Simulation of the factors affecting β-glucan levels during the cultivation of oats

A Monte Carlo simulation technique was employed to simulate the factors influencing the level of β-glucan content in both hulled (HO) and naked (NO) oat cultivars during cultivation of the crop. Probability density functions were used to model the uncertainty and variability in the input factors. A scenario analysis was subsequently developed to look at the impact of different model assumptions and input parameters. The simulated mean β-glucan level in harvested oats grain was 3.50 and 4.25 g/100 g for hulled (HO) and naked (NO), respectively. A sensitivity analysis highlighted that cultivar selection was the most important input parameter compared to other inputs in determining the final β-glucan level (correlation coefficients of 0.64 and 0.79 for HO and NO, respectively). The analysis also indicated the positive effect of delayed sowing on β-glucan content (correlation coefficients of 0.32 and 0.25 for HO and NO, respectively). Germination and storage factors showed a negative impact on the final β-glucan levels. The scenario analysis shows the applicability of the proposed model for various agronomic practices. This approach establishes a quantitative scientific ranking of factors influencing β-glucan levels during the cultivation of oats.     

Detection of the lunasin peptide in oats (Avena sativa L)

We report the first discovery of lunasin in oats (Avena sativa L). Lunasin is a novel cancer preventive, anti-inflammatory and cholesterol-reducing peptide originally isolated from soy and later found in cereals (barley, rye, wheat, triticale). Lunasin was detected in oats using LC–MS/MS analysis. The chromatograms and mass spectra of lunasin isolated from five oat genotypes were compared with those of the synthetic lunasin peptide. We measured the lunasin content in harvests of two years and found that all tested oat genotypes contained the lunasin peptide. However, we observed genotype-related fluctuations in the lunasin content. Notably, the middle early oat variety ‘Ivory’ contained the highest and the most stable lunasin level at 0.197 ± 0.01 mg per g of grain in year 2010 and 0.195 ± 0.009 mg per g of grain in 2011. We also characterized the selected oat genotypes by measuring the contents of protein, β-glucans, fat, starch and moisture in the grains. However, we did not find correlation between lunasin and protein, and β-glucan content. Lunasin isolated from oat showed similar to the synthetic lunasin antioxidant effects. The detection of lunasin complements a list of bioactive compounds present in oats and strengthens recommendations to use oat products.     

Chemical composition and sensory characteristics of oat flakes: A comparative study of naked oat flakes from China and hulled oat flakes from western countries

Oats are generally considered as a health food and widely accepted by human beings nowadays. Oat flakes are the main commercial oat products around the world. In order to understand the chemical composition and sensory characteristics of the naked oat flakes from China and the hulled oat flakes from western countries, 37 flake samples from China and 44 samples from western countries (8 from the USA, 8 from Canada, 5 from Sweden, 8 from Denmark, 7 from the United Kingdom, and 8 from New Zealand) were investigated in the present study. The results indicated that naked oat flakes showed significantly higher (P < 0.01) contents of lipid and Na, a higher level of whiteness (P < 0.05) and lower (P < 0.01) contents of β-glucan and Fe, compared to hulled oat flakes from western countries. No significant differences of Zn, Ca, and total ash contents were observed between naked oat flakes and hulled oat flakes. In addition, naked oat flakes showed significantly higher water absorption index at room temperature (P < 0.01) when compared with hulled oat flakes. Hulled oat flakes showed higher sensory evaluation score than naked oat flakes (P < 0.01).     

Detect unique molecular structure associated with physiochemical properties in CDC varieties of oat grain with unique nutrient traits [Feed Type vs. Milling Type] in comparison with barley grain using advanced molecular spectroscopy as a non-destructive biological tool

The objective of this study was to determinate grain unique protein inherent molecular structure that are related physiochemical and nutrient profiles in CDC developed oat varieties [CDC Nasser (Feed Type) and CDC Seabiscuit (Milling Type)] grown in cool climate condition in western Canada in comparison with conventional barley variety of CDC Meredith as a control using advanced molecular spectroscopy. Multivariate analyses, including an agglomerative hierarchical cluster analysis (CLA) and principal component analysis (PCA), were performed to identify protein molecular structural differences among the grains. The results revealed that CDC Seabiscuit contained greater (P < 0.05) protein structural Amide I and II than CDC Nasser and CDC Meredith, while the greater (P < 0.005) structural Amide I to II area and height ratios was detected in CDC Meredith. New oat grains had greater (P < 0.05) β-sheet height than barley grains, however, there was no difference in α-helix to β-sheet ratio values among the varieties. In conclusion, CDC Nasser and CDC Meredith had no difference in protein molecular structural features, while CDC Seabiscuit contains different protein structural characteristics as compared to CDC Meredith grain. The molecular structure features are highly associated with physiochemical and nutrient profiles in grains, which indicate that it also affect nutrient utilization and availability.     

Development of standard fingerprints of naked oats using chromatography combined with principal component analysis and cluster analysis

Oat samples of different varieties were collected from various habitats for the determination of avenacoside, β-glucan and fatty contents. The variation coefficients of the three components were 12.13%, 20.79% and 22.46%, respectively. Thus, those three indicators cannot represent the information of all samples, and are not suitable for evaluating the quality of oat raw materials and products. Fatty acid profiles were analyzed using gas chromatography combined with principal component analysis (PCA) and cluster analysis. Fourteen leather oat varieties were distinguished through a PCA scores scatterplot. Forty-six naked oat varieties were selected by cluster analysis and eleven characteristic peaks in these naked oats were identified. Finally, accurate fatty acid standard fingerprints of naked oats were constructed. The results of methodological indicated high precision, reproducibility and stability, in line with fingerprint testing requirements. This study fills the knowledge gap for naked oat fingerprint information, expands the grain fatty acid database, and lays the foundations of a grain nutritional liposome identification technology system.     

Molecular characterisation of 36 oat varieties and in vitro assessment of their suitability for coeliacs’ diet

Coeliac disease (CD) is a chronic intolerance to gluten, contained mainly in wheat, rye and barley. The only therapy at present is the lifelong exclusion of gluten from the diet.Whether oats can be considered safe for CD patients has long been debated, and oats have been included among gluten-free ingredients only recently (EU Regulation 41/2009), provided the gluten content does not exceed 20 ppm.The aim of this study was to evaluate the suitability of 36 different oat cultivars for CD patients using biochemical and immunochemical approaches. The cross-reactivity between avenins and gliadins was evaluated by both SDS-PAGE/Immunoblotting and ELISA.The protein pattern of each oat cultivar showed both qualitative and quantitative differences that correlated with different binding affinity for specific anti-gliadin antibodies in immunoblotting. In most oat samples, the content of cross-reactive proteins measured by ELISA was below 20 ppm, but in a few varieties was above 80 ppm.Although the taxonomic and biochemical characteristics of oats allow to conclude that their use could be safe for CD patients, it is essential to select those cultivars having the lowest level of gluten-like proteins.     

Impact of native form oat β-glucan on starch digestion and postprandial glycemia

Whole grain oats, as a rich source of β-glucan, have been shown beneficial to glycemic control. In the current study, the impact of native form β-glucan in oat grains (NFO-glucan) on starch digestion and postprandial glycemia was investigated. The dry-milling prepared NFO-glucan sample was enriched with native form β-glucan (15.6%), and an in vitro starch digestion assay of NFO-glucan (0.5% starch equivalent) showed a significant decrease of starch digestion rate compared to oat starch (0.5%, w/v). However, pretreatment by either β-glucanase or pepsin significantly increased the starch digestion. Consistently, an in vivo examination on the postprandial glycemia of the cooked NFO-glucan sample using a mouse model displayed a significant decrease of postprandial glycemia compared to gelatinized oat starch. Further experiment on the pasting property of NFO-glucan sample by a rapid visco-analyser demonstrated both β-glucan and protein affected its viscosity profiles. Scanning Electronic Microscope (SEM) observation revealed a network-like native structure of β-glucan that might encapsulate protein and starch to reduce the enzyme accessibility and so the digestion of starch. Novel food processing technologies to maintain the native form of β-glucan in oat grains might be a better way to modulate the postprandial glycemia of oat-based whole grain foods.     

Effect of heat treatment on the flavor of oat flakes

In order to assess the effect of heat treatment procedure on the flavor and volatile compounds of oats, raw oats, kiln and dried oats, dehulled oats and oat flakes were analysed. A sensory profile method was used to monitor changes in flavor. It changed from hay-like for raw oats into nutty, bread-like for oat flakes. Headspace solid phase microextraction (SPME) and solvent assisted flavor evaporation (SAFE) techniques were applied for isolation of aroma compounds. The most abundant compound in headspace was hexanal – its concentration varied from 176 to 1671 μg/kg depending on the processing stage. The key aroma compounds of oat flakes identified using gas chromatography – olfactometry and aroma extract dilution analysis (AEDA) were 2-methyl-3-furanthiol with roast/cooked oatmeal flavor together with methional, dimethyl trisulfide, 1-octen-3-ol, 2-methyl-3,5-diethylpyrazine.     

Digestibility of starch fractions in wholegrain rolled oats

A practical in vitro method was tested for measuring differences in rapidly digested starch (RDS measured at 20 min), slowly digested starch (SDS between 20 and 120 min) and inaccessible digestible starch (IDS as carbohydrate digested after homogenising at 120 min to release inaccessible starch and digesting for a further 40 min) in wholegrain cereal samples retaining some grain structure, using in vitro pancreatic digestion after a “gastric” pepsin–HCl pre-treatment. The persistence of digestive capacity, the influence of homogenising on digestive capacity, and the benefit of adding supplementary amyloglucosidase after 120 min digestion were tested as effects on capacity to digest a further 2.5 g portion of finely ground wholegrain added to selected 120 min digests. The results showed that sufficient digestive capacity remained to digest the IDS released by homogenising the wholegrains after 120 min prior digestion. The method measured all fractions with good precision (CV < 6%), and was shown to be capable of measuring a wide degree of variation in starch fractions of differing digestibility in rolled oats from an oat breeding population, so may be useful in detecting the effects of variations in grain structure that influence the glycemic impact of wholegrain products.     

Occurrence and Stabilities of Oat Trypsin and Chymotrypsin Inhibitors

Nine chymotrypsin and four trypsin inhibitors have been extracted and separated from ungerminated oat grains. The inhibitors fell into two groups, based on their heat and pH stabilities. Members of the most abundant group are labile and are inactivated at 80 °C or at pHs of 3·3 or lower. Members of the second group are stable and are resistant to boiling for 30 min. On germination, the labile inhibitors are inactivated after 2 days and the stable chymotrypsin inhibitors after 3 days. Most of the labile inhibitors from ungerminated grain are destroyed when incubated at 20 °C for 20 h but addition of PMSF, a serine protease inhibitor, prevented their inactivation. Labile inhibitors in extracts of ungerminated oats are inactivated on incubation with an extract prepared from germinated oats, but not in the presence of PMSF. Most oat chymotrypsin and trypsin inhibitors are heat labile and pH sensitive. These inhibitors are apparently inactivated by serine proteinase(s) already present in ungerminated grain.     

Variation in Oat Groats Due to Variety, Storage and Heat Treatment. II: Sensory Quality

A sensory profiling analysis of heat-processed oats (Avena sativaL.) was performed. The oat grains were of three varieties (Kapp, Mustang and Svea), stored at different relative humidities (30, 55 or 80%) for 3·5 or 15·5 months and heat-treated either with or without prior dehulling. The main differences in sensory attributes were related to the various thermal processes. Processed dehulled samples, particularly of theMustangvariety, had the highest intensities of oat odour, oat flavour, fresh odour and fresh flavour. Samples processed with hulls, in particular the varieties Kapp and Svea had the highest intensities of odour and flavour, rancid odour and flavour and bitterness. The sensory profile of processed oats were described partly by variations in phenolic compounds of low molecular weight, fat acidity and moisture content after processing. Twenty-nine per cent of the variation in odour and flavour attributes was explained by the 11 phenolic compounds analysed. Water content and the phenolic compoundsp-coumaric acid, vanillin,p-hydroxybenzaldehyde and coniferyl alcohol were significantly correlated (P<0·05) to high levels of rancidity, flavour intensity and bitterness and low levels of freshness, oat odour and flavour. The avenanthramides were related mainly to low levels of flavour intensity and rancid odour and flavour. Caffeic acid and fat acidity were related to low intensities of sweetness and aftertaste.     

Grain weight changes over time in ancient cereal crops: Potential roles of climate and genetic improvement

Inferences of grain weight (GW) for cereals cultivated in the past could be useful to track early agronomic improvements. Though strongly genetically determined, GW also depends on environmental conditions, such as water availability. In the archaeological context, we can estimate GW and plant water status from grain dimensions and carbon isotope discrimination (Δ¹³C), respectively. In this study we attempted to determine the role of environmental changes on the evolution of GW of naked wheat (Triticum aestivum/durum) and hulled barley (Hordeum vulgare) in the Ebro Depression (NE Spain) during the last four millennia. To that end, we examined charred grains from nine archaeological sites, from the Bronze Age (ca. 1950 BCE) to the end of the Middle Ages (XVth century). Estimated GW in archaeological grains (averaging ca. 19.5 mg for both species) was significantly lower than in present rainfed cereals in the area (ca. 35 mg). In contrast, for both species mean Δ¹³C values in archaeological grains were similar to or even greater than in modern material (16.3‰ and 15.5‰, respectively). Accordingly, we conclude that the most recent increase in GW cannot be attributed to increased water availability, but probably to empirical breeding efforts which would have started not before the beginning of the CE.     

Genetic and environmental variability in total and soluble β-glucan in European oat genotypes

A growing interest in oat (Avena ssp.) soluble fibre (β-glucan) is related to its role in the promotion of human health, and to its utilization in the production of functional foods with increased health benefits. Genetic variability and environmental conditions can exert significant effects on the grain β-glucan content. In this study 658 European oat genotypes grown in different environments in 2008 or 2009 within the European Project “Avena genetic resources for quality in human consumption” were analysed for total β-glucan content; the soluble fraction of β-glucan was also determined in a sub-set of 165 samples. Total β-glucan content ranged from 2.85 to 6.77% d.m. and the soluble fraction from 2.05 to 5.29% d.m. The estimated percentage of the soluble fraction ranged from 50.7 to 87.0%. β-glucan content and solubility were significantly influenced by both genotype and growing environment. Hierarchical cluster analysis allowed accessions with similar β-glucan compositions to be grouped. The accessions with the highest contents of both fractions included Avena sativa varieties from several countries and wild species. Finally, the data obtained were used to develop a NIRS calibration equation to predict the contents of total and soluble β-glucan in both naked and husked genotypes.     

Starch granule morphology in oat endosperm

Mature and developing oat (Avena sativa) grains were sectioned and image analysis methods used to estimate the starch granule-size distribution and morphology in endosperm cells. This showed that oat endosperm cells contain two types of starch granule: compound starch granules such as those seen in rice endosperm and in most other grasses; and simple granules similar to the B-type starch granules seen in the endosperm of Triticeae species such as wheat (Triticum aestivum). The simple granules in oats are similar in size and relative abundance to B-type granules in Triticeae suggesting that they may share a common evolutionary origin. However, there is a fundamental difference between oats and Triticeae in the timing of granule initiation during grain development. In Triticeae, the B-type granules initiate several days after the A-type granules whereas in oats, both the simple and compound granule types initiate at the same time, in early grain development.     

Fundamental evaluation of the impact of high Hydrostatic Pressure on oat batters

The use of grains alternative to wheat or rye is a challenging task for cereal technologists, and currently new technologies are under investigation as tools to improve the performances of these alternative grains. In this work the effects of high Hydrostatic Pressure (HP) on oat batters were investigated. Oat batters were treated for 10 min at 200, 300, 350, 400 or 500 MPa. Scanning electron microscopy and bright field microscopy showed that high HP significantly affected oat batter microstructure, and both starch and proteins were affected. Treatment at high HP significantly improved batter viscosity and elasticity. At pressures ≤300 MPa the increase in the viscous component was higher than the increase in the elastic component. On the contrary, at pressures ≥350 MPa the elastic component was predominant. Differential scanning calorimetry revealed that high HP induced starch gelatinisation, which started at 300 MPa and was almost complete after treatment at 500 MPa. High HP also affected water- and salt-soluble as well as urea-soluble oat proteins. Analysis of proteins soluble in different buffers revealed that pressures ≥300 MPa induced the formation of urea-insoluble complexes and/or disulfide bonds. Overall, the extent of starch gelatinisation and protein modification was dependent on the applied pressure, but the results collected so far clearly show that high HP can be used to improve the functionality of oat batters.     

Spring wheat response to timing of water deficit through sink and grain filling capacity

Water and nitrogen (N) availability are the main factors influencing crop growth globally. Poorly distributed or insufficient water for crop growth requirements decreases yields in drought-prone areas such as those with a Mediterranean type environment. Cereal grain yield is a complex trait of interrelated components: plants per unit land area, spikes per plant, spikelets per spike, grains per spikelet, and single grain weight (SGW). The effect of water limitation and timing on development of yield components was studied in detail at the spike level in spring wheat (Triticum aestivum L.) cultivar Amaretto. An experiment with three watering treatments (control watering, CONT; drought prior to pollination, DR1 and terminal drought, DR2) was arranged in a large greenhouse (20 m × 30 m), with the use of standard field-trial machinery. Automated blackout curtains were used to control day length, which was set to correspond to that at 40°N. With watering treatments, two N application rates (60 and 120 kg N ha⁻¹) were used to investigate the N effect and potential watering × N interaction on yield formation and realisation. The water deficit effect exceeded the effect of N on fertile floret and grain number and SGW. DR1 strongly reduced the number of fertile florets and grains, whereas terminal drought reduced the number of grains per spike. Resuming the watering at pollination markedly enhanced photosynthesis, and hence grain filling capacity, resulting in the highest SGW in DR1. Enhancement in availability of key resources was associated with reduced rate of fertile floret and grain abortion, which resulted in higher grain to fertile floret ratio in DR1. Spikelets in the mid-section of the spike dominated yield formation in all treatments. In DR1 this was especially emphasised as 53% of the grain yield was produced in spikelets 4–6, whereas in DR2 and CONT this was 45 and 41%, respectively. Grains in proximal position in the spikelets produced about 80% of the spike grain yield, the proportion being slightly higher in stressed plants and plants receiving 60 kg N. No marked N × water deficit treatment interaction occurred for any of the measured parameters.     

CO2-defatted oats: Solubility,emulsification and foaming properties

Functional properties of conventional oat materials are relatively poor with respect to foam and emulsion formation and stabilization. This is largely due to the poor solubility of oat proteins and the presence of lipids in aqueous extracts of oats. In the experimental part of this study, extracts were prepared from different type oat flours (oat endosperm flour, oat fine flour, CO₂-defatted whole oat flour and CO₂-defatted oat flour) with a buffered aqueous extraction procedure at acidic (pH 4.5 and 6.5) and basic (pH 8.5 and 10.5) regions. The solubility of proteins was the highest at pH 10.5 and NaCl concentration of 2%. Among the extracts, CO₂-oat flour showed improved foaming and emulsifying properties at basic pH values. The presence of 0.1% NaCl resulted in the lowest foam volumes, but the emulsion activity and stability values being the highest. Sucrose addition resulted in increased foam and emulsion stability of suspensions. Heat treatment at 80 °C impaired foam properties, whereas the stability of emulsions increased with the increase in temperature from 20 °C to 80 °C. CO₂-extracted oats can be useful raw materials in beverages and other aqueous applications where protein functionality plays an important role.     

The effect of heat treatment on the soluble protein content of oats

The effect of heat treatment on the soluble protein content in oat groats (Kerstin commercial variety) was evaluated using asymmetric flow field-flow fractionation (AF4) in combination with online multiangle light scattering (MALS) and UV detection. The AF4 method was used to separate the monomeric proteins from globulin hexamer and aggregate proteins and β-glucan polysaccharides in the soluble oat protein fraction. The total amount of soluble protein (with respect to total protein) was reduced to 35.7 ± 4.5 wt. % in heat treated oats from 74.6 ± 5.3 wt. % in non-heat treated oats. The ratio of monomeric to globulin hexamer and aggregate proteins was reduced from 1.82 to 1.48 as a result of heat treatment. Sodium-dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis revealed the selective elimination of protein bands associated with the albumin and prolamin protein fractions as a result of heat treatment. These results were supported through amino acid analysis by cation exchange chromatography coupled with UV detection which revealed a reduction in amino acid residues associated with prolamin. The globulin proteins were found to be less sensitive to heat treatment.     

Lipid removal enhances separation of oat grain cell wall material from starch and protein

Effects of lipid removal on the fine milling and air classification processing of oats were studied. Lipid removal by supercritical carbon dioxide (SC-CO₂) extraction enabled concentration of the main components of oats - starch, protein, lipids and cell walls - into specific fractions. Using defatted oats as raw material, the highest β-glucan concentration of the cell wall-enriched fraction was 33.9% as compared to 17.1% without lipid removal. This was probably due to more efficient milling yielding smaller particles, and release of starchy material from cellular structures during milling of defatted oats, resulting in better classification. The removal of lipids also enabled separation of an oat protein concentrate with a protein concentration of 73.0% and a mass yield of 5.0%. A trial with 2310 kg of oat groats showed that the process based on defatting and dry fractionation was also industrially applicable.     

Yield dilution of grain Zn in wheat grown in open-top chamber experiments with elevated CO2 and O3 exposure

Wheat (Triticum aestivum L.) grain Zn data from six open-top chamber experiments performed in south-west Sweden were combined to study the relationship between Zn accumulation and grain yield, grain protein, and yield components. Treatments included, in addition to open-top chamber controls, elevated CO₂, elevated O₃, combined CO₂ and O₃ exposure, combined elevated CO₂ and supplemental irrigation, supplemental irrigation, and ambient air comparison plots. The grain Zn concentration was strongly correlated with grain protein (R² = 0.90) over the range of the experimental treatments, representing non-soil factors. A significant yield dilution effect was found for Zn. For a 10% increase in grain yield, Zn yield was increased by 6.8% on average. Effects on Zn yield correlated strongly with effects on grain protein yield, with a slope close to unity, showing that yield dilution effects for grain Zn and grain protein were similar. Treatment effects on grain Zn concentration were related to effects on grain weight (P < 0.01) and grain number (P < 0.05), but not to harvest index. It was concluded that yield stimulation caused by rising CO₂ concentrations is likely to lead to reduced Zn concentrations of wheat grain, thus reducing the nutritional quality.