Degradation Kinetics of Catechin in Aqueous Solution in the Presence of Ascorbic Acid or Octanoyl Ascorbate

Abstract

L-Ascorbic acid is a water-soluble vitamin known as vitamin C, and widely used as an additive in foods and cosmetics due to its strong reducing ability. The lipasecatalyzed synthesis of 6-O-acyl ascorbate through the condensation of ascorbic acid and fatty acid in an organic solvent has been reported [1,2]. The enzymatic synthesis of the acyl ascorbates would be more advantageous than a chemical method due to the simplicity of its reaction process and its high regioselectivity. Acyl ascorbate is an amphilic antioxidant, as it consists of ascorbic acid and a fatty acid as the hydrophilic antioxidant and lipophilic group, respectively. It has been reported that the ascorbates, such as 6-O-palmitoyl ascorbate, have an antitumor activity and metastasis-inhibitory ef fects [3,4]. Therefore, acyl ascorbate would be expected to be a useful food additive. We have also synthesized acyl ascorbates using an immobilized lipase in a batch or continuous reactor [5,6], evaluated their surfactant properties [7] and their antioxidative ability against linoleic acid [8], and used them for the microencapsulation of lipids [9]. However, there has been no report about the antioxidative property of acyl ascorbate against a water-soluble and unstable compound in aqueous solution, though knowledge of its behavior in aqueous solution is required for its effective use. Catechins are recognized as constituents of green tea with an antioxidative activity [10] and suppressive ability against adipocyte differentiation [11]. Most tea drinks containing catechins are low acid beverages, and kept warm in the vending system during the cold season. Furthermore, heat processing at high temperature is required to sterilize the spores of thermophilic anaerobes. Thus, the stability of tea catechins in aqueous solution has been investigated under various conditions by many researchers [12,13], and the degradation is kinetically examined using first-order kinetics [14,15]. Degradation Kinetics of Catechin in Aqueous Solution in the Presence of Ascorbic Acid or Octanoyl Ascorbate