Linda Dykes

Proanthocyanidin profile of cowpea (Vigna unguiculata) reveals catechin-O-glucoside as the dominant compound

Proanthocyanidin (PA) profile and content can have important nutritional and health implications on plant foods. Six diverse cowpea phenotypes (black, red, green, white, light-brown and golden-brown) were investigated for PA composition using normal-phase HPLC and reversed-phase UPLC-TQD-MS. Catechin and (epi)afzelechin were the major flavan-3-ol units. Unusual composition was observed in all cowpea phenotypes with significant degrees of glycosylation in the monomers and dimers. The PA content of cowpea (dry basis) ranged between 2.2 and 6.3 mg/g. Monomeric flavan-3-ols were the largest group of PA (36-69%) in cowpea, with catechin-7-O-glucoside accounting for most (about 88%) of the monomers. The oligomers with degree of polymerization (DP) 2-4 ranged from 0.41 to 1.3 mg/g (15-20%), whereas DP>10 polymers accounted for only 13.5% of PA. Future studies that highlight the impact of the unusual cowpea PA profile on nutritional and bioactive properties of this important legume are warranted.

Flavonoid composition of lemon-yellow sorghum genotypes.

Flavonoid composition of lemon-yellow sorghums grown in two locations in Texas, USA was evaluated and compared with that of white and red sorghums using high performance liquid chromatography (HPLC-PDA). Sorghums from Lubbock were brighter in colour and had minimal weathering compared to those from College Station. Sorghums with red/purple secondary plant colour had the highest levels of 3-deoxyanthocyanidins (8-187μg/g) and their levels were highest in grains from College Station (39-187μg/g). Pericarp colour did not have any effect on 3-deoxyanthocyanidin levels (p>0.05). The tan plant lemon-yellow sorghum Tx2953 had the highest levels of flavones (268-362μg/g). Among the genotypes, lemon-yellow sorghums had the highest levels of flavanones (134-1780μg/g), which are located in the pericarp and their levels were increased in the grains with a bright yellow pericarp and minimal weathering. The high flavanone levels in lemon-yellow sorghums makes this sorghum genotype a good source of those compounds.

Phenolic composition and inhibitory effect against oxidative DNA damage of cooked cowpeas as affected by simulated in vitro gastrointestinal digestion.

Cowpeas contain phenolic compounds with potential health benefits. The effect of simulated gastrointestinal digestion on phenolic composition of cooked cowpeas and the ability of the digests to inhibit radical-induced DNA damage was determined. A red and a cream-coloured cowpea type were used. The phenolic composition of acetone extracts and enzyme digests of cooked cowpeas was determined using UPLC-MS. Compounds such as p-hydroxybenzoic acid, p-coumaric acid, coumaroylaldaric acid and feruloylaldaric acid were present in the acetone extracts of the cooked cowpeas but were not detected in the enzyme digests. Glycosides of quercetin and myricetin decreased upon in vitro gastrointestinal digestion of cooked cowpeas whereas flavan-3-ols were hardly present except catechin glucoside. The enzyme digest of the red cowpea type was about thrice as effective as that of the cream cowpea type in protecting DNA from oxidative damage. The observation that enzyme digests of cooked cowpeas inhibited radical-induced DNA damage suggests that cowpea phenolics retain some radical scavenging activity after gastrointestinal digestion.

Ultra Performance Liquid Chromatography–Tandem Quadrupole Mass Spectrometry Profiling of Anthocyanins and Flavonols in Cowpea (Vigna unguiculata) of Varying Genotypes

The structure of flavonoids in food plants affects bioactivity and important nutritional attributes, like micronutrient bioavailability. This study investigated flavonol and anthocyanin compositions of cowpea (Vigna unguiculata) of varying genotypes. Black, red, green, white, light brown, and golden brown cowpea phenotypes were analyzed for anthocyanins and flavonols using ultra performance liquid chromatography-tandem quadrupole mass spectrometry. Eight anthocyanins and 23 flavonols (15 newly identified in cowpea) were characterized. Mono-, di-, and tri(acyl)glycosides of quercetin were predominant in most phenotypes; myricetin and kaempferol glycosides were present only in specific phenotypes. The red phenotypes had the highest flavonol content (880-1060 μg/g), whereas green and white phenotypes had the lowest (270-350 μg/g). Only black (1676-2094 μg/g) and green (875 μg/g) phenotypes had anthocyanins, predominantly delphinidin and cyanidin 3-O-glucosides. Cowpea phenotype influenced the type and amount of flavonoids accumulated in the seed; this may have implications in selecting varieties for nutrition and health applications.

Thermal stability of 3-deoxyanthocyanidin pigments

3-Deoxyanthocyanidins are promising natural colourants due to their unique properties compared to anthocyanins. However, thermal stability of 3-deoxyanthocyanidins is largely unknown. Thermal stability of crude and pure 3-deoxyanthocyanidins was determined at 95 °C/2 h and 121 °C/30 min, at pH 1-7 using HCl, formic or citric acid as acidulants. The colour retention of crude and pure 3-deoxyanthocyanidins (79-89% after 95 °C/2 h and 39-118% after 121 °C/30 min) was high compared to literature reports for anthocyanins under similar treatments. pH significantly affected the thermal stability of 3-deoxyanthocyanidins: Colour retention was better at pH 1-2 (70.2-118%) than at pH 3-7 (39.0-86.8%). Chalcones were identified as the major heat degradation products at pH 3-7. Slow rate of chalcone formation and resistance to C-ring fission were identified as the major contributors to thermal stability of 3-deoxyanthocyanidins. Overall, the heat stability of 3-deoxyanthocyanidins indicates good potential for food use.

Influence of Genetic Background on Anthocyanin and Copigment Composition and Behavior during Thermoalkaline Processing of Maize.

Visual color is a primary quality factor for foods purchase; identifying factors that influence in situ color quality of pigmented maize during processing is important. Twenty-four genetically distinct pigmented maize hybrids (red/blue, blue, red, and purple) were used to investigate the effect of pigment and copigment composition on color stability during nixtamalization and tortilla chip processing. The red/blue and blue samples generally contained higher proportions of acylated anthocyanins (mainly cyanidin-3-(6″-malonylglucoside)) than the red and purple color classes. Phenolic amides were the major extractable copigments in all samples (450-764 μg/g), with red samples containing the most putrescines and blue samples containing the most spermidines. Even though samples with higher proportions of acylated anthocyanins retained more pigments during processing, this did not relate to final product color quality. In general, the red/blue samples retained their color quality the best and thus are good candidates for genetic improvement for direct processing into alkalized products.

Condensed Tannins in Traditional Wet-Cooked and Modern Extrusion-Cooked Sorghum Porridges

ABSTRACT The profile and quantities of condensed tannins (CT) in foods are affected by processing due to their highly reactive nature, which may affect their antioxidant activity and the nutritional value of the foods. The objective was to compare the quantity and profile of condensed tannins in traditional wet-cooked and modern ready-to-eat extrusion-cooked sorghum porridges. CT were analyzed using normal-phase HPLC with fluorescence detection and their content was compared to CT and total phenols determined with standard colorimetric assays. Both the traditionally prepared and instant porridges had significantly reduced CT polymers (DP > 8), with retentions of 38 and 9%, respectively, of the CT present in the whole grain. Oligomer (DP 2–8) and monomer (DP 1) contents in traditional porridges were not significantly different from those of grain. In extruded porridges, the oligomers were reduced and the monomer content was increased. The extractable CT oligomers and monomers in the extrusion-cooked sorghu...

Impact of Novel Sorghum Bran Diets on DSS-Induced Colitis

We have demonstrated that polyphenol-rich sorghum bran diets alter fecal microbiota; however, little is known regarding their effect on colon inflammation. Our aim was to characterize the effect of sorghum bran diets on intestinal homeostasis during dextran sodium sulfate (DSS)-induced colitis. Male Sprague-Dawley rats (N = 20/diet) were provided diets containing 6% fiber from cellulose, or Black (3-deoxyanthocyanins), Sumac (condensed tannins) or Hi Tannin Black (both) sorghum bran. Colitis was induced (N = 10/diet) with three separate 48-h exposures to 3% DSS, and feces were collected. On Day 82, animals were euthanized and the colon resected. Only discrete mucosal lesions, with no diarrhea or bloody stools, were observed in DSS rats. Only bran diets upregulated proliferation and Tff3, Tgfβ and short chain fatty acids (SCFA) transporter expression after a DSS challenge. DSS did not significantly affect fecal SCFA concentrations. Bran diets alone upregulated repair mechanisms and SCFA transporter expression, which suggests these polyphenol-rich sorghum brans may suppress some consequences of colitis.

TRANSFORMATION OF ADSORBED AFLATOXIN B1 ON SMECTITE AT ELEVATED TEMPERATURES

Aflatoxins cause liver damage and suppress immunity. Through adsorption, smectites can be used to reduce the bioavailability of aflatoxins. To further reduce the toxicity of aflatoxins and to eliminate the treatments of aflatoxin-loaded smectites, the ability to degrade the aflatoxin adsorbed to non-toxic or less toxic compounds is desirable. The objective of the present study was to investigate the effects of temperature and the exchange cation on the transformation of adsorbed aflatoxin B1 on smectite. An AfB1-Ca-smectite (sm) complex was synthesized. To enhance the Lewis acidity of the complexes, the exchanged calcium in the complex was replaced with Mn and Cu to obtain AfB1-Mn-sm and AfB1-Cu-sm complexes, respectively. The aflatoxin-sm complexes and pure aflatoxin B1 were dried at 60°C in aluminum cups, and heated from 100 to 200°C in 25°C steps. Aflatoxin B1 and its transformation products were extracted with methanol after the heat treatment. The extracts were analyzed using UV spectroscopy, high performance liquid chromatography (HPLC)-fluorescence/UV, ultra-performance liquid chromatography (UPLC)-photodiode array (PDA), and electrospray ionization-tandem quadrupole-mass spectrometry (ESI-TQDMS). The solid residues were analyzed using Fourier-transform infrared spectroscopy (FTIR). The UV and FTIR spectra of the AfB1-sm clay residue extracts obtained after heating had decreased AfB1 peak intensities and shifted peak positions with increased heating temperature. Significant shifts in band positions and changes in the shape of the UV spectra were observed in the extracts from the AfB1-Ca-sm complex heated at 175°C, the AfB1-Cu-sm complex heated at 150°C, and the AfB1-Mn-sm complex heated at 125°C. The HPLC and UPLCMS analyses of AfB1-sm complex extracts indicated a gradual decrease in AfB1 concentration with increased heating temperature and the formation of aflatoxins B2, B2a, M1, M2, and other unidentified compounds. No new compound was observed in the extracts of pure aflatoxin B1 after a comparable heating experiment. These results suggest that smectite can effectively convert aflatoxin to other less toxic forms at elevated temperatures. Smectite ion exchange with Cu or Mn transition-metal cations and heat treatment induced more efficient conversion of the adsorbed aflatoxin B1 molecules to other compounds.

Utilization of African Grains in Nutritionally Unique Foods

African grains vary significantly in kernel structure, processing properties, and nutritionally important components. The major African grains are sorghum, pearl millet, fonio, teff, and finger millet. They are used as whole ground grains or they are pearled to remove the pericarp as bran. The type of grains grown in the region varies depending upon the variety which has been used for centuries. Some special grains are grown and used for special foods. We focus on sorghum because it is widely used in Africa and India. For example the sorghums in India are grown in the rainy season and also in the dry season. The rabi or dry season sorghums have white softer kernels because there is little rain during production. For the wet season, lemon-yellow sorghums are usually preferred. In Africa, sorghum is used in production of many different foods, from beer to an array of porridges. The use of whole grains from sorghum provides an excellent array of products with good nutritional value that differ in color and other attributes. Sorghums can be used effectively to produce gluten-free products that are attractive, nutritious, and profitable. The supply chain for special sorghums is improving but still limited. Sorghum has relatively high grain yields and is well adapted to a range of environments. Sorghums are strong competitors in gluten-free foods as well as other food systems that use sorghum bran or whole grain in blends. Sorghum ranges from bland flavor and light color to dark chocolate-like colors with unique phytochemicals. It’s a productive crop with high grain yields adapted to hot dry areas where other crops are not well adapted. For example it will produce grain under hot dry conditions where maize fails and is contaminated with aflatoxins. Sorghum varies in composition and kernel structure and is consumed as porridges, flat breads, couscous, and a wide variety of fermented products and composites with cowpeas and other grains. Most sorghums are milled by decortication to remove the pericarp to produce food products, usually porridges and couscous, or endosperm particles cooked into thick and thin porridges. Some very soft floury sorghums are ground into whole grain meal or flour and used in numerous foods. In some cases, only soft floury sorghums can be grown and they often contain tannins which control grain deterioration and bird damage in the field. Tannin sorghums are soft and cannot be decorticated so they are used as ground whole porridges especially when hard work is being done. The tannin sorghums are preferred since they “stay with the person longer” than white sorghum porridges. Special foods made from high tannin sorghums are provided to new mothers. In some cases, the pigments of sorghum are used as a colorant for foods. Sorghum hybrids are high yielding and can be milled into an array of gluten-free and slowly digested products. Sorghums are often misunderstood because they have tannins which adversely affect the nutritional value of high tannin sorghums. Thus, for feeding animals the tannin sorghums are not preferred because they negatively affect digestibility and thus reduce the feed efficiency of the grains. Therefore, the industry has discounted the feeding value of tannin sorghum grains. Tannin sorghums are said to be bird-proof but birds will eat tannin sorghum if other foods are unavailable. The tannins protect the grain against mold deterioration in the field. Sorghums vary significantly in phytochemicals depending upon their genetics. Sorghum is a practical source of desirable phenolics from tannins to flavonoids. Some varieties have very high levels of condensed tannins while others have exceptionally high levels of rare 3-deoxyanthocyanins. Sorghums with lemon-yellow pericarp have very high levels of flavanones. Other sorghums, especially tan and red sorghums, have high levels of flavones. Sorghum has much higher levels of phenols than other cereals in general but different sorghums vary in type and quantities of phenolics. For example, Onyx is a special sorghum with high levels of 3-deoxyanthocyanidins which was released by Texas AgriLife Research. This is a unique characteristic that produces red pigments which turn black when they are exposed to sunlight. These types are high in 3deoxyanthocyanin compounds and may or may not contain condensed tannins. It is a very effective colorant for food products with more tolerance to high pH than vegetable and fruit pigments. The combination of tannins and other flavonoids present in sorghum make it an effective source of phytochemicals because it is easily grown and processed into food products. Sorghums that contain condensed tannins are used for special foods where slower digestion is desired and unique color is an advantage. Tannin grains can be decorticated to produce bran with high levels of tannins and, before or after roasting, they can be used to produce attractive colored products similar to 1 Cereal Quality Lab, Texas A&M University, College Station, Texas. 2 Corresponding author. E-mail: lrooney@tamu.edu.