The Malliard reaction, first described 100 years ago, produces many of the wonderful smells we associate with cooking including that of freshly baked bread, a grilled steak or roasting coffee. It is also involved in the production of some potentially cancer-causing compounds in our food, such as acrylamide and can even occur within our bodies, contributing to diseases such as cataracts and diabetes.
The Malliard reaction involves the reaction between an amino acid or protein and a reducing sugar, such as glucose. The initial reaction produces an unstable glycosylamine which can rearrange and/or breakdown into many different products. The exact products which will form depend of the reaction conditions used (e.g. temperature and pH) as well as which sugar and amino acid/protein is used. Amino acid structure, in particular, play a key role in determining the odor properties of the products – reactions with valine tend to produce smells associated with rye bread, with cysteine, meat-like smells are produced, while glycine products are often associated with beerlike odors.
The Malliard reaction has been studied intensively by the food industry, however, it is also of interest in terms of human health. In 2002, it was discovered that heavily processed food, for example french fries, biscuits and pet food, contained high levels of acrylamide, a Malliard product which is a potential carcinogen (cancer-causing). Within our bodies the Maillard reaction can occur in the lens of the eye, contributing to the formation of nuclear cataracts while methylglyoxal , a product of the Malliard reaction, can cause cellular damage if allowed to circulate in the bloodstream.
This blog post is based on an article from the October 1st edition of Chemical & Engineering News which can be found here.
A youtube video which briefly touches on the Malliard reaction (as well as discussing caramelisation) can be found on foodtv on Youtube.