Enzymatic acylation of blackcurrant (Ribes nigrum) anthocyanins and evaluation of lipophilic properties and antioxidant capacity of derivatives

Enzymatic acylation of cyanidin-3-O-glucoside with aromatic and aliphatic acid methyl ester: Structure-stability relationships of acylated derivatives

Anthocyanins are water-soluble pigments, but they tend to be unstable in aqueous solutions. Modification of their molecular structure offers a viable approach to alter their intrinsic properties and enhance stability. Aromatic and aliphatic acid methyl esters were used as acyl donors in the enzymatic acylation of cyanidin-3-O-glucoside (C3G), and their analysis was conducted using ultraperformance liquid chromatography-mass spectrometry (UPLC-MS). The highest conversion rate achieved was 96.41 % for cyanidin-3-O-(6″-feruloyl) glucoside. Comparative evaluations of stability revealed that aromatic acyl group-conjugated C3G exhibited superior stability enhancement compared with aliphatic acyl group derivatives. The stability of aliphatic C3G decreased with increasing carbon chain length. The molecular geometries of different anthocyanins were optimized, and energy level calculations using density functional theory (DFT) identified their sites with antioxidant activities. Computational calculations aligned with the in vitro antioxidant assay results. This study provided theoretical support for stabilizing anthocyanins and broadened the application of acylated anthocyanins as food colorants and nutrient supplements.

Effect of glycosylation, acylation and pyranylation at cyanidin C-ring on its interaction with vitamin C in apple juice beverage matrix

BACKGROUND

Synchronous degradation between anthocyanin and vitamin C was found in fruit and vegetable juice matrices. To investigate whether the C-ring of anthocyanin is the key site of this interaction, cyanidin with four different C-ring modifications (3-glucosylation, 3,5-diglucosylation, 6″-malonylation, pyranylation) was added to vitamin C-containing apple juice, and the changes of anthocyanin retention, vitamin C retention, color, antioxidative activity and differential metabolites were analyzed.

RESULTS

The anthocyanin retention was in the order of pyranylation >6″-malonylation >3,5-diglucosylation >3-glucosylation. The vitamin C retention was in the order of 6″-malonylation > pyranylation >3,5-diglucosylation >3-glucosylation. The order of color stability was the same as that of anthocyanin retention, and the order of antioxidative activity was opposite to that of vitamin C retention. The results showed that modification at the C-ring limited the activity of anthocyanin, and suggested that the C-ring was one of the key sites for anthocyanin and vitamin C interaction. The shared differential metabolite of all apple juice matrices added with different anthocyanins was trans-hinokiresinol, which was likely generated from anthocyanin skeleton reacted with certain compounds in apple juice.

CONCLUSION

This study showed that modification of the anthocyanin C-ring could affect the anthocyanin and vitamin C interaction to some extent, which provided valuable insights for the application of anthocyanin C-ring modification in shelf-life quality control of typical fruit and vegetable beverages with the coexistence of anthocyanin and vitamin C. © 2024 Society of Chemical Industry.

A novel carboxymethyl cellulose/gum xanthan and citric acid-based film that enhances the precision of blackcurrant anthocyanin-induced color detection for beef spoilage tracking

Leveraging blackcurrant anthocyanin (BC) as an indicator and carboxymethyl cellulose (CMC), gum xanthan (GX), and citric acid (CA) as film fabricating materials, an innovative amine-responsive beef freshness intelligent film, known as CGC-BC, was successfully created. It was found that the physical characteristics, sensitivity to the biogenic amine reaction, and original color of the film were all highly influenced by the pH of the film-forming solutions. The film's freshness monitoring ability was assessed at 4, 25, and 35 °C, and various color changes were employed to monitor beef deterioration. ΔE values and the visual color difference of the low-concentration (SCG-BC-0.08 and SCG-BC-0.16) ammonia-sensitive indicator films demonstrated significant color changes than the high-concentration (SCG-BC-0.24 and SCG-BC-0.32) films. The films biodegradation (37.16 to 51.49%) ability was enhanced with increase in the proportions of BC. As the TVB-N and pH values of beef increased with the different temperatures and time and different color changes were observed from red to pink, black to brown, and yellow.

Esterification of black bean anthocyanins with unsaturated oleic acid, and application characteristics of the product

Esterification of anthocyanins with saturated fatty acids have been widely investigated, while that with unsaturated fatty acids is little understood. In this study, crude extract (purity ∼ 35 %) of cyanidin-3-O-glucoside (C3G) from black bean seed coat was utilized as reaction substrate, and enzymatically acylated with unsaturated fatty acid (oleic acid). Optimization of various reaction parameters finally resulted in the highest acylation rate of 54.3 %. HPLC-MS/MS and NMR analyses elucidated the structure of cyanidin-3-O-glucoside-oleic acid ester (C3G-OA) to be cyanidin-3-O-(6″-octadecene)-glucoside. Introduction of oleic acid into C3G improved the lipophilicity, antioxidant ability, and antibacterial activity. Further, the color and substance stability analyses showed that the susceptibility of C3G and C3G-OA to different thermal, peroxidative, and illuminant treatments were highly pH dependent, which suggested individual application guidelines. Moreover, C3G-OA showed lower toxicity to normal cell (QSG-7701) and better inhibitory effect on the proliferation of HepG2 cells than C3G, which indicated its potential anti-tumor bioactivity.

Role of lingonberry press cake in producing stable herring protein isolates via pH-shift processing: A dose response study

The effects of cross-processing lingonberry press cake (LPC) (2.5-30 %, dw/dw) with herring co-products on protein yield, oxidative stability and color of pH-shift-produced protein isolates were investigated. Even at 2.5 % LPC, the formation of volatile oxidation-derived aldehydes, including hexanal, (E)-2-hexenal, heptanal, octanal, and 2,4-heptadienal, were prevented during the actual protein isolate production. Adding 10 % LPC successfully prevented formation of all these aldehydes also during eight days ice storage which was explained by the partitioning of phenolics, especially ideain (1.09 mg/g dw) and procyanidin A1 (65.5 mg/g dw), into isolates. Although higher amounts of LPC (20-30 %) further prolonged the oxidation lag phase, it reduced total protein yield, increased the consumption of acid and base, and darkened protein isolates. Therefore, it is recommended to use 10 % LPC when pH-shift-processing sensitive fish raw materials as a route to mitigate lipid oxidation and at the same time promote industrial symbiosis and more circular food production.

Dietary Sources, Stabilization, Health Benefits, and Industrial Application of Anthocyanins-A Review

Natural phytochemicals are well known to protect against numerous metabolic disorders. Anthocyanins are vacuolar pigments belonging to the parent class of flavonoids. They are well known for their potent antioxidant and gut microbiome-modulating properties, primarily responsible for minimizing the risk of cardiovascular diseases, diabetes, obesity, neurodegenerative diseases, cancer, and several other diseases associated with metabolic syndromes. Berries are the primary source of anthocyanin in the diet. The color and stability of anthocyanins are substantially influenced by external environmental conditions, constraining their applications in foods. Furthermore, the significantly low bioavailability of anthocyanins greatly diminishes the extent of the actual health benefits linked to these bioactive compounds. Multiple strategies have been successfully developed and utilized to enhance the stability and bioavailability of anthocyanins. This review provides a comprehensive view of the recent advancements in chemistry, biosynthesis, dietary sources, stabilization, bioavailability, industrial applications, and health benefits of anthocyanins. Finally, we summarize the prospects and challenges of applications of anthocyanin in foods.

Unlocking the health potential of anthocyanins: a structural insight into their varied biological effects

Anthocyanins have become increasingly important to the food industry due to their colorant features and many health-promoting activities. Numerous studies have linked anthocyanins to antioxidant, anti-inflammatory, anticarcinogenic properties, as well as protection against heart disease, certain types of cancer, and a reduced risk of diabetes and cognitive disorders. Anthocyanins from various foods may exhibit distinct biological and health-promoting activities owing to their structural diversity. In this review, we have collected and tabulated the key information from various recent published studies focusing on investigating the chemical structure effect of anthocyanins on their stability, antioxidant activities, in vivo fate, and changes in the gut microbiome. This information should be valuable in comprehending the connection between the molecular structure and biological function of anthocyanins, with the potential to enhance their application as both colorants and functional compounds in the food industry.

Strategy for the Enzymatic Acylation of the Apple Flavonoid Phloretin Based on Prior α-Glucosylation

The acylation of flavonoids serves as a means to alter their physicochemical properties, enhance their stability, and improve their bioactivity. Compared with natural flavonoid glycosides, the acylation of nonglycosylated flavonoids presents greater challenges since they contain fewer reactive sites. In this work, we propose an efficient strategy to solve this problem based on a first α-glucosylation step catalyzed by a sucrose phosphorylase, followed by acylation using a lipase. The method was applied to phloretin, a bioactive dihydrochalcone mainly present in apples. Phloretin underwent initial glucosylation at the 4'-OH position, followed by subsequent (and quantitative) acylation with C8, C12, and C16 acyl chains employing an immobilized lipase from Thermomyces lanuginosus. Electrospray ionization-mass spectrometry (ESI-MS) and two-dimensional nuclear magnetic resonance spectroscopy (2D-NMR) confirmed that the acylation took place at 6-OH of glucose. The water solubility of C8 acyl glucoside closely resembled that of aglycone, but for C12 and C16 derivatives, it was approximately 3 times lower. Compared with phloretin, the radical scavenging capacity of the new derivatives slightly decreased with 2,2-diphenyl-1-picrylhydrazyl (DPPH) and was similar to 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS•+). Interestingly, C12 acyl-α-glucoside displayed an enhanced (3-fold) transdermal absorption (using pig skin biopsies) compared to phloretin and its α-glucoside.

Preparation and characterization of smart indicator films based on gellan gum/modified black rice anthocyanin/curcumin for improving the stability of natural anthocyanins

In order to improve the stability of natural anthocyanins in intelligent packaging materials, this work first modified black rice anthocyanins (BRA) by acylation with acetic acid, then modified the acylated BRA by co-coloring with different ratios of curcumin (CUR), and finally added the mixed indicator to gellan gum (GG) to develop intelligent packaging films with good stability. The UV spectroscopy results showed that acetic acid had successfully modified the BRA, while the thermal, photostability and pH stability of the modified black rice anthocyanin (MBRA) were significantly enhanced. The indicators of BRA, MBRA and MBRA mixed with CUR showed excellent pH sensitivity in different buffer solutions. The SEM, FT-IR and XRD results indicated apparent crystalline aggregates on the surface of the films added with a high concentration of CUR. Compared with GG-BRA film, GG-MBRA film improved all properties except for antioxidant performance. Notably, the GG-MBRA/CUR series composite films exhibited significant improvements over the GG-BRA and GG-MBRA films in terms of optical characteristics, mechanical properties, water vapor barrier, oxidation resistance, and color stability; meanwhile, all films exhibited excellent pH sensitivity. Considering all the properties of the films, GG-MBRA/CUR3 film has tremendous potential as a smart indicator film for improving freshness accuracy.

Enzymatic Acylation of Black Rice Anthocyanins and Evaluation of Antioxidant Capacity and Stability of Their Derivatives

In this study, the structure of the anthocyanin fractions isolated from black rice (Oryza sativa L.) was modified by the enzyme catalysis method using caffeic acid as an acyl donor. At the same time, the effects of the acylation on the lipophilicity, antioxidant activity, and stability of black rice anthocyanins were comprehensively evaluated. The structural analyses of acylated derivatives based on ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, ultra-high-performance liquid chromatography-high-resolution mass spectrometry, and thermogravimetric analysis revealed that caffeic acid was efficiently grafted onto the anthocyanins of black rice through an acylated reaction, while the acylation binding site was on glucoside. When the mass ratios of anthocyanins to caffeic acid were 1:1, the A319/AVis-max value of acylated anthocyanins reached 6.37. Meanwhile, the lipophilicity of acylated derivatives was enhanced. The antioxidant capacity (DPPH and FRAP) and stability (thermal, pH, and light stability) were significantly increased. Overall, the study results provide deeper insights into controlling anthocyanin homeostasis in food processing, broadening the application of colored grain products.

Enzymatic molecular modification of water-soluble polyphenols: Synthesis, structure, bioactivity and application

The poor lipophilicity and instability of water-soluble polyphenols limit their bioavailability and application in food. However, increasing attention has been given to water-soluble polyphenols due to their multiple biological activities, which prompts the modification of the structure of water-soluble polyphenols to improve their lipophilicity and stability and enable more efficient application. This review presents the enzymatic biosynthesis of lipophilic derivatives of water-soluble polyphenols, which will change the molecular structure of water-soluble polyphenols based on the loss of hydroxyl or carboxyl groups. Therefore, the effects of reaction factors on the structure of polyphenol derivatives and the change in their bioactivities will be further analyzed. Previous studies have shown that lipases, solvent systems, and hydrophobic groups are major factors influencing the synthesis and lipophilicity of polyphenol derivatives. Moreover, the biological activities of polyphenol derivatives were changed to a certain extent, such as through the enhancement or weakening of antioxidant activity in different systems and the increase in anti-influenza virus activity and antibacterial activity. The improvement of lipophilicity also expands polyphenol application in food. This review may contribute to the efficient synthesis of lipophilic derivatives of water-soluble polyphenols to extend the utilization and application range of polyphenols.

Progress on molecular modification and functional applications of anthocyanins

Anthocyanins have attracted a lot of attention in the fields of natural pigments, food packaging, and functional foods due to their color, antioxidant, and nutraceutical properties. However, the poor chemical stability and low bioavailability of anthocyanins currently limit their application in the food industry. Various methods can be used to modify the structure of anthocyanins and thus improve their stability and bioavailability characteristics under food processing, storage, and gastrointestinal conditions. This paper aims to review in vitro modification methods for altering the molecular structure of anthocyanins, as well as their resulting improved properties such as color, stability, solubility, and antioxidant properties, and functional applications as pigments, sensors and functional foods. In industrial production, by mixing co-pigments with anthocyanins in food systems, the color and stability of anthocyanins can be improved by using non-covalent co-pigmentation. By acylation of fatty acids and aromatic acids with anthocyanins before incorporation into food systems, the surface activity of anthocyanins can be activated and their antioxidant and bioactivity can be improved. Various other chemical modification methods, such as methylation, glycosylation, and the formation of pyranoanthocyanins, can also be utilized to tailor the molecular properties of anthocyanins expanding their range of applications in the food industry.

Metabolomics revealed metabolite biomarkers of antioxidant properties and flavonoid metabolite accumulation in purple rice after grain filling

The correlation between flavonoids, phenolic metabolites and the total antioxidant capacity is well established. However, specific biomarkers of metabolites with antioxidant properties in purple rice grains remain unidentified. This study integrated nontargeted metabolomics, quantitative detection of flavonoids and phenolic compounds, and physiological and biochemical data to identify metabolite biomarkers of the antioxidant properties of purple rice grains after filling. The findings demonstrated a significant enhancement in the biosynthesis of flavonoids during the middle and late filling stages in purple rice grains. Additionally, the pathways involved in anthocyanin and flavonoid biosynthesis were significantly enriched. Catalase (CAT), phenylalanine ammonia-lyase (PAL), total phenols (TP), flavonoids (FD), and oligomeric proanthocyanidin (OPC) were significantly correlated with philorizin, myricetin 3-galactoside, and trilobatin. Phlorizin, myricetin 3-galactoside, and trilobatin were metabolite biomarkers of antioxidant properties in purple rice grains. This study provides new ideas for the cultivation of high-quality coloured rice varieties with high antioxidant activity.

Himalayan Sources of Anthocyanins and Its Multifunctional Applications: A Review

Anthocyanins, the colored water-soluble pigments, have increasingly drawn the attention of researchers for their novel applications. The sources of anthocyanin are highly diverse, and it can be easily extracted. The unique biodiversity of the Himalayan Mountain range is an excellent source of anthocyanin, but it is not completely explored. Numerous attempts have been made to study the phytochemical aspects of different Himalayan plants. The distinct flora of the Himalayas can serve as a potential source of anthocyanins for the food industry. In this context, this review is an overview of the phytochemical studies conducted on Himalayan plants for the estimation of anthocyanins. For that, many articles have been studied to conclude that plants (such as Berberis asiatica, Morus alba, Ficus palmata, Begonia xanthina, Begonia palmata, Fragaria nubicola, etc.) contain significant amounts of anthocyanin. The application of Himalayan anthocyanin in nutraceuticals, food colorants, and intelligent packaging films have also been briefly debated. This review creates a path for further research on Himalayan plants as a potential source of anthocyanins and their sustainable utilization in the food systems.

Pharmacological Activities and Chemical Stability of Natural and Enzymatically Acylated Anthocyanins: A Comparative Review

Anthocyanins (ANCs) are naturally occurring water-soluble pigments responsible for conferring red, blue, and purple colors to fruits, vegetables, flowers, and grains. Due to their chemical structure, they are highly susceptible to degradation by external factors, such as pH, light, temperature, and oxygen. Naturally acylated anthocyanins have proven to be more stable in response to external factors and exhibit superior biological effects as compared with their non-acylated analogues. Therefore, synthetic acylation represents a viable alternative to make the application of these compounds more suitable for use. Enzyme-mediated synthetic acylation produces derivatives that are highly similar to those obtained through the natural acylation process, with the main difference between these two pathways being the catalytic site of the enzymes involved in the synthesis; acyltransferases catalyze natural acylation, while lipases catalyze synthetic acylation. In both cases, their active sites perform the addition of carbon chains to the hydroxyl groups of anthocyanin glycosyl moieties. Currently, there is no comparative information regarding natural and enzymatically acylated anthocyanins. In this sense, the aim of this review is to compare natural and enzyme-mediated synthetic acylated anthocyanins in terms of chemical stability and pharmacological activity with a focus on inflammation and diabetes.

Enzymatic Acylation of Flavonoids from Bamboo Leaves: Improved Lipophilicity and Antioxidant Activity for Oil-Based Foods

The goal of this study was to expand the applications of bamboo leaf flavonoids (BLFs) by improving their lipophilicity through enzymatic acylation with vinyl cinnamate. Characterization of the acylated BLFs using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, high-resolution electrospray ionization mass spectrometry, electrospray ionization with tandem mass spectrometry, and ¹H nuclear magnetic resonance spectroscopy indicated that acylation occurred at the C6-OH position of glucoside moieties. The highest degree of acylation (18.61%) was obtained by reacting BLFs with vinyl cinnamate (1:5, w/w) at 60 °C for 48 h. Acylation significantly improved the lipophilicity of BLFs and their capacity to inhibit lipid peroxidation, as evidenced by the reduced production of lipid hydroperoxides and malondialdehyde in rapeseed oil and rapeseed oil-in-water emulsions during storage at 37 °C for 15 days. The study findings provide important data that will enable the use of BLFs in lipid or lipophilic matrices, such as oil-based foods.

Anthocyanins: Modified New Technologies and Challenges

Anthocyanins are bioactive compounds belonging to the flavonoid class which are commonly applied in foods due to their attractive color and health-promoting benefits. However, the instability of anthocyanins leads to their easy degradation, reduction in bioactivity, and color fading in food processing, which limits their application and causes economic losses. Therefore, the objective of this review is to provide a systematic evaluation of the published research on modified methods of anthocyanin use. Modification technology of anthocyanins mainly includes chemical modification (chemical acylation, enzymatic acylation, and formation of pyran anthocyanidin), co-pigmentation, and physical modification (microencapsulation and preparation of pickering emulsion). Modification technology of anthocyanins can not only increase bioavailability and stability of anthocyanin but also can improve effects of anthocyanin on disease prevention and treatment. We also propose potential challenges and perspectives for diversification of anthocyanin-rich products for food application. Overall, integrated strategies are warranted for improving anthocyanin stabilization and promoting their further application in the food industry, medicine, and other fields.

Enhancing the Hydrolysis and Acyl Transfer Activity of Carboxylesterase DLFae4 by a Combinational Mutagenesis and In-Silico Method

In the present study, a feruloyl esterase DLFae4 identified in our previous research was modified by error-prone PCR and site-directed saturation mutation to enhance the catalytic efficiency and acyltransferase activity further. Five mutants with 6.9–118.9% enhanced catalytic activity toward methyl ferulate (MFA) were characterized under the optimum conditions. Double variant DLFae4-m5 exhibited the highest hydrolytic activity (270.97 U/mg), the Km value decreased by 83.91%, and the Kcat/Km value increased by 6.08-fold toward MFA. Molecular docking indicated that a complex hydrogen bond network in DLFae4-m5 was formed, with four of five bond lengths being shortened compared with DLFae4, which might account for the increase in catalytic activity. Acyl transfer activity assay revealed that the activity of DLFae4 was as high as 1550.796 U/mg and enhanced by 375.49% (5823.172 U/mg) toward 4-nitrophenyl acetate when residue Ala-341 was mutated to glycine (A341G), and the corresponding acyl transfer efficiency was increased by 7.7 times, representing the highest acyltransferase activity to date, and demonstrating that the WGG motif was pivotal for the acyltransferase activity in family VIII carboxylesterases. Further experiments indicated that DLFae4 and variant DLFae4 (A341G) could acylate cyanidin-3-O-glucoside effectively in aqueous solution. Taken together, our study suggested the effectiveness of error-prone PCR and site-directed saturation mutation to increase the specific activity of enzymes and may facilitate the practical application of this critical feruloyl esterase.

Lingonberry (Vaccinium vitis-idaea) press-cake as a new processing aid during isolation of protein from herring (Clupea harengus) co-products

High acid-consumption and lipid oxidation are challenges when recovering functional proteins from herring co-products via pH-shift-processing. Here, lingonberry press-cake (LP), which is abundant in organic acids and phenolics, was added to alkali-solubilized herring-co-product-proteins (2.5-30 % LP per dry weight) aiming to aid protein precipitation, save hydrochloric acid (HCl) and provide oxidative stability. The results revealed 5-30 % LP addition reduced HCl-consumption by 13-61 % and 19-79 % when precipitating proteins at pH 5.5 and 6.5, respectively. Higher LP% decreased protein content and lightness of protein isolates but raised the lipid content. Precipitation at pH 6.5 used less acid, reduced total protein yield and raised moisture content and darkness of isolates. Contrary to controls, lipid oxidation-derived volatiles did not develop in protein isolates precipitated with 10 % and 30 % LP, neither during the process itself nor during 21 days on ice. Altogether, LP was identified as a promising all-natural processing-aid to use during herring protein isolation.

Anthocyanins as Promising Molecules Affecting Energy Homeostasis, Inflammation, and Gut Microbiota in Type 2 Diabetes with Special Reference to Impact of Acylation

Anthocyanins, the red-orange to blue-violet colorants present in fruits, vegetables, and tubers, have antidiabetic properties expressed via modulating energy metabolism, inflammation, and gut microbiota. Acylation of the glycosyl moieties of anthocyanins alters the physicochemical properties of anthocyanins and improves their stability. Thus, acylated anthocyanins with probiotic-like property and lower bioavailability are likely to have different biological effects from nonacylated anthocyanins on diabetes. This work highlights recent findings on the antidiabetic effects of acylated anthocyanins from the perspectives of energy metabolism, inflammation, and gut microbiota compared to the nonacylated anthocyanins and particularly emphasizes the cellular and molecular mechanisms associated with the beneficial effects of these bioactive molecules, providing a new perspective to explore the different biological effects induced by structurally different anthocyanins. Acylated anthocyanins may have greater modulating effects on energy metabolism, inflammation, and gut microbiota in type 2 diabetes compared to nonacylated anthocyanins.

Protein-binding approaches for improving bioaccessibility and bioavailability of anthocyanins

Color is an important characteristic of food. Over the last 15 years, more attention has been paid to natural colorants because of the rising demand for clean-label food products. Anthocyanins, which are a group of phytochemicals responsible for the purple, blue or red hues of many plants, offer a market advantage. In addition, anthocyanin-rich foods are associated with protection against cardiovascular disease, thrombosis, diabetes, cancer, microbial-based disorders, neurological disorders, and vision ailments. However, the real health value of anthocyanins, whether as a natural colorant or a functional ingredient, is dependent on the ultimate bioaccessibility and bioavailability in the human body. Many animal and human clinical studies revealed that, after intake of anthocyanin-rich foods or anthocyanin extracts, only trace amounts (< 1% of ingested content) of anthocyanins or their predicted metabolites were detected in plasma after a standard blood draw, which was indicative of low bioavailability of anthocyanins. Protein binding to anthocyanins is a strategy that has recently been reported to enhance the ultimate bioactivity, bioaccessibility, and bioavailability of anthocyanins as compared to anthocyanins delivered without a protein carrier. Therefore, in this review, we address anthocyanin properties in food processing and digestion, anthocyanin-protein complexes used in food matrices, and changes in the bioaccessibility and bioavailability of anthocyanins when bound into anthocyanin-protein complexes in foods. Finally, we summarize the challenges and prospects of this delivery system for anthocyanin pigments.

Optimization of Major Extraction Variables to Improve Recovery of Anthocyanins from Elderberry by Response Surface Methodology

Elderberry, which is well known for its richness in anthocyanin, is attracting attention in the bioindustry as a functional material with high antioxidant capacity. The aim of this study is to optimize extraction conditions to more effectively recover anthocyanins from elderberry. In a fundamental experiment to determine the suitable solvent, various GRAS reagents, such as acetone, ethanol, ethyl acetate, hexane, and isopropyl alcohol, were used, and total phenol and anthocyanin contents were detected as 9.0 mg/g-biomass and 5.1 mg/g-biomass, respectively, only in the extraction using ethanol. Therefore, ethanol was selected as the extraction solvent, and an experimental design was performed to derive a response surface model with temperature, time, and EtOH concentration as the main variables. The optimal conditions for maximal anthocyanin recovery were determined to be 20.0 °C, 15.0 min, and 40.9% ethanol, and the total anthocyanin content was 21.0 mg/g-biomass. In addition, the total phenol and flavonoid contents were detected as 67.4 mg/g-biomass and 43.8 mg/g-biomass, respectively. The very simple and economical extraction conditions suggested in this study contributed to improving the utilization potential of anthocyanin, a useful antioxidant derived from elderberry.

A facile and efficient synthesis approach of salidroside esters by whole-cell biocatalysts in organic solvents

Salidroside, the main bioactive compound isolated from the plant source of Rhodiola rosea L, possesses broad-spectrum pharmacological activities, but suffers from the low cell membranes permeability and alimentary absorption due to its high polarity. Therefore, a whole-cell catalytic strategy for the synthesis of salidroside esters was explored to improve its lipophilicity. The results showed that Aspergillus oryzae demonstrated the highest biocatalytic activity among the microbial strains tested. For the synthesis of salidroside caprylate, the optimum conditions of reaction medium, Aspergillus oryzae amount, molar ratio of vinyl caprylate to salidroside and reaction temperature were acetone, 30 mg/ml, 10°C and 40°C, respectively. Under these conditions, the initial reaction rate was 15.36 mM/h, and substrate conversion and regioselectivity all reached 99%. Moreover, the results indicated that although various 6'-monoesters derivatives of salidroside were exclusively obtained with excellent conversions (96%-99%), the reaction rate varied greatly with different chain-length acyl donors. This study details an efficient and cost-effective biocatalytic approach for the synthesis of salidroside esters by using Aspergillus oryzae as a catalyst for the first time. Considering the whole cell catalytic efficiency and operational stability, this strategy may provide a new opportunity to develop green industrial processes production for ester derivatives of salidroside and its analogues.

Improvement of stability and lipophilicity of pelargonidin-3-glucoside by enzymatic acylation with aliphatic dicarboxylic acid

Dicarboxylic acids derived acylated-anthocyanins are common in nature, which can also be obtained by enzymatic acylation of anthocyanins. However, little research have focused on the properties of anthocyanins with dicarboxylic acid derivatives due to the complexity of isolation, detection, and identification. In this work, pelargonidin-3-glucoside (Pg3G) was acylated with various dicarboxylic acids. The conversion yields of acylated Pg3G were positively associated with carbon chain lengths of dicarboxylic acids. The primary acylated products were identified as pelargonidin-3-(6″-malonyl) glucoside, pelargonidin-3-(6″-succinyl) glucoside, and pelargonidin-3-(6″-glutaryl) glucoside using LC-MS and NMR. Furthermore, the three acylated Pg3G derivatives exhibited improved thermostability and enhanced lipophilicity compared with Pg3G. The improved thermostability was attributed to the influence of dicarboxylic acids substituent on the distribution of flavylium cation, quinoidal base, hemiketal, cis-chalcone, and trans-chalcone at the equilibrium condition. Overall, our research provided insights about the improved stability and lipophilicity of pelargonidin-3-glucoside following enzymatic acylation with aliphatic dicarboxylic acids.

Mini-Review on the Enzymatic Lipophilization of Phenolics Present in Plant Extracts with the Special Emphasis on Anthocyanins

Different plant extracts have the potential to be important sources of phenolic compounds. Their antibacterial, antifungal and antioxidant properties are of interest to researchers due to various possibilities for use in the pharmacy, cosmetic and food industries. Unfortunately, the direct application of phenolics in food is limited because of their hydrophilic nature and low solubility. The review is devoted to the recent advances in the methods of lipophilization of phenolic extracts along with the use of enzymes. The concept of extract modification instead of single compound modification is based on the expected synergistic effect of many phenolic compounds. The main focus is on the phenolic compounds found in fruits, flowers and leaves of different common and underutilized as well as medicinal, folk-medicinal or endemic plants. The compiled papers point to the great interest in the modification of anthocyanins, highly active but often unstable phenolics. Some examples of other flavonoids are also outlined. The possible applications of the lipophilized plant extracts are presented for improving the stability of edible oils, decreasing the content of acrylamide, exhibiting higher color stability in thermal processing and increasing the nutritional value.

Antimicrobial activity of cyanidin-3-O-glucoside-lauric acid ester against Staphylococcus aureus and Escherichia coli

Enzymatic acylation of anthocyanin with fatty acid improves its lipophilic solubility and application potential. Nevertheless, evaluation of functional properties of product is premise for application. This study investigated the antimicrobial potential and the underlying mechanisms of an acylated anthocyanin, namely, cyanidin-3-O-glucoside-lauric acid ester (C3G-LA), to provide guidelines for its application. C3G-LA exhibited outstanding antibacterial activity against Staphylococcus aureus [minimum inhibitory concentration (MIC) = 0.3125 mg/mL] and modest activity against Escherichia coli (MIC = 5 mg/mL). Moreover, C3G-LA manifested bactericide ability against S. aureus at 0.625 mg/mL. Decreases in membrane integrity (by 96% and 92% at MIC in S. aureus and E. coli, respectively), intracellular ATP concentration (by 96% and 92%) and intracellular pH (by 11% and 9%) and changes in cellular morphology altogether indicated the dysfunction of cell membrane under C3G-LA treatment. These findings demonstrated that C3G-LA could be adopted as an alternative food preservative against foodborne pathogens.

Acylation of Anthocyanins and Their Applications in the Food Industry: Mechanisms and Recent Research Advances

Anthocyanins are extensively used as natural non-toxic compounds in the food industry due to their unique biological properties. However, the instability of anthocyanins greatly affects their industrial application. Studies related to acylated anthocyanins with higher stability and increased solubility in organic solvents have shown that the acylation of anthocyanins can improve the stability and fat solubility of anthocyanins. However, relevant developments in research regarding the mechanisms of acylation and applications of acylated anthocyanins are scarcely reviewed. This review aims to provide an overview of the mechanisms of acylation and the applications of acylated anthocyanins in the food industry. In the review, acylation methods, including biosynthesis, semi-biosynthesis, and chemical and enzymatic acylation, are elaborated, physicochemical properties and biological activities of acylated anthocyanins are highlighted, and their application as colourants, functionalizing agents, intelligent indicators, and novel packaging materials in the food industry are summarized. The limitations encountered in the preparation of acylated anthocyanins and future prospects, their applications are also presented. Acylated anthocyanins present potential alternatives to anthocyanins in the food industry due to their functions and advantages as compared with non-acylated analogues. It is hoped that this review will offer further information on the effective synthesis and encourage commercialization of acylated anthocyanins in the food industry.

Research progress of anthocyanin prebiotic activity: A review

BACKGROUND

Anthocyanins are a kind of flavonoids and natural water-soluble pigments, which endow fruits, vegetables, and plants with multiple colors. They are important source of new products with prebiotic activity. However, there is no systematic review documenting prebiotic activity of anthocyanins and their structural analogues. This study aims to fill this gap in literature.

PURPOSE

The objective of this review is to summarize and evaluate the prebiotic activity of anthocyanin's, and discuss the physical and molecular modification methods to improve their biological activities.

STUDY DESIGN AND METHODS

In this review, the databases (PubMed, Google Scholar, Web of Science, Researchgate and Elsevier) were searched profoundly with keywords (anthocyanin's, prebiotics, probiotics, physical embedding and molecular modification).

RESULTS

A total of 34 articles were considered for reviewing. These studies approved that anthocyanins play an important role in promoting the proliferation of probiotics, inhibiting the growth of harmful bacteria and improving the intestinal environment. In addition, physical embedding and molecular modification have also been proved to be effective methods to improve the prebiotic activity of anthocyanins. Anthocyanins could promote the production of short chain fatty acids, accelerate self degradation and improve microbial related enzyme activities to promote the proliferation of probiotics. They inhibited the growth of harmful bacteria by inhibiting the expression of harmful bacteria genes, interfering with the role of metabolism related enzymes and affecting respiratory metabolism. They promoted the formation of a complete intestinal barrier and regulated the intestinal environment to keep the body healthy. Physical embedding, including microencapsulation and colloidal embedding, greatly improved the stability of anthocyanins. On the other hand, molecular modification, especially enzymatic modification, significantly improved the biological activities (antioxidant, prebiotic activity and so on) of anthocyanins.

CONCLUSION

All these research results displayed by this review indicate that anthocyanins are a useful tool for developing prebiotic products. The better activities of the new anthocyanins formed by embedding and modification may make them become more effective raw materials. Our review provides a scientific basis for the future research and application of anthocyanins.

Berry By-Products in Combination with Antimicrobial Lactic Acid Bacteria Strains for the Sustainable Formulation of Chewing Candies

The purpose of this research was to develop formulations of chewing candies (CCs) in a sustainable manner by using berry by-products in combination with antimicrobial lactic acid bacteria (LAB) strains. To implement this aim, the optimal quantities of by-products from lyophilised raspberry (Rasp) and blackcurrant (Bcur) from the juice production industry were selected. Prior to use, Lactiplantibacillus plantarum LUHS135, Liquorilactobacillusuvarum LUHS245, Lacticaseibacillusparacasei LUHS244, and Pediococcus acidilactici LUHS29 strains were multiplied in a dairy industry by-product-milk permeate (MP). The antimicrobial activity of the selected ingredients (berry by-products and LAB) was evaluated. Two texture-forming agents were tested for the CC formulations: gelatin (Gl) and agar (Ag). In addition, sugar was replaced with xylitol. The most appropriate formulation of the developed CCs according to the product's texture, colour, total phenolic compound (TPC) content, antioxidant activity, viable LAB count during storage, overall acceptability (OA), and emotions (EMs) induced in consumers was selected. It was established that the tested LAB inhibited three pathogens out of the 11 tested, while the blackcurrant by-products inhibited all 11 tested pathogens. The highest OA was shown for the CC prepared with gelatin in addition to 5 g of Rasp and 5 g of Bcur by-products. The Rasp and LUHS135 formulation showed the highest TPC content (147.16 mg 100 g^-1 d.m.), antioxidant activity (88.2%), and LAB count after 24 days of storage (6.79 log₁₀ CFU g^-1). Finally, it was concluded that Gl, Rasp and Bcur by-products, and L. plantarum LUHS135 multiplied in MP are promising ingredients for preparing CCs in a sustainable manner; the best CC formula consisted of Gl, Rasp by-products, and LUHS135 and showed the highest OA (score 9.52) and induced the highest intensity of the EM 'happy' (0.231).

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.

Enzymatic acylation of raspberry anthocyanin: Evaluations on its stability and oxidative stress prevention

Raspberry anthocyanins were isolated and purified by XAD-7HP macroporous resin and silica gel column chromatography. Anthocyanins were then acylated with methyl salicylate as catalyzed by lipase under reduced pressure, and the conversion rate was 84.26%. LC-MS and NMR were used to identify the structure, and the stability, antioxidant capacity and protective ability of the acylated anthocyanins against oxidative damage were determined. The results showed that cyanindin-3-O-glucoside (C3G) was the primary anthocyanin in raspberry, and the binding site of acylation was on the glucoside C-6, and the product was cyanidin-3-(6-salicyloyl) glucoside (C3-6(S) G). After acylation, its stability in light, heat and oxidation environments could be significantly improved, and acylated ACN showed insignificant changes in antioxidant capacities to scavenge DPPH and ABTS free radicals, as well as oxygen free radical absorptive capacity (ORAC). And it could also effectively prevent the release of ROS caused by oxidative damage and alleviate oxidative stress damage.

Sources and relative stabilities of acylated and nonacylated anthocyanins in beverage systems

Anthocyanins are considered as the largest group of water-soluble pigments found in the vacuole of plant cells, displaying range of colors from pink, orange, red, purple and blue. They belong to flavonoids, a polyphenolic subgroup. Application of anthocyanins in food systems as natural food colourants is limited due to the lack of stability under different environmental conditions such as light, pH, heat etc. Anthocyanins esterified with one or more acid groups are referred as acylated anthocyanins. Based on the presence or absence of acyl group, anthocyanins are categorized as acylated and nonacylated anthocyanins. Acylated anthocyanins are further classified as mono, di, tri, tetra acylated anthocyanins according to the number of acyl groups present in the anthocyanin. This review classifies common anthocyanin sources into non-acylated, mono-, di-, tri- and tetra-acylated anthocyanins based on the major anthocyanins present in these sources. The relative stabilities of these anthocyanins with respect to thermal, pH and photo stress in beverage systems are specifically discussed. Common anthocyanin sources such as elderberry, blackberry, and blackcurrant mainly contain nonacylated anthocyanins. Red radish, purple corn, black carrot also mainly contain mono acylated anthocyanins. Red cabbage and purple sweet potato have both mono and diacylated anthocyanins. Poly acylated anthocyanins show relatively higher stability compared with nonacylated and monoacylated anthocyanins. Several techniques such as addition of sweeteners, co-pigmentation and acylation techniques could enhance the stability of nonacylated anthocyanins. Flowers are main sources of polyacylated anthocyanins having higher stability, yet they have not been commercially exploited for their anthocyanins.

A review on enzymatic acylation as a promising opportunity to stabilizing anthocyanins

Anthocyanins are naturally occurring bioactive compounds found mainly in fruits, vegetables, and grains. They are usually extracted due to their biological properties and great potential for technological applications. These compounds have characteristic pH-dependent colorations that are natural dyes since they come in different colors. However, they are susceptible to processing conditions, remarkably light, temperature, and oxygen. The acylated anthocyanins showed better stability characteristics, and therefore, an acylation process of these compounds could improve their applications. The enzymatic acylation was effective and showed promising results. The current review provides an overview of the works that performed enzymatic acylation of anthocyanins and studies on the stability, antioxidant activity, and lipophilicity. In general, enzymatically acylated anthocyanins showed better stability to light and temperature than non-acylated compounds. In addition, they were liposoluble, a characteristic that allows their addition to products with lipid matrices. The results showed that these compounds formed by enzymatic acylation have perspectives of application mainly as natural colorants in food products. Therefore, the enzymatic acylation of anthocyanins appears viable to increase the industrial applicability of anthocyanins. There are still some gaps to be filled in process optimization, the reuse of enzymes, and toxicity analysis of the acylated compounds formed.

A pH-intelligent response fish packaging film: Konjac glucomannan/carboxymethyl cellulose/blackcurrant anthocyanin antibacterial composite film

Blackcurrant anthocyanins (BCA) can be used to improve the structure and properties of konjac glucomannan (KGM)/carboxymethyl cellulose (CMC) composite film. In this study, the microstructure of the KGM/CMC/BCA composite film was evaluated. The results show that BCA is uniformly dispersed in the KC matrix, which changes the mechanical properties of the film (tensile strength (TS): 55.00 → 38.44 MPa and elongation at break (EB): 8.60 → 3.67%) and barrier properties (water vapor permeability (WVP): 0.67 → 2.53 g·mm/m² day kPa). With the addition of BCA (0.05, 0.15, 0.20 wt%), the composite film exhibits higher thermal stability. Among them, 0.15 wt% has the best thermal stability. The composite film also shows the antioxidant and antibacterial properties of BCA, and has an inhibitory effect on food-borne pathogens. The composite film will show different colors in different buffers, which can be observed with the naked eye. Therefore, KGM/CMC/BCA film can be applied to smart food packaging to realize real-time monitoring of meat product quality.

Spray-drying of casein/pectin bioconjugate microcapsules containing grape (Vitis labrusca) by-product extract

Novel microcapsules containing grape peel by-product extract were obtained. In this pursuit, complex coacervation of casein/pectin bioconjugate and spray-drying were combined. We have investigated the role of the dispersion feed rate (F_R), drying air inlet temperature (I_T) and drying air flow rate (A_R) in the drying yield, microencapsulation efficiency, total polyphenols and anthocyanins contents, antioxidant activity, and morphology of the products. Also, the first-order degradation kinetics of the phytochemicals for both the extract and dried microcapsules was assessed and compared. The loss on the phytochemicals during spray-drying was attenuated in up to 88%, and the I_T was the main factor affecting the particle properties. The polyphenols on the extract interacted with the polymers, influencing the assemble of the bioconjugate and the particle's features. Such microencapsulation strategy enhanced the thermal stability of the phytochemicals and rendered biocompatible and biodegradable products of which the nutraceutical and cosmeceutical application may have potential.

Acetylated pelargonidin-3-O-glucoside exhibits promising thermostability, lipophilicity, and protectivity against oxidative damage by activating Nrf2/ARE pathway

Anthocyanins are natural products displayed diverse bioactivities, but low stability and bioavailability limit their applications. Acylated anthocyanins were found to possess higher stability, while their bioactivities are still obscure. In...

Blackcurrant (Ribes nigrum L.) and Kamchatka Honeysuckle (Lonicera caerulea var. Kamtschatica) Extract Effects on Technological Properties, Sensory Quality, and Lipid Oxidation of Raw-Cooked Meat Product (Frankfurters)

Oxidation is one of the most prevalent factors responsible for meat product deterioration. Due to their potential health risks, commonly used synthetic antioxidants are beginning to be frowned upon by customers. The industry is searching for a natural replacement. In our study, we incorporated blackcurrant (Ribes nigrum L.) and Kamchatka honeysuckle (Lonicera caerulea var. Kamtschatica) extracts into raw-cooked meat products (frankfurters) as natural antioxidants. We observed that both extracts at concentrations of 3 mL·kg^-1 were able to significantly (α = 0.05) postpone lipid oxidation in our samples, with results comparable to vitamin C (0.5 mg·kg^-1) addition. Moreover, we did not observe negative effects of the extracts on the product's color, pH, or textural properties. Negative results were reported in the sensory evaluation of honeysuckle addition samples. This could have been caused by the natural strong and bitter taste of honeysuckle, which was transferred to the extracts and, subsequently, into the meat product.

Ultrahigh Pressure Facilitates the Acylation of Malvidin and Chlorogenic Acid to Increase the Stability and Protective Effect of Malvidin Derivatives on H2O2-Induced ARPE-19 Cells

We explored the effects of ultrahigh-pressure technology and chlorogenic acid on the color stability and structure-activity relationship of malvidin (MV). Experimental conditions were optimized through single-factor experiments and response surface analysis at a pressure of 300 MPa, mass ratio of MV to chlorogenic acid of 1:3.64 (w/w), and time of 5 min. Compared with MV, MV derivatives showed higher stability and in vitro antioxidant activity. X-ray diffraction analysis, UV-vis spectroscopy, Fourier transform infrared spectroscopy, high-performance liquid chromatography, and mass spectrometry were conducted to determine the structures of MV derivatives for the first time. Ultrahigh pressure facilitated acylation of chlorogenic acid and MV and produced four new MV derivatives. Analysis of the effect of malvidin-3-O-6-(acrylic acid-(2-hydroxy, 4-carboxy-cyclohexanol) ester)-guaiacol (Mv3ACEC) on ARPE-19 cells exposed to H₂O₂ by RNA transcriptome sequencing showed that Mv3ACEC simultaneously inhibited various inflammatory and apoptotic signal transduction pathways, exerted a synergistic effect, and partly inhibited cell apoptosis through the MAPK signaling pathway. Therefore, the results show that ultrahigh pressure will cause acylation of chlorogenic acid and MV to produce four new MV derivatives, and MV derivatives protect ARPE-19 cells from H₂O₂-induced oxidative stress.

Acylated anthocyanins: A review on their bioavailability and effects on postprandial carbohydrate metabolism and inflammation

Anthocyanins, the natural red and purple colorants of berries, fruits, vegetables, and tubers, improve carbohydrate metabolism and decrease the risk factors of metabolic disorders, but their industrial use is limited by their chemical instability. Acylation of the glycosyl moieties of anthocyanins, however, changes the chemical properties of anthocyanins and provides enhanced stability. Thus, acylated anthocyanins are more usable as natural colorants and bioactive components of innovative functional foods. Acylated anthocyanins are common in pigmented vegetables and tubers, the consumption of which has the potential to increase the intake of health-promoting anthocyanins as part of the daily diet. For the first time, this review presents the current findings on bioavailability, absorption, metabolism, and health effects of acylated anthocyanins with comparison to more extensively investigated nonacylated anthocyanins. The structural differences between nonacylated and acylated anthocyanins lead to enhanced color stability, altered absorption, bioavailability, in vivo stability, and colonic degradation. The impact of phenolic metabolites and their potential health effects regardless of the low bioavailability of the parent anthocyanins as such is discussed. Here, purple-fleshed potatoes are presented as a globally available, eco-friendly model food rich in acylated anthocyanins, which further highlights the industrial possibilities and nutritional relevance of acylated anthocyanins. This work supports the academic community and industry in food research and development by reviewing the current literature and highlighting gaps of knowledge.

Identification and Characterization of a Novel Carboxylesterase Belonging to Family VIII with Promiscuous Acyltransferase Activity Toward Cyanidin-3-O-Glucoside from a Soil Metagenomic Library

An alkaline esterase, designated as EstXT1, was identified through functional screening from a metagenomic library. Sequence analysis revealed that EstXT1 belonged to the family VIII carboxylesterases and contained a characteristic conserved S-x-x-K motif and a deduced catalytic triad Ser56-Lys59-Tyr165. EstXT1 exhibited the strongest activity toward methyl ferulate at pH 8.0 and temperature 55°C and retained over 80% of its original activity after incubation in the pH range of 7.0-10.6 buffers. Biochemical characterization of the recombinant enzyme showed that it was activated by Zn²⁺ and Co²⁺ metal ion, while inhibited by Cu²⁺ and CTAB. EstXT1 exhibited significant promiscuous acyltransferase activity preferred to the acylation of benzyl alcohol acceptor using short-chain pNP-esters (C2-C8) as acyl-donors. A structure-function analysis indicated that a WAG motif is essential to acyltransferase activity. This is the first report example that WAG motif plays a pivotal role in acyltransferase activity in family VIII carboxylesterases beside WGG motif. Further experiment indicated that EstXT1 successfully acylated cyanidin-3-O-glucoside in aqueous solution. The results from the current investigation provided new insights for the family VIII carboxylesterase and lay a foundation for the potential applications of EstXT1 in food and biotechnology fields.

Malvidin and its derivatives exhibit antioxidant properties by inhibiting MAPK signaling pathways to reduce endoplasmic reticulum stress in ARPE-19 cells

Malvidin (MV) and its derivatives, such as malvidin-3-O-guaiacol (Mv3C) and malvidin-3-O-6-(acrylic acid-(2-hydroxy,4-carboxy-cyclohexanol)ester)-guaiacol (Mv3ACEC), are natural compounds with antioxidant properties. However, the basic mechanisms underlying their functional activities are unclear. In this study, we show that MV, Mv3C, and Mv3ACEC inhibit reactive oxygen species production and malondialdehyde content, promote glutathione peroxidase activity, and increase superoxide dismutase levels in ARPE-19 cells treated with H₂O₂. Western blotting and immunofluorescence analysis revealed that MV, Mv3C, and Mv3ACEC regulate mitogen-activated protein kinase signal transduction pathways related to endoplasmic reticulum stress. Interestingly, Mv3C and Mv3ACEC showed greater beneficial properties than MV. Our results show that MV and its derivatives have potential as therapeutic compounds for ocular diseases associated with oxidative stress, such as age-related macular degeneration.

Antioxidant activities of chlorogenic acid derivatives with different acyl donor chain lengths and their stabilities during in vitro simulated gastrointestinal digestion

In this study, chlorogenic acid (CA) was acylated with vinyl esters of different carbon chain lengths under the action of the lipase Lipozyme RM. Five CA derivatives (C2-CA, C4-CA, C6-CA, C8-CA, and C12-CA) with different lipophilicities were obtained, and their digestive stabilities and antioxidant activities were evaluated. The lipophilicities were positively correlated with the digestive stabilities of CA derivatives. The antioxidant activities of CA derivatives did not change with the reduction of phenolic hydroxyl groups, and their capacity to scavenge 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+•) and 1,1-diphenyl-2-picrylhydrazyl (DPPH•) were similar to those of CA. In cellular antioxidant activity (CAA) tests, it was found that the capacity of these derivates to cross cell membranes were enhanced upon enhancing lipophilicity, and their antioxidant activities were improved. C12-CA showed the best antioxidant activity with a median effective dose (EC50) of 9.40 μg/mL, which was significantly lower than that of CA (i.e., 29.08 μg/mL).

Enzymatic acylation of rutin with benzoic acid ester and lipophilic, antiradical, and antiproliferative properties of the acylated derivatives

Rutin (3',4',5,7-tetrahydroxy-flavone-3-rutinoside) was enzymatically acylated with benzoic acid and its esters (methyl benzoate and vinyl benzoate) using Thermomyces lanuginosus lipase (Lipozyme TLIM). The acylation reaction was optimized by varying the reaction medium, reaction temperature, acyl donor, substrate molar ratio, and reaction time. The highest conversion yield (76%) was obtained in tert-amyl alcohol (60 °C, 72 hr) using vinyl benzoate (molar ratio of 1:10) as acyl donor. The acylation occurred at the 2'''-OH and 4'''-OH of the rhamnose unit and the 2''-OH position of the glucose moieties. Three novel rutin acylated derivatives (compounds 1-3) were purified and characterized by HR-MS and 1D and 2D NMR spectroscopy. We found that acylation significantly improved lipophilicity, capacity to inhibit lipid peroxidation, anticancer capacity and substantially maintained the antioxidant activity of rutin. This research provides important insights in the acylation of flavonoids with different glycosyl moieties. PRACTICAL APPLICATION: In this study, three novel rutin derivatives were successfully synthesized and the highest conversion yield (76%) was obtained by reacting the rutin and vinyl benzoate at molar ratio of 1:10 in tert-amyl alcohol for 72 hr at 60 °C. Introducing a benzoic acid substituent into rutin molecule significantly improved their lipophilicity and inhibition of lipid peroxidation in lipophilic system. Furthermore, this study demonstrated that acylation significantly improved anticancer capacity and substantially maintained the antioxidant activity.