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.