Effects of water availability on free amino acids, sugars, and acrylamide-forming potential in potato

Two decades of research in dietary acrylamide: What do we know today

After nearly two decades since acrylamide was first raised as a potential safety issue in foods, significant progress has been made in understanding its formation during cooking, how to reduce levels in the most concerned foods, and the possible cancer risk to humans. Despite the huge wealth of knowledge gathered on this topic over the past years, a few new discoveries in occurrence, mitigation, analysis and risk assessment are worthy to note. This short review highlights the salient novelties pertaining to acrylamide, particularly in the areas of formation & analysis, existing and possible future regulations in the European Union, and finally considerations that may lead to possibly revisiting the toxicity of acrylamide and the main metabolite, glycidamide.

Genetic architecture of tuber-bound free amino acids in potato and effect of growing environment on the amino acid content

Free amino acids in potato tubers contribute to their nutritional value and processing quality. Exploring the natural variation in their accumulation in tubers across diverse genetic backgrounds is critical to potato breeding programs aiming to enhance or partition their distribution effectively. This study assessed variation in the tuber-bound free amino acids in a diversity panel of tetraploid potato clones developed and maintained by the Texas A&M Potato Breeding Program to explore their genetic basis and to obtain genomic-estimated breeding values for applied breeding purposes. Free amino acids content was evaluated in tubers of 217 tetraploid potato clones collected from Dalhart, Texas in 2019 and 2020, and Springlake, Texas in 2020. Most tuber amino acids were not affected by growing location, except histidine and proline, which were significantly lower (- 59.0%) and higher (+ 129.0%), respectively, at Springlake, Texas (a location that regularly suffers from abiotic stresses, mainly high-temperature stress). Single nucleotide polymorphism markers were used for genome-wide association studies and genomic selection of clones based on amino acid content. Most amino acids showed significant variations among potato clones and moderate to high heritabilities. Principal component analysis separated fresh from processing potato market classes based on amino acids distribution patterns. Genome-wide association studies discovered 33 QTL associated with 13 free amino acids. Genomic-estimated breeding values were calculated and are recommended for practical potato breeding applications to select parents and advance clones with the desired free amino acid content.

Determination of the effect of abiotic stress on the oxidative potential of edible potato tubers

Stress factors occurring during the growing season and potato storage, can negatively affect the quality of tubers, including an increased tendency to enzymatic darkening. Abiotic stress due to water shortage is a major factor limiting agricultural production. The purpose of the study was to determine the effect of cultivation technology based on the use of biostimulant, hydrogel and irrigation as well as storage on the propensity to darkening and the content of sugars and organic acids. The results show that genotypic and technological variability in interaction with growing season conditions had a significant (p < 0.05) effect on the oxidative potential (OP) of potato tubers. The Denar cultivar, compared to the 'Gardena', was characterized by a lower tendency to enzymatic darkening. Application of biostimulant and hydrogel generally contributed to lowering the oxidative potential of the tested cultivars. The application of anti-stress agents had no effect on organic acid content. The long-term storage caused an increase in the content of total sugars (TS) (22%), reducing sugars (RS) (49%), chlorogenic acid (ACH) (11%), and loss of ascorbic acid (AA) (6%) in the tubers which contributed to an increase in the oxidative potential of potato tubers (16%). The correlation coefficients obtained (p < 0.05) confirm the dependence of OP on the concentration of organic acids.

Garlic Ecotypes Utilise Different Morphological, Physiological and Biochemical Mechanisms to Cope with Drought Stress

Drought negatively affects plants by altering morphological, physiological and metabolic processes and ultimately reducing yields. Garlic (Allium sativum L.), an important member of the Alliaceae family, is also sensitive to drought and maximizing the yield of garlic bulbs is largely dependent on water availability. The objective of this study was to determine the effects of drought stress on morphological and physiological characteristics, as well as on phenolic, sugar, inulin and free amino acid content and antioxidant activity in two Croatian garlic ecotypes, 'Istarski crveni' (IC) and Istarski bijeli (IB). Drought was induced by using polyethylene glycol 8000 (PEG) solution (-0.6 MPa) starting 21 days after clove planting and lasted for 20 days. Drought reduced plant height, number of leaves and plant weight, but increased root length in both ecotypes compared to the control treatment. Among the physiological parameters, significant differences were observed between the two ecotypes studied in the spectral characteristics of the leaves, namely reflection in red, green and blue, VAL, values of the vegetation indices related to the chlorophyll content (CHI, GI), and the anthocyanin content (ARI). Ecotype IC showed higher antioxidant activity in the control treatment due to higher total phenolic content (TPC), but under drought conditions higher DPPH radical scavenging activity was determined in ecotype IB and higher values of FRAP in IC. Sucrose and glucose generally decreased under drought, while inulin increased in IB but decreased in IC. Total free amino acid content increased under drought in both ecotypes. In conclusion, drought tolerance of IB might be associated with increased accumulation of inulin and higher levels of amino acids, especially those shown to contribute to drought resistance. In IC, drought tolerance is associated with an increase in some amino acid compounds and better root growth in depth, probably due to a more efficient translocation of sucrose to the underground part of the plant.

Irrigation Management in Potato (Solanum tuberosum L.) Production: A Review

Limited water resources coupled with the increase of the human population calls for more efficient use of water in irrigated agriculture. Potato (Solanum tuberosum L.) is one of the most widely grown crops worldwide and is very sensitive to water stress due to its shallow rooting system. With the dilemma of potato sensitivity to drought and limited available water resources restricting crop production, researchers and crop growers have been investigating different approaches for optimizing potato yield and improving crop water use efficiency under different irrigation methods. While potato response to water is affected by other management practices such as fertilizer management, the present review is focused on the potato response to water under different environments and different irrigation methods and the impact on potato quality and potato diseases. Variable results obtained from research studies indicate the non-transferability of the results from one location to another as potato cultivars are not the same and potato breeders are still making effort to develop new high-yielding varieties to increase crop production and or develop new varieties for a specific trait to satisfy consumers exigence. This review is a valuable source of information for potato growers and scientists as it is not only focused on the impact of irrigation regimes on potato yield and water productivity as most reviews on water management, but it also presents the impact of irrigation regime on diseases in potatoes, tuber specific gravity, metabolite content of the tubers and the quality of the processed potato products.

Potato Tuber Chemical Properties in Storage as Affected by Cultivar and Nitrogen Rate: Implications for Acrylamide Formation

Recently released potato cultivars Dakota Russet and Easton were bred for low reducing sugars, and low acrylamide-forming potential in French fries. The objectives of this study were to determine: (1) the effects of nitrogen rate and storage time on tuber glucose concentrations in different cultivars; (2) the relationships between acrylamide, glucose, and asparagine for the new cultivars and Russet Burbank. The study was conducted at Becker, Minnesota over a period of two years on a loamy sand soil under irrigated conditions. All cultivars were subjected to five N rates from 135 to 404 kg ha⁻¹ in a randomized complete block design. Following harvest, tubers were stored at 7.8 °C and sampled at 0, 16, and 32 weeks. Dakota Russet and Easton had significantly lower concentrations of stem- and bud-end glucose, asparagine, and acrylamide than those of Russet Burbank in both years. The effect of storage time on glucose concentration was significant but differed with cultivar and year. N rate effects on stem- and bud-end glucose concentrations were cultivar and storage time dependent. After 16 weeks of storage, both asparagine and acrylamide concentrations linearly increased with increasing N rate. Glucose concentration was positively correlated with acrylamide concentration (r² = 0.61). Asparagine concentration was also positively correlated with acrylamide concentration (r² = 0.45) when the asparagine:glucose ratio was <1.306. The correlation between fry color and stem-end glucose concentration was significant over three cultivars in both years, but stronger in a growing season with minimal environmental stress. Taken together, these results suggest that while acrylamide formation during potato processing is a complex process affected by agronomic practices, environmental conditions during the growing season, and storage conditions, cultivar selection may be the most reliable method to minimize acrylamide in fried products.

Lysine, Lysine-Rich, Serine, and Serine-Rich Proteins: Link Between Metabolism, Development, and Abiotic Stress Tolerance and the Role of ncRNAs in Their Regulation

Lysine (Lys) is indispensable nutritionally, and its levels in plants are modulated by both transcriptional and post-transcriptional control during plant ontogeny. Animal glutamate receptor homologs have been detected in plants, which may participate in several plant processes through the Lys catabolic products. Interestingly, a connection between Lys and serotonin metabolism has been established recently in rice. 2-Aminoadipate, a catabolic product of Lys appears to play a critical role between serotonin accumulation and the color of rice endosperm/grain. It has also been shown that expression of some lysine-methylated proteins and genes encoding lysine-methyltransferases (KMTs) are regulated by cadmium even as it is known that Lys biosynthesis and its degradation are modulated by novel mechanisms. Three complex pathways co-exist in plants for serine (Ser) biosynthesis, and the relative preponderance of each pathway in relation to plant development or abiotic stress tolerance are being unfolded slowly. But the phosphorylated pathway of L-Ser biosynthesis (PPSB) appears to play critical roles and is essential in plant metabolism and development. Ser, which participates indirectly in purine and pyrimidine biosynthesis and plays a pivotal role in plant metabolism and signaling. Also, L-Ser has been implicated in plant responses to both biotic and abiotic stresses. A large body of information implicates Lys-rich and serine/arginine-rich (SR) proteins in a very wide array of abiotic stresses. Interestingly, a link exists between Lys-rich K-segment and stress tolerance levels. It is of interest to note that abiotic stresses largely influence the expression patterns of SR proteins and also the alternative splicing (AS) patterns. We have checked if any lncRNAs form a cohort of differentially expressed genes from the publicly available PPSB, sequence read archives of NCBI GenBank. Finally, we discuss the link between Lys and Ser synthesis, catabolism, Lys-proteins, and SR proteins during plant development and their myriad roles in response to abiotic stresses.

Acrylamide in food: Progress in and prospects for genetic and agronomic solutions

Acrylamide is a processing contaminant and Group 2a carcinogen that was discovered in foodstuffs in 2002. Its presence in a range of popular foods has become one of the most difficult problems facing the food industry and its supply chain. Wheat, rye and potato products are major sources of dietary acrylamide, with biscuits, breakfast cereals, bread (particularly toasted), crispbread, batter, cakes, pies, French fries, crisps and snack products all affected. Here we briefly review the history of the issue, detection methods, the levels of acrylamide in popular foods and the risk that dietary acrylamide poses to human health. The pathways for acrylamide formation from free (non-protein) asparagine are described, including the role of reducing sugars such as glucose, fructose and maltose and the Maillard reaction. The evolving regulatory situation in the European Union and elsewhere is discussed, noting that food businesses and their suppliers must plan to comply not only with current regulations but with possible future regulatory scenarios. The main focus of the review is on the genetic and agronomic approaches being developed to reduce the acrylamide-forming potential of potatoes and cereals and these are described in detail, including variety selection, plant breeding, biotechnology and crop management. Obvious targets for genetic interventions include asparagine synthetase genes, and the asparagine synthetase gene families of different crop species are compared. Current knowledge on crop management best practice is described, including maintaining optimum storage conditions for potatoes and ensuring sulphur sufficiency and disease control for wheat.

Meta-analysis of drought-tolerant genotypes in Oryza sativa: A network-based approach

BACKGROUND

Drought is a severe environmental stress. It is estimated that about 50% of the world rice production is affected mainly by drought. Apart from conventional breeding strategies to develop drought-tolerant crops, innovative computational approaches may provide insights into the underlying molecular mechanisms of stress response and identify drought-responsive markers. Here we propose a network-based computational approach involving a meta-analytic study of seven drought-tolerant rice genotypes under drought stress.

RESULTS

Co-expression networks enable large-scale analysis of gene-pair associations and tightly coupled clusters that may represent coordinated biological processes. Considering differentially expressed genes in the co-expressed modules and supplementing external information such as resistance/tolerance QTLs, transcription factors, network-based topological measures, we identify and prioritize drought-adaptive co-expressed gene modules and potential candidate genes. Using the candidate genes that are well-represented across the datasets as 'seed' genes, two drought-specific protein-protein interaction networks (PPINs) are constructed with up- and down-regulated genes. Cluster analysis of the up-regulated PPIN revealed ABA signalling pathway as a central process in drought response with a probable crosstalk with energy metabolic processes. Tightly coupled gene clusters representing up-regulation of core cellular respiratory processes and enhanced degradation of branched chain amino acids and cell wall metabolism are identified. Cluster analysis of down-regulated PPIN provides a snapshot of major processes associated with photosynthesis, growth, development and protein synthesis, most of which are shut down during drought. Differential regulation of phytohormones, e.g., jasmonic acid, cell wall metabolism, signalling and posttranslational modifications associated with biotic stress are elucidated. Functional characterization of topologically important, drought-responsive uncharacterized genes that may play a role in important processes such as ABA signalling, calcium signalling, photosynthesis and cell wall metabolism is discussed. Further transgenic studies on these genes may help in elucidating their biological role under stress conditions.

CONCLUSION

Currently, a large number of resources for rice functional genomics exist which are mostly underutilized by the scientific community. In this study, a computational approach integrating information from various resources such as gene co-expression networks, protein-protein interactions and pathway-level information is proposed to provide a systems-level view of complex drought-responsive processes across the drought-tolerant genotypes.

Construction of a network describing asparagine metabolism in plants and its application to the identification of genes affecting asparagine metabolism in wheat under drought and nutritional stress

A detailed network describing asparagine metabolism in plants was constructed using published data from Arabidopsis (Arabidopsis thaliana) maize (Zea mays), wheat (Triticum aestivum), pea (Pisum sativum), soybean (Glycine max), lupin (Lupus albus), and other species, including animals. Asparagine synthesis and degradation is a major part of amino acid and nitrogen metabolism in plants. The complexity of its metabolism, including limiting and regulatory factors, was represented in a logical sequence in a pathway diagram built using yED graph editor software. The network was used with a Unique Network Identification Pipeline in the analysis of data from 18 publicly available transcriptomic data studies. This identified links between genes involved in asparagine metabolism in wheat roots under drought stress, wheat leaves under drought stress, and wheat leaves under conditions of sulfur and nitrogen deficiency. The network represents a powerful aid for interpreting the interactions not only between the genes in the pathway but also among enzymes, metabolites and smaller molecules. It provides a concise, clear understanding of the complexity of asparagine metabolism that could aid the interpretation of data relating to wider amino acid metabolism and other metabolic processes.

Effects of variety, year of cultivation and sulphur supply on the accumulation of free asparagine in the grain of commercial wheat varieties

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Widely differing free asparagine concentration in wheat from two harvest years.

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Wide range of acrylamide-forming potential (AFP) in 73 commercial wheat varieties.

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Eight varieties identified with consistently low AFP, seven of them soft types, but benefit of using a low AFP variety is lost if sulphur supply is inadequate.

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Selecting varieties for low AFP solely on the basis of them being soft would be simplistic.

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Information on free asparagine concentration should be available at variety launch.

Free asparagine concentration, which is the determining factor for acrylamide-forming potential in cereals, was measured in grain from wheat grown in field trials in the United Kingdom in 2011–2012 and 2012–2013. There were 25 varieties in 2012 and 59 in 2013, with eleven present in both trials. The trials were split-plot, with half of each plot supplied with sulphur and the other half not. The varietal means (mmol per kg) for free asparagine in the sulphur-fed wheat ranged from 1.521 to 2.687 in 2011–2012 and 0.708 to 11.29 in 2012–2013. Eight varieties were identified as having consistently low free asparagine concentration. There was a differential response of varieties to sulphur, and much higher levels of free asparagine in 2012–2013 versus 2011–2012. Given the short commercial lifespan of some wheat varieties, it is concluded that information on free asparagine concentration should be made available when a variety is launched.

Acrylamide-forming potential of potatoes grown at different locations, and the ratio of free asparagine to reducing sugars at which free asparagine becomes a limiting factor for acrylamide formation

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Location of cultivation affects potato composition and acrylamide-forming potential.

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Effects of variety and storage interact with those of location.

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Dramatic differences in free asparagine concentration in potatoes grown at two sites.

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Concentration of reducing sugars is the primary determinant of acrylamide formation.

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Ratio of free asparagine to reducing sugars determines whether free asparagine affects acrylamide formation.

Acrylamide is produced from free asparagine and reducing sugars during high-temperature cooking and food processing, and potato products are major contributors to dietary acrylamide intake. The present study analysed twenty varieties of potatoes grown at two sites (Doncaster and Woburn) in the United Kingdom to assess the effect of location of cultivation on acrylamide-forming potential. Analysis of variance revealed a full site by variety nested within type (French fry, boiling and crisping) by storage interaction for acrylamide (p < 0.003, F-test), reducing sugars and total sugars (p < 0.001, F-test). There was much greater free asparagine in potatoes grown at the Doncaster site compared with the Woburn site. Modelling of the relationship between the ratio of free asparagine to reducing sugars and the levels of acrylamide identified a value of 2.257 ± 0.149 as the tipping point in the ratio below which free asparagine concentration could affect acrylamide formation.

Oxidative versus Non-oxidative Decarboxylation of Amino Acids: Conditions for the Preferential Formation of Either Strecker Aldehydes or Amines in Amino Acid/Lipid-Derived Reactive Carbonyl Model Systems

Comparative formation of both 2-phenylethylamine and phenylacetaldehyde as a consequence of phenylalanine degradation by carbonyl compounds was studied in an attempt to understand if the amine/aldehyde ratio can be changed as a function of reaction conditions. The assayed carbonyl compounds were selected because of the presence in the chain of both electron-donating and electron-withdrawing groups and included alkenals, alkadienals, epoxyalkenals, oxoalkenals, and hydroxyalkenals as well as lipid hydroperoxides. The obtained results showed that the 2-phenylethylamine/phenylacetaldehyde ratio depended upon both the carbonyls and the reaction conditions. Thus, it can be increased using electron-donating groups in the chain of the carbonyl compound, small amounts of carbonyl compound, low oxygen content, increasing the pH, or increasing the temperature at pH 6. Opposed conditions (use of electron-withdrawing groups in the chain of the carbonyl compound, large amounts of carbonyl compound, high oxygen contents, low pH values, and increasing temperatures at low pH values) would decrease the 2-phenylethylamine/phenylacetaldehyde ratio, and the formation of aldehydes over amines in amino acid degradations would be favored.

Effects of CO2 enrichment and drought pretreatment on metabolite responses to water stress and subsequent rehydration using potato tubers from plants grown in sunlit chambers

Experiments were performed using naturally sunlit Soil-Plant-Atmosphere Research chambers that provided ambient or twice ambient CO2. Potato plants were grown in pots that were water sufficient (W), water insufficient for 12-18 days during both vegetative and tuber development stages (VR), or water insufficient solely during tuber development (R). In the ambient CO2 treatment, a total of 17 and 20 out of 31 tuber metabolites differed when comparing the W to the R and VR treatments, respectively. Hexoses, raffinose, mannitol, branched chain amino acids, phenylalanine and proline increased, although most organic acids remained unchanged or decreased in response to drought. Osmolytes, including glucose, branched chain amino acids and proline, remained elevated following 2 weeks of rehydration in both the ambient and elevated CO2 treatments, whereas fructose, raffinose, mannitol and some organic acids reverted to control levels. Failure of desiccated plant tissues to mobilize specific osmolytes after rehydration was unexpected and was likely because tubers function as terminal sinks. Tuber metabolite responses to single or double drought treatments were similar under the same CO2 levels but important differences were noted when CO2 level was varied. We also found that metabolite changes to water insufficiency and/or CO2 enrichment were very distinct between sink and source tissues, and total metabolite changes to stress were generally greater in leaflets than tubers.

Metabolite profiling of barley grain subjected to induced drought stress: responses of free amino acids in differently adapted cultivars

To investigate cultivar-specific metabolite changes upon drought stress in barley grain, differently adapted cultivars were field-grown under drought conditions using a rain-out shelter and under normal weather conditions (2010-2012). The grain was subjected to a gas chromatography-mass spectrometry-based metabolite profiling approach allowing the analyses of a broad spectrum of lipophilic and hydrophilic low molecular weight constituents. Multi- and univariate analyses demonstrated that there are grain metabolites which were significantly changed upon drought stress, either decreased or increased in all cultivars. On the other hand, for proteinogenic free amino acids increased concentrations were consistently observed in all seasons only in cultivars for which no drought resistance/tolerance had been described. Consistent decreases were seen only in the group of stress tolerant/resistant cultivars. These cultivar-specific correlations were particularly pronounced for branched-chain amino acids. The results indicate that free amino acids may serve as potential markers for cultivars differently adapted to drought stress.