Crusts could be cancer-fighters

For centuries Man has chewed on the faithful crust of the land - bread. Produced, in some form or other, in almost every food culture across the globe, bread has an integral place in the diet of mankind.

Long considered a bulking agent - potentially rich in dietary fibre - to beat the hunger pangs, new research from Germany suggests that our old favourite could be a rich source of antioxidants. Or more precisely, that our mothers were right - we should eat the crust.

Previous studies have suggested that bread contains compounds that have a cancer-fighting potential and much focus has been placed on its abundance of dietary fibre, 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, lead study researcher and formerly with the German Research Centre of Food Chemistry in Garching, Germany.

Using a conventional sourdough mixture containing rye and wheat flour, Hofmann and his associates analysed 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, 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 colour associated with the surface of baked breads. The same reaction also produces flavour 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 because the smaller pieces contain more surface area on which these reactions can occur in comparison to larger bread products, like loaves and buns, claims the researcher.

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

Full findings of the study are published in the 6 November issue of the Journal of Agricultural and Food Chemistry.​