Authors: R. Sharma, Y. Pathak
Affilation: Florida State University, United States
Pages: 79 - 82
Keywords: acyl ascorbate, immobilized lipase, continuous production, amphiphilic food nanoadditive, antioxidative emulsifier
Nanoadditive Acyl ascorbates were synthesized through the condensation of various fatty acids with L-ascorbic acid using immobilized lipase in a water-soluble organic solvent, and their properties as food additive were examined. The optimal conditions, which were the type of organic solvent, reaction temperature, the initial concentrations of substrates and the molar ratio of fatty acid to ascorbic acid, for the enzymatic synthesis in a batch reaction were determined. The continuous production of acyl ascorbate was carried out using a continuous stirred tank reactor (CSTR) and plug flow reactor (PFR) at 50oC, and each productivity was ca. 6.0 x 10 for CSTR and 1.9 x 103 g/(L-reactor•d) for PFR for at least 11 days, respectively. The temperature dependences of the solubility of acyl ascorbate in both soybean oil and water could be expressed by the van’t Hoff equation, and the dissolution enthalpy, H, values for the soybean oil and water were ca. 20 and 90 kJ/mol, respectively, irrespective of the acyl chain length. The decomposition kinetics of saturated acyl ascorbate in an aqueous solution and air was empirically expressed by the Weibull equation, and the rate constant, k, was estimated. The activation energy, E, for the rate constant for the decomposition in both systems depended on the acyl chain length. The surface tensions of acyl ascorbates in an aqueous solution were measured by the Wilhelmy method, and the critical micelle concentration (CMC) and the residual area per molecule were calculated. The CMC values were independent of temperature but dependent on the pH. The effect of pH of aqueous phase on the stability of O/W emulsion prepared using acyl ascorbate as an emulsifier was examined, and the high stability at pHs 5 and 6 was ascribed to the largely negative surface-charge of droplets in the emulsion. The addition of saturated acyl ascorbate, whose acyl chain length was from 8 to 16, lengthened the induction period for the oxidation of linoleic acid in a bulk and microcapsule with maltodextrin as a wall material. The oxidative stability in bulk system increased with increasing the acyl chain length, whereas that in the microcapsule was the highest at the acyl chain length of 10. The esterification of various polyunsaturated fatty acids, such as linoleic, - and -linolenic, dihomo--linolenic, arachidonic, eicosapentaenoic, docosahexaenoic and conjugated linoleic acids with ascorbic acid and subsequent microencapsulation significantly improved their oxidative stability.