Stability of Catechin in Aqueous Solution with Coexistent Ascorbic Acid or Octanoyl Ascorbate and Organic Acid

Abstract

The degradation kinetics of catechin in aqueous solution in the presence of l-ascorbic acid or octanoyl l-ascorbate, which was synthesized through the immobilized-lipase-catalyzed condensation of ascorbic and octanoic acids in acetonitrile, and of various organic acids were expressed by a first-order equation. The stability of catechin was reduced by the addition of ascorbic acid or octanoyl ascorbate at a concentration of 10 mmol/L, although the rate constant, k, for degradation in the presence of ascorbic acid or octanoyl ascorbate decreased with increasing citric acid concentration. Malic, lactic and sorbic acids were also effective for decelerating the oxidative degradation by ascorbic acid and octanoyl ascorbate, but their suppressive effects on the degradation of catechin differed between the solutions containing ascorbic acid and octanoyl ascorbate. This indicates that octanoyl ascorbate acts on catechin with a different mechanism from that of ascorbic acid.Keywords: catechin, octanoyl ascorbate, organic acid, degradation kinetics, first-order equation *To whom correspondence should be addressed. E-mail: wysyk@hiro.kindai.ac.jp IntroductionCatechins are known constituents of green tea and have physiological functions, including antioxidative activity (Huang and Frankel, 1997) and the ability to suppress adipocyte differentiation (Furuyashiki et al., 2004). Drinks containing catechins also tend to contain acidic additives, such as water-soluble organic acids, with the most common acidifier being citric acid. The stability of tea catechins in aqueous solution has been investigated by many researchers (Chen et al., 1998;Friedman and Jürgens, 2000;Tanaka and Kouno, 2003). More recently, Aoshima and Ayabe studied methods to prevent the deterioration of catechin-enriched green tea (Aoshima and Ayabe, 2007). Ortiz et al. examined the effects of storage relative humidity and addition of other ingredients, such as citric and ascorbic acids, on catechin stability in green tea powder (Ortiz et al., 2008). l-Ascorbic acid is a water-soluble vitamin known as vitamin C and is widely used as an additive in foods and beverages due to its strong reducing ability. 6-O-Acyl ascorbate, which is synthesized through the condensation of ascorbic acid and fatty acid using an immobilized lipase in an organic solvent, has both higher and lower suppressive activities than ascorbic acid, depending on their concentrations in aqueous solution (Watanabe et al., 2009). In this study, the effects of the coexistence of octanoyl ascorbate, which is one of the most soluble acyl ascorbates in water, and citric acid on the degradation of catechin was compared with the case of ascorbic acid. (+)-Catechin solution, not green tea extracts, was selected as a simple system to investigate this, as complex reactions, such as the intermolecular coupled-oxidation between catechol ring and hydroxy o-quinone of catechins, may occur for solutions with mixed catechins (Tanaka and Kouno, 2003). Materials and MethodsMaterials (+)-Catechin (purity: 98%) was ...

Effect of Ascorbic Acid or Acyl Ascorbate on the Stability of Catechin in Oil‐In‐Water Emulsion

“…The data indicates that the emulsions were stable during the measurements for the catechin degradation regardless of initial mean diameter. The degradation kinetics of catechin was assumed to be expressed by firstorder kinetics [18]:…”

“…We have studied the influence of ascorbic acid or octanoyl ascorbate, which is one of the most soluble acyl ascorbates in water, on the degradation of (? )-catechin in an aqueous solution, and that of the coexistence of octanoyl ascorbate and citric acid on the catechin stability [17,18]. However, the effect of acyl ascorbate on the stability of catechins in the emulsion, which is a more complex system, is not clear.…”

Antioxidative Properties of Acyl Ascorbates on Lipid Oxidation in Bulk, Disperse and Microcapsule Systems

“…(Fig. 1), and examined their properties as an antioxidant and emulsifier (Kuwabara et al, 2003a(Kuwabara et al, , 2003b(Kuwabara et al, , 2003c(Kuwabara et al, , 2005Watanabe et al, 1999Watanabe et al, , 2000aWatanabe et al, , 2001aWatanabe et al, , 2001bWatanabe et al, , 2002Watanabe et al, , 2003Watanabe et al, , 2004Watanabe et al, , 2005Watanabe et al, , 2008aWatanabe et al, , 2008bWatanabe et al, , 2009aWatanabe et al, , 2009bWatanabe et al, , 2010aWatanabe et al, , 2010bWatanabe et al, , 2012. In this context, first, the optimal conditions for enzymatic synthesis of acyl ascorbate using an immobilized lipase in a batch reaction system are found.…”