Nitrogen and sulfur effects on hard winter wheat quality and asparagine concentration

Different wheat loci are associated to heritable free asparagine content in grain grown under different water and nitrogen availability

KEY MESSAGE

Different wheat QTLs were associated to the free asparagine content of grain grown in four different conditions. Environmental effects are a key factor when selecting for low acrylamide-forming potential. The amount of free asparagine in grain of a wheat genotype determines its potential to form harmful acrylamide in derivative food products. Here, we explored the variation in the free asparagine, aspartate, glutamine and glutamate contents of 485 accessions reflecting wheat worldwide diversity to define the genetic architecture governing the accumulation of these amino acids in grain. Accessions were grown under high and low nitrogen availability and in water-deficient and well-watered conditions, and plant and grain phenotypes were measured. Free amino acid contents of grain varied from 0.01 to 1.02 mg g-1 among genotypes in a highly heritable way that did not correlate strongly with grain yield, protein content, specific weight, thousand-kernel weight or heading date. Mean free asparagine content was 4% higher under high nitrogen and 3% higher in water-deficient conditions. After genotyping the accessions, single-locus and multi-locus genome-wide association study models were used to identify several QTLs for free asparagine content located on nine chromosomes. Each QTL was associated with a single amino acid and growing environment, and none of the QTLs colocalised with genes known to be involved in the corresponding amino acid metabolism. This suggests that free asparagine content is controlled by several loci with minor effects interacting with the environment. We conclude that breeding for reduced asparagine content is feasible, but should be firmly based on multi-environment field trials.

KEY MESSAGE

Different wheat QTLs were associated to the free asparagine content of grain grown in four different conditions. Environmental effects are a key factor when selecting for low acrylamide-forming potential.

Enhancing nitrogen use efficiency and yield of maize (Zea mays L.) through Ammonia volatilization mitigation and nitrogen management approaches

Management of nitrogen (N) fertilizer is a critical factor that can improve maize (Zea mays L.) production. On the other hand, high volatilization losses of N also pollute the air. A field experiment was established using a silt clay soil to examine the effect of sulfur-coated urea and sulfur from gypsum on ammonia (NH3) emission, N use efficiency (NUE), and the productivity of maize crop under alkaline calcareous soil. The experimental design was a randomized complete block (RCBD) with seven treatments in three replicates: control with no N, urea150 alone (150 kg N ha-1), urea200 alone (200 kg N ha-1), urea150 + S (60 kg ha-1 S from gypsum), urea200 + S, SCU150 (sulfur-coated urea) and SCU200. The results showed that the urea150 + S and urea200 + S significantly reduced the total NH3 by (58 and 42%) as compared with the sole application urea200. The NH3 emission reduced further in the treatment with SCU150 and SCU200 by 74 and 65%, respectively, compared to the treatment with urea200. The maize plant biomass, grain yield, and total N uptake enhanced by 5-14%, 4-17%, and 7-13, respectively, in the treatments with urea150 + s and urea200 + S, relative to the treatment with urea200 alone. Biomass, grain yield, and total N uptake further increased significantly by 22-30%, 25-28%, and 26-31%, respectively, in the treatments with SCU150 and SCU200, relative to the treatment with urea200 alone. The applications of SCU150 enhanced the nitrogen use efficiency (NUE) by (72%) and SCU200 by (62%) respectively, compared with the sole application of urea200 alone. In conclusion, applying S-coated urea at a lower rate of 150 kg N ha-1 compared with a higher rate of 200 kg N ha-1 may be an effective way to reduce N fertilizer application rate and mitigate NH3 emission, improve NUE, and increase maize yield. More investigations are suggested under different soil textures and climatic conditions to declare S-coated urea at 150 kg N ha-1 as the best application rate for maize to enhance maize growth and yield.

Adding pulse flours to cereal-based snacks and bakery products: An overview of free asparagine quantification methods and mitigation strategies of acrylamide formation in foods

Thermal processing techniques can lead to the formation of heat-induced toxic substances. Acrylamide is one contaminant that has received much scientific attention in recent years, and it is formed essentially during the Maillard reaction when foods rich in carbohydrates, particularly reducing sugars (glucose, fructose), and certain free amino acids, especially asparagine (ASN), are processed at high temperatures (>120°C). The highly variable free ASN concentration in raw materials makes it challenging for food businesses to keep acrylamide content below the European Commission benchmark levels, while avoiding flavor, color, and texture impacts on their products. Free ASN concentrations in crops are affected by environment, genotype, and soil fertilization, which can also influence protein content and amino acid composition. This review aims to provide an overview of free ASN and acrylamide quantification methods and mitigation strategies for acrylamide formation in foods, focusing on adding pulse flours to cereal-based snacks and bakery products. Overall, this review emphasizes the importance of these mitigation strategies in minimizing acrylamide formation in plant-based products and ensuring safer and healthier food options.

Reducing the Risk of Acrylamide and Other Processing Contaminant Formation in Wheat Products

Wheat is a staple crop, consumed worldwide as a major source of starch and protein. Global intake of wheat has increased in recent years, and overall, wheat is considered to be a healthy food, particularly when products are made from whole grains. However, wheat is almost invariably processed before it is consumed, usually via baking and/or toasting, and this can lead to the formation of toxic processing contaminants, including acrylamide, 5-hydroxymethylfurfural (HMF) and polycyclic aromatic hydrocarbons (PAHs). Acrylamide is principally formed from free (soluble, non-protein) asparagine and reducing sugars (glucose, fructose and maltose) within the Maillard reaction and is classified as a Group 2A carcinogen (probably carcinogenic to humans). It also has neurotoxic and developmental effects at high doses. HMF is also generated within the Maillard reaction but can also be formed via the dehydration of fructose or caramelisation. It is frequently found in bread, biscuits, cookies, and cakes. Its molecular structure points to genotoxicity and carcinogenic risks. PAHs are a large class of chemical compounds, many of which are genotoxic, mutagenic, teratogenic and carcinogenic. They are mostly formed during frying, baking and grilling due to incomplete combustion of organic matter. Production of these processing contaminants can be reduced with changes in recipe and processing parameters, along with effective quality control measures. However, in the case of acrylamide and HMF, their formation is also highly dependent on the concentrations of precursors in the grain. Here, we review the synthesis of these contaminants, factors impacting their production and the mitigation measures that can be taken to reduce their formation in wheat products, focusing on the role of genetics and agronomy. We also review the risk management measures adopted by food safety authorities around the world.

Chlorophyll Meter: A Precision Agricultural Decision-Making Tool for Nutrient Supply in Durum Wheat (Triticum turgidum L.) Cultivation under Drought Conditions

How crop biodiversity adapts to drought conditions and enhances grain yield became the most important issue facing agronomists and plant breeders at the turn of the century. Variations in genetic response, inadequacy of nutrients in the soil, and insufficient access to nutrients are factors that aggravate drought stressors. The development of screening tools for identifying drought tolerance is important in the deployment of durum wheat varieties suited to drought-prone environments. An experiment was conducted to evaluate durum wheat varieties under a range of nutrient supplies in naturally imposed drought conditions. The treatments consisting of two nitrogen regimes (i.e., control and 60 kg ha−1), four durum wheat varieties, and three types of nutrients (control, sulfur, and zinc) that were arranged in a split-split plot design with three replications. Both foliar-based sulfur and zinc fertilization were employed at the flag leaf stage, at a rate of 4 and 3-L ha−1, respectively. The results showed a significant (p < 0.05) genetic variation in chlorophyll concentration, grain protein content, tillering potential, and leaf area index. Varieties that contained better leaf chlorophyll content had improved grain yield by about 8.33% under 60 kg/ha nitrogen. A combined application of nitrogen and zinc at flag leaf stage significantly improved grain yield of Duragold by about 21.3%. Leaf chlorophyll content was found to be a more important trait than spikes per m2 to discriminate durum wheat varieties. Foliar application of sulfur increased the grain yield of drought-stressed plants by about 12.23%. Grain yield and protein content were strongly correlated with late-season SPAD readings. Significant (p < 0.05) correlation coefficients were obtained between normalized difference vegetation index, leaf area index, grain yield, and protein content with late-season chlorophyll content, revealing the importance of chlorophyll content in studying and identifying drought-tolerant varieties.

Exploring Variability of Free Asparagine Content in the Grain of Bread Wheat (Triticum aestivum L.) Varieties Cultivated in Italy to Reduce Acrylamide-Forming Potential

Acrylamide, a suspected human carcinogen, is generated during food processing at high temperatures in the Maillard reaction, which involves reducing sugars and free asparagine. In wheat derivatives, free asparagine represents a key factor in acrylamide formation. Free asparagine levels in the grain of different wheat genotypes has been investigated in recent studies, but little is known about elite varieties that are cultivated in Italy. Here, we analysed the accumulation of free asparagine in a total of 54 bread wheat cultivars that are relevant for the Italian market. Six field trials in three Italian locations over two years were considered. Wholemeal flours obtained from harvested seeds were analysed using an enzymatic method. Free asparagine content ranged from 0.99 to 2.82 mmol/kg dry matter in the first year, and from 0.55 to 2.84 mmol/kg dry matter in the second year. Considering the 18 genotypes that were present in all the field trials, we evaluated possible environment and genetic influences for this trait. Some cultivars seemed to be highly affected by environment, whereas others showed a relative stability in free asparagine content across years and locations. Finally, we identified two varieties showing the highest free asparagine levels in our analysis, representing potential useful materials for genotype x environment interaction studies. Two other varieties, which were characterized by low amounts of free asparagine in the considered samples, may be useful for the food industry and for future breeding programs aimed to reduce acrylamide-forming potential in bread wheat.

Comparative Study Effect of Urea-Sulfur Fertilizers on Nitrogen Uptake and Maize Productivity

Combined nitrogen (N) and sulfur (S) fertilization is a good management strategy to reduce N loss and increase the efficiency of N fertilizers to achieve high grain yields and quality. Field trials for 2 yrs. (2018-2019) were conducted to evaluate the comparative advantage of conventional urea (150 N kg ha^-1) compared to urea+ ammonium sulfate (150 N kg ha^-1), urea+ calcium sulfate (150 N kg ha^-1), and urea cocrystals (CaSO₄.4urea) (150 N kg ha^-1) when applied as nitrogen fertilizers to the maize. The statistics show a significant treatments effect on developed corn cobs, fresh and dry cob yields and grain yield, with 1000 grains with better results in 2019 than in 2018. The fertilization treatments affected grain yields significantly for 2018 and 2019, respectively. Urea+ ammonium sulfate and urea cocrystal provided a significant increase in grain yields by 10.5% and 7.50%, respectively, compared to urea in 2018, w1hereas, in 2019, urea cocrystal supplied the grain yields with a significant increase of 23.07% compared to urea, followed by urea + calcium sulfate which provided a 10.46% increase compared to urea. The study highlights that using urea-sulfur fertilizers enhanced the release of mineral nitrogen in the soil, improved the grain's N uptake by the plant and increased maize grain yields.

Effects of Cysteine and Inorganic Sulfur Applications at Different Growth Stages on Grain Protein and End-Use Quality in Wheat

The aim of this study was to test the significant effects of inorganic sulfur and cysteine on grain protein and flour quality in wheat and to provide a theoretical basis of wheat cultivation techniques with high yield and quality. In the field experiment, a winter wheat cultivar, Yangmai 16, was used, and five treatments were established, i.e., S0 (no sulfur fertilizer application during the whole wheat growth period), S(B)60 (60 kg ha-1 inorganic sulfur fertilizer was applied as the basal fertilizer), Cys(B)60 (60 kg ha-1 cysteine sulfur fertilizer was applied as the basal fertilizer), S(J)60 (60 kg ha-1 inorganic sulfur fertilizer was applied as the jointing fertilizer), and Cys(J)60 (60 kg ha-1 cysteine sulfur fertilizer was applied as the jointing fertilizer). The fertilizer application at jointing stage showed a better influence than basal fertilizer application on protein quality; for the content of albumin, gliadin, and high molecular weight glutenin (HMW-GS), Cys(J)60 was the best among these treatments. An increase of 7.9%, 24.4%, 43.5%, 22.7% and 36.4% was found in grain yield, glutenin content, glutenin macro-polymer (GMP), low molecular weight glutenin (LMW-GS), and S content under Cys(J)60, in relation to the control, respectively. A similar trend was found in the end-use quality, as exemplified by an increase of 38.6%, 10.9%, 60.5%, and 109.8% in wet gluten content, dry gluten content, sedimentation volume, and bread-specific volume, respectively; a decrease of 69.3% and 69.1% in bread hardness and bread chewiness was found under Cys(J)60. In terms of application period, topdressing at jointing stage is compared with base fertilizer, the sulfur fertilizer application at jointing stage showed larger effects on grain protein and flour quality, from the different types of sulfur fertilizer, the application of cysteine performed better than the use of inorganic sulfur. The Cys(J)60 exhibited the best effects on protein and flour quality. It was suggested that sufficient sulfur application at jointing stage has the potential to enhance the grain protein and flour quality.

Using the Haney Soil Test to Predict Nitrogen Requirements in Winter Wheat (Triticum aestivum L.)

Managing nitrogen (N) is one of the of the biggest challenges in achieving environmental and economic sustainability in the agroecosystem. As N fertilizer prices have increased significantly, farmers are considering a revised N recommendation to optimize crop production, while addressing negative environmental impacts of excess N in water bodies. This study analyzes the accuracy of using the Haney Soil Test (HST) to predict the N requirement (HSTNR) of winter wheat (Triticum aestivum L.) in a semi-arid climate. The accuracy of the HST to predict the economically optimum N rate (EONR) was dependent on in-season precipitation. In drought conditions, the HSTNR was 33 kg N ha−1 lower on average than the EONR. Conversely, in wetter years, the HSTNR was 35 kg N ha−1 higher than the EONR. Net return was approximately USD 19 ha−1 lower than that with the EONR under both precipitation scenarios. Similar differences were found for protein content. There was a strong correlation between soil respiration and the soil health calculation, within the HST, and the difference between the net return on yield from the HSTNR and the EONR yield. These indicators may serve as useful metrics for formulating soil health-based N recommendations in winter wheat. However, in drought-prone areas, the HSTNR may significantly underpredict the EONR in many years due to an overestimation of N mineralization.

Sulfur and nitrogen nutrition status in flag leaf and shoot samples collected from wheat growing areas in Çukurova, Central Anatolia and GAP regions of Turkey

Sulfur (S) deficiency in soils and plants has been increased in the recent decade which is reducing crop yield and quality. Unfortunately, no extensive study has been conducted on S nutritional status of plants in Turkey. In this study, soil and plant samples were collected from Çukurova, Central Anatolia and GAP regions where wheat is extensively cultivated. Plant samples either as flag leaf or the whole shoot were collected depending on growth stage of wheat crop at sample collection. Similarly, surface (0-20 cm) and sub-surface (20-40 cm) soil samples were collected from plant sampling sites and a total 963 plant and 1947 soil samples were collected during the study. The S concentration in flag leaf samples varied between 0.18 and 0.67%, 0.11-0.59% and 0.17-0.82% for central Anatolia, Çukurova and GAP regions, respectively. According to S concentration in flag leaf samples, 99% of the plants in Çukurova region were found sufficient in S nutrition. However, 49% of the samples collected from central Anatolia and GAP regions were deficient in S. Critical N:S ratio indicating S nutrition status of plants was lower than the widely accepted critical value of 17. This low N:S ratio was a consequence of deficient N nutrition rather than S nutrition. Moreover, it was observed that plant available SO4-S concentration of soils varied within and among sampled provinces with an average value of 20.6 and 31.6 mg kg-1 for surface and sub-surface samples, respectively. The SO4-S concentration increased with increasing soil depth. The results indicate a significantly positive correlation between S concentration in plant shoot and plant available SO4-S concentration in soils. In conclusion, S-containing fertilizer use in central Anatolia and GAP regions must be considered as an important approach for the prevention of yield and quality losses. Furthermore, rapid and sensitive plant and soil analysis methods are needed, which must also consider the local and site-specific conditions.

The combined effects of elevated atmospheric CO2 and cadmium exposure on flavonoids in the leaves of Robinia pseudoacacia L. seedlings

Flavonoids participate in several plant processes such as growth and physiological protection in adverse environments. In this study, we investigated the combined effects of eCO₂ and cadmium (Cd)-contaminated soils on the total flavonoid and monomer contents in the leaves of Robinia pseudoacacia L. seedlings. Elevated CO₂, Cd, and eCO₂+ Cd increased the total flavonoids in the leaves relative to the control, and eCO₂ mostly increased (p < 0.05) the total flavonoid content under Cd exposure. Elevated CO₂ increased (p < 0.05) robinin, rutin, and acacetin contents in the leaves of 45-day seedlings and decreased (p < 0.05) the content of robinin and acacetin at 90 and 135 d under Cd exposure except for robinin at day 45 under Cd1 and acacetin on day 135 under Cd1. Quercetin content decreased (p < 0.05) under the combined conditions relative to Cd alone. Kaempferol in the leaves was only detected under eCO₂ on day 135. The responses of total chlorophyll, total soluble sugars, starch, C, N, S, and the C/N ratio in the leaves to eCO₂ significantly affected the synthesis of total flavonoids and monomers under Cd exposure. Overall, rutin was more sensitive to eCO₂+ Cd than the other flavonoids. Cadmium, CO_2, and time had significant interactive effects on the synthesis of flavonoids in the leaves of R. pseudoacacia L. seedlings. Elevated CO₂ may improve the protection and defense system of seedlings grown in Cd-contaminated soils by promoting the synthesis of total flavonoids, although robinin, rutin, quercetin, and acacetin yields may reduce with time. Additionally, increased Cd in the leaves suggested that eCO₂ could improve the phytoremediation of Cd-contaminated soils.

Molecular characterization and environmental impacts of water-soluble organic compounds of bio-oil from the thermochemical treatment of domestic sewage sludge

Water-soluble organic compounds derived from bio-oil (WOCB) are regarded as potential risk sources of sludge thermochemical treatment. This study showed that 10.35 mg of water-soluble organic carbon and 1.32 mg of water-soluble organic nitrogen were released per gram of sludge when the final temperature of thermochemical treatment was 600 °C. WOCB was mainly formed at 300-500 °C. Furthermore, FT-ICR MS results indicated that high temperatures promoted deamination reactions, and low molecular weight (LMW) compounds with low oxygen number polymerized into aromatic compounds with increasing temperature. Noteworthily, WOCB released at 20-600 °C showed strong phytotoxicity to wheat. LMW compounds with lignin/carboxylic rich alicyclic molecules (CRAM)-like structures derived from low temperatures (200-400 °C) induced this inhibitory effect, but lipids containing nitrogen and sulfur from high temperatures (400-600 °C) can act as nutrients to promote wheat growth. This study provides theoretical support for the risk control and benefits assessments of sludge thermochemical treatment.

The Effect of Amending Soil with Waste Elemental Sulfur on the Availability of Selected Macroelements and Heavy Metals

Elemental sulfur of waste origin may be a valuable sulfur source for plants. However, assessing the suitability of environmental use of a waste material should confirm there is no harmful effect of the material on soil environment. The purpose of the incubation experiment was to assess the availability of selected elements (P, K, Ca, Mg, Fe, Mn, Zn, Cu, Cr, Ni, Pb, Cd) in soils supplemented with waste elemental sulfur. The research was conducted on two soils: light and heavy, and with three sulfur doses applied to each soil. Available forms of elements in the soils were extracted 60 days after the waste introduction, with three reagents: 0.01 mol L−1 CaCl2, Mehlich 3 and 1 mol L−1 HCl. Additionally, to determine the impact of the introduced sulfur on soil acidification, soil pH was periodically checked during the experiment. The sulfur addition intensified acidification of the light soil, and, to a lesser extent, of the heavy soil. The acidifying effect was stronger when the sulfur dose was higher. The content of available forms of elements in the soils depended mainly on the strength of the used extractants (generally, the highest amounts were extracted with 1 mol L−1 HCl and the lowest with 0.01 mol L−1 CaCl2). The effect of sulfur introduction on element availability was small. No harmful effect on element availability in soils was stated.

Bioavailability of Sulfur from Waste Obtained during Biogas Desulfurization and the Effect of Sulfur on Soil Acidity and Biological Activity

Sulfur deficiency has been recognized as a limiting factor for crop production in many regions of the world. A 120-day incubation experiment was conducted to assess the effect of the applied waste elemental sulfur on sulfur bioavailability in soil. Four doses of sulfur were applied: 10, 20, 30 and 60 mg S kg−1 dry matter (d.m.) of soil. In order to assess the effect of soil pH adjustment on sulfur oxidation, the research was conducted on two sets of soil samples: one set of soil samples had natural pH, and the second one was limed before sulfur application. Application of waste sulfur slightly affected the soil pH, and increased the content of available sulfur in soil proportionally to sulfur dose. A beneficial effect of waste sulfur application on soil dehydrogenase and catalase activity was found. Liming reduced soil acidity, and significantly increased sulfate content and soil enzymatic activity. Waste elemental sulfur may be an alternative source of sulfur, supplementing the deficiencies of this element in soils. The described way of sulfur waste reuse corresponds with the increasingly common approach to create waste-free technologies in all economy.

The Sulphur Response in Wheat Grain and Its Implications for Acrylamide Formation and Food Safety

Free (soluble, non-protein) asparagine concentration can increase many-fold in wheat grain in response to sulphur deficiency. This exacerbates a major food safety and regulatory compliance problem for the food industry because free asparagine may be converted to the carcinogenic contaminant, acrylamide, during baking and processing. Here, we describe the predominant route for the conversion of asparagine to acrylamide in the Maillard reaction. The effect of sulphur deficiency and its interaction with nitrogen availability is reviewed, and we reiterate our advice that sulphur should be applied to wheat being grown for human consumption at a rate of 20 kg per hectare. We describe the genetic control of free asparagine accumulation, including genes that encode metabolic enzymes (asparagine synthetase, glutamine synthetase, glutamate synthetase, and asparaginase), regulatory protein kinases (sucrose nonfermenting-1 (SNF1)-related protein kinase-1 (SnRK1) and general control nonderepressible-2 (GCN2)), and basic leucine zipper (bZIP) transcription factors, and how this genetic control responds to sulphur, highlighting the importance of asparagine synthetase-2 (ASN2) expression in the embryo. We show that expression of glutamate-cysteine ligase is reduced in response to sulphur deficiency, probably compromising glutathione synthesis. Finally, we describe unexpected effects of sulphur deficiency on carbon metabolism in the endosperm, with large increases in expression of sucrose synthase-2 (SuSy2) and starch synthases.