Enzymatic synthesis of steryl hydroxycinnamates and their antioxidant activity

Abstract

Steryl hydroxycinnamates are of increasing interest as they are antioxidant esters of phytosterols with potential cholesterol lowering properties. Apart from ferulates, also other plant steryl hydroxycinnamates have been identified in natural products. In this study hydroxycinnamic acid derivatives were ethylated enzymatically using Rhizomucor miehei lipase (yields from 16 to 97%), and transesterified by lipase from Candida rugosa to yield steryl hydroxycinnamates (yields from <LOQ to 55%). The influence of the structural differences between the hydroxycinnamic acid derivatives on the esterification yields was very different for the two lipases applied. Furthermore, the antioxidant activity of steryl and stearyl hydroxycinnamates was evaluated by DPPH radical scavenging activity and in two methyl linoleate systems. In bulk methyl linoleate, free sinapic acid showed the highest antioxidant activity over other sinapates, whereas in emulsified methyl linoleate, stearyl sinapate was highest. In conclusion, the enzymatic synthesis and antioxidant activity of steryl hydroxycinnamates is highly dependent on the acid structure. Practical applications: The enzymatic esterification of hydroxycinnamic acids is an environmentally friendly procedure to generate nonpolar hydroxycinnamates. These compounds have a broadened field of application due to their adapted polarity, and therefore potentially have an improved antioxidant activity in a wider range of food applications including multiphase systems. In the case of steryl hydroxycinnamates, the nonpolar part of the molecule brings additional health benefits, such as the cholesterol lowering properties, which makes them even more interesting as possible food additives with multiple technological and nutritional advantages. Hydroxycinnamic acids were ethylated enzymatically using R. miehei lipase, and transesterified by lipase from C. rugosa to yield steryl hydroxycinnamates. The influence of the structural differences between the hydroxycinnamic acids on the esterification yields was very different for the two lipases applied. Furthermore, the antioxidant activity of steryl and octadecyl hydroxycinnamates was evaluated by DPPH radical scavenging activity and in bulk and emulsified methyl linoleate system.

Synthesis of Steryl Hydroxycinnamates to Enhance Antioxidant Activity of Rapeseed Oil and Emulsions

“…Antioxidant properties of phenolic acids derivatives can be predicted by specific structure-activity relationships (SAR). Lipophilic, antioxidant and biological functions of phenolic acids depend on the number of hydroxyl groups in the aromatic ring and orto-substitution with the electron donor methoxy group, which increases the stability of the phenoxy radical [ 1 , 2 , 3 , 4 ]. Phenolic acids can be divided into two major groups such as hydroxycinnamic acids (HCA) and the hydroxybenzoic acids (HBA).…”

“…Phenolic acids can be divided into two major groups such as hydroxycinnamic acids (HCA) and the hydroxybenzoic acids (HBA). The main HCA: p-coumaric (p-CouA), caffeic (CA), ferulic (FA), and sinapic (SA) acids and their derivatives are natural and the most common bioactive compounds in plants, oilseeds and cereals [ 4 , 5 ]. Among them hydroxycinnamate steryl esters (HSEs), mainly esterified to esters of p-CouA or FA are present in plants and plant-derived foods.…”

“…It is known that structural variations of phytosteryl esters affect their antioxidant activity (AA) [ 16 ]. Currently, different analytical methods: 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), cupric reducing antioxidant capacity (CUPRAC), oxygen radical absorbance capacity (ORAC), β-carotene bleaching, and reducing power assay have been used for analysis of antioxidant properties of phytosteryl esters [ 4 , 6 , 16 , 20 , 21 , 22 , 23 ]. However, degradation products and oxidative stability of edible oils enriched with phytosteryl esters were analyzed using chromatographic methods and Rancimat test, respectively [ 15 , 16 , 23 ].…”

“…In general, chemical, enzymatic or chemoenzymatic esterifications, and transesterification have been often proposed for the synthesis of phytosteryl esters of fatty acids, whereas the esterification of phytosterols with phenolic acids were reported only by some authors [ 4 , 6 , 7 , 8 , 16 , 20 , 21 , 22 , 23 ]. Recently, microwave and ultrasound irradiations have been successfully applied in esterification of phytosteryl esters [ 6 , 24 ].…”

“…Recently, microwave and ultrasound irradiations have been successfully applied in esterification of phytosteryl esters [ 6 , 24 ]. Steryl ferulates were synthesized by different pathways, while an enzymatic and chemoenzymatic methods for esterification of phytosterols with CA, CouA, SA, and vanillic acid (VA) were mainly used [ 4 , 6 , 7 , 8 , 16 , 20 , 21 , 22 , 23 ].…”