Enzymatic Modification for Ascorbic Acid and Alpha-Tocopherol to Enhance their Stability in Food and Nutritional Applications

ABSTRACT

Antioxidants protect cells against the effects of harmful free radicals and play an important role in preventing many human diseases (e.g. cancer, atherosclerosis, neurodegeneration, inflammatory disorders, etc.) and aging itself. In addition, antioxidant molecules are employed to prevent unsaturated oil products from becoming rancid during storage and thus extend oil life. The modification –chemical or enzymatic- of natural antioxidants in order to increase their miscibility and/or stability towards the action of light and/or oxygen renders a series of “semisynthetic” antioxidants with great impact in the food and feed industries. In this review, we will discuss the enzymatic modifications of antioxidant vitamins C and E. L-Ascorbic acid (vitamin C) is the major water-soluble natural antioxidant acting as a free radical scavenger, and plays an important role in regenerating vitamin E. However, due to the low miscibility of ascorbic acid with ..-tocopherol, it is necessary to use ascorbyl fatty acid derivatives. Thus, esters of L-ascorbic acid with long-chain fatty acids (esp. palmitic or stearic) are employed as additives (E-304) in foods rich in lipids. The enzymatic synthesis of acyl L-ascorbates offers some advantages compared with the current chemical process, such as its high regioselectivity and the moderate reaction conditions. Vitamin E enhances the oxidative stability of polyunsaturated fatty acids from peroxidation acting as a free radical scavenger and is generally administered in the form of all-rac-..-tocopheryl acetate or succinate to increase its stability. Several approaches have been described for the enzyme-catalysed synthesis of vitamin E acetate, based on the transesterification of vinyl acetate with vitamin E, or the regioselective hydrolysis of ..-isophorone followed by reaction with isophytol. The above vitamin C and E derivatives may have impact not only as food preservatives but also as components of functional foods.