Bread crusts rich in antioxidants

The best thing since sliced bread may be bread crust: Researchers in Germany have discovered that the crust is a rich source of antioxidants and may provide a much stronger health benefit than the rest of the bread.

This is good news for those who like to complement their holiday meals with bread stuffing, which is rich in crust, but bad news for those who prefer to remove crusts from their bread, as they may be sacrificing healthful antioxidants. The research findings are scheduled to appear in the Nov. 6 print issue of the Journal of Agricultural and Food Chemistry, a peer-reviewed publication of the American Chemical Society, the world’s largest scientific society.

Although previous studies have suggested that bread contains compounds that have a cancer-fighting potential, much focus has been placed on its abundance of dietary fiber, which is believed by some to help prevent colon cancer. The current study is the first to identify a cancer-fighting compound that is concentrated in the crust, says Thomas Hofmann, Ph.D., lead researcher for the study and formerly with the German Research Center of Food Chemistry in Garching, Germany. He is currently a full professor at the University of Munster, Germany.

Using a conventional sourdough mixture containing rye and wheat flour, Hofmann and his associates analyzed bread crust, bread crumbs (the pale softer part of the bread) and flour for antioxidant content and activity. They found that the process of baking bread produced a novel type of antioxidant, called pronyl-lysine, that was eight times more abundant in the crust than in the crumb. The compound was not present in the original flour.

Using human intestinal cells, Hofmann’s collaborator Veronika Faist, Ph.D., a researcher at the Institute of Human Nutrition and Food Science in Kiel, Germany, showed that this crust-derived antioxidant is the most effective component in bread for boosting the level of phase II enzymes, which have been shown in previous studies to play a role in cancer prevention.

The researchers are currently conducting animal tests to determine whether bread crust and pure pronyl-lysine actually boost antioxidant levels in plasma, but results have not yet been published.

Pronyl-lysine is formed by the reaction of the protein-bound amino acid L-lysine and starch as well as reducing sugars in the presence of heat. Chemists have long known that this same process, called a Maillard reaction, is responsible for producing the brown color associated with the surface of baked breads. The same reaction also produces flavor compounds and other types of antioxidants.

Pronyl-lysine is formed during baking in both yeast-based and yeast-free bread, also known as “tea bread.” The antioxidant is likely to be more abundant when bread is broken down into smaller pieces and baked, as with stuffing, because the smaller pieces contain more surface area on which these reactions can occur in comparison to larger bread products, like loaves and buns, the researcher says.

In general, dark-colored breads (such as pumpernickel and wheat) contain higher amounts of these antioxidants than light-colored breads (such as white bread). Strong over-browning of bread, however, reduces the level of these antioxidants, says Hofmann.

Funding for this study was provided by the German research associations FEI and the AiF and Germany’s Ministry of Economics and Technology.