Glycation

Glycation (sometimes called non-enzymatic glycosylation) is the result of the typically covalent bonding of a sugar molecule, such as glucose or fructose, to a protein or lipid molecule, without the controlling action of an enzyme. Glycation may occur either inside the body (endogenous glycation) or outside the body (exogenous glycation). It is a haphazard process that impairs the functioning of biomolecules, and does not require the expenditure of ATP. Glycosylation, in contrast, is the enzyme-mediated ATP-dependent attachment of sugars to protein or lipid molecules at defined sites on the target molecule. It is an important form of post-translational modification of proteins and is required for the functioning of the mature molecule.

Much of the early laboratory research work on fructose glycations used inaccurate assay techniques that led to drastic underestimation of the importance of fructose in glycation.

Exogenous, meaning outside the body, may also be referred to as dietary or pre-formed. Exogenous glycations and advanced glycation endproducts (AGEs) are formed when sugars are cooked with proteins or fats. Temperatures over 120 °C (~248 °F) greatly accelerate the reactions, but lower temperatures with longer cooking times also promote their formation.

These compounds are absorbed by the body during digestion with about 10% efficiency. Browning reactions (usually Maillard type reactions) are evidence of pre-formed glycations. Indeed, sugar is often added to products such as french fries and baked goods to enhance browning. Glycation may also contribute to the formation of acrylamide, a potential carcinogen, during cooking. Until recently, it was thought that exogenous glycations and AGEs were negligible contributors to inflammation and disease states, but recent work has shown that they are important.

Food manufacturers have added AGEs to foods, especially in the last 50 years, as flavor enhancers and colorants to improve appearance. Foods with significant browning, caramelization, or directly added preformed AGEs can be high in these compounds. A very partial listing of foods with very high exogenous AGEs includes donuts, barbecued meats, cake, and dark colored soda pop.

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