Reducing acrylamide precursors in raw materials derived from wheat and potato

Genome-Wide Identification and Expression Profiling of the α-Amylase (AMY) Gene Family in Potato

Starch degradation provides energy and signaling molecules for plant growth, development, defense, and stress response. α-amylase (AMY) is one of the most important enzymes in this process. Potato tubers are rich in starch, and the hydrolysis of starch into sugar negatively impacts the frying quality of potato. Despite its importance, the AMY gene family has not been fully explored in potatoes. Here, we performed a detailed analysis of the StAMY gene family to determine its role in potato. Twenty StAMY genes were identified across the potato genome and were divided into three subgroups. The promoters of StAMY genes contained an array of cis-acting elements involved in growth and development, phytohormone signaling, and stress and defense responses. StAMY8, StAMY9, StAMY12, and StAMY20 were specifically expressed in mature tubers. Different StAMY gene family members tended to be upregulated in response to β-aminobutyric acid (BABA), Phytophthora infestans (P. infestans), benzothiadiazole (BTH), heat, salt, and drought stress. In addition, different StAMY gene family members tended to be responsive to abscisic acid (ABA), indole-3-acetic acid (IAA), gibberellic acid (GA3), and 6-benzylaminopurine (BAP) treatment. These results suggest that StAMY gene family members may be involved in starch and sugar metabolism, defense, stress response, and phytohormone signaling. The results of this study may be applicable to other starchy crops and lay a foundation for further research on the functions and regulatory mechanisms of AMY genes.

Reducing Acrylamide Formation Potential by Targeting Free Asparagine Accumulation in Seeds

Acrylamide is a probable carcinogen in humans and is formed when reducing sugars react with free asparagine (Asn) during thermal processing of food. Although breeding for low reducing sugars worked well in potatoes, it is less successful in cereals. However, reducing free Asn in cereals has great potential for reducing acrylamide formation, despite the role that Asn plays in nitrogen transport and amino acid biosynthesis. In this perspective, we summarize the efforts aimed at reducing free Asn in cereal grains and discuss the potentials and challenges associated with targeting this essential amino acid, especially in a seed-specific manner.

Acrylamide in potato chips in Iran, health risk assessment and mitigation

This study aimed to determine the acrylamide content in potato chips sold in Kermanshah, Iran and assess the potential health concerns associated with acrylamide exposure. HPLC-DAD was used to analyse 120 samples across 40 brands. The possible non-carcinogenic risk index for adults was below 1 for all 40 brands (100%), but for children it was only below 1 for 9 brands (22.5%) and above 1 for 31 brands (77.5%). Regarding the possible carcinogenic risk index, for adults only 1 out of 40 brands rated > 10-4, whereas for children all brands rated > 10-4. This shows that children's exposure to acrylamide through potato chips consumption in Kermanshah can be considered a risk on cancer and exposure of adults requires attention and monitoring. The best way to reduce acrylamide in potato chips and associated health risks is to improve the production process, especially temperature and time.

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.

Comparative compositions of grain of tritordeum, durum wheat and bread wheat grown in multi-environment trials

Three genotypes each of bread wheat, durum wheat and tritordeum were grown in randomized replicated field trials in Andalusia (Spain) for two years and wholemeal flours analysed for a range of components to identify differences in composition. The contents of all components that were determined varied widely between grain samples of the individual species and in most cases also overlapped between the three species. Nevertheless, statistically significant differences between the compositions of the three species were observed. Notably, tritordeum had significantly higher contents of protein, some minerals (magnesium and iron), total phenolics and methyl donors. Tritordeum also had higher levels of total amino acids (but not asparagine) and total sugars, including raffinose. By contrast, bread wheat and tritordeum had similar contents of the two major dietary fibre components in white flour, arabinoxylan and β-glucan, with significantly lower contents in durum wheat.

Comparative Compositions of Grain of Bread Wheat, Emmer and Spelt Grown with Different Levels of Nitrogen Fertilisation

Five cultivars of bread wheat and spelt and three of emmer were grown in replicate randomised field trials on two sites for two years with 100 and 200 kg nitrogen fertiliser per hectare, reflecting low input and intensive farming systems. Wholemeal flours were analysed for components that are suggested to contribute to a healthy diet. The ranges of all components overlapped between the three cereal types, reflecting the effects of both genotype and environment. Nevertheless, statistically significant differences in the contents of some components were observed. Notably, emmer and spelt had higher contents of protein, iron, zinc, magnesium, choline and glycine betaine, but also of asparagine (the precursor of acrylamide) and raffinose. By contrast, bread wheat had higher contents of the two major types of fibre, arabinoxylan (AX) and β-glucan, than emmer and a higher AX content than spelt. Although such differences in composition may be suggested to result in effects on metabolic parameters and health when studied in isolation, the final effects will depend on the quantity consumed and the composition of the overall diet.

Mitigation of Acrylamide in Potato Chips by Pre-drying and Pulsed Electric Field Treatment

The object of this work was to study the effects of preliminary vacuum drying (VD), pulsed electric field (PEF) treatment, frying temperature on color, oil uptake, and acrylamide (AA) content in fried potato chips. The results of this study indicated that an increase of frying temperature from 120 to 180°C led to a decrease of frying time of around 70% for untreated and PEF pre-treated samples. The color value of L* and a* decreased with the increase of frying temperature, and those values of the sample pre-treated by PEF were significantly higher compared to those obtained from untreated samples. The PEF pre-treatment promoted the reduction of oil content of fried samples by up to 17.6, 14.2, and 16% compared with untreated samples at the frying temperatures of 120, 150, and 180°C, respectively. Higher efficiency was observed by applying the preliminary VD in the case of the frying temperature of 150°C. Furthermore, it was revealed that PEF pre-treatment and preliminary VD application lead to a synergetic effect on the reduction of AA content in potato chips. For example, with the initial moisture ratio of 0.5, pre-dried by VD and pre-treated by PEF, the AA content was noticeably decreased from 2,220 to 311 μg/kg compared to untreated and undehydrated samples at the frying temperature of 150°C. Our findings provide reference for a new pre-treatment to mitigate AA formation and to improve the quality of potato chips.

Suppression of the tonoplast sugar transporter StTST3.2 improves quality of potato chips

Which sugar transporter regulates sugar accumulation in tubers is largely unknown. Accumulation of reducing sugar (RS) in potato (Solanum tuberosum L.) tubers negatively affects the quality of tubers undergoing the frying process. However, little is known about the genes involved in regulating RS content in tubers at harvest. Here, we have identified two tonoplast sugar transporter (TST) 3-type isoforms (StTST3.1 and StTST3.2) in potato. Quantitative real-time PCR results indicate that StTST3.1 and StTST3.2 possess distinct expression patterns in various potato tissues. StTST3.2 was found to be the expressed TST3-type isoform in tubers. Further subcellular localization analysis revealed that StTST3.2 was targeted to the tonoplast. Silencing of StTST3.2 in potato by stable transformation resulted in significantly lower RS content in tubers at harvest or after room temperature storage, suggesting StTST3.2 plays an important role in RS accumulation in tubers. Accordingly, compared with the unsilenced control, potato chips processed from StTST3.2-silenced tubers exhibited lighter color and dramatically decreased acrylamide production at harvest or after room temperature storage. In addition, we demonstrated that silencing of StTST3.2 has no significant effect on potato growth and development. Thus, suppression of StTST3.2 could be another effective approach for improving processing quality and decreasing acrylamide content in potato tubers.

Low Acrylamide Flatbreads from Colored Corn and Other Flours

Dietary acrylamide formed during baking and frying of plant-based foods such as bread and other cereal products, coffee, fried potatoes, and olives is reported to induce genotoxic, carcinogenic, neurotoxic, and antifertility properties in vivo, suggesting the need to keep the acrylamide content low with respect to widely consumed heat-processed food including flatbreads. Due to the fact that pigmented corn flours contain biologically active and health-promoting phenolic and anthocyanin compounds, the objective of this study was to potentially define beneficial properties of flatbread by evaluating the acrylamide content determined by high-performance liquid chromatography/mass spectrometry (HPLC/MS) with a detection limit of 1.8 µg/kg and proximate composition by standard methods of six experimental flatbreads made from two white, two blue, one red, and one yellow corn flours obtained by milling commercial seeds. Acrylamide content was also determined in experimental flatbreads made from combinations in quinoa flour, wheat flour, and peanut meal with added broccoli or beet vegetables and of commercial flatbreads including tortillas and wraps. Proximate analysis of flatbreads showed significant differences in protein and fat but not in carbohydrate, mineral, and water content. The acrylamide content of 16 evaluated flatbreads ranged from 0 to 49.1 µg/kg, suggesting that these flatbreads have the potential to serve as low-acrylamide functional foods. The dietary significance of the results is discussed.

Asparagine accumulation in chicory storage roots is controlled by translocation and feedback regulation of asparagine biosynthesis in leaves

The presence of acrylamide (AA), a potentially carcinogenic and neurotoxic compound, in food has become a major concern for public health. AA in plant-derived food mainly arises from the reaction of the amino acid asparagine (Asn) and reducing sugars during processing of foodstuffs at high temperature. Using a selection of genotypes from the chicory (Cichorium intybus L.) germplasm, we performed Asn measurements in storage roots and leaves to identify genotypes contrasting for Asn accumulation. We combined molecular analysis and grafting experiments to show that leaf to root translocation controls Asn biosynthesis and accumulation in chicory storage roots. We could demonstrate that Asn accumulation in storage roots depends on Asn biosynthesis and transport from the leaf, and that a negative feedback loop by Asn on CiASN1 expression impacts Asn biosynthesis in leaves. Our results provide a new model for Asn biosynthesis in root crop species and highlight the importance of characterizing and manipulating Asn transport to reduce AA content in processed plant-based foodstuffs.

Effect of Microwave Heating on the Acrylamide Formation in Foods

Acrylamide (AA) is a neurotoxic and carcinogenic substance that has recently been discovered in food. One of the factors affecting its formation is the heat treatment method. This review discusses the microwave heating as one of the methods of thermal food processing and the influence of microwave radiation on the acrylamide formation in food. In addition, conventional and microwave heating were compared, especially the way they affect the AA formation in food. Available studies demonstrate differences in the mechanisms of microwave and conventional heating. These differences may be beneficial or detrimental depending on different processes. The published studies showed that microwave heating at a high power level can cause greater AA formation in products than conventional food heat treatment. The higher content of acrylamide in microwave-heated foods may be due to differences in its formation during microwave heating and conventional methods. At the same time, short exposure to microwaves (during blanching and thawing) at low power may even limit the formation of acrylamide during the final heat treatment. Considering the possible harmful effects of microwave heating on food quality (e.g., intensive formation of acrylamide), further research in this direction should be carried out.

Acrylamide in daily food in the metropolitan area of Hanoi, Vietnam

Acrylamide, a colourless and odourless crystalline solid, formed via the Maillard reaction in food, has been reported with harmful properties for humans, such as toxicity and carcinogenicity. Three hundred and four processed food samples from 17 product types, collected in Hanoi, Vietnam, were analyzed by LC-MS/MS to measure the acrylamide concentration. The limit of detection (LOD) and the limit of quantification (LOQ) of acrylamide were 1 µg Kg^-1 and 3 µg Kg^-1, respectively. Effectively, the highest acrylamide content is usually found in processed food, which is one of the primary reasons of increased acrylamide content in food. All French fried samples contained acrylamide above 500 µg kg^-1. Acrylamide concentration in non-fried noodle, vermicelli, rice noodle, phở, dried vegetable, and rice cracker is lower than in potato chips, fried potatoes, fried cake, and fried noodles. The results could be helpful to estimate exposure and risk assessment of acrylamide in Vietnam.

Defining genetic and chemical diversity in wheat grain by 1H-NMR spectroscopy of polar metabolites

SCOPE

The application of high-throughput 1H nuclear magnetic resonance (1H-NMR) of unpurified extracts to determine genetic diversity and the contents of polar components in grain of wheat.

METHODS AND RESULTS

Milled whole wheat grain was extracted with 80:20 D2 O:CD3 OD containing 0.05% d4 -trimethylsilylpropionate. 1H-NMR spectra were acquired under automation at 300°K using an Avance Spectrometer operating at 600.0528 MHz. Regions for individual metabolites were identified by comparison to a library of known standards run under identical conditions. The individual 1H-NMR peaks or levels of known metabolites were then compared by Principal Component Analysis using SIMCA-P software.

CONCLUSIONS

High-throughput 1H-NMR is an excellent tool to compare the extent of genetic diversity within and between wheat species, and to quantify specific components (including glycine betaine, choline, and asparagine) in individual genotypes. It can also be used to monitor changes in composition related to environmental factors and to support comparisons of the substantial equivalence of transgenic lines.

Acrylamide and 5-hydroxymethylfurfural formation during biscuit baking. Part II: Effect of the ratio of reducing sugars and asparagine

This study investigated acrylamide and 5-hydroxymethylfurfural (HMF) formation during biscuit baking. Four types of wheat flour with different molar ratios of total fructose and glucose to asparagine were investigated. Nevertheless, the molar ratio in all four biscuit doughs exceeded one after proofing due to enzyme action. Data obtained after baking were used to develop a mechanistic model, based on the asparagine-related pathway, for acrylamide and HMF formation in the four baked biscuit types. Asparagine reacted with fructose to form a Schiff base before decarboxylation to produce acrylamide without Amadori rearrangement product and sugar fragmentation. Fructose contributed considerably to acrylamide formation and to HMF formation via caramelization in all four biscuit types. No clear correlation was found between acrylamide and HMF in baked biscuits, nor between asparagine and the sum of glucose and fructose concentrations in the wheat flour.

Free asparagine and sugars profile of cereal species: the potential of cereals for acrylamide formation in foods

Cereals-based food is one of the major source of Maillard reaction products in the diet. Free amino acids and reducing sugars are considered to be the main precursors in the formation of these heat-induced compounds. In order to determine genetic resources with reduced potential for acrylamide formation, the content of sugars as well as free asparagine were analysed in a total of 30 cultivars of 10 varieties belonging to eight species (Triticum aestivum var. lutescens, T. aestivum var. alba, T. aestivum var. compactum, T. durum, T. spelta, T. dicoccum, Secale cereale, Hordeum vulgare var. nudum, Avena sativa var. nudum, and Zea mays var. indentata) grown at the same location in the 2015 growing season. Our results provide evidence of differences in the content of sugars and asparagine between and within species of small grain cereals and maize. The highest content of glucose, fructose and asparagine was found in cultivars of rye and hull-less oat. All maize varieties examined contained significantly higher amounts of non-reducing and total sugars (on average 1.25% and 2.36%, respectively) than small cereal grain species. Principal component analysis showed a high positive correlation between monoreducing sugars and asparagine in bread wheat, durum wheat and hull-less barley.

UV-C treatment on physiological response of potato (Solanum tuberosum L.) during low temperature storage

The storage of potato tuber (Solanum tuberosum L.) at low temperatures minimizes sprouting and disease but can cause cold-induced sweetening (CIS), which leads to the production of the cancerogenic substance acrylamide during the frying processing. The aim of this research was to investigate the effects of UV-C treatment on CIS in cold stored potato tuber. 'Atlantic' potatoes were treated with UV-C for an hour and then stored at 4 °C up to 28 days. The UV-C treatment significantly prevented the increase of malondialdehyde content (an indicator of the prevention of oxidative injury) in potato cells during storage. The accumulation of reducing sugars, particularly fructose and glucose, was significantly reduced by UV-C treatment possibly due to the regulation of the gene cascade, sucrose phosphate synthase, invertase inhibitor 1/3, and invertase 1 in potato tuber, which were observed to be differently expressed between treated and untreated potatoes during low temperature storage. In summary, UV-C treatment prevented the existence of oxidative injury in potato cells, thus, lowered the amount of reducing sugar accumulation during low temperature storage of potato tubers.

Silencing of vacuolar invertase and asparagine synthetase genes and its impact on acrylamide formation of fried potato products

Acrylamide is produced in a wide variety of carbohydrate-rich foods during high-temperature cooking. Dietary acrylamide is a suspected human carcinogen, and health concerns related to dietary acrylamide have been raised worldwide. French fries and potato chips contribute a significant proportion to the average daily intake of acrylamide, especially in developed countries. One way to mitigate health concerns related to acrylamide is to develop potato cultivars that have reduced contents of the acrylamide precursors asparagine, glucose and fructose in tubers. We generated a large number of silencing lines of potato cultivar Russet Burbank by targeting the vacuolar invertase gene VInv and the asparagine synthetase genes StAS1 and StAS2 with a single RNA interference construct. The transcription levels of these three genes were correlated with reducing sugar (glucose and fructose) and asparagine content in tubers. Fried potato products from the best VInv/StAS1/StAS2-triple silencing lines contained only one-fifteenth of the acrylamide content of the controls. Interestingly, the extent of acrylamide reduction of the best triple silencing lines was similar to that of the best VInv-single silencing lines developed previously from the same potato cultivar Russet Burbank. These results show that an acrylamide mitigation strategy focused on developing potato cultivars with low reducing sugars is likely to be an effective and sufficient approach for minimizing the acrylamide-forming potential of French fry processing potatoes.

(1)H-NMR screening for the high-throughput determination of genotype and environmental effects on the content of asparagine in wheat grain

Free asparagine in cereals is known to be the precursor of acrylamide, a neurotoxic and carcinogenic product formed during cooking processes. Thus, the development of crops with lower asparagine is of considerable interest to growers and the food industry. In this study, we describe the development and application of a rapid (1)H-NMR-based analysis of cereal flour, that is, suitable for quantifying asparagine levels, and hence acrylamide-forming potential, across large numbers of samples. The screen was applied to flour samples from 150 bread wheats grown at a single site in 2005, providing the largest sample set to date. Additionally, screening of 26 selected cultivars grown for two further years in the same location and in three additional European locations in the third year (2007) provided six widely different environments to allow estimation of the environmental (E) and G x E effects on asparagine levels. Asparagine concentrations in the 150 genotypes ranged from 0.32 to 1.56 mg/g dry matter in wholemeal wheat flours. Asparagine levels were correlated with plant height and therefore, due to recent breeding activities to produce semi-dwarf varieties, a negative relationship with the year of registration of the cultivar was also observed. The multisite study indicated that only 13% of the observed variation in asparagine levels was heritable, whilst the environmental contribution was 36% and the GxE component was 43%. Thus, compared to some other phenotypic traits, breeding for low asparagine wheats presents a difficult challenge.

Reducing the potential for processing contaminant formation in cereal products

Processing contaminants may be defined as substances that are produced in a food when it is cooked or processed, are not present or are present at much lower concentrations in the raw, unprocessed food, and are undesirable either because they have an adverse effect on product quality or because they are potentially harmful. The presence of very low levels of processing contaminants in common foods is becoming an increasingly important issue for the food industry, as developments in analytical techniques and equipment bring foods under closer and closer scrutiny. This review considers the formation of lipid oxidation products, hydrogenation of polyunsaturated fatty acids to prevent lipid oxidation and the associated risk of trans fatty acid formation. The formation of acrylamide in the Maillard reaction is described, as well as the genetic and agronomic approaches being taken to reduce the acrylamide-forming potential of cereal grain. The multiple routes for the formation of furan and associated chemicals, including hydroxymethylfurfuryl, are also described. The evolving regulatory and public perception situations for these processing contaminants and their implications for the cereal supply chain are discussed, emphasising the need for cereal breeders to engage with the contaminants issue.

Genetic variation and possible SNP markers for breeding wheat with low-grain asparagine, the major precursor for acrylamide formation in heat-processed products

BACKGROUND

In products made from wheat (Triticum aestivum) flour, acrylamide formation is almost exclusively determined by the level of free asparagine in the grain. Genetic variability for grain asparagine content was evaluated in order to assess the potential for acrylamide mitigation by breeding.

RESULTS

Free asparagine levels in the grains of 92 varieties varied from 137 to 471 mg kg⁻¹, representing an approximate threefold difference between the low- and high-asparagine genotypes. Heritability was low, with a value of 32%, indicating that breeding cultivars with inherently low grain asparagine would be a challenge. A genome-wide scan with single-nucleotide polymorphism (SNP) markers identified nine SNPs that were significantly (P < 0.001) associated with variation in free asparagine. The significant SNPs were localized on chromosome 5A, and explained between 14% and 24% of the observed variation. These putative SNPs are candidates for further studies to develop molecular markers.

CONCLUSION

Significant genetic variation exists for reducing acrylamide precursors in wheat flour, indicating that breeding and genetics could play an important role in mitigating the acrylamide risk in wheat products. The study identified a region on chromosome 5A that could provide a basis for further research to develop functional markers.

Photosynthetic assimilation of ¹⁴C into amino acids in potato (Solanum tuberosum) and asparagine in the tubers

Asparagine is the predominant free amino acid in potato tubers and the present study aimed to establish whether it is imported from the leaves or synthesised in situ. Free amino acid concentrations are important quality determinants for potato tubers because they react with reducing sugars at high temperatures in the Maillard reaction. This reaction produces melanoidin pigments and a host of aroma and flavour volatiles, but if free asparagine participates in the final stages, it results in the production of acrylamide, an undesirable contaminant. ¹⁴CO₂ was supplied to a leaf or leaves of potato plants (cv. Saturna) in the light and radioactivity incorporated into amino acids was determined in the leaves, stems, stolons and tubers. Radioactivity was found in free amino acids, including asparagine, in all tissues, but the amount incorporated in asparagine transported to the tubers and stolons was much less than that in glutamate, glutamine, serine and alanine. The study showed that free asparagine does not play an important role in the transport of nitrogen from leaf to tuber in potato, and that the high concentrations of free asparagine that accumulate in potato tubers arise from synthesis in situ. This indicates that genetic interventions to reduce free asparagine concentration in potato tubers will have to target asparagine metabolism in the tuber.

Evidence for the complex relationship between free amino acid and sugar concentrations and acrylamide-forming potential in potato

Free amino acids and reducing sugars participate in the Maillard reaction during high-temperature cooking and processing. This results not only in the formation of colour, aroma and flavour compounds, but also undesirable contaminants, including acrylamide, which forms when the amino acid that participates in the reaction is asparagine. In this study, tubers of 13 varieties of potato (Solanum tuberosum), which had been produced in a field trial in 2010 and sampled immediately after harvest or after storage for 6 months, were analysed to show the relationship between the concentrations of free asparagine, other free amino acids, sugars and acrylamide-forming potential. The varieties comprised five that are normally used for crisping, seven that are used for French fry production and one that is used for boiling. Acrylamide formation was measured in heated flour, and correlated with glucose and fructose concentration. In French fry varieties, which contain higher concentrations of sugars, acrylamide formation also correlated with free asparagine concentration, demonstrating the complex relationship between precursor concentration and acrylamide-forming potential in potato. Storage of the potatoes for 6 months at 9°C had a significant, variety-dependent impact on sugar and amino acid concentrations and acrylamide-forming potential.

Effects of nitrogen and sulfur fertilization on free amino acids, sugars, and acrylamide-forming potential in potato

Nitrogen (N) fertilizer is used routinely in potato (Solanum tuberosum) cultivation to maximize yield. However, it also affects sugar and free amino acid concentrations in potato tubers, and this has potential implications for food quality and safety because free amino acids and reducing sugars participate in the Maillard reaction during high-temperature cooking and processing. This results in the formation of color, aroma, and flavor compounds, but also some undesirable contaminants, including acrylamide, which forms when the amino acid that participates in the final stages of the reaction is asparagine. Another mineral, sulfur (S), also has profound effects on tuber composition. In this study, 13 varieties of potato were grown in a field trial in 2010 and treated with different combinations of N and S. Potatoes were analyzed immediately after harvest to show the effect of N and S fertilization on concentrations of free asparagine, other free amino acids, sugars, and acrylamide-forming potential. The study showed that N application can affect acrylamide-forming potential in potatoes but that the effect is type- (French fry, chipping, and boiling) and variety-dependent, with most varieties showing an increase in acrylamide formation in response to increased N but two showing a decrease. S application reduced glucose concentrations and mitigated the effect of high N application on the acrylamide-forming potential of some of the French fry-type potatoes.

Effects of variety and nutrient availability on the acrylamide-forming potential of rye grain

Acrylamide is a probable human carcinogen that forms in plant-derived foods when free asparagine and reducing sugars react at high temperatures. The identification of rye varieties with low acrylamide-forming potential or agronomic conditions that produce raw material with low acrylamide precursor concentrations would reduce the acrylamide formed in baked rye foods without the need for additives or potentially costly changes to processes. This work compared five commercial rye varieties grown under a range of fertilisation regimes to investigate the effects of genotype and nutrient (nitrogen and sulphur) availability on the accumulation of acrylamide precursors. A strong correlation was established between the free asparagine concentration of grain and the acrylamide formed upon heating. The five rye varieties accumulated different concentrations of free asparagine in the grain, indicating that there is genetic control of this trait and that variety selection could be useful in reducing acrylamide levels in rye products. High levels of nitrogen fertilisation were found to increase the accumulation of free asparagine, showing that excessive nitrogen application should be avoided in order not to exacerbate the problem of acrylamide formation. This effect of nitrogen was mitigated in two of the varieties by the application of sulphur.

Kinetic model for the formation of acrylamide during the finish-frying of commercial french fries

Acrylamide is formed from reducing sugars and asparagine during the preparation of French fries. The commercial preparation of French fries is a multistage process involving the preparation of frozen, par-fried potato strips for distribution to catering outlets, where they are finish-fried. The initial blanching, treatment in glucose solution, and par-frying steps are crucial because they determine the levels of precursors present at the beginning of the finish-frying process. To minimize the quantities of acrylamide in cooked fries, it is important to understand the impact of each stage on the formation of acrylamide. Acrylamide, amino acids, sugars, moisture, fat, and color were monitored at time intervals during the frying of potato strips that had been dipped in various concentrations of glucose and fructose during a typical pretreatment. A mathematical model based on the fundamental chemical reaction pathways of the finish-frying was developed, incorporating moisture and temperature gradients in the fries. This showed the contribution of both glucose and fructose to the generation of acrylamide and accurately predicted the acrylamide content of the final fries.

Added versus accumulated sugars on color development and acrylamide formation in french-fried potato strips

Added (glucose addition) versus accumulated (in situ sugar development via cold-temperature storage) sugar treatments were investigated in relation to acrylamide formation within fried potato strips at standardized levels of finish-fried color (Agtron color scores ranged from 36 to 84). The added sugar treatment exhibited a relatively reduced rate of acrylamide formation and generally possessed a lower and less variable acrylamide content (61-1290 ng/g) than the accumulated sugar scheme (61-2191 ng/g). In a subsequent experiment, added fructose applied to strip surfaces via dipping prior to frying favored acrylamide formation over color development relative to added glucose, for which the reverse trend was observed. Thus, where acrylamide differences were noted between added and accumulated sugar treatments (given equivalent Agtron color scores), this result was likely aided by the relative higher fructose content in strips of the accumulated sugar scheme rather than simply a greater relative concentration of total reducing sugars.

A new isoform of thioredoxin h group in potato, SbTRXh1, regulates cold-induced sweetening of potato tubers by adjusting sucrose content

In order to study the molecular mechanism of the cold-induced sweetening (CIS) of potato tubers, a novel isoform of thioredoxin h group, SbTRXh1, which was up-regulated early in the 4 °C storage of CIS-resistant potato (Solanum berthaultii) tubers, was cloned in present research. The genetic transformation of over-expression (OE) and RNA interference (RNAi) of SbTRXh1 into potato cv. E-Potato 3 (E3) was carried out to clarify its function in CIS regulation. The results showed that the transcripts of SbTRXh1 in either OE- or RNAi-tubers were strongly induced in 4 °C storage and quantitatively related to the reducing sugar (RS) accumulation, indicating that SbTRXh1 is involved in the CIS process of potato tubers. Regression analysis between the transcripts and protein contents of SbTRXh1 showed a very significant logarithmic relationship implying that the expression of SbTRXh1 may be mainly regulated at transcriptional level. Further monitoring the variation of the sugar contents in cold-stored tubers demonstrated a linear relationship between RS and sucrose (Suc). Thus, it can be inferred that SbTRXh1 may function in the Suc-RS pathway for CIS regulation of potato tubers.

KEY MESSAGE

SbTRXh1 is primarily demonstrated to be involved in the regulation of cold-induced sweetening (CIS) of potato tubers, and it may function in the Suc-RS pathway for CIS regulation.

Suppression of the vacuolar invertase gene prevents cold-induced sweetening in potato

Potato (Solanum tuberosum) is the third most important food crop in the world. Potato tubers must be stored at cold temperatures to prevent sprouting, minimize disease losses, and supply consumers and the processing industry with high-quality tubers throughout the year. Unfortunately, cold storage triggers an accumulation of reducing sugars in tubers. High-temperature processing of these tubers results in dark-colored, bitter-tasting products. Such products also have elevated amounts of acrylamide, a neurotoxin and potential carcinogen. We demonstrate that silencing the potato vacuolar acid invertase gene VInv prevents reducing sugar accumulation in cold-stored tubers. Potato chips processed from VInv silencing lines showed a 15-fold acrylamide reduction and were light in color even when tubers were stored at 4°C. Comparable, low levels of VInv gene expression were observed in cold-stored tubers from wild potato germplasm stocks that are resistant to cold-induced sweetening. Thus, both processing quality and acrylamide problems in potato can be controlled effectively by suppression of the VInv gene through biotechnology or targeted breeding.

The influence of tuber mineral element composition as a function of geographical location on acrylamide formation in different Italian potato genotypes

BACKGROUND

The present study was aimed at examining the effect of tuber mineral composition, distinctive for geographical location, on the expression of acrylamide precursors in three potato genotypes (Arinda, Rossa di Cetica and Sieglinde) in three Italian potato cultivation regions (Puglia, Sicily and Tuscany).

RESULTS

Sucrose and amino acids were not correlated with acrylamide formation. In contrast, reducing sugars, limiting with respect to the principal amino acid precursor asparagine, were positively correlated with acrylamide. From analysis of variance, both acrylamide and reducing sugars were not significant for variety but highly significant for location, with higher levels occurring in all three varieties cultivated in Tuscany, followed by Sicily and Puglia respectively. Reducing sugars were negatively correlated with K and Ca and positively correlated with Zn and Cu. Neither N nor P was correlated with reducing sugar content. Path analysis, a statistical technique distinguishing causation and correlation between variables, was implemented to provide additional insight on the interactions between mineral elements and reducing sugars under open field conditions. The variation in reducing sugars in all three varieties was shown to be attributable to Zn.

CONCLUSION

Cultivation location has a significant impact on the composition of tuber mineral elements and, as a result, on genotype in the expression of reducing sugars. The negative correlation between Zn and K and the variation in reducing sugar content attributed to the element Zn, which is particularly available in acid soils, are important factors warranting future research aimed at reducing acrylamide formation from an agronomic perspective.

Free amino acids and sugars in rye grain: implications for acrylamide formation

Acrylamide forms from free asparagine and sugars during cooking, and products derived from the grain of cereals, including rye, contribute a large proportion of total dietary intake. In this study, free amino acid and sugar concentrations were measured in the grain of a range of rye varieties grown at locations in Hungary, France, Poland, and the United Kingdom and harvested in 2005, 2006, and 2007. Genetic and environmental (location and harvest year) effects on the levels of acrylamide precursors were assessed. The data showed free asparagine concentration to be the main determinant of acrylamide formation in heated rye flour, as it is in wheat. However, in contrast to wheat, sugar, particularly sucrose, concentration also correlated both with asparagine concentration and with acrylamide formed. Free asparagine concentration was shown to be under genetic (G), environmental (E), and integrated (G x E) control. The same was true for glucose, whereas maltose and fructose were affected mainly by environmental factors and sucrose was largely under genetic control. The ratio of variation due to varieties (genotype) to the total variation (a measure of heritability) for free asparagine concentration in the grain was 23%. Free asparagine concentration was closely associated with bran yield, whereas sugar concentration was associated with low Hagberg falling number. Rye grain was found to contain much higher concentrations of free proline than wheat grain, and less acrylamide formed per unit of asparagine in rye than in wheat flour.

Effects of genotype and environment on free amino acid levels in wheat grain: implications for acrylamide formation during processing

Acrylamide forms from free asparagine and reducing sugars during cooking, with asparagine concentration being the key parameter determining the formation in foods produced from wheat flour. In this study free amino acid concentrations were measured in the grain of varieties Spark and Rialto and four doubled haploid lines from a Spark x Rialto mapping population. The parental and doubled haploid lines had differing levels of total free amino acids and free asparagine in the grain, with one line consistently being lower than either parent for both of these factors. Sulfur deprivation led to huge increases in the concentrations of free asparagine and glutamine, and canonical variate analysis showed clear separation of the grain samples as a result of treatment (environment, E) and genotype (G) and provided evidence of G x E interactions. Low grain sulfur and high free asparagine concentration were closely associated with increased risk of acrylamide formation. G, E, and G x E effects were also evident in grain from six varieties of wheat grown at field locations around the United Kingdom in 2006 and 2007. The data indicate that progress in reducing the risk of acrylamide formation in processed wheat products could be made immediately through the selection and cultivation of low grain asparagine varieties and that further genetically driven improvements should be achievable. However, genotypes that are selected should also be tested under a range of environmental conditions.