Characterization of carotenoid pigments in mature and developing kernels of selected yellow-endosperm sorghum varieties

Identifying molecular targets for modulating carotenoid accumulation in rice grains

Carotenoids are potential antioxidants offering extensive human health benefits including protection against chronic diseases. Augmenting the supply of health-benefiting compounds/metabolites through dietary supplements is the most sustainable way for a healthy life. Our study compares the traditional rice cultivar Kavuni and the white rice variety ASD 16. RNA-Seq analysis was carried out in the maturing panicles of Kavuni, which are enriched with antioxidants such as the therapeutic carotenoid lutein, polyphenols, and anthocyanins, along with "ASD 16", a popularly eaten white rice variety, to elucidate the molecular networks regulating accumulation of health benefiting compounds. Systematic analysis of transcriptome data identified preferential up-regulation of carotenoid precursors (OsDXS, OsGGPS) and key carotenoid biosynthetic genes (OsPSY1, OsZ-ISO) in the maturing grains of Kavuni. Our study also identified enhanced expression of OsLYC-E, OsCYP97A, and OsCYP97C transcripts involved in the alpha-carotenoid biosynthetic pathway and thereby leading to elevated lutein content in the grains of Kavuni. Kavuni grains showed preferential down-regulation of negative regulators of carotenoid metabolism viz., AP2 and HY5 and preferential up-regulation of positive modulators of carotenoid metabolism viz., Orange, OsDjB7, and OsSET29, thus creating a favorable molecular framework for carotenoid accumulation. Our study has unearthed valuable gene control points for precise manipulation of carotenoid profiles through CRISPR-based gene editing in rice grains. Perturbation of carotenoid biosynthesis holds unprecedented potential for the rapid development of the next generation of 'Golden rice'.

Grain yellowness is an effective predictor of carotenoid content in global sorghum populations

Identification of high carotenoid germplasm is crucial to assist breeders in provitamin-A biofortification of sorghum (Sorghum bicolor [L.] Moench). High-performance liquid chromatography is the gold standard for carotenoid quantification, however, it is not feasible for large scale phenotyping due to its high cost and low throughput. In this study, we tested the feasibility of using grain color as a high-throughput method of carotenoid biofortification breeding. We hypothesized that visual, color-based selection can be an effective strategy to identify high-carotenoid accessions. Yellow grain had significantly higher carotenoid content than red, brown, and white grain. The degree of yellowness could distinguish the presence or absence of carotenoids, but could not distinguish carotenoid concentrations within yellow-only accessions. The degree of luminosity of the grain, however, was able to better predict carotenoid concentrations within yellow-only accessions. Genome-wide association studies identified significant marker-trait associations for qualitative and quantitative grain color traits and carotenoid concentrations near carotenoid pathway genes-ZEP, PDS, CYP97A, NCED, CCD, and LycE-three of which were common between grain color and carotenoid traits. These findings suggest that using grain color as a method for screening germplasm may be an effective high-throughput selection tool for prebreeding and early-stage breeding in carotenoid biofortification.

Evaluation of nutritional and functional properties of anatomical parts of two sorghum (Sorghum bicolor) varieties

Compositional differences exist among grain varieties as well as in the content of respective fractions. The proximate composition, amino acids, mineral contents, and functional properties of white and brown sorghum and its anatomical parts (dehulled and bran) were studied. The results showed that the bran had higher crude protein, crude fat, crude fibre, and ash contents for both sorghum varieties than the whole grain and dehulled samples. Likewise, significantly (p ≤ 0.05) higher essential and non-essential amino acids and minerals, particularly calcium, zinc, potassium were recorded for the bran samples compared to the whole grains or dehulled ones. With regard to the functional properties, the hydration capacity, hydration index, water, and oil absorption capacities of the dehulled samples were significantly (p ≤ 0.05) lower than the other investigated samples, except for bulk density, which was significantly (p ≤ 0.05) higher. In contrast, none of the swelling capacities differed significantly in any of the samples. In conclusion, sorghum bran has significant potential in the food industry and could be an excellent material for formulating high-fibre foods and serving as a nutritionally-rich food ingredient.

Unraveling transcriptomics of sorghum grain carotenoids: a step forward for biofortification

BACKGROUND

Sorghum (Sorghum bicolor [L.] Moench) is a promising target for pro-vitamin A biofortification as it is a global staple crop, particularly in regions where vitamin A deficiency is prevalent. As with most cereal grains, carotenoid concentrations are low in sorghum, and breeding could be a feasible strategy to increase pro-vitamin A carotenoids to biologically relevant concentrations. However, there are knowledge gaps in the biosynthesis and regulation of sorghum grain carotenoids, which can limit breeding effectiveness. The aim of this research was to gain an understanding of the transcriptional regulation of a priori candidate genes in carotenoid precursor, biosynthesis, and degradation pathways.

RESULTS

We used RNA sequencing of grain to compare the transcriptional profile of four sorghum accessions with contrasting carotenoid profiles through grain development. Most a priori candidate genes involved in the precursor MEP, carotenoid biosynthesis, and carotenoid degradation pathways were found to be differentially expressed between sorghum grain developmental stages. There was also differential expression of some of the a priori candidate genes between high and low carotenoid content groups at each developmental time point. Among these, we propose geranyl geranyl pyrophosphate synthase (GGPPS), phytoene synthase (PSY), and phytoene desaturase (PDS) as promising targets for pro-vitamin A carotenoid biofortification efforts in sorghum grain.

CONCLUSIONS

A deeper understanding of the controls underlying biosynthesis and degradation of sorghum grain carotenoids is needed to advance biofortification efforts. This study provides the first insights into the regulation of sorghum grain carotenoid biosynthesis and degradation, suggesting potential gene targets to prioritize for molecular breeding.

Carotenoids Occurring in Maize Affect the Redox Homeostasis of Fusarium graminearum and Its Production of Type B Trichothecene Mycotoxins: New Insights Supporting Their Role in Maize Resistance to Giberella Ear Rot

Fusarium graminearum is the causal agent of Gibberella ear rot (GER) in maize, a devastating fungal disease resulting in yield reduction and contamination of grains with type B trichothecene (TCTB) mycotoxins. Reducing GER damage requires the implementation of an integrated management strategy in which the use of resistant maize genotypes is a key factor. The present study aimed at providing new phenotyping tools to improve breeding pipelines by investigating the yet understudied contribution of carotenoids to GER resistance. Here, we demonstrated for the first time the efficiency of carotenoid extracts from various maize genotypes to inhibit the production of TCTB by F. graminearum. We further suggested that zeaxanthin could be a key actor of this inhibition efficiency, notably via a negative transcriptional control of several biosynthetic genes of the TCTB pathway. Besides, we demonstrated that zeaxanthin treatments led to profound perturbations in the fungal redox homeostasis by affecting the expression of key genes encoding ROS detoxifying enzymes, several of them being involved in F. graminearum virulence during plant infection. Altogether, our data support the contribution of carotenoids to the mechanisms employed by maize to counteract F. graminearum infection and its production of TCTB.

Carotenoid Cleavage Dioxygenase 1 Catalyzes Lutein Degradation To Influence Carotenoid Accumulation and Color Development in Foxtail Millet Grains

Foxtail millet is a minor but economically important crop in certain regions of the world. Millet color is often used to judge grain quality, yet the molecular determinants of millet coloration remain unclear. Here, we explored the relationship between SiCCD1 and millet coloration in yellow and white millet varieties. Carotenoid levels declined with grain maturation and were negatively correlated with SiCCD1 expression, which was significantly higher in white millet as compared to yellow millet during the color development stage. Cloning of the SiCCD1 promoter and CDS sequences from these different millet varieties revealed the presence of two additional cis-regulatory elements within the SiCCD1 promoter in white millet varieties, including an enhancer-like GC motif element associated with anoxic specific inducibility and a GCN4-motif element associated with endosperm expression. Dual-luciferase reporter assays confirmed that SiCCD1 promoter fragments containing these additional cis-acting elements derived from white millet varieties were significantly more active than those from yellow millet varieties, consistent with the observed SiCCD1 expression patterns. Further in vitro enzyme detection assays confirmed that SiCCD1 primarily targets and degrades lutein. Together, these data suggest that SiCCD1 promoter variation was a key factor associated with the observed differences in SiCCD1 expression, which in turn led to the difference in millet coloration.

Evaluating the Shelf Life and Sensory Properties of Beef Steaks from Cattle Raised on Different Grass Feeding Systems in the Western United States

Consumer interest in grass-fed beef has been steadily rising due to consumer perception of its potential benefits. This interest has led to a growing demand for niche market beef, particularly in the western United States. Therefore, the objective of this study was to assess the impact of feeding systems on the change in microbial counts, color, and lipid oxidation of steaks during retail display, and on their sensory attributes. The systems included: conventional grain-fed (CON), 20 months-grass-fed (20GF), 25-months-grass-fed (25GF) and 20-months-grass-fed + 45-day-grain-fed (45GR). The results indicate that steaks in the 20GF group displayed a darker lean and fat color, and a lower oxidation state than those in the 25GF group. However, the feeding system did not have an impact on pH or objective tenderness of beef steaks. In addition, consumers and trained panelist did not detect a difference in taste or flavor between the 20GF or 25GF steaks but expressed a preference for the CON and 45GR steaks, indicating that an increased grazing period may improve the color and oxidative stability of beef, while a short supplementation with grain may improve eating quality.

Bioactive Compounds and Biological Activities of Sorghum Grains

Sorghum is the fifth most commonly used cereal worldwide and is a rich source of many bioactive compounds. We summarized phenolic compounds and carotenoids, vitamin E, amines, and phytosterols in sorghum grains. Recently, with the development of detection technology, new bioactive compounds such as formononetin, glycitein, and ononin have been detected. In addition, multiple in vitro and in vivo studies have shown that sorghum grains have extensive bio-logical activities, such as antioxidative, anticancer, antidiabetic, antiinflammatory, and antiobesity properties. Finally, with the establishment of sorghum phenolic compounds database, the bound phenolics and their biological activities and the mechanisms of biological activities of sorghum bioactive compounds using clinical trials may be researched.

Advancing provitamin A biofortification in sorghum: Genome-wide association studies of grain carotenoids in global germplasm

Vitamin A deficiency is one of the most prevalent nutritional deficiencies worldwide. Sorghum [Sorghum bicolor L. (Moench)] is a major cereal crop consumed by millions of people in regions with high vitamin A deficiency. We quantified carotenoid concentrations in a diverse sorghum panel using high-performance liquid chromatography and conducted a genome-wide association study (GWAS) of grain carotenoids to identify genes underlying carotenoid variation. There was moderate variation for β-carotene (00.8 μg g^-1 ), lutein (0.3-9.4 μg g^-1 ), and zeaxanthin (0.2-9.1 μg g^-1 ), but β-cryptoxanthin and α-carotene were nearly undetectable. Genotype had the largest effect size, at 81% for zeaxanthin, 62% for β-carotene, and 53% for lutein. Using multiple models, GWAS identified several significant associations between carotenoids and single nucleotide polymorphisms (SNPs), some of which colocalized with known carotenoid genes that have not been previously implicated in carotenoid variation. Several of the candidate genes identified have also been identified in maize (Zea mays L.) and Arabidopsis (Arabidopsis thaliana) carotenoid GWAS studies. Notably, an SNP inside the putative ortholog of maize zeaxanthin epoxidase (ZEP) had the most significant association with zeaxanthin and with the ratio between lutein and zeaxanthin, suggesting that ZEP is a major gene controlling sorghum carotenoid variation. Overall findings suggest there is oligogenic inheritance for sorghum carotenoids and suitable variation for marker-assisted selection. The high carotenoid germplasm and significant associations identified in this study can be used in biofortification efforts to improve the nutritional quality of sorghum.

The influence of weather conditions on bioactive compound content in sorghum grain

Sorghum is the fifth most important cereal in the world in terms of the cropped area. It is mainly grown for feeding animals and it is also used in the food industry. Sorghum grain is generally a rich source of antioxidants such as polyphenols and carotenoids. For this reason, it is considered as a good source of bioactive food components and it has health-promoting properties. Sorghum is a gluten-free cereal grown in many regions worldwide, primarily in the tropical and subtropical regions. However, new hybrids and forms of sorghum are capable to produce seeds also in temperate climate. The aim of this study was to conduct the influence of weather conditions on bioactive compound content in sorghum grain. The quantitative analysis of selected bioactive compounds, such as phenolic acids, flavonoids, carotenoids, and phytosterols, was carried out. The tested material comprised grain of two varieties: ‘Sweet Susana’ and ‘Sweet Caroline’, which have different color of grain: red and white. The research material was obtained from growing seasons 2016–2018. Quantitative analysis of free phenolic acids, total carotenoids, and total phytosterols was performed by ultra-performance liquid chromatography (UPLC) after prior basic hydrolysis followed by acid. An ultra-efficient liquid chromatograph coupled with an absorption-based detector (UPLC-PDA) was used for these analyses. The results showed the variability of the content of bioactive compounds depending on weather conditions.

Nutritionally Enhanced Sorghum for the Arid and Semiarid Tropical Areas of Africa

To help alleviate malnutrition in Africa, nutritionally enhanced sorghum was developed through genetic transformation to increase pro-vitamin A (β-carotene) accumulation and stability, to improve iron and zinc bioavailability, and to improve protein digestibility. Through many years of efforts, significant achievements have been made for these goals. We generated nutritionally enhanced sorghum lines with enhanced and stabilized pro-vitamin A that provide 20-90% of the Estimated Average Requirement (EAR) for children under age 3, lines with a 90% reduction in phytate that increase iron and zinc bioavailability and provide 40-80% of the EAR for iron and zinc, and lines that show no reduction in protein digestibility after cooking compared with normal levels. Once these nutritionally enhanced sorghum lines have undergone biosafety examination and have been deregulated, they will be ready for incorporation into sorghum varieties that will benefit Africa and other areas that rely upon sorghum as a staple food.

Elevated vitamin E content improves all-trans β-carotene accumulation and stability in biofortified sorghum

Micronutrient deficiencies are common in locales where people must rely upon sorghum as their staple diet. Sorghum grain is seriously deficient in provitamin A (β-carotene) and in the bioavailability of iron and zinc. Biofortification is a process to improve crops for one or more micronutrient deficiencies. We have developed sorghum with increased β-carotene accumulation that will alleviate vitamin A deficiency among people who rely on sorghum as their dietary staple. However, subsequent β-carotene instability during storage negatively affects the full utilization of this essential micronutrient. We determined that oxidation is the main factor causing β-carotene degradation under ambient conditions. We further demonstrated that coexpression of homogentisate geranylgeranyl transferase (HGGT), stacked with carotenoid biosynthesis genes, can mitigate β-carotene oxidative degradation, resulting in increased β-carotene accumulation and stability. A kinetic study of β-carotene degradation showed that the half-life of β-carotene is extended from less than 4 wk to 10 wk on average with HGGT coexpression.

Bottlenecks in carotenoid biosynthesis and accumulation in rice endosperm are influenced by the precursor-product balance

The profile of secondary metabolites in plants reflects the balance of biosynthesis, degradation and storage, including the availability of precursors and products that affect the metabolic equilibrium. We investigated the impact of the precursor-product balance on the carotenoid pathway in the endosperm of intact rice plants because this tissue does not normally accumulate carotenoids, allowing us to control each component of the pathway. We generated transgenic plants expressing the maize phytoene synthase gene (ZmPSY1) and the bacterial phytoene desaturase gene (PaCRTI), which are sufficient to produce β-carotene in the presence of endogenous lycopene β-cyclase. We combined this mini-pathway with the Arabidopsis thaliana genes AtDXS (encoding 1-deoxy-D-xylulose 5-phosphate synthase, which supplies metabolic precursors) or AtOR (the ORANGE gene, which promotes the formation of a metabolic sink). Analysis of the resulting transgenic plants suggested that the supply of isoprenoid precursors from the MEP pathway is one of the key factors limiting carotenoid accumulation in the endosperm and that the overexpression of AtOR increased the accumulation of carotenoids in part by up-regulating a series of endogenous carotenogenic genes. The identification of metabolic bottlenecks in the pathway will help to refine strategies for the creation of engineered plants with specific carotenoid profiles.

Plastids and Carotenoid Accumulation

Plastids are ubiquitously present in plants and are the organelles for carotenoid biosynthesis and storage. Based on their morphology and function, plastids are classified into various types, i.e. proplastids, etioplasts, chloroplasts, amyloplasts, and chromoplasts. All plastids, except proplastids, can synthesize carotenoids. However, plastid types have a profound effect on carotenoid accumulation and stability. In this chapter, we discuss carotenoid biosynthesis and regulation in various plastids with a focus on carotenoids in chromoplasts. Plastid transition related to carotenoid biosynthesis and the different capacity of various plastids to sequester carotenoids and the associated effect on carotenoid stability are described in light of carotenoid accumulation in plants.

Biochemical changes in phenols, flavonoids, tannins, vitamin E, β-carotene and antioxidant activity during soaking of three white sorghum varieties

OBJECTIVE

To investigate the changes in total phenols, flavonoids, tannins, vitamin E, β-carotene and antioxidant activity during soaking of three white sorghum varieties.

METHODS

The changes in total phenols, total flavonoids, tannins, phenolic acids compounds, flavonoid components, vitamin E, β-carotene and antioxidant activity during soaking of sorghum grains were determined.

RESULTS

Total phenols, total flavonoids, tannins, vitamin E, β-carotene and antioxidant activity in raw sorghum were ranged from 109.21 to 116.70, 45.91 to 54.69, 1.39 to 21.79 mg/100 g, 1.74 to 5.25, 0.54 to 1.19 mg/kg and 21.72% to 27.69% and 25.29% to 31.97%, respectively. The above measured compounds were significantly decreased after soaking. p-Hydroxybenzoic acid, vanillic acid, syringic acid and cinnamic acid represent the major phenolic acids in Dorado variety. While ferulic acid, p-coumaric acid, gallic acid and caffeic acid represent the major phenolic acids in Shandaweel-6. On the other hand, protocatechuic acid represents the major phenolic acids in Giza-15. Regarding flavonoids components, Dorado was the highest variety in kampferol and naringenin while Shandaweel-6 was the highest variety in luteolin, apigenin, hypersoid, quercetin and christen. Finally, Giza-15 was the highest variety in catechin. Phenolic acids, flavonoid compounds and antioxidant activities were decreased after soaking.

CONCLUSIONS

Sorghum varieties have moderate quantities from total phenols, total flavonoids, tannins, phenolic acids compounds, flavonoid components, vitamin E, β-carotene and antioxidant activity which decreased after soaking.

Effect of different carotenoid-containing diets on the vitamin A levels and colour parameters in Iberian pigs' tissues: utility as biomarkers of traceability

Retinol and fat colour parameters in Iberian pigs fed on different carotenoid-containing diets were assessed. Thirty animals in two groups were considered: Iberian breed pigs fed on acorns and grass (Montanera) and on concentrate (Cebo). Carotenoids and retinoids were analysed in the diets and in plasma, liver and perirenal fat of the animals by HPLC and HPLC-MS. Retinol levels in plasma and fat were similar in Montanera and Cebo animals. The utility of retonids and colour parameters as traceability index was also explored. Retinoids in liver classified correctly 93% of the animals according to their diet L* and hab. CIELAB parameters of the perirenal fat discriminated correctly 78.6% of the animals according to their diet. L* values for the Montanera animals were significantly different (P<0.01) from those fed on concentrate. It can be claimed that the liver retinol profile and fat colour parameters can be useful for feeding traceability purposes in Iberian pigs breed in Montanera and Cebo.

Bioaccessibility of carotenoids from transgenic provitamin A biofortified sorghum

Biofortified sorghum (Sorghum bicolor (L.) Moench) lines are being developed to target vitamin A deficiency in Sub-Saharan Africa, but the delivery of provitamin A carotenoids from such diverse germplasms has not been evaluated. The purpose of this study was to screen vectors and independent transgenic events for the bioaccessibility of provitamin A carotenoids using an in vitro digestion model. The germplasm background and transgenic sorghum contained 1.0-1.5 and 3.3-14.0 μg/g β-carotene equivalents on a dry weight basis (DW), respectively. Test porridges made from milled transgenic sorghum contained up to 250 μg of β-carotene equivalents per 100 g of porridge on a fresh weight basis (FW). Micellarization efficiency of all-trans-β-carotene was lower (p < 0.05) from transgenic sorghum (1-5%) than from null/nontransgenic sorghum (6-11%) but not different between vector constructs. Carotenoid bioaccessibility was significantly improved (p < 0.05) by increasing the amount of coformulated lipid in test porridges from 5% w/w to 10% w/w. Transgenic sorghum event Homo188-A contained the greatest bioaccessible β-carotene content, with a 4-8-fold increase from null/nontransgenic sorghum. While the bioavailability and bioconversion of provitamin A carotenoids from these grains must be confirmed in vivo, these data support the notion that biofortification of sorghum can enhance total and bioaccessible provitamin A carotenoid levels.

Nutritious crops producing multiple carotenoids--a metabolic balancing act

Plants and microbes produce multiple carotenoid pigments with important nutritional roles in animals. By unraveling the basis of carotenoid biosynthesis it has become possible to modulate the key metabolic steps in plants and thus increase the nutritional value of staple crops, such as rice (Oryza sativa), maize (Zea mays) and potato (Solanum tuberosum). Multigene engineering has been used to modify three different metabolic pathways simultaneously, producing maize seeds with higher levels of carotenoids, folate and ascorbate. This strategy may allow the development of nutritionally enhanced staples providing adequate amounts of several unrelated nutrients. By focusing on different steps in the carotenoid biosynthesis pathway, it is also possible to generate plants with enhanced levels of several nutritionally-beneficial carotenoid molecules simultaneously.

Profiles of carotenoids, anthocyanins, phenolics, and antioxidant activity of selected color waxy corn grains during maturation

Waxy corns are becoming increasingly consumed as fresh foods or as raw materials for whole grain foods facilitating human consumption in China, so they are usually harvested before complete maturity. Unfortunately, information on functional properties of immature waxy corns is very limited. Therefore, we investigated the profiles of carotenoids, anthocyanins, phenolics, and the antioxidant activity in three types of waxy corn with different colors (white, yellow, and black) during maturation, as well as a normal corn (yellow) used as control. The results showed that black waxy corn had the highest quantity of anthocyanins, phenolics and the best antioxidant activity, yellow corn contained a relatively large amount of carotenoids, while white corn had the lowest amounts of carotenoids, anthocyanins, phenolics, and antioxidant capacity. For each type of waxy corn, the higher carotenoids were found at the M2 stage (no major difference between the M1 and M2 stages for yellow corn). The levels of anthocyanin and phenolics decreased for white and yellow corns, contrary to those for black corn during maturation. The antioxidant activity determined by scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH), the ferric reducing antioxidant power (FRAP), and the Trolox equivalent antioxidant capacity (TEAC) assays increased with ripening, but no difference was found between the M2 and maturity stages for yellow and black corns. For white corn, the DPPH radical scavenging activity first increased and then decreased, while the antioxidant activity determined by TEAC and FRAP assay decreased during maturation. Differences in these parameters indicate that types and harvesting time have significant influences on functional properties of waxy corns.

Changes in the main nutrients, phytochemicals, and antioxidant activity in yellow corn grain during maturation

Immature corn grains are becoming increasingly popular as a snack/vegetable, facilitating human consumption in some countries. Of particular interest were their nutritional and functional properties. Therefore, plants at stages M1 (74 DAS), M2 (86 DAS), M3 (98 DAS), and maturity stage (116 DAS), where DAS refers to days after seeding, were investigated for changes of the nutrients, phytochemicals, and antioxidant activity in corn grains during maturation. Results revealed that during maturation of corn grains, the content of reducing sugar and crude protein decreased while starch and total lipids increased (p < 0.05). Total carotenoids first decreased, then increased, and then decreased to minimum at maturity stage. Analysis of the main carotenoid compounds determined by HPLC showed that lutein first increased and then decreased (p < 0.05), whereas the reverse was found for beta-cryptoxanthin. The change in zeaxanthin was consistent with total carotenoids. Total phenolic content decreased; nevertheless, different phenolic fractions varied with various maturation stages. The antioxidant activity determined by DPPH and FRAP assay in total phenolic extracts decreased during maturation, which may explain that antioxidant activity can be attributed to soluble phenolic and total phenolic content.

Carotenoid bioaccessibility from whole grain and degermed maize meal products

Although yellow maize (Zea mays) fractions and products are a source of dietary carotenoids, only limited information is available on the bioavailability of these pigments from maize-based foods. To better understand the distribution and bioavailability of carotenoid pigments from yellow maize (Z. mays) products, commercial milled maize fractions were screened for carotenoid content as were model foods including extruded puff, bread, and wet cooked porridge. Carotenoid content of maize fractions ranged from a low of 1.77-6.50 mg/kg in yellow maize bran (YCB) to 12.04-17.94 mg/kg in yellow corn meal (YCM). Lutein and zeaxanthin were major carotenoid species in maize milled fractions, accounting for approximately 70% of total carotenoid content. Following screening, carotenoid bioaccessibility was assessed from model foods using a simulated three-stage in vitro digestion process designed to measure transfer of carotenoids from the food matrix to bile salt lipid micelles (micellarization). Micellarization efficiency of xanthophylls was similar from YCM extruded puff and bread (63 and 69%), but lower from YCM porridge (48%). Xanthophyll micellarization from whole yellow corn meal (WYCM) products was highest in bread (85%) and similar in extruded puff and porridge (46 and 47%). For extruded puffs and breads, beta-carotene micellarization was 10-23%, but higher in porridge (40-63%), indicating that wet cooking may positively influence bioaccessibility of apolar carotenes. The results suggest that maize-based food products are good dietary sources of bioaccessible carotenoids and that specific food preparation methods may influence the relative bioaccessibility of individual carotenoid species.

The maize phytoene synthase gene family: overlapping roles for carotenogenesis in endosperm, photomorphogenesis, and thermal stress tolerance

Carotenoids are essential for photosynthesis and photoprotection; they also serve as precursors to signaling molecules that influence plant development and biotic/abiotic stress responses. With potential to improve plant yield and nutritional quality, carotenoids are targets for metabolic breeding/engineering, particularly in the Poaceae (grass family), which includes the major food crops. Depending on genetic background, maize (Zea mays) endosperm carotenoid content varies, and therefore breeding-enhanced carotenoid levels have been of ongoing interest. The first committed step in the plastid-localized biosynthetic pathway is mediated by the nuclear-encoded phytoene synthase (PSY). The gene family in maize and other grasses contains three paralogs with specialized roles that are not well understood. Maize endosperm carotenoid accumulation requires PSY1 expression. A maize antibody was used to localize PSY1 to amyloplast envelope membranes and to determine PSY1 accumulation in relation to carotenoid accumulation in developing endosperm. To test when and if PSY transcript levels correlated with carotenoid content, advantage was taken of a maize germplasm diversity collection that exhibits genetic and chemical diversity. Total carotenoid content showed statistically significant correlation with endosperm transcript levels at 20 d after pollination for PSY1 but not PSY2 or PSY3. Timing of PSY1 transcript abundance, previously unknown, provides critical information for choosing breeding alleles or properly controlling introduced transgenes. PSY1 was unexpectedly found to have an additional role in photosynthetic tissue, where it was required for carotenogenesis in the dark and for heat stress tolerance. Leaf carotenogenesis was shown to require phytochrome-dependent and phytochrome-independent photoregulation of PSY2 plus nonphotoregulated PSY1 expression.