguments that come up are at least similar to those that have arisen in regard to the question of whether or not there is a minimal level of radiation exposure below which no harm is caused, but above which there is harm that increases with dosage. Accordingly, celiac patients must choose arbitrarily the path they feel comfortable with.
Here are some references that deal with the question of peptide toxicity. It is not a simple situation:
- Shewry, P. R., Tatham, A. S., Kasarda, D. D. Cereal proteins and coeliac disease. In Coeliac Disease, Ed. M. N. Marsh. Blackwell Scientific, London 1992;pp. 305-348.
- Kasarda, D. D. Toxic cereal grains in coeliac disease. In: Gastrointestinal Immunology and Gluten Sensitive Disease: Proc. 6th International Symp. On Coeliac Disease, C. Feighery and C. OFarrelly, eds., Oak Tree Press, Dublin 1994;pp. 203-220.
- Wieser, H., Belitz, H.-D., Idar, D., Ashkenazi, A. Coeliac activity of the gliadin peptides CT-1 and CT-2. Zeitschrift fur Lebensmittel-Untersuchung und-Forschung 1986;182:115-117.
- De Ritis, G., Auricchio, S., Jones, H. W., Lew, E. J.-L., Bernardin, J. E., Kasarda, D. D. In vitro (organ culture) studies of the toxicity of specific A-gliadin peptides in celiac disease Gastroenterology 1988;94:41-49.
- Fluge, 0, K. Sletten, G. Fluge, Aksnes, L., S. Elsayed. In vitro toxicity of purified gluten peptides tested by organ culture. Journal of Pediatric Gastroenterology and Nutrition 1994;18:186-192.
- Sturgess, R., Day, P., Ellis, H. J., Lundin, K. A., Gjertsen, H. A, Kontakou, M., Ciclitira, P. J. Wheat peptide challenge in coeliac disease. Lancet 1994;343:758-761.
- Marsh, M. N., Morgan, S., Ensari, A., Wardle, T., Lobley, R., Mills, C., Auricchio, S. In vivo activity of peptides 31-43, 44-55, 56-68 of a-gliadin in gluten sensitive enteropathy (GSE). Supplement to Gastroenterology 1995;108:A871.