Enzymatic Acylation of Anthocyanins Isolated from Alpine Bearberry ( Arctostaphylos alpina) and Lipophilic Properties, Thermostability, and Antioxidant Capacity of the Derivatives

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.

Covalent Interactions of Anthocyanins with Proteins: Activity-Based Protein Profiling of Cyanidin-3-O-glucoside

Anthocyanins are common natural pigments with a variety of physiological activities. Traditional perspectives attribute their molecular mechanism to noncovalent interactions influencing signaling pathways. However, this ignores the nature of its benzopyrylium skeleton, which readily reacts with the electron-rich groups of proteins. Here, we modified cyanidin-3-O-glucoside (C3G) via activity-based protein profiling technology by our previous synthesis route and prepared the covalent binding probe (C3G-Probe) and the noncovalent photoaffinity probe (C3G-Diazirine). The properties of C3G's covalent binding to proteins were also discovered by comparing the labeling of the two probes to the whole HepG2 cell proteome. We further explored its target proteins and enriched pathways in HepG2 and HeLa cells. Western blot analysis further confirmed the covalent binding of C3G to four target proteins: insulin-degrading enzyme, metal cation symporter ZIP14, spermatid perinuclear RNA-binding protein, and Cystatin-B. Pathway analysis showed that covalent targets of C3G were concentrated in metabolic pathways and several ribonucleoprotein complexes that were also coenriched. The results of this study provide new insights into the interaction of the naturally active molecule C3G with proteins.

Recent insight into the advances and prospects of microbial lipases and their potential applications in industry

Enzymes play a crucial role in various industrial sectors. These biocatalysts not only ensure sustainability and safety but also enhance process efficiency through their unique specificity. Lipases possess versatility as biocatalysts and find utilization in diverse bioconversion reactions. Presently, microbial lipases are gaining significant focus owing to the rapid progress in enzyme technology and their widespread implementation in multiple industrial procedures. This updated review presents new knowledge about various origins of microbial lipases, such as fungi, bacteria, and yeast. It highlights both the traditional and modern purification methods, including precipitation and chromatographic separation, the immunopurification technique, the reversed micellar system, the aqueous two-phase system (ATPS), and aqueous two-phase flotation (ATPF), moreover, delves into the diverse applications of microbial lipases across several industries, such as food, vitamin esters, textile, detergent, biodiesel, and bioremediation. Furthermore, the present research unveils the obstacles encountered in employing lipase, the patterns observed in lipase engineering, and the application of CRISPR/Cas genome editing technology for altering the genes responsible for lipase production. Additionally, the immobilization of microorganisms' lipases onto various carriers also contributes to enhancing the effectiveness and efficiencies of lipases in terms of their catalytic activities. This is achieved by boosting their resilience to heat and ionic conditions (such as inorganic solvents, high-level pH, and temperature). The process also facilitates the ease of recycling them and enables a more concentrated deposition of the enzyme onto the supporting material. Consequently, these characteristics have demonstrated their suitability for application as biocatalysts in diverse industries.

Enhanced Enzymatic Synthesis of Puerarin Palmitate with Different Acyl Donors for Lipid Solubility Improvement

Puerarin is a flavonoid known as a natural antioxidant found in the root of Pueraria robata. Its antioxidant, anticancer, and anti-inflammatory effects have attracted attention as a potential functional ingredient in various bioindustries. However, puerarin has limited bioavailability owing to its low lipid solubility and stability. Acylation is proposed as a synthesis method to overcome this limitation. In this study, lipase-catalyzed acylation of puerarin and various acyl donors was performed, and the enzymatic synthetic condition was optimized. Under the condition (20 g/L of Novozym 435, palmitic anhydride, 1:15, 40 °C, tetrahydrofuran (THF)), the synthesis of puerarin ester achieved a significantly high conversion (98.97%) within a short time (3 h). The molecule of the synthesized puerarin palmitate was identified by various analyses such as liquid chromatography-mass spectrometry (LC-MS), Fourier-transform infrared spectroscopy (FT-IR), and carbon-13 nuclear magnetic resonance (13C NMR). The lipid solubility and the radical scavenging activity were also evaluated. Puerarin palmitate showed a slight decrease in antioxidant activity, but lipid solubility was significantly improved, improving bioavailability. The high conversion achieved for puerarin esters in this study will provide the foundation for industrial applications.

Bio-based active packaging: Gallic acid modified agarose coatings in grass carp (Ctenopharyngodon idellus) preservation

Antioxidant and antimicrobial agarose coatings were developed by grafting gallic acid through the carbodiimide coupling method. Structural characterization revealed that the carboxyl group of gallic acid was successfully grafted onto the C6-OH of D-galactose in agarose, with the highest observed grafting ratio being 13.73 %. The grafting of gallic acid significantly increased the antioxidant and bacteriostatic activities of the agarose. As the grafting ratio of gallic acid-modified agarose (GaAg) increased from 0 to 13.73 %, the scavenging ratio of DPPH and the inhibition ratio of β-carotene bleaching were observed to increase from 0 % to 65.92 % and 6.89 % to 73.46 %, respectively. GaAg exhibited up to 100 % inhibition of Escherichia coli and Staphylococcus aureus. The physicochemical properties of gel strength, viscosity, gelling temperature and melting temperature decreased to 971.3 g/cm2, 17.9 mPa·s, 31.7 °C and 84.1 °C, respectively. The gel contact angle was increased from 22.1° to 73.6°. Fish preservation tests have demonstrated that it effectively inhibited bacterial growth, prevented fat oxidation, blocked light, reduced moisture loss, and enhanced the overall quality of grass carp (Ctenopharyngodon idellus) fillets during refrigeration, which was more effective than native agarose in extending the shelf life of fish. Therefore, GaAg holds promise as an aquatic product preservative.

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.

Computer-Aided Lipase Engineering for Improving Their Stability and Activity in the Food Industry: State of the Art

As some of the most widely used biocatalysts, lipases have exhibited extreme advantages in many processes, such as esterification, amidation, and transesterification reactions, which causes them to be widely used in food industrial production. However, natural lipases have drawbacks in terms of organic solvent resistance, thermostability, selectivity, etc., which limits some of their applications in the field of foods. In this systematic review, the application of lipases in various food processes was summarized. Moreover, the general structure of lipases is discussed in-depth, and the engineering strategies that can be used in lipase engineering are also summarized. The protocols of some classical methods are compared and discussed, which can provide some information about how to choose methods of lipase engineering. Thermostability engineering and solvent tolerance engineering are highlighted in this review, and the basic principles for improving thermostability and solvent tolerance are summarized. In the future, comput er-aided technology should be more emphasized in the investigation of the mechanisms of reactions catalyzed by lipases and guide the engineering of lipases. The engineering of lipase tunnels to improve the diffusion of substrates is also a promising prospect for further enhanced lipase activity and selectivity.

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.

Green-Efficient Enzymatic Synthesis and Characterization of Liposoluble 6'/6″-O-Lauryl Phenolic Glycosides with Enhanced Intestinal Permeability

Arbutin, salidroside, polydatin, and phlorizin are typically natural bioactive phenolic glycosides. To improve the liposolubility and bioavailability, highly liposoluble derivatives including 6'-O-lauryl arbutin, 6'-O-lauryl salidroside, 6″-O-lauryl polydatin, and 6″-O-lauryl phlorizin were efficiently synthesized by enzymatic acylation in a green solvent 2-MeTHF. Their reaction conversions reached 84.4, 99.5, 99.8, and 89.1%, respectively, when catalyzed by Lipozyme 435 at 20 mg/mL at 50 °C. As expected, the derivatives had high log P (1.66-2.37) and retained good antioxidant activity, making them potential alternatives to butylated hydroxytoluene (BHT) and tert-butyl-hydroquinone (TBHQ) in lipid systems. Then, the intestinal permeability characteristics and metabolism of phenolic glycosides and their derivatives were investigated based on Caco-2 monolayers. The permeability of polydatin and phlorizin was mainly through active transport, but that of arbutin and salidroside involved both passive diffusion and active uptake. The acylated derivatives suffered from severe CES-mediated hydrolysis but exhibited a larger transported amount than phenolic glycosides.

The chromogenic mechanism of natural pigments and the methods and techniques to improve their stability: A systematic review

Pigments have become a very important part of food research, not only adding sensory properties to food, but also providing functional properties to the food system. In this paper, we review the source, structure, modification, encapsulation and current status of the three main types of natural pigments that have been studied in recent years: polyphenolic flavonoids, tetraterpenoids and betaines. By examining the modification of pigment, the improvement of their stability and the impact of new food processing methods on the pigments, a deeper understanding of the properties and applications of the three pigments is gained, the paper reviews the research status of pigments in order to promote their further research and provide new innovations and ideas for future research in this field.

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.

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.

Structural Features of Small Molecule Antioxidants and Strategic Modifications to Improve Potential Bioactivity

This review surveys the major structural features in various groups of small molecules that are considered to be antioxidants, including natural and synthetic compounds alike. Recent advances in the strategic modification of known small molecule antioxidants are also described. The highlight is placed on changing major physicochemical parameters, including log p, bond dissociation energy, ionization potential, and others which result in improved antioxidant activity.

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.

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.

Blueberry Anthocyanins from Commercial Products: Structure Identification and Potential for Diabetic Retinopathy Amelioration

The aim of the present study was to determine the major anthocyanins of blueberry extracts from northeast China and explore their vision health improvement effects. HPLC-Q-TOF-MS/MS results suggested that six different anthocyanins were accurately identified, among which the Cy-3-glu (C3G) was the most abundant, ranging from 376.91 ± 7.91 to 763.70 ± 4.99 μM. The blueberry extract contained a higher purity of anthocyanins, and the anthocyanosides reached 342.98 mg/kg. The anti-oxidative stress function of C3G on HG-treated ARPE-19 cells were evaluated, and showed that the GSSG level of HG-cells pretreated with 10 μM C3G was significantly decreased, while the Nrf2 and NQO1 gene expression levels were increased. Further molecular docking (MD) results indicated that the C3G displayed favorable binding affinity towards REDD1, and only the B-ring of the C3G molecule displayed binding interactions with the CYS-140 amino acids within the REDD1 protein. It implied that the oxidative stress amelioration effects of C3G on the ARPE-19 cells were related to the REDD1 protein, which was probably via the Nrf2 pathways, although further studies are needed to provide mechanism evidence. The present study provides novel insights into understanding the roles of blueberry anthocyanins in ameliorating oxidative stress-induced BRB damage in the retina.

Functionalization of 7-Hydroxy-pyranoflavylium: Synthesis of New Dyes with Extended Chromatic Stability

This work reports the functionalization of pyranoflavyliums pigment using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride coupling chemistry. Four cinnamic acids were used to establish an ester bond with the hydroxyl group of the pyranoflavylium, namely 4-dimethylamino-, 4-amino-, 4-bromo-, and trans-cinnamic acids. The experimental condition, namely the molar ratios, solvent, and reaction time, were adjusted to obtain higher reaction yields in a reduced period. Excellent reaction yields of 68%, 85%, 94%, and 99% were achieved for 4-amino, trans-, 4-bromo, and 4-dimethylamino pyranoflavylium cinnamates, respectively. The structure of the functionalized pigments was fully clarified using one-dimensional (1H) and two-dimensional (COSY, HSQC, and HMBC) NMR experiments and HRSM analysis. Regardless of the type of functionalization, the UV-Visible spectrum showed a bathochromic shift (red region) on the maximum absorption wavelength and the absence of acid-base reactions throughout a broad pH range in comparison to the pyranoflavylium precursor. This work offers a valuable environmentally friendly, quick, and straightforward alternative to flavylium compounds' challenging and labor-intensive functionalization, resulting in novel dyes with higher stability and dissimilar chromatic features.

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.

Recent Advances in Lipases and Their Applications in the Food and Nutraceutical Industry

Lipases are efficient enzymes with promising applications in the nutraceutical and food industry, as they can offer high yields, pure products under achievable reaction conditions, and are an environmentally friendly option. This review addresses the production of high-value-added compounds such as fatty acid esters, with the potential to be used as flavoring agents or antioxidant and antimicrobial agents, as well as structured lipids that offer specific functional properties that do not exist in nature, with important applications in different food products, and pharmaceuticals. In addition, the most recent successful cases of reactions with lipases to produce modified compounds for food and nutraceuticals are reported.

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.

Modification of flavonoids: methods and influences on biological activities

Flavonoids are important active ingredients in plant-based food, which have many beneficial effects on health. But the low solubility, poor oral bioavailability, and inferior stability of many flavonoids may limit their applications in the food, cosmetics, and pharmaceutical industries. Structural modification can overcome these shortcomings to improve and extend the application of flavonoids. The study of how to modify flavonoids and the influence of various modifications on biological activity have drawn great interest in the current literature. In this review, the working principles and operating conditions of modification methods were summarized along with their potential and limitations in terms of operational safety, cost, and productivity. The influence of various modifications on biological activities and the structure-activity relationships of flavonoids derivatives were discussed and highlighted, which may give guidance for the synthesis of highly effective active agents. In addition, the safety of flavonoids derivatives is reviewed, and future research directions of flavonoid modification research are discussed.

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.

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.

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...

Recent advances in the enzymatic synthesis of lipophilic antioxidant and antimicrobial compounds

Due to the increase in the consumption of highly processed food in developed countries, as well as, a growing number of foodborne diseases, exploration of new food additives is an issue focusing on scientific attention and industrial interest. Functional compounds with lipophilic properties are remarkably desirable due to the high susceptibility to the deterioration of lipid-rich food products. This paper in a comprehensive manner provides the current knowledge about the enzymatic synthesis of lipophilic components that could act as multifunctional food additives. The main goal of enzymatic lipophilization of compounds intentionally added to food is to make these substances soluble in lipids and/or to obtain environmentally friendly surfactants. Moreover, lipase-catalyzed syntheses could result in changes in the antioxidant and antimicrobial activities of phenolic compounds, carbohydrates, amino acids (oligopeptides), and carboxylic acids. The review describes also the implementation of a new trend in green chemistry, where apart from simple and uncomplicated chemical compounds, the modifications of multi-compound mixtures, such as phenolic extracts or essential oils have been carried out.

Natural and Synthetic Flavylium-Based Dyes: The Chemistry Behind the Color

Flavylium compounds are a well-known family of pigments because they are prevalent in the plant kingdom, contributing to colors over a wide range from shades of yellow-red to blue in fruits, flowers, leaves, and other plant parts. Flavylium compounds include a large variety of natural compound classes, namely, anthocyanins, 3-deoxyanthocyanidins, auronidins, and their respective aglycones as well as anthocyanin-derived pigments (e.g., pyranoanthocyanins, anthocyanin-flavan-3-ol dimers). During the past few decades, there has been increasing interest among chemists in synthesizing different flavylium compounds that mimic natural structures but with different substitution patterns that present a variety of spectroscopic characteristics in view of their applications in different industrial fields. This Review provides an overview of the chemistry of flavylium-based compounds, in particular, the synthetic and enzymatic approaches and mechanisms reported in the literature for obtaining different classes of pigments, their physical-chemical properties in relation to their pH-dependent equilibria network, and their chemical and enzymatic degradation. The development of flavylium-based systems is also described throughout this Review for emergent applications to explore some of the physical-chemical properties of the multistate of species generated by these compounds.

Enzymatic acylation of lutein with a series of saturated fatty acid vinyl esters and the thermal stability and anti-lipid oxidation properties of the acylated derivatives

Lutein was enzymatically acylated with saturated fatty acid vinyl esters of different lengths of carbon chain (C₆ -C₁₄ ) under the action of Candida antarctica lipase B (Novozyme 435). The acylation reaction was optimized by considering substrate molar ratio, reaction solvent, type of enzyme, and reaction time. The highest yield (88%) was obtained using the Novozyme 435 to catalyze the acylation reaction of lutein and vinyl decanoate (lutein/vinyl decanoate molar ratio of 1/10) for 16 h in methyl tert-butyl ether. Ten lutein esters were synthesized, isolated, and purified, which were characterized by Fourier-transform infrared spectroscopy, high-resolution mass spectrometry, and nuclear magnetic resonance spectroscopy. We found that the acylation of lutein improved its antioxidant capacity in lipid system and thermal stability. Our study extended the potential application of lutein in lipophilic food, cosmetic, and pharmaceutical industries. Practical Application: Enzyme acylation of lutein improved its antioxidant capacity in lipid system and thermal stability, extended its potential application in food, cosmetic, and pharmaceutical industries. In addition, our study also provided a new perspective and cognition for the further development and utilization of lutein.

Efficient Enzymatic Synthesis of Lipophilic Phenolic Glycoside Azelaic Acid Esters and Their Depigmenting Activity

In this paper, an enzymatic route for synthesizing phenolic glycoside azelaic acid esters was successfully set up via lipase-catalyzed esterification and transesterification. Among the lipases tested, Candida antarctica lipase B (Novozyme 435) showed the highest activity in catalyzing esterification and Thermomyces lanuginosus (Lipozyme TLIM) gave the highest substrate conversion in catalyzing transesterification for the synthesis of ester. The addition of 4A molecular sieves into the reaction system is found to be an effective method for in situ absorption of the byproduct water and methanol, with which the substrate conversions of the enzymatic esterification and transesterification were 98.7 and 95.1%, respectively. Also, the main product ratios in transesterification were above 99.0% with lipozyme TLIM as a catalyst because the hydrolysis reaction was hindered. The results of the physical and biological properties indicate that all esters had higher Clog p values than their parent compounds. Also, the esters showed higher intracellular tyrosinase inhibitory and depigmentating activities than phenolic glycosides, azelaic acid (AA), and their physical mixtures due to their higher membrane penetration and tyrosinase inhibitory effects. In particular, piceid 6″-O-azelaic acid ester (PIA) showed the strongest inhibitory effect against melanin production. Its inhibitory rate was 77.4% at a concentration of 0.25 mM, about 4.2 times higher than that of arbutin (18.5%).

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.

A comprehensive review on innovative and advanced stabilization approaches of anthocyanin by modifying structure and controlling environmental factors

Anthocyanins are pigments abundant in fruits and vegetables, and commonly applied in foods due to attractive colour and health-promoting benefits. However, instability of anthocyanins leads to their easy degradation, reduced bioactivity, and colour fading in food processing, limiting their application and causing economic losses. Stability of anthocyanins depends on their own structures and environmental factors. For structural factors, modification including copigmentation, acylation and biosynthesis is a potential solution to increase anthocyanin stability due to forming stable structures. With regard to environmental factors, encapsulation such as microencapsulation, liposome and nanoparticles has been shown effectively to enhance the stability. We proposed the potential challenges and perspectives for the diversification of anthocyanin-rich products for food application, particularly, introduction of hazards, technical limitations, interaction with other ingredients in food system and exploration of pyranoanthocyanins. The integrated strategies are warranted for improving anthocyanin stabilization for promoting their further application in food industry.

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.

Fatty Acid Stable Carbon Isotope Ratios Combined with Oxidation Kinetics for Characterization and Authentication of Walnut Oils

Walnut oil is vulnerable to oxidation due to its high content of polyunsaturated fatty acids and adulteration due to its high price. This study investigated 12 typical walnut oils from six main walnut-producing areas in China, using differential scanning calorimetry (DSC), Rancimat test, gas chromatography (GC), elemental analyzer-isotope ratio mass spectrometry (EA-IRMS) and GC-IRMS combined with oxidation kinetic analysis, Pearson correlation analysis, and principal component analysis (PCA). The melting and crystallization profiles using DSC indicated that walnut oils with a relatively high crystal onset temperature tended to be more stable against oxidation. Oleic acid was found to be the most characteristic fatty acid in walnut oil, with a content ranging from 13.84 to 35.08%. Two walnut oils with the highest oleic acid contents of 35.08 and 32.78% had the highest activation energies in nonisothermal DSC. Their predicted shelf lives based on the Rancimat test were 3.5-4.0 times longer than that of the oil with the highest α-linolenic acid at 4 °C and 3.1-3.5 times longer at 25 °C. The δ¹³C values of walnut oils were determined by EA-IRMS, and the δ¹³C values of fatty acids were determined by GC-IRMS. Fatty acid stable carbon isotope ratios combined with PCA were successfully applied to intuitively discriminate different walnut oils. The results suggested that fatty acid δ¹³C values determined by IRMS combined with chemometrics and lipid compositions are promising as a powerful means of vegetable oil authentication and discrimination.

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.

Efficient Concentration of Functional Polyphenols Using Their Interaction with Gelatin

Among polyphenol compounds, the flavan-3-ol structure, which is the basic unit of green tea catechins and the galloyl groups contained in green tea catechins are known to exhibit various functions. In this paper, we discuss how to concentrate highly functional polyphenol compounds by exploiting the interaction between gelatin and the catechol structures. First, we confirmed the interaction between heat-stabilized gelatin and flavan-3-ol derivatives, including synthesized compounds. When green tea leaf extract containing a large amount of flavan-3-ol derivatives was incubated with gelatin, most of the polyphenol compounds it contained were adsorbed. Because the compounds adsorbed on gelatin could not be eluted, DPPH radical and ABTS radical scavenging activity tests were conducted using the as-prepared gelatin-polyphenol complex. Radical scavenging activity was observed when the compounds were adsorbed on gelatin and heating at 90 °C for 5 min did not have a significant effect on their activity. These results suggest that functional polyphenols can be efficiently concentrated using heat-stabilized gelatin and retain their functionality while adsorbed.

Cyanidin-3-glucoside Lipophilic Conjugates for Topical Application: Tuning the Antimicrobial Activities with Fatty Acid Chain Length

Background: Natural anthocyanins present a low solubility in lipophilic media, which compromises their effective application in lipophilic systems. In this work, cyanidin-3-O-glucoside (Cy3glc) was esterified by the addition of fatty acids with increasing chain-lengths and a structure-activity relationship was performed towards the description of the best analog for skin-care applications. Methods: By enzymatic hemi-synthesis, it was possible to obtain 5 structurally related derivatives of cyanidin-3-O-glucoside with successive C2 increments in the aliphatic chain. The stability in hanks buffer and DMEM with or without FBS was followed by HPLC. The cytotoxicity against keratinocytes was evaluated by MTT assay. The antioxidant capacity was determined by using the fluorescent probe DCF-DA. The effect on enzyme activity was evaluated towards tyrosinase, collagenase, and elastase enzymes by colorimetric assays. MIC and MBC values were obtained against reference strains and against multidrug-resistant isolates. Results: In physiological conditions, cy3glc−fatty acid derivatives are more stable and may be converted to the native anthocyanin. The 5 conjugates showed lower antioxidant capacity and enzymatic inhibitory activities in comparison to the anthocyanin precursor. However, concerning the antibacterial activity, the insertion of a fatty acid chain sprouted the antibacterial activity, showing a clear biphasic effect and a more effective effect on Gram-positive bacteria. Conclusions: Cy3glc-C10 was the most effective compound considering the antimicrobial activity, although a general reduction was observed among the other activities evaluated. This work prompt further assays with a different panoply of derivatives ranging other features including saturation vs. unsaturation, even vs. odd carbon content and linear vs. branched.

Red beet (Beta vulgaris) betalains and grape (Vitis vinifera) anthocyanins as colorants in white currant juice - Effect of storage on degradation kinetics, color stability and sensory properties

Red beet betalains, grape anthocyanins, and their mixtures were used as colorants in white currant juice. Storage stability of the compounds was evaluated using liquid chromatography and the degradation kinetic order and parameters were calculated. Degradation of betalains followed first-order kinetics, while the degradation of anthocyanins did not have any trend toward any order kinetics. The coexisting anthocyanins and their concentration affected the rate constant of betalains. Betalains degraded faster than anthocyanins, their mixtures promoted respective degradation. Pyruvate derivatives of anthocyanins showed better stability. During storage, all samples became more yellowish with CIELab method and lighter in color. In the projective mapping sensory test, samples were distinguished by the colorant type as the main criteria and the storage time as the second criteria. Anthocyanin (described as 'dark' and 'natural') was preferred by sensory panelists over betalain (described as 'pink' and 'unnatural'), as were the fresh samples over stored samples.

Investigation of acute, subacute and subchronic toxicities of anthocyanin derived acylation reaction products and evaluation of their antioxidant activities in vitro

Previously, anthocyanins were successfully acylated with lauric acid using Novozym 435 lipase, and the corresponding products were confirmed to have higher stability. As novel synthetic compounds, their toxicological safety has not been evaluated. Therefore, acute, subacute and subchronic toxicities of anthocyanin-lauric acid derivatives (ALDs) were investigated while their antioxidant activities were also evaluated in vitro. The acute toxicity results showed that the 50% lethal dose (LD₅₀) of ALDs in mice was >10 g kg^-1. Subsequently, the subacute toxicity test was conducted by oral administration of ALDs at doses of 0.63, 1.25 and 2.50 g kg^-1 for 28 days. No adverse effect of ALDs on body weight, food/water intake, organ coefficient and histology was observed. Though there were some fluctuations in AST and ALT, the tested biochemical parameters were maintained within the normal ranges. The subchronic toxicity test results demonstrated that less than 0.60 g of ALDs per kg BW intake did not affect mortality, body weight, food/water intake, gross pathology, histology, hematology and serum biochemistry. Furthermore, cyanidin-3-(6''-dodecanoyl)-glucoside, the main component of ALDs, had a beneficial reducing power and a strong DPPH˙, ABTS⁺˙, and O^2-˙ scavenging activity. This study provides an imperative reference to the safety of ALDs, suggesting their application as novel colorants or antioxidants in food and therapeutics.