A novel chemoenzymatic synthesis of phytosteryl caffeates and assessment of their antioxidant activity

Advances and Challenges in Plant Sterol Research: Fundamentals, Analysis, Applications and Production

Plant sterols (PS) are cholesterol-like terpenoids widely spread in the kingdom Plantae. Being the target of extensive research for more than a century, PS have topped with evidence of having beneficial effects in healthy subjects and applications in food, cosmetic and pharmaceutical industries. However, many gaps in several fields of PS's research still hinder their widespread practical applications. In fact, many of the mechanisms associated with PS supplementation and their health benefits are still not fully elucidated. Furthermore, compared to cholesterol data, many complex PS chemical structures still need to be fully characterized, especially in oxidized PS. On the other hand, PS molecules have also been the focus of structural modifications for applications in diverse areas, including not only the above-mentioned but also in e.g., drug delivery systems or alternative matrixes for functional foods and fats. All the identified drawbacks are also superimposed by the need of new PS sources and technologies for their isolation and purification, taking into account increased environmental and sustainability concerns. Accordingly, current and future trends in PS research warrant discussion.

Synthesis of hydrophilic glyceryl monocaffeate with economical catalyst cation-exchange resin Amberlyst-35

BACKGROUND

Caffeic acid (CA) has anti-oxidation and anti-inflammatory. However, the poor hydrophilicity of CA limits its biological activities. In this work, hydrophilic glyceryl monocaffeate (GMC) was synthesized by esterification using different caffeoyl donors (deep eutectic solvent and solid CA). Cation-exchange resins were used as the catalysts. The effects of reaction conditions were also investigated.

RESULTS

The mass transfer limitation of esterification was eliminated using deep eutectic solvent. Compared with the previous catalysts (immobilized lipase Novozym 435), an economic cation-exchange resin, Amberlyst-35 (A-35), showed good catalytic performance for GMC preparation. The activation energies of GMC synthesis and CA conversion were 43.71 kJ mol^-1 and 43.07 kJ mol^-1 , respectively. The optimal reaction conditions were a temperature reaction of 90 °C, catalyst load of 7%, glycerol/CA molar ratio of 5:1 (mol mol^-1 ), and reaction time of 24 h, which resulted in a maximum GMC yield and CA conversion of 69.75 ± 1.03% and 82.23 ± 2.02%, respectively.

CONCLUSION

The results of the work showed a promising alternative for the synthesis of GMC. © 2023 Society of Chemical Industry.

Enzymatic lipophilization of bioactive compounds with high antioxidant activity: a review

Food products contain bioactive compounds such as phenolic and polyphenolic compounds and vitamins, resulting in a myriad of biological characteristics such as antimicrobial, anticarcinogenic, and antioxidant activities. However, their application is often restricted because of their relatively low solubility and stability in emulsions and oil-based products. Therefore, chemical, enzymatic, or chemoenzymatic lipophilization of these compounds can be achieved by grafting a non-polar moiety onto their polar structures. Among different methods, enzymatic modification is considered environmentally friendly and may require only minor downstream processing and purification steps. In recent years, different systems have been suggested to design the synthetic reaction of these novel products. This review presents the new trends in this area by summarizing the essential enzymatic modifications in the last decade that led to the synthesis of bioactive compounds with attractive antioxidative properties for the food industry by emphasizing on optimization of the reaction conditions to maximize the production yields. Lastly, recent developments regarding characterization, potential applications, emerging research areas, and needs are highlighted.

Catalytic Routes to Produce Polyphenolic Esters (PEs) from Biomass Feedstocks

Polyphenolic esters (PEs) are valuable chemical compounds that display a wide spectrum of activities (e.g., anti-oxidative effects). As a result, their production through catalytic routes is an attractive field of research. The present review aims to discuss recent studies from the literature regarding the catalytic production of PEs from biomass feedstocks, namely, naturally occurred polyphenolic compounds. Several synthetic approaches are reported in the literature, mainly bio-catalysis and to a lesser extent acid catalysis. Immobilized lipases (e.g., Novozym 435) are the preferred enzymes thanks to their high reactivity, selectivity and reusability. Acid catalysis is principally investigated for the esterification of polyphenolic acids with fatty alcohols and/or glycerol, using both homogeneous (p-toluensulfonic acid, sulfonic acid and ionic liquids) and heterogeneous (strongly acidic cation exchange resins) catalysts. Based on the reviewed publications, we propose some suggestions to improve the synthesis of PEs with the aim of increasing the greenness of the overall production process. In fact, much more attention should be paid to the use of new and efficient acid catalysts and their reuse for multiple reaction cycles.

Chemoenzymatic approaches to plant natural product inspired compounds

Covering: 2003 up to the end of 2021Complex molecules produced by plants have provided us with a range of medicines, flavour and fragrance compounds and pesticides. However, there are challenges associated with accessing these in an economically viable manner, including low natural abundance and the requirement for complex multi-step synthetic strategies. Chemoenzymatic approaches provide a valuable alternative strategy by combining traditional synthetic methods with biocatalysis. This review highlights recent chemoenzymatic syntheses towards plant natural products and analogues, focusing on the advantages of incorporating biocatalysts into a synthetic strategy.

An efficient and robust continuous-flow bioreactor for the enzymatic preparation of phytosterol esters based on hollow lipase microarray

In this study, a continuous-flow bioreactor packed with well-organized lipase microarrays was developed for the sustainable synthesis of functional lipid-phytosterol esters (PEs). Hollow mesoporous silicon spheres with a suitable pore size were prepared for lipase immobilization, and the hydrophobic modification endowed the lipase with excellent catalytic activity and stability. The results showed that the condensely packed lipase microarrays offered large specific surface areas and guaranteed the thorough interaction between the lipase and substrates in the continuous-flow bioreactor. Meanwhile, the substrate could pass through the reactor at 1 mL/min with a high conversion of 93.6% due to the hollow structure of the packing spheres. Moreover, the reactors were able to produce 1564 g PEs/g catalyst in a continuous 30-day processing period, which set the highest records for PEs synthesis. This sustainable and highly-converting flow system provided a feasible path for scale-up production of PEs in the food processing area.

Lipases as Effective Green Biocatalysts for Phytosterol Esters’ Production: A Review

Lipases are versatile enzymes widely used in the pharmaceutical, cosmetic, and food industries. They are green biocatalysts with a high potential for industrial use compared to traditional chemical methods. In recent years, lipases have been used to synthesize a wide variety of molecules of industrial interest, and extraordinary results have been reported. In this sense, this review describes the important role of lipases in the synthesis of phytosterol esters, which have attracted the scientific community’s attention due to their beneficial effects on health. A systematic search for articles and patents published in the last 20 years with the terms “phytosterol AND esters AND lipase” was carried out using the Scopus, Web of Science, Scielo, and Google Scholar databases, and the results showed that Candida rugosa lipases are the most relevant biocatalysts for the production of phytosterol esters, being used in more than 50% of the studies. The optimal temperature and time for the enzymatic synthesis of phytosterol esters mainly ranged from 30 to 101 °C and from 1 to 72 h. The esterification yield was greater than 90% for most analyzed studies. Therefore, this manuscript presents the new technological approaches and the gaps that need to be filled by future studies so that the enzymatic synthesis of phytosterol esters is widely developed.

Enzymes, In Vivo Biocatalysis, and Metabolic Engineering for Enabling a Circular Economy and Sustainability

Since the industrial revolution, the rapid growth and development of global industries have depended largely upon the utilization of coal-derived chemicals, and more recently, the utilization of petroleum-based chemicals. These developments have followed a linear economy model (produce, consume, and dispose). As the world is facing a serious threat from the climate change crisis, a more sustainable solution for manufacturing, i.e., circular economy in which waste from the same or different industries can be used as feedstocks or resources for production offers an attractive industrial/business model. In nature, biological systems, i.e., microorganisms routinely use their enzymes and metabolic pathways to convert organic and inorganic wastes to synthesize biochemicals and energy required for their growth. Therefore, an understanding of how selected enzymes convert biobased feedstocks into special (bio)chemicals serves as an important basis from which to build on for applications in biocatalysis, metabolic engineering, and synthetic biology to enable biobased processes that are greener and cleaner for the environment. This review article highlights the current state of knowledge regarding the enzymatic reactions used in converting biobased wastes (lignocellulosic biomass, sugar, phenolic acid, triglyceride, fatty acid, and glycerol) and greenhouse gases (CO₂ and CH₄) into value-added products and discusses the current progress made in their metabolic engineering. The commercial aspects and life cycle assessment of products from enzymatic and metabolic engineering are also discussed. Continued development in the field of metabolic engineering would offer diversified solutions which are sustainable and renewable for manufacturing valuable chemicals.

A comprehensive review on polarity, partitioning, and interactions of phenolic antioxidants at oil-water interface of food emulsions

There has been a growing interest in developing effective strategies to inhibit lipid oxidation in emulsified food products by utilization of natural phenolic antioxidants owing to their growing popularity over the past decades. However, due to the complexity of emulsified systems, the inhibition mechanism of phenolic antioxidants against lipid oxidation is rather complicated and not yet fully understood. In order to highlight the importance of polarity of phenolic antioxidants in emulsified systems according to the polar paradox, this review covers the recent progress on chemical, enzymatic, and chemoenzymatic lipophilization techniques used to modify the polarity of antioxidants. The partitioning behavior of phenolic antioxidants at the oil-water interface, which can be influenced by the presence of synthetic surfactants and/or antioxidant emulsifiers (e.g., polysaccharides, proteins, and phospholipids), is discussed. In addition, the emerging phenolic antioxidants among phenolic acids, flavonoids, tocopherols, and stilbenes applied in food emulsions are elaborated. As well, the interactions of polar-nonpolar antioxidants are stressed as a promising strategy to induce synergistic interactions at oil-water interface for improved oxidative stability of emulsions.

A review on chemical and physical modifications of phytosterols and their influence on bioavailability and safety

Phytosterols have been shown to lower cholesterol levels and to have antioxidant, anti-inflammatory and other biological activities. However, the high melting point and poor solubility limit their bioavailability and practical application. It is advantageous to modify phytosterols chemically and physically. This article reviews and discusses the chemical and physical modifications of phytosterols, as well as their effects on the bioavailability and possible toxicity in vivo. The current research on chemical modifications is mainly focused on esterification to increase the oil solubility and water solubility. For physical modifications (mainly microencapsulation), there are biopolymer-based, surfactant-based and lipid-based nanocarriers. Both chemical and physical modifications of phytosterols can effectively increase the absorption and bioavailability. The safety of modified phytosterols is also an important issue. Phytosterol esters are generally considered to be safe. However, phytosterol oxides, which may be produced during the synthesis of phytosterol esters, have shown toxicity in animal models. The toxicity of nanocarriers also needs further studies.

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

In recent years, steryl esters have found potential applications in food, pharmaceutical and cosmetic industries. Therefore, three hydroxycinnamate steryl esters (HSEs): β-sitosteryl sinapate (β-SSA), β-sitosteryl caffeate (β-SCA), and β-sitosteryl ferulate (β-SFA) were synthesized by chemical approach and their antioxidant activity (AA) were analyzed by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) assays. The values of inhibitory concentration (IC₅₀) of each ester needed to inhibit 50% of the DPPH radical (IC_50(DPPH) = 238.9, 78.3, 290.0 µmol/L for β-SSA, β-SCA, and β-SFA, respectively) and ABTS radical cation (IC_50(ABTS) = 174.6, 106.7, 206.0 µmol/L for β-SSA, β-SCA, and β-SFA, respectively) were estimated and compared with antioxidant potential of phenolic acids. Moreover, the effect of HSEs addition in the concentrations range between 0.01% and 0.5% on the AA of refined rapeseed oil, mayonnaise and margarine was evaluated. Chemical structures of the synthesized HSEs and their concentrations strongly affect the AA of fat products. Oil and emulsions supplemented with higher concentrations of HSEs had significantly higher AA than control samples. Unfortunately, lower concentrations of HSEs (0.01% and 0.02%) did not increase the AA of fat products. However, steryl phenolates added in higher amounts can be considered as potential antioxidants delaying the oxidation processes of studied fats.

Enhancement of Antioxidant Activity in O/W Emulsion and Cholesterol-Reducing Capacity of Epigallocatechin by Derivatization with Representative Phytosterols

In this study, derivatization of epigallocatechin (EGC) by representative phytosterols (stigmasterol and β-sitosterol) was performed employing Steglich esterification. The structural identity and purity of epigallocatechin β-sitosterol (ESi) and epigallocatechin stigmasterol (ESt) were confirmed by NMR, FT-IR, and HPLC-MS. Further evaluation of ESi and ESt revealed their extraordinary antioxidant activities in O/W emulsion. Two different radical sources in oil or aqueous phase were applied to explore the antioxidant behavior in O/W emulsion. The mechanism was further investigated by fluorescent microscopy and transmission electron microscopy (TEM). Furthermore, incorporation of EGC with stigmasterol and β-sitosterol notably enhanced the cholesterol-reducing activity. TEM studies suggested the hydrogen bonding of EGC strengthened the aggregation network of ESi and ESt in the bile salt micelle. The exceptional properties of ESi and ESt signified their intriguing utilization in the food industry.

Caffeates and Caffeamides: Synthetic Methodologies and Their Antioxidant Properties

Polyphenols are secondary metabolites of plants and include a variety of chemical structures, from simple molecules such as phenolic acids to condensed tannins and highly polymerized compounds. Caffeic acid (3,4-dihydroxycinnamic acid) is one of the hydroxycinnamate metabolites more widely distributed in plant tissues. It is present in many food sources, including coffee drinks, blueberries, apples, and cider, and also in several medications of popular use, mainly those based on propolis. Its derivatives are also known to possess anti-inflammatory, antioxidant, antitumor, and antibacterial activities, and can contribute to the prevention of atherosclerosis and other cardiovascular diseases. This review is an overview of the available information about the chemical synthesis and antioxidant activity of caffeic acid derivatives. Considering the relevance of these compounds in human health, many of them have been the focus of reviews, taking as a center their obtaining from the plants. There are few revisions that compile the chemical synthesis methods, in this way, we consider that this review does an important contribution.

Enhancement of Galloylation Efficacy of Stigmasterol and β-Sitosterol Followed by Evaluation of Cholesterol-Reducing Activity

In this study, incorporation of gallic acid into typical phytosterols (β-sitosterol and stigmasterol) through Steglich esterification was optimized employing the protection and deprotection strategy. A novel mechanism leading to side esterification was discovered. Complication of the phenolic hydroxyl groups and side reactions were successfully reduced under the optimized conditions. The structural identity and purity of galloyl stigmasterol and galloyl β-sitosterol were confirmed by NMR, FT-IR, and HPLC-MS. Evaluation of galloyl β-sitosterol and galloyl stigmasterol revealed their excellent antioxidant and cholesterol-reducing activities. Significant enhancement of cholesterol-reducing activity by galloylation was unveiled especially for β-sitosterol. Galloyl β-sitosterol had slightly better antioxidant activity at ambient temperature and better cholesterol-reducing activity. Molecular modeling suggested that a subtle difference of galloyl β-sitosterol and galloyl stigmasterol in activities could be attributed to variation of molecular rigidity and conformation. The excellent properties of galloyl β-sitosterol and galloyl stigmasterol suggested their great potential application in the food industry.

Potential of rare actinomycetes in the production of metabolites against multiple oxidant agents

CONTEXT

Actinobacteria are a precious source of novel bioactive metabolites with potential pharmaceutical applications.

OBJECTIVES

Representatives of 11 genera of rare Actinobacteria were selected for the evaluation of antioxidant activity.

MATERIAL AND METHODS

Fermentation broths of the Actinobacteria were extracted and dosage of 10 to 2000 µg/mL were applied for in vitro antioxidant-related bioassays. Cytotoxicity was assessed at the concentration of 2.5-20 µg/mL.

RESULTS

In the DPPH scavenging activity, 15 out of 52 extracts showed 17.0-26.8% activity in quantitative evaluation. Metabolites of five prominent antioxidant producing strains protected the DNA (pUC19) against UV-induced photolyzed H₂O₂-oxidative degradation. The potent antioxidant extracts inhibited two oxidative enzymes of xanthine oxidase in the range of 17.5-45.2% (three extracts had IC₅₀ less than allopurinol) and lipoxygenase in the range of 36-55% (all five extracts had IC₅₀ values less than daidzein). All these extracts could also protect eythrocytes from iron-induced hemolysis with ED₅₀ values in a range of 0.014-1.25 mg/mL. Growth restoration of the yeast cells lacking the sod1 gene was observed by the antioxidant metabolite of Saccharothrix ecbatanensis UTMC 537 at the concentration of 1 mg/mL.

CONCLUSIONS

The presence of nonidentical metabolites might be responsible for antioxidant and enzyme inhibitory activities of S. ecbatanensis, newly described actinobacterium in family Pseudonocardiaceae. The scavenging of the free electrons, protection of DNA and model yeast cells against oxidative stress, in addition to the inhibition of the oxidating enzymes are the main mechanisms of the antioxidant effect of the introduced resource in this study.

Enzymatic synthesis of bioactive compounds with high potential for cosmeceutical application

Cosmeceuticals are cosmetic products containing biologically active ingredients purporting to offer a pharmaceutical therapeutic benefit. The active ingredients can be extracted and purified from natural sources (botanicals, herbal extracts, or animals) but can also be obtained biotechnologically by fermentation and cell cultures or by enzymatic synthesis and modification of natural compounds. A cosmeceutical ingredient should possess an attractive property such as anti-oxidant, anti-inflammatory, skin whitening, anti-aging, anti-wrinkling, or photoprotective activity, among others. During the past years, there has been an increased interest on the enzymatic synthesis of bioactive esters and glycosides based on (trans)esterification, (trans)glycosylation, or oxidation reactions. Natural bioactive compounds with exceptional theurapeutic properties and low toxicity may offer a new insight into the design and development of potent and beneficial cosmetics. This review gives an overview of the enzymatic modifications which are performed currently for the synthesis of products with attractive properties for the cosmeceutical industry.

Biotransformation: a green and efficient way of antioxidant synthesis

Antioxidant compounds play a vital role in human physiology. They prevent the oxidation of biomolecules by scavenging free radicals produced during physiochemical processes and/or as a result of several pathological states. A balance between the reactive oxygen species (free radicals) and antioxidants is essential for proper physiological conditions. Excessive free radicals cause oxidative stress which can lead to several human diseases. Therefore, synthesis of the effective antioxidants is crucial in managing the oxidative stress. Biotransformation has evolved as an effective technique for the production of structurally diverse molecules with a wide range of biological activities. This methodology surpasses the conventional chemical synthesis due to the fact that enzymes, being specific in nature, catalyze reactions affording products with excellent regio- and stereoselectivities. Structural transformation of various classes of compounds such as alkaloids, steroids, flavonoids, and terpenes has been carried out through this technique. Several bioactive molecules, especially those having antioxidant potential have also been synthesized by using different biotransformation techniques and enzymes. Hydroxylated, glycosylated, and acylated derivatives of phenols, flavonoids, cinnamates, and other molecules have proven abilities as potential antioxidants. A critical review of the biotransformation of these compounds into potent antioxidant metabolites is presented here.

A novel continuous flow biosynthesis of caffeic acid phenethyl ester from alkyl caffeate and phenethanol in a packed bed microreactor

Caffeic acid phenethyl ester (CAPE) is a rare natural ingredient with several biological activity, but the industrial production of CAPE using lipase-catalyzed esterification of caffeic acid (CA) and 2-phenylethanol (PE) in ionic liquids is hindered by low substrate concentrations and a long reaction time. To establish a high-efficiency bioprocess for obtaining CAPE, a novel continuous flow biosynthesis of CAPE from alkyl caffeate and PE in [Bmim][Tf2N] using a packed bed microreactor was successfully carried out. Among the tested alkyl caffeates and lipases, methyl caffeate and Novozym 435, respectively, were selected as the suitable substrate and biocatalyst. Under the optimum conditions selected using response surface methodology, a 93.21% CAPE yield was achieved in 2.5h using a packed bed microreactor, compared to 24h using a batch reactor. The reuse of Novozym 435 for 20 cycles and continuous reaction for 9 days did not result in any decrease in activity.

Rapid synthesis of propyl caffeate in ionic liquid using a packed bed enzyme microreactor under continuous-flow conditions

Propyl caffeate has the highest antioxidant activity among caffeic acid alkyl esters, but its industrial production via enzymatic transesterification in batch reactors is hindered by a long reaction time (24h). To develop a rapid process for the production of propyl caffeate in high yield, a continuous-flow microreactor composed of a two-piece PDMS in a sandwich-like microchannel structure was designed for the transesterification of methyl caffeate and 1-propanol catalyzed by Novozym 435 in [B mim][CF3SO3]. The maximum yield (99.5%) in the microreactor was achieved in a short period of time (2.5h) with a flow rate of 2 μL/min, which kinetic constant Km was 16 times lower than that of a batch reactor. The results indicated that the use of a continuous-flow packed bed enzyme microreactor is an efficient method of producing propyl caffeate with an overall yield of 84.0%.

A novel chemoenzymatic synthesis of propyl caffeate using lipase-catalyzed transesterification in ionic liquid

Propyl caffeate has the highest antioxidant capacity in the caffeate alkyl esters family, but industrial production of propyl caffeate is hindered by low yields using either the chemical or enzymatic catalysis method. To set up a high-yield process for obtaining propyl caffeate, a novel chemoenzymatic synthesis method using lipase-catalyzed transesterification of an intermediate methyl caffeate or ethyl caffeate and 1-propanol in ionic liquid was established. The maximum propyl caffeate yield of 98.5% was obtained using lipase-catalyzed transesterification under the following optimal conditions: Novozym 435 as a biocatalyst, [Bmim][CF3SO3] as a medium, a molar ratio of methyl caffeate to 1-propanol of 1:5, a mass ratio of methyl caffeate to lipase of 1:20, and a reaction temperature of 60°C. The two-step conversion of caffeic acid to propyl caffeate via methyl caffeate is an efficient way to prepare propyl caffeate with an overall yield of 82.7%.

Efficient solvent-free synthesis of phytostanyl esters in the presence of acid-surfactant-combined catalyst

An efficient approach based on the synthesis of phytostanyl esters with an acid-surfactant-combined catalyst in a solvent-free system was developed. The effect of catalyst dose, substrate molar ratio, reaction temperature, and acyl donor was considered. The reaction conditions were further optimized by response surface methodology, and a high yield of phytostanyl laurate (>92%) was obtained under optimum conditions: 3.17:1 molar ratio of lauric acid to plant stanols, 4.01% catalyst dose (w/w), 119 °C, and 4.1 h. FT-IR, MS, and NMR were adopted to confirm the chemical structure of phytostanyl laurate. Meanwhile, the physiochemical properties of different phytostanyl esters were investigated. Compared with phytostanols, the prepared phytostanyl esters had much lower melting temperature and higher oil solubility. There was no obvious difference in melting and solidification properties between sunflower oil with phytostanyl laurate (<5%) or oleate (<10%) and the original sunflower oil, suggesting that the esterification of phytostanols greatly facilitated their corporation into oil-based foods.