Prospects for economical natural colorants: insights from maize

Genetic analysis of pericarp pigmentation variation in Corn Belt dent maize

The US standard for maize commercially grown for grain specifies that yellow corn can contain at maximum 5% corn of other colors. Inbred parents of commercial hybrids typically have clear pericarp, but transgressive segregants in breeding populations can display variation in pericarp pigmentation. We identified 10 doubled haploid biparental populations segregating for pigmented pericarp and evaluated qualitative genetic models using chi-square tests of observed and expected frequencies. Pigmentation ranged from light to dark brown color, and pigmentation intensity was quantitatively measured across 1,327 inbred lines using hue calculated from RGB pixel values. Genetic mapping was used to identify loci associated with pigmentation intensity. For 9 populations, pigmentation inheritance best fit a hypothesis of a 2- or 3-gene epistatic model. Significant differences in pigment intensity were observed across populations. W606S-derived inbred lines with the darkest pericarp often had clear glumes, suggesting the presence of a novel P1-rw allele, a hypothesis supported by a significant quantitative trait locus peak at P1. A separate quantitative trait locus region on chromosome 2 between 221.64 and 226.66 Mbp was identified in LH82-derived populations, and the peak near p1 was absent. A genome-wide association study using 416 inbred lines from the Wisconsin Diversity panel with full genome resequencing revealed 4 significant associations including the region near P1. This study supports that pericarp pigmentation among dent maize inbreds can arise by transgressive segregation when pigmentation in the parental generation is absent and is partially explained by functional allelic variation at the P1 locus.

Tartary Buckwheat (Fagopyrum tataricum) FtTT8 Inhibits Anthocyanin Biosynthesis and Promotes Proanthocyanidin Biosynthesis

Tartary buckwheat (Fagopyrum tataricum) is an important plant, utilized for both medicine and food. It has become a current research hotspot due to its rich content of flavonoids, which are beneficial for human health. Anthocyanins (ATs) and proanthocyanidins (PAs) are the two main kinds of flavonoid compounds in Tartary buckwheat, which participate in the pigmentation of some tissue as well as rendering resistance to many biotic and abiotic stresses. Additionally, Tartary buckwheat anthocyanins and PAs have many health benefits for humans and the plant itself. However, little is known about the regulation mechanism of the biosynthesis of anthocyanin and PA in Tartary buckwheat. In the present study, a bHLH transcription factor (TF) FtTT8 was characterized to be homologous with AtTT8 and phylogenetically close to bHLH proteins from other plant species. Subcellular location and yeast two-hybrid assays suggested that FtTT8 locates in the nucleus and plays a role as a transcription factor. Complementation analysis in Arabidopsis tt8 mutant showed that FtTT8 could not recover anthocyanin deficiency but could promote PAs accumulation. Overexpression of FtTT8 in red-flowering tobacco showed that FtTT8 inhibits anthocyanin biosynthesis and accelerates proanthocyanidin biosynthesis. QRT-PCR and yeast one-hybrid assay revealed that FtTT8 might bind to the promoter of NtUFGT and suppress its expression, while binding to the promoter of NtLAR and upregulating its expression in K326 tobacco. This displayed the bidirectional regulating function of FtTT8 that negatively regulates anthocyanin biosynthesis and positively regulates proanthocyanidin biosynthesis. The results provide new insights on TT8 in Tartary buckwheat, which is inconsistent with TT8 from other plant species, and FtTT8 might be a high-quality gene resource for Tartary buckwheat breeding.

Sequence variations associated with novel purple-pericarp super-sweetcorn compared to its purple-pericarp maize and white super-sweetcorn parents

Recently, a novel purple-pericarp super-sweetcorn line, 'Tim1' (A1A1.sh2sh2) was derived from the purple-pericarp maize 'Costa Rica' (A1Sh2.A1Sh2) and white shrunken2 (sh2) super-sweetcorn 'Tims-white' (a1sh2.a1sh2), however, information regarding anthocyanin biosynthesis genes controlling purple colour and sweetness gene is lacking. Specific sequence differences in the CDS (coding DNA sequence) and promoter regions of the anthocyanin biosynthesis structural genes, anthocyanin1 (A1), purple aleurone1 (Pr1) and regulatory genes, purple plant1 (Pl1), plant colour1 (B1), coloured1 (R1), and the sweetcorn structural gene, shrunken2 (sh2) were investigated using the publicly available annotated yellow starchy maize, B73 (NAM5.0) as a reference genome. In the CDS region, the A1, Pl1 and R1 gene sequence differences of 'Tim1' and 'Costa Rica' were similar, as they control purple-pericarp pigmentation. However, the B1 gene showed similarity between the 'Tim1' and 'Tims-white' lines, which may indicate that it does not have a role in controlling pericarp colour, unlike the report of a previous study. In the case of the Pr1 gene, in contrast to 'Costa Rica', 6- and 8-bp dinucleotide (TA) repeats were observed in the promoter region of the 'Tims-white' and 'Tim1' lines, respectively, indicating the defective functionality (redder colour in 'Tim1' rather than purple in 'Costa Rica') of the recessive pr1 allele. In sweetcorn, the structural gene (sh2), sequence showed similarity between purple-sweet 'Tim1' and its white-sweet parent 'Tims-white', as both display a shrunken phenotype in their mature kernels. These findings revealed that the developed purple-sweet line is different to the reference yellow-nonsweet line in both the anthocyanin biosynthesis and sweetcorn genes.

Transcriptome Analysis Revealed the Potential Molecular Mechanism of Anthocyanidins' Improved Salt Tolerance in Maize Seedlings

Anthocyanin, a kind of flavonoid, plays a crucial role in plant resistance to abiotic stress. Salt stress is a kind of abiotic stress that can damage the growth and development of plant seedlings. However, limited research has been conducted on the involvement of maize seedlings in salt stress resistance via anthocyanin accumulation, and its potential molecular mechanism is still unclear. Therefore, it is of great significance for the normal growth and development of maize seedlings to explore the potential molecular mechanism of anthocyanin improving salt tolerance of seedlings via transcriptome analysis. In this study, we identified two W22 inbred lines (tolerant line pur-W22 and sensitive line bro-W22) exhibiting differential tolerance to salt stress during seedling growth and development but showing no significant differences in seedling characteristics under non-treatment conditions. In order to identify the specific genes involved in seedlings' salt stress response, we generated two recombinant inbred lines (RILpur-W22 and RILbro-W22) by crossing pur-W22 and bro-W22, and then performed transcriptome analysis on seedlings grown under both non-treatment and salt treatment conditions. A total of 6100 and 5710 differentially expressed genes (DEGs) were identified in RILpur-W22 and RILbro-W22 seedlings, respectively, under salt-stressed conditions when compared to the non-treated groups. Among these DEGs, 3160 were identified as being present in both RILpur-W22 and RILbro-W22, and these served as commonly stressed EDGs that were mainly enriched in the redox process, the monomer metabolic process, catalytic activity, the plasma membrane, and metabolic process regulation. Furthermore, we detected 1728 specific DEGs in the salt-tolerant RILpur-W22 line that were not detected in the salt-sensitive RILbro-W22 line, of which 887 were upregulated and 841 were downregulated. These DEGs are primarily associated with redox processes, biological regulation, and the plasma membrane. Notably, the anthocyanin synthesis related genes in RILpur-W22 were strongly induced under salt treatment conditions, which was consistented with the salt tolerance phenotype of its seedlings. In summary, the results of the transcriptome analysis not only expanded our understanding of the complex molecular mechanism of anthocyanin in improving the salt tolerance of maize seedlings, but also, the DEGs specifically expressed in the salt-tolerant line (RILpur-W22) provided candidate genes for further genetic analysis.

Anthocyanins in metabolites of purple corn

Purple corn (Zea mays L.) is a special variety of corn, rich in a large amount of anthocyanins and other functional phytochemicals, and has always ranked high in the economic benefits of the corn industry. However, most studies on the stability of agronomic traits and the interaction between genotype and environment in cereal crops focus on yield. In order to further study the accumulation and stability of special anthocyanins in the growth process of purple corn, this review starts with the elucidation of anthocyanins in purple corn, the biosynthesis process and the gene regulation mechanism behind them, points out the influence of anthocyanin metabolism on anthocyanin metabolism, and introduces the influence of environmental factors on anthocyanin accumulation in detail, so as to promote the multi-field production of purple corn, encourage the development of color corn industry and provide new opportunities for corn breeders and growers.

GWAS of grain color and tannin content in Chinese sorghum based on whole-genome sequencing

Seventy-three QTL related to grain color and tannin content were identified in Chinese sorghum accessions, and a new recessive allelic variant of TAN2 gene was discovered. Sorghum is mainly used for brewing distilled liquors in China. Since grain tannins play an important role in liquor brewing, accurately understanding the relationship between grain color and tannin content can provide basis for selection standards of tannin sorghum. We resequenced a panel of 242 Chinese sorghum accessions and performed population structure and genome-wide association study (GWAS) to identify quantitative trait locus (QTL) affecting pericarp color, testa pigment, and tannin content. Phylogenetic analysis, principal component analysis (PCA), and admixture model were used to infer population structure. Two distinct genetic sub-populations were identified according to their corresponding northern and southern geographic origin. To investigate the genetic basis of natural variation in sorghum grain color, GWAS with 2,760,264 SNPs was conducted in four environments using multiple models (Blink, FarmCPU, GLM, and MLM). Seventy-three QTL were identified to be associated for the color of exocarp, mesocarp, testa, and tannin content on all chromosomes except chromosome 5, of which 47 might be novel QTL. Some important QTL were found to colocalize with orthologous genes in the flavonoid biosynthetic pathway from other plants, including orthologous of Arabidopsis (Arabidopsis thaliana) TT2, TT7, TT12, TT16 and AT5G41220 (GST), as well as orthologous of rice (Oryza sativa) MYB61 and OsbHLH025. Our investigation of the variation in grain color and tannin content in Chinese sorghum germplasm may help guide future sorghum breeding for liquor brewing.

Profiling and Quantification of Anthocyanins in Purple-Pericarp Sweetcorn and Purple-Pericarp Maize

Purple-pericarp sweetcorn accessions, derived from crossing purple-pericarp maize with white shrunken2 sweetcorn, were assessed for differences in anthocyanin profile at both sweetcorn eating stage and at full kernel maturity. The ‘Tim1’ sweetcorn line developed a similar total anthocyanin concentration to its ‘Costa Rica’ parent when assessed at sweetcorn-eating stage. At full maturity it surpassed the purple maize parent, but this was mainly due to the presence of starch diluting the anthocyanin concentration of the latter. The anthocyanin/colour relationship was affected by both total anthocyanin concentration and the ratio of cyanidin- to pelargonidin-based anthocyanins. Malonylation of anthocyanins was also found to vary and did not appear to be linked with either cyanidin:pelargonidin ratio or total anthocyanin concentration. In addition, anthocyanin synthesis was affected by kernel maturity at harvest, with colour development increasing in conjunction with a progression of anthocyanin development across the kernel surface. Pigmentation was present in the aleurone, pericarp and vitreous endosperm of kernels of the purple-pericarp maize parent and purple-pericarp sweetcorn accessions when fully mature, but pigmentation was only apparent in the pericarp at sweetcorn-eating stage. Importantly for consumers, anthocyanin pigmentation covered almost the entire kernel surface at sweetcorn-eating stage.

Breaking the tight genetic linkage between the a1 and sh2 genes led to the development of anthocyanin-rich purple-pericarp super-sweetcorn

The existence of purple-pericarp super-sweetcorn based on the supersweet mutation, shrunken2 (sh2), has not been previously reported, due to its extremely tight genetic linkage to a non-functional anthocyanin biosynthesis gene, anthocyaninless1 (a1). Generally, pericarp-pigmented starchy purple corn contains significantly higher anthocyanin. The development of purple-pericarp super-sweetcorn is dependent on breaking the a1-sh2 tight genetic linkage, which occurs at a very low frequency of < 1 in 1000 meiotic crossovers. Here, to develop purple-pericarp super-sweetcorn, an initial cross between a male purple-pericarp maize, 'Costa Rica' (A1Sh2.A1Sh2) and a female white shrunken2 super-sweetcorn, 'Tims-white' (a1sh2.a1sh2), was conducted. Subsequent self-pollination based on purple-pericarp-shrunken kernels identified a small frequency (0.08%) of initial heterozygous F3 segregants (A1a1.sh2sh2) producing a fully sh2 cob with a purple-pericarp phenotype, enabled by breaking the close genetic linkage between the a1 and sh2 genes. Resulting rounds of self-pollination generated a F6 homozygous purple-pericarp super-sweetcorn (A1A1.sh2sh2) line, 'Tim1'. Genome sequencing revealed a recombination break between the a1 and yz1 genes of the a1-yz1-x1-sh2  multigenic interval. The novel purple-pericarp super-sweetcorn produced a similar concentration of anthocyanin and sugar as in its purple-pericarp maize and white super-sweetcorn parents, respectively, potentially adding a broader range of health benefits than currently exists with standard yellow/white sweetcorn.

Nature's palette: An emerging frontier for coloring dairy products

Consumers all across the world are looking for the most delectable and appealing foods, while also demanding products that are safer, more nutritious, and healthier. Substitution of synthetic colorants with natural colorants has piqued consumer and market interest in recent years. Due to increasing demand, extensive research has been conducted to find natural and safe food additives, such as natural pigments, that may have health benefits. Natural colorants are made up of a variety of pigments, many of which have significant biological potential. Because of the promising health advantages, natural colorants are gaining immense interest in the dairy industry. This review goes over the use of various natural colorants in dairy products which can provide desirable color as well as positive health impacts. The purpose of this review is to provide an in-depth look into the field of food (natural or synthetic) colorants applied in dairy products as well as their potential health benefits, safety, general trends, and future prospects  in food science and technology. In this paper, we listed a plethora of applications of natural colorants in various milk-based products.

Influence of Red Corn Rich in Anthocyanins on Productive Traits, Blood Metabolic Profile, and Antioxidative Status of Fattening Lambs

Simple Summary

In order to prevent lamb distress during weaning and avoid the occurrence of oxidative stress leading to diminished production performance, health status, or product quality, feeds rich in polyphenols (anthocyanins) are increasingly used in ruminant feeding. In the present study, lambs were allocated into three groups, with 10 lambs per group. The feed mixture for the control group (C) contained yellow corn. Lambs in experimental group I were fed feed mixtures containing yellow corn replaced by red corn at 50% (RC50). In experimental group II, red corn fully replaced (100%) yellow corn (RC100) in the lambs’ feed. The results of the present study indicate a positive effect of red corn rich in anthocyanins on the metabolic profile without any changes in the productive traits of lambs.

Abstract

In this study, we aimed to evaluate the effects of different proportions of red corn rich in anthocyanins on the diet of fattening lambs considering their productive traits, blood metabolic profile, and antioxidative status. The research was carried out with 30 Merinolandschaf lambs, 90 days old and weaned. The feed mixture for lambs (n = 10) of the control group contained yellow corn, while in the feed mixture of experimental group I (n = 10), yellow corn was replaced with red corn at 50% (RC50), and in experimental group II (n = 10), yellow corn was 100% replaced with red corn (RC100). An automatic three-part differential haematology analyser was used to determine haematological parameters in whole blood, and biochemical parameters were determined in blood serum using a biochemical analyser. A diet containing red corn did not affect productive traits or the majority of the examined parameters. However, higher blood haemoglobin content, increased aspartate aminotransferase and creatine kinase activity, and decreased glucose and non-esterified fatty acids concentrations were found in the serum of RC100 lambs. These results indicate a positive effect of red corn rich in anthocyanins on the metabolic profile without any changes in the productive traits of lambs.

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.

Playing with colours: genetics and regulatory mechanisms for anthocyanin pathway in cereals

Cereals form the most important source of energy in our food. Currently, demand for coloured food grains is significantly increasing globally because of their antioxidant properties and enhanced nutritional value. Coloured grains of major and minor cereals are due to accumulation of secondary metabolites like carotenoids and flavonoids such as anthocyanin, proanthocyanin, phlobaphenes in pericarp, aleurone, lemma, testa or seed coat of grains. Differential accumulation of colour in grains is regulated by several regulatory proteins and enzymes involved in flavonoid and caroteniod biosynthesis. MYB and bHLH gene family members are the major regulators of these pathways. Genes for colour across various cereals have been extensively studied; however, only a few functional and allele-specific markers to be utilized directly in breeding programmes are reported so far. In this review, while briefly discussing the well studied and explored carotenoid pathway, we focus on a much more complex anthocyanin pathway that is found across cereals. The genes and their orthologs that are responsible for encoding key regulators of anthocyanin biosynthesis are discussed. This review also focuses on the genetic factors that influence colour change in different cereal crops, and the available/reported markers that can be used in breeding programs for utilizing this pathway for enhancing food and nutritional security.

Evolution of the Subgroup 6 R2R3-MYB Genes and Their Contribution to Floral Color in the Perianth-Bearing Piperales

Flavonoids, carotenoids, betalains, and chlorophylls are the plant pigments responsible for floral color. Anthocyanins, a class of flavonoids, are largely responsible for the red, purple, pink, and blue colors. R2R3-MYB genes belonging to subgroup 6 (SG6) are the upstream regulatory factors of the anthocyanin biosynthetic pathway. The canonical members of these genes in Arabidopsis include AtMYB75, AtMYB90, AtMYB113, and AtMYB114. The Aristolochiaceae is an angiosperm lineage with diverse floral groundplans and perianth colors. Saruma henryi exhibits a biseriate perianth with green sepals and yellow petals. All other genera have sepals only, with colors ranging from green (in Lactoris) to a plethora of yellow to red and purple mixtures. Here, we isolated and reconstructed the SG6 R2R3-MYB gene lineage evolution in angiosperms with sampling emphasis in Aristolochiaceae. We found numerous species-specific duplications of this gene lineage in core eudicots and local duplications in Aristolochiaceae for Saruma and Asarum. Expression of SG6 R2R3-MYB genes examined in different developmental stages and plant organs of four Aristolochiaceae species, largely overlaps with red and purple pigments, suggesting a role in anthocyanin and flavonoid synthesis and accumulation. A directed RNA-seq analysis corroborated our RT-PCR analyses, by showing that these structural enzymes activate during perianth development in Aristolochia fimbriata and that the regulatory genes are expressed in correlation with color phenotype. Finally, the reconstruction of the flavonoid and anthocyanin metabolic pathways using predicted peptides from transcriptomic data show that all pivotal enzymes are present in the analyzed species. We conclude that the regulatory genes as well as the biosynthetic pathway are largely conserved across angiosperms. In addition, the Aristolochiaceae emerges as a remarkable group to study the genetic regulatory network for floral color, as their members exhibit an outstanding floral diversity with elaborate color patterns and the genetic complement for SG6 R2R3-MYB genes is simpler than in core eudicot model species.

Linking anthocyanin diversity, hue, and genetics in purple corn

While maize with anthocyanin-rich pericarp (purple corn) is rising in popularity as a source of natural colorant for foods and beverages, information on color range and stability-factors associated with anthocyanin decorations and compositional profiles-is currently limited. Furthermore, to maximize the scalability and meet growing demands, both anthocyanin concentrations and agronomic performance must improve in purple corn varieties. Using the natural anthocyanin diversity present in a purple corn landrace, Apache Red, we generated a population with variable flavonoid profiles-flavanol-anthocyanin condensed forms (0-83%), acylated anthocyanins (2-72%), pelargonidin-derived anthocyanins (5-99%), C-glycosyl flavone co-pigments up to 1904 µg/g, and with anthocyanin content up to 1598 µg/g. Each aspect of the flavonoid profiles was found to play a role in either the resulting extract hue or intensity. With genotyping-by-sequencing of this population, we mapped aspects of the flavonoid profile. Major quantitative trait loci (QTLs) for anthocyanin type were found near loci previously identified only in aleurone-pigmented maize varieties [Purple aleurone1 (Pr1) and Anthocyanin acyltransferase1 (Aat1)]. A QTL near P1 (Pericarp color1) was found for both flavone content and flavanol-anthocyanin condensed forms. A significant QTL associated with peonidin-derived anthocyanins near a candidate S-adenosylmethionine-dependent methyltransferase was also identified, warranting further investigation. Mapping total anthocyanin content produced signals near Aat1, the aleurone-associated bHLH R1 (Colored1), the plant color-associated MYB, Pl1 (Purple plant1), the aleurone-associated recessive intensifier, In1 (Intensifier1), and several previously unidentified candidates. This population represents one of the most anthocyanin diverse pericarp-pigmented maize varieties characterized to date. Moreover, the candidates identified here will serve as branching points for future research studying the genetic and molecular processes determining anthocyanin profile in pericarp.

Temperature and Maturity Stages Affect Anthocyanin Development and Phenolic and Sugar Content of Purple-Pericarp Supersweet Sweetcorn during Storage

Purple-pericarp sweetcorn (PPS) is a novel product, requiring both purple pigment development and maintenance of sweetness. Storage period and temperature had a profound impact on total anthocyanin accumulation (TAC) and sugar content. While TAC remained relatively unchanged during 14-day storage at 4 °C, the first recorded observation of continuing accumulation of anthocyanin and phenolic compounds was concurrent with an increase in purple pigment coverage across the surface of the kernel at 23 °C. TAC in PPS significantly increased, doubling after 14 days at 23 °C. Anthocyanin concentration and kernel coverage were also affected by harvest maturity. The results indicated that biosynthesis of anthocyanins is still occurring during postharvest storage of PPS. A significant decline in sugar concentration was also observed during storage with a greater decline at 23 °C. As anthocyanin accumulation and maintaining sweetness are important factors for sweetcorn, identifying storage temperatures that optimize both quality criteria are required.

Colored Corn: An Up-Date on Metabolites Extraction, Health Implication, and Potential Use

Colored (orange, pink, red, purple, and blue) corn strongly attracted attention on its healthy properties mainly due to its anthocyanin and carotenoid composition which is also responsible for its pigmentation. The present review summarized the recent updates on the extraction and chemical characterization of the main plant secondary metabolites present in colored seeds, kernel, cob, husk, and silk. The main approaches used to stabilize the extracts have been discussed as well as their food and non-food uses. Both in vitro and in vivo (animal models) studies on the different effects (antibacterial, antimutagenic, antioxidant, and anti-inflammatory activities, effects on metabolic syndrome, diabetes, glucose and lipidic metabolism, and neuroprotection) of pigmented extracts on animal and human health have been summarized.

Grown to be Blue-Antioxidant Properties and Health Effects of Colored Vegetables. Part II: Leafy, Fruit, and Other Vegetables

The current trend for substituting synthetic compounds with natural ones in the design and production of functional and healthy foods has increased the research interest about natural colorants. Although coloring agents from plant origin are already used in the food and beverage industry, the market and consumer demands for novel and diverse food products are increasing and new plant sources are explored. Fresh vegetables are considered a good source of such compounds, especially when considering the great color diversity that exists among the various species or even the cultivars within the same species. In the present review we aim to present the most common species of colored vegetables, focusing on leafy and fruit vegetables, as well as on vegetables where other plant parts are commercially used, with special attention to blue color. The compounds that are responsible for the uncommon colors will be also presented and their beneficial health effects and antioxidant properties will be unraveled.