Biocatalytic synthesis and antioxidant capacities of ascorbyl esters by Novozym 435 in tert-butanol system using different acyl donors

Abstract

Novozym 435 was used to catalyze the synthesis of fatty acid (FA) ascorbyl esters in tert-butanol using methyl palmitate, oleic and linoleic acids, and soybean oil as acyl donors. Response surface methodology (RSM) and three-level-four-factor central composite rotatable design (CCRD) were employed to optimize the synthesis parameters of ascorbyl palmitate, such as Novozym 435 dosage, reaction temperature, reaction duration and L-ascorbyl acid/methyl palmitate molar ratio. Under the optimized conditions, the yield of ascorbyl palmitate was up to 78.2%. The proposed model on ascorbyl palmitate yield showed a satisfactory coefficient of R² (87.89%), and was experimentally verified. Some other ascorbyl esters were also biosynthesized using oleic and linoleic acids and soybean oil as acyl donors under the optimal conditions. The antioxidant capacities of the derivative ascorbyl esters were evaluated by different assays, including hydroxyl and superoxide anion radical scavenging activities, reduction assay and lipid oxidative degradation. Compared to the common antioxidants of TBHQ, BHT, BHA, V_C and V_E, it is important to note that a mixture of soybean oil ascorbyl esters exhibits the highest hydroxyl radical scavenging and reduction capacities; ascorbyl palmitate showed the highest superoxide anion radical scavenging and lipid oxidative degradation activities. It can be conclude that the derivative ascorbyl esters may be used as potential antioxidants in improving food quality and stability.

Key words: Novozym 435, esterification, ascorbyl palmitate, unsaturated fatty acid ascorbyl ester, mixture of fatty acid ascorbyl esters, antioxidant activity.