Food tastes best when browned.
Food in always complex unless you are studying something quite simple such as a beverage with few ingredients (vitamin water, anyone?). Even sucrose has a complex chemistry, more of which I will share in a future post. So individual NEB reactions cannot be isolated in food. Quite often intermediates and products from one reaction become intermediates in another reaction, especially in the Maillard reaction. Thus, most food chemistry textbooks use Non-Enzymatic Browning (NEB) as synonymous with the Maillard reaction. However, the other NEB reaction cause browning in food without the use of enzymes.
Both caramelization and lipid oxidation cause browning in certain foods, i.e. sugar-based and fried foods, respectively. Ascorbic acid degradation is significant in food with a low pH (high acidity) especially in citrus juices. The reaction of flavanoids is important in highly colored foods as the colorful anthocyanins degrade and lose their color. The reaction of flavanoids may also be important in soy protein, but less because of a color change and more due to a lose of isoflavones.
NEB Intro Part 1
My major interest in food chemistry is how food changes during processing and storage. I am especially interested in how color changes take place. The reactions I am interested in are called Non Enzymatic Browning reactions to differentiate them from the browning that occurs when you cut an apple or banana, which involves an enzyme.
Non enzymatic browning (NEB, non enzymic browning) reactions are the most important reactions in food, and, no, I am not biased. Just image the aroma of melting chocolate, freshly baked bread or a roasting leg of lamb, the golden color of a croissant, the dark amber color of a well brewed beer; caramels, toast. These are all caused NEB reactions.
There are five different NEB reactions and I intend over the next few months to write about each of them:
- Caramelization – browning of sugar, especially sucrose
- Lipid Oxidation – the oxidation of fats and oils; including rancidity
- Break down of flavonoids – highly c0lored compounds can also lose their color
- Degradation of ascorbic acid (Vitamin C) – AsA is unstable even without oxygen
- The Maillard Reaction – reaction between carbonyl compounds and amino acids
Numbers (3) and (4) are not typically on a list of NEB reactions, but I did my thesis on ascorbic acid browning and it definitely goes brown without oxygen and without enzymes. The degradation of flavonoids is one I have added and came to me in flash of inspiration when at a conference. I am sharing it with you now, so this is new even though I had the idea three or four years ago.
This is such a cool reaction mechanism. It was designed by John E Hodge in a what is now a citation classic. It sums up the Maillard Reaction, which is as complicated as the reaction scheme above suggests. This is such a classical scheme that it is known as the “Hodge Scheme”. I find that pretty impressive; it would be great if there was ever a “Lab Cat” reaction scheme.
Hodge was an African American who gained an MA from the University of Kansas in 1940 and worked for the USDA for more than 40 years. Sadly, there was no Wikipedia page for this amazing man, so I started one. If any one knows anymore information about him, please, please add to the Wikipedia page.
Hodge, J. E. (1953). “Chemistry of browning reactions in models systems.” Journal of Agricultural and Food Chemistry 1(15): 928-943.
Citation Classic (pdf)
John E Hodge Bio