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.

This study explored how high hydrostatic pressure (HHP) and proteins (i.e., BSA and HSA) influence the color and chemical stability of cyanidin-3-O-glucoside (C3G) at neutral pH. HHP treatments (100-500 MPa, 0-20 min, 25 °C) did not affect C3G content in phosphate buffer (PB) and MOPS buffer. However, significant color loss of C3G occurred in PB due to pressure-induced pH reduction (e.g., from 7 to 4.8 at 500 MPa), which accelerated the hydration of C3G, converting it from colored to colorless species. Consequently, MOPS buffer was employed for subsequent stability experiments to assess the impact of protein and HHP on the thermal, storage, and UV light stability of C3G. Initially, rapid color loss occurred during heating and storage, primarily due to the reversible hydration of C3G until equilibrium with colorless species was reached, followed by slower parallel degradation. HSA increased the fraction of colored species at equilibrium but accelerated thermal degradation, while BSA had minimal effects. UV light irradiation accelerated the degradation of C3G colored species, causing direct degradation without conversion to colorless species, a process further intensified by the presence of proteins. HHP exhibited a negligible effect on C3G stability regardless of protein addition. These findings provide insights into anthocyanin stability under HHP and protein interactions, contributing to the development of future formulation and processing strategies for improved stability and broader applications.

Blotches in floral organs attract pollinators and promote pollination success. Tree peony (Paeonia suffruticosa Andr.) is an internationally renowned cut flower with extremely high ornamental and economic value. Blotch formation on P. suffruticosa petals is predominantly attributed to anthocyanin accumulation. However, the endogenous regulation of blotch formation in P. suffruticosa remains elusive. Here, we identified the regulatory modules governing anthocyanin-mediated blotch formation in P. suffruticosa petals, which involves the transcription factors PsMYB308, PsMYBPA2, and PsMYB21. PsMYBPA2 activated PsF3H expression to provide sufficient precursor substrate for anthocyanin biosynthesis. PsMYB21 activated both PsF3H and PsFLS expression and promoted flavonol biosynthesis. The significantly high expression of PsMYB21 in non-blotch regions inhibited blotch formation by competing for anthocyanin biosynthesis substrates, while conversely, its low expression in the blotch region promoted blotch formation. PsMYB308 inhibited PsDFR and PsMYBPA2 expression to directly prevent anthocyanin-mediated blotch formation. Notably, a smaller blotch area, decreased anthocyanin content, and inhibition of anthocyanin structural gene expression were observed in PsMYBPA2-silenced petals, while the opposite phenotypes were observed in PsMYB308-silenced and PsMYB21-silenced petals. Additionally, PsMYBPA2 and PsMYB308 interacted with PsbHLH1-3, and their regulatory intensity on target genes was synergistically regulated by the PsMYBPA2-PsbHLH1-3 and PsMYB308-PsbHLH1-3 complexes. PsMYB308 also competitively bound to PsbHLH1-3 with PsMYBPA2 to fine-tune the regulatory network to prevent overaccumulation of anthocyanin in blotch regions. Overall, our study uncovers a complex R2R3-MYB transcriptional regulatory network that governs anthocyanin-mediated blotch formation in P. suffruticosa petals, providing insights into the molecular mechanisms underlying blotch formation in P. suffruticosa.

The pH-responsive hydrogels have potential applications in food visualization detection, but their fragile mechanical properties limit their applicability. The excellent mechanical properties and thermal stability of aramid nanofibers (ANFs) can improve the structural stability of hydrogels. In this study, the surface properties of ANFs were enhanced through modification to improve their surface activity. The modified ANFs, designated as ANF-SN, were produced following treatment with a mixture of sulfuric acid (H2SO4) and nitric acid (HNO3), which led to increased reactivity and dispersibility of the ANFs due to the proliferation of active groups on their nanofiber surface. The preferred anthocyanin extract from purple sweet potatoes (purple sweet potato extract [PSPE]) had significant color responses to pH (2-12) and ammonia vapor. A stable dual-network colorimetric hydrogel was fabricated by combining ANF-SN, polyvinyl alcohol/sodium alginate (PVA/SA), and PSPE through a two-step method (freeze-thawing and staining). Characterization analysis showed that the strong acid modification of ANFs effectively improved their chemical reactivity. ANF-SN was better than ANF in promoting the formation of hydrogen bond networks, enhancing hydrogel network structures, and improving the viscoelasticity of hydrogels. The optimal hydrogel indicator PVA/SA/ANF-SN/PSPE had good color responsiveness and sensitivity to ammonia. It can also be used to further determine shrimp freshness value using a smartphone and RGB color-picking software.

The anthocyanin accumulation in juvenile tissues can enhance the ornamental value, attract pollinators, and help improve abiotic stress. Although transcriptional regulation studies of anthocyanin have been relatively extensive, there are few reports on the mechanism of anthocyanin accumulation in young tissues. This study reveals that many juvenile citrus tissues (flowers, leaves, and pericarp) undergo transient accumulation of anthocyanins, exhibiting a red coloration. Using weighted gene co-expression network analysis (WGCNA) identified CitWRKY75 as a candidate gene. After detecting the expression levels of CitWRKY75 in various citrus juvenile tissues, the expression trend of CitWRKY75 was highly consistent with the red exhibiting and fading. Overexpression of CitWRKY75 in tobacco significantly increased the anthocyanin content. LUC and yeast one-hybrid assay demonstrated that CitWRKY75 could bind to the promoter of CitRuby1(encoding the key transcription factor promoting anthocyanin accumulation) and promote its expression. Finally, comparing the expression levels of CitWRKY75 and CitRuby1 in the late development stage of blood orange found that CitWRKY75 was not the main regulatory factor for anthocyanin accumulation in the later stage. This study used reverse genetics to identify a transcription factor, CitWRKY75, upstream of CitRuby1, which promotes anthocyanin accumulation in citrus juvenile tissues.
UNASSIGNED: The online version contains supplementary material available at 10.1007/s11032-024-01490-9.

Light exposure significantly impacted the coloration and metabolism of Auricularia cornea, although the underlying mechanisms remain unclear. This study aimed to test the apparent color and pigment metabolic profiles of A. cornea in response to red (λp = 630 nm) and blue (λp = 463 nm) visible light exposure. Colorimeter analysis showed that fruiting bodies appeared bright-white under red-light and deeper-red under blue-light, both with a yellow tinge. On the 40th day of light-exposure, bodies were collected for metabolite detection. A total of 481 metabolites were targeted analysis, resulting in 18 carotenoids and 11 anthocyanins. Under red and blue light exposure, the total carotenoids levels were 1.1652 μg/g and 1.1576 μg/g, the total anthocyanins levels were 0.0799 μg/g and 0.1286 μg/g, respectively. Four differential metabolites and three putative gene linked to the visual coloration of A. cornea were identified. This pioneering study provides new insights into the role of light in regulating A. cornea pigmentation and metabolic profile.

As a new type of packaging method, the anthocyanin-based pH-sensitive indicator film has gained much attention owing to low cost, small size, and visually informative property. In this study, an intelligent film based on chitosan/gelatin (CG) matrix with Zingiber striolatum Diels (ZSD) anthocyanin for fish freshness monitoring was developed. The film properties, including thickness, moisture content, color, mechanical properties, UV-vis light barrier property, as well as pH and ammonia sensitivity, were evaluated. The CG-ZSD films exhibited a more compact structure when compared with the CG film. The CG-ZSD20 film showed the highest elongation at break (6.33 ± 0.62%) and lowest tensile strength (20.0 ± 0.58 MPa). FTIR spectra revealed the strong hydrogen bond interactions between ZSD and polymer matrix. Film incorporated with 15% anthocyanin extract has increased melting temperature at 118.9 °C, and a lower weight loss (13.8%) at melting temperature. In pH 1-14 buffer, the color of CG-ZSD films underwent a significant change from red to yellow-green. The CG-ZSD15 film was utilized for monitoring fish freshness and showed visible color changes from deep purple to brown. The total volatile basic nitrogen content and pH value changes of fish were closely related to the visual color changes in film. This demonstrated that the film was a highly pH-sensitive film for quantifying fish freshness in real-time.

This study aimed to optimize subcritical water extraction process, characterize chemical composition and investigate the biological activities of Nitraria sibirica Pall. (NSP) anthocyanin. Overall, the optimization was achieved under following conditions: extraction temperature 140 °C, extraction time 45 min and flow rate 7 mL/min with the extraction yield of 1.075 mg/g. 3 cyanidin, 3 petunidin, 1 delphinidin and 1 pelargonidin compounds were identified in the anthocyanic extract from NSP via UPLC-Triple-TOF-MS/MS. NSP anthocyanin exhibited better DPPH free-radical scavenging activity than ascorbic acid. It displayed superior α-glucosidase inhibition activity, which was ∼14 times higher than that of acarbose. Moreover, enzyme kinetics results indicated that NSP anthocyanin behaved as a reversible, mixed-type inhibitor. Molecular docking and molecular dynamics simulation results revealed that NSP anthocyanin interacted with α-glucosidase mainly via van der Waals forces, hydrogen bond and possessed fairly stable configuration. Therefore, NSP anthocyanin is a promising α-glucosidase inhibitor for diabetes mellitus.

Rehmannia piasezkii is a kind of medicinal plants, of the Orobanchaceae family, and well known for its large pink or purple corolla. However, no research on the molecular mechanism of flower color formation in R. piasezkii has been conducted so far. In this study, we investigated the transcriptome of root, stem, leaf and corollas of R. piasezkii using transcriptome sequencing technology and assembled 144,582 unigenes. A total of 58 anthocyanin biosynthetic genes were identified in the R. piasezkii transcriptome, fourteen of which were highly correlated with anthocyanin content, especially RpF3H2, RpDFR2, RpANS1, RpANS2 and RpUFGT. Totally, 35 MYB genes with FPKM values greater than 5 were identified in the R. piasezkii transcriptome, including an R2R3 MYB transcriptional factor RpMYB1, which belongs to subgroup 6 of the R2R3 MYB family. Agrobacterium-mediated transient expression of Nicotiana benthamiana revealed that overexpression of RpMYB1 could activate the expression of structural genes in anthocyanin synthesis pathway and promote the accumulation of anthocyanins in N. benthamiana leaves, indicating that RpMYB1 is a positive regulator of anthocyanin synthesis. Furthermore, combined transient overexpression of RpMYB1 with RpANS1, RpMYB1+RpANS1 with other structural genes all could further enhance the accumulation of anthocyanins in N. benthamiana leaves. Permanent overexpression of RpMYB1 in R. glutinosa promoted anthocyanin accumulation and expression levels of RgCHS, RgF3H, RgDFR and RgANS. Further evidence from dual-luciferase assay suggested that RpMYB1 could bind to the promoter of RpDFR2 and hence activating its expression. These findings provide insight into the molecular regulation in anthocyanin biosynthesis in R. piasezkii and provide valuable genetic resources for the genetic improvement of flower color.

Identification of anthocyanin relies heavily on authentic anthocyanin standards and the detection instruments employed, and both of these made tremendous improvement in the past decades. Here, with 118 authentic anthocyanin standards and state-of-the-art detection method, we comprehensively analyze the anthocyanin composition of the most commonly seen, deep-colored berries and grains in China. Cyanidin-3-O-glucoside is the overwhelmingly major anthocyanin in all the berries and grains examined, including blue honeysuckle, blueberry, cranberry, elderberry, mulberry, black rice, and black soybean, which accounts for an average of 82% of the total anthocyanins with a little variation between them. Peonidin-3-O-glucoside is the second most abundant anthocyanin ranging from 2.6%-14.9% of the total anthocyanins. Pelargonidin-3,5-O-diglucoside is only found in blue honeysuckle, and besides that, berries and grains share a dominant portion of common anthocyanins among them. This study primes the survey of anthocyanin in common Chinese foods for the establishment of a nutrition database.