Free Asparagine Research Articles

The impact of home storage conditions on the accumulation of acrylamide precursors in potato tubers

AbstractThe aim of this work was to investigate the impact of domestic storage conditions on total reducing sugars and free asparagine in fresh potatoes to understand the implications for acrylamide‐forming potential. Current advice to consumers is that potatoes should be stored in a dark cool place, but not in the refrigerator based on an expectation that home storage in the refrigerator will result in “cold sweetening” and increased acrylamide‐forming potential. Potato tubers of two common varieties (King Edward and Nectar) were obtained from four independent sources and were sampled from commercial store conditions on three occasions between November 2018 and May 2019. Tuber reducing sugar contents were assessed under conditions that mimicked home storage, at either 18 or 5°C during a 15‐day treatment period. There was a similar pattern of reducing sugar content in tubers from all four sources. For tubers stored at 5°C, reducing sugar levels showed little or no variation over the 15‐day time‐course. Differences in reducing sugar contents between varieties and between the source of tubers of the same variety were far higher than those observed dependent on cold storage. For tubers stored at 18°C, total reducing sugar levels remained the same or decreased over 15 days of storage. Decreases in sugar content were not consistent between samples, varying by sampling point, source and cultivar. Tuber asparagine content was independent of storage temperature with no significant differences in asparagine observed between tuber samples stored at 5 or 18°C for 15 days. In some tuber samples, storage at 5°C significantly retarded sprouting compared with samples stored at 18°C, indicating the potential for refrigerator storage to extend shelf life and reduce waste. The premise that home storing potato tubers at 5°C postpurchase increases levels of reducing sugars and therefore acrylamide‐forming potential is not supported by these data. Much larger sources of variation were from other factors.

Roasted Rye as a Coffee Substitute: Methods for Reducing Acrylamide.

Acrylamide is assumed to be a potential carcinogen, and reference values have therefore been implemented in EU legislation. Thus, the food industry needs to reduce the acrylamide content in consumer products to the lowest possible value. In this study, roasted rye was evaluated for its suitability as a coffee substitution product with respect to its acrylamide content. The influence of process modifiers, free asparagine content, storage, and rye type on the final content of acrylamide was investigated. Changes in carbohydrate composition and brightness caused by the roasting process were described. Sample analysis was conducted via GC-MS and HPLC-CAD. Existing methods were adapted to roasted rye as the sample matrix. CaCl2 and asparaginase treatment as well as pH adjustments prior to roasting did not prove to reduce the acrylamide content. A significantly (* p < 0.027) lower free asparagine content in the raw material resulted in a lower formation of acrylamide in the final product. The acrylamide content significantly decreased (**** p < 0.0001) after 3 (1100 ± 18 µg kg−1) and 6 (490 ± 7 µg kg−1) months of long-term storage. Only samples stored for 6 months (490 ± 7 µg kg−1) met the EU acrylamide content requirements (<500 µg kg−1) for grain-based coffee substitution products.

Processing strategies to decrease acrylamide formation, reducing sugars and free asparagine content in potato chips from three commercial cultivars

Potato chips are among the highest contributors to the dietary intake of acrylamide, a potent neurotoxin and likely carcinogen in heat-processed foods. The present study aimed to determine the effects of frying conditions and additive treatments on reducing sugars, asparagine levels, and acrylamide formation in fried potato chips. Three commercially important chipping cultivars (Atlantic, Snowden, and Vigor) were tested using different frying times (3, 5, and 7 min) and temperatures (160, 170, 180, and 190 °C). Acrylamide formation in chips was found to be cultivar-specific and increased with increasing frying time and temperature. The acrylamide levels were significantly lower in chips processed at high temperatures for short frying times than in those processed at low temperatures for long frying times. In all cultivars, acrylamide synthesis was accompanied by significant decreases in the levels of reducing sugars and asparagine. The cultivar exhibiting the lowest acrylamide levels in the processed potato chips was Snowden, while the conditions most conducive to acrylamide formation in all cultivars were frying at 190 °C for 7 min. Using a 7 min frying time, decreasing the frying temperature from 190 to 160 °C mitigated the acrylamide formation in potato chips processed from Atlantic, Snowden and Vigor by 84, 67, and 78%, respectively. We also examined the effects of additives, such as 1% acetic acid, 1% citric acid, 0.1 M sodium chloride, 0.1 M calcium chloride, 0.5% ascorbic acid, or 1 M l-glycine, during the blanching of potato slices prior to frying. Blanching in distilled water led to the greatest decreases (19–59%) in acrylamide formation in all cultivars. Our findings provide the basis for new processing strategies to mitigate acrylamide formation and improve the quality of chips from these, and possibly other, potato cultivars.

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.

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

Grain protein concentration and composition are key factors affecting winter wheat quality and are influenced by wheat genotype, available fertility, and growing conditions. These same parameters can affect free asparagine concentration in grain, and elevated asparagine can lead to acrylamide production in baked food products, which can be a health concern. The objectives of this study were to determine the effect of genotype, nitrogen (N), and sulfur (S) fertility on protein concentration, protein quality, dough rheology, and asparagine concentration in winter wheat grown on S-deficient soils. Treatments were arranged in a 3 × 2 × 4 factorial design in 2017 and 3 × 2 × 5 factorial design in 2018. There were three levels of N (56, 101 and 146 kg ha−1), two levels of S (0 and 22 kg ha−1), four levels of genotype in 2017, and five levels of genotype in 2018. Protein composition was evaluated as the percent polymeric protein using size exclusion high performance liquid chromatography. In both years, the ratio of polymeric to monomeric protein was increased by sulfur fertilization. Solvent retention capacity (SRC) was evaluated using the whole grain lactic acid-sodium dodecyl sulfate test. In 2018, S application increased the SRC by 217%–308%. However, in 2017, SRC improvement was limited to two genotypes and was modest, likely a consequence of the reduced protein concentration in S-treated plots. Free asparagine concentration averaged 9.8 μmol/g and 20.9 μmol/g in 2017 and 2018, respectively. Asparagine concentration in grain was affected by N, S, genotype, and their interactions. Sulfur application substantially reduced asparagine concentrations in both years. Dough rheology was evaluated in the 2018 trial using the farinograph test. Sulfur application increased average farinograph stability from 9.2 min to 14.6 min. Farinograph stability was effectively predicted by the SRC test (R2 = 0.78). These results demonstrate the importance of ensuring adequate S fertility in winter wheat production.

Acrylamide formation in biscuits made of different wholegrain flours depending on their free asparagine content and baking conditions

Due to a high content of bioactive compounds with beneficial health effects, wholegrain flours of different cereals have been extensively used in the confectionery industry. However, according to our study, cereal species and their varieties have different potential for the formation of acrylamide in biscuits. In this study, wholegrain flours of eight genotypes of small grain cereals (bread wheat, durum wheat, soft wheat, hard wheat, triticale, rye, hulless barley and hulless oat) and four genotypes of maize (white-, yellow- and red-coloured standard seeded maize, and blue-coloured popping maize) were used to prepare biscuits. The biscuits were baked at 180 °C for 7, 10 and 13 min. At 180 °C, acrylamide was detected at all baking times, reaching a final concentration of 72.3 up to 861.7 μg/kg after 13 min of baking in refined bread wheat-based biscuits and hulless oat-based biscuits, respectively. Data indicated that acrylamide in biscuits could not exactly correspond to free asparagine in flour. However, hulless oat, durum wheat and rye flour with the highest content of free asparagine of 859.8, 603.2 and 530.3 mg/kg, respectively, generated most acrylamide in biscuits baked for 13 min. The lowest content of acrylamide was found in biscuits prepared from refined bread wheat flour and wholegrain red maize flour that also contained the lowest content of free asparagine. After baking for 7, 10 and 13 min, the content of acrylamide in these samples was 17.9 and 24.4 μg/kg, 51.9 and 28.7 μg/kg and 72.3 and 95.2 μg/kg, respectively. The results suggest that the use of cereal flours low in free asparagine can be an effective strategy for acrylamide mitigation in biscuits, together with the use of lower thermal load during baking.

Impact of Row Distance and Seed Density on Grain Yield, Quality Traits, and Free Asparagine of Organically Grown Wheat

Organic farming faces challenges providing sufficient nutrient supply as manure and crop rotations are often the major nutrient inputs. Larger row distances and fewer seed densities can support nitrogen availability by giving more space to the single plant. As free asparagine (Asn) the main precursor of acrylamide (AA) in plants is closely related to nitrogen uptake and storage, the question arose whether free Asn will be affected by row distance and seed densities in organic farming. This study investigated the effect of row distance and seed density on yield, yield components, baking quality, and free Asn in organic farming. A two-year field trial was carried out including two winter wheat cultivars, two row distances, and two seed densities. Year and cultivar highly influenced all traits. The impact of both treatments was mainly caused by interaction. Nevertheless, enlarged row distances raised baking quality, while free Asn was changed to a minor extent. Thus, we recommend larger row distances for raising baking quality without increasing free Asn. Seed density is of minor relevance. The close relation found between free Asn and grains per spike (R2 = 0.72) indicates that smaller grains contain more Asn than bigger grains. This opens new insights into Asn synthesis during grain development and offers a potential prediction of Asn amounts.

Acrylamide-Formation Potential of Cereals: What Role Does the Agronomic Management System Play?

As bakery products contribute considerably to the daily intake of the carcinogen acting substance acrylamide (AA), the aim of this study was to evaluate the impact of the management system (conventional vs. organic farming) on AA precursor levels of free asparagine (Asn) across different cultivars of the cereal species, namely winter wheat (Triticum aestivum), winter spelt (Triticum aestivum ssp. spelta) and winter rye (Secale cereale) with simultaneous consideration of gained grain yields and flour qualities. For this purpose, orthogonal field trials were established at two sites in Southwest Germany over two growing seasons (2006–2007 and 2007–2008). The results indicated a significant impact of the management system on free Asn contents in white flour. Across all species, free Asn contents in the white flour was 26% lower under organic compared to conventional farming. The impact of the management system on individual cultivars was obvious with a maximum reduction in free Asn contents of 50% in wheat cultivars if organically produced (e.g., for cultivars Ludwig, Privileg, Capo). For spelt, a significant impact of the management system was only found in 2008 with a reduction in free Asn of up to 25% if organically produced. Across both cropping systems, cultivar Franckenkorn reached the lowest levels of free Asn. For rye, a significant impact of the management system was observed only in 2007 with 33% higher Asn amounts in the conventional management system. Independent of the cropping system, rye reached the highest levels of free Asn followed by wheat and spelt. Depending on species, there was also an impact of the two systems on crude protein. The organically cropped wheat had a significantly lower level, but this was not observed for spelt and for rye only in 2007. The possible reason for the low free Asn content in the organically produced wheat flour could partially be the lower crude protein amount. Furthermore, the results indicated that lower AA contents in bakery products can be achieved by proper selection of species (e.g., 66% lower if rye is replaced by wheat) and cultivars. With an appropriate choice of the cultivar, a reduction of up to 65% was possible within wheat, along with a reduction of 44% within spelt and 12.5% within rye. In summary, the results indicated that organically produced wheat especially offers the opportunity to significantly lower the AA potential of bread and bread rolls by the choice of raw materials low in free Asn.

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.

Contrasting gene expression patterns in grain of high and low asparagine wheat genotypes in response to sulphur supply

BackgroundFree asparagine is the precursor for acrylamide formation during cooking and processing of grains, tubers, beans and other crop products. In wheat grain, free asparagine, free glutamine and total free amino acids accumulate to high levels in response to sulphur deficiency. In this study, RNA-seq data were acquired for the embryo and endosperm of two genotypes of bread wheat, Spark and SR3, growing under conditions of sulphur sufficiency and deficiency, and sampled at 14 and 21 days post anthesis (dpa). The aim was to provide new knowledge and understanding of the genetic control of asparagine accumulation and breakdown in wheat grain.ResultsThere were clear differences in gene expression patterns between the genotypes. Sulphur responses were greater at 21 dpa than 14 dpa, and more evident in SR3 than Spark. TaASN2 was the most highly expressed asparagine synthetase gene in the grain, with expression in the embryo much higher than in the endosperm, and higher in Spark than SR3 during early development. There was a trend for genes encoding enzymes of nitrogen assimilation to be more highly expressed in Spark than SR3 when sulphur was supplied. TaASN2 expression in the embryo of SR3 increased in response to sulphur deficiency at 21 dpa, although this was not observed in Spark. This increase in TaASN2 expression was accompanied by an increase in glutamine synthetase gene expression and a decrease in asparaginase gene expression. Asparagine synthetase and asparaginase gene expression in the endosperm responded in the opposite way. Genes encoding regulatory protein kinases, SnRK1 and GCN2, both implicated in regulating asparagine synthetase gene expression, also responded to sulphur deficiency. Genes encoding bZIP transcription factors, including Opaque2/bZIP9, SPA/bZIP25 and BLZ1/OHP1/bZIP63, all of which contain SnRK1 target sites, were also expressed. Homeologues of many genes showed differential expression patterns and responses, including TaASN2.ConclusionsData on the genetic control of free asparagine accumulation in wheat grain and its response to sulphur supply showed grain asparagine levels to be determined in the embryo, and identified genes encoding signalling and metabolic proteins involved in asparagine metabolism that respond to sulphur availability.

Primary metabolite contents are correlated with seed protein and oil traits in near-isogenic lines of soybean

Soybean (Glycine max [L.] Merr.) is an important source of human dietary protein and vegetable oil. A strong negative correlation between protein and oil contents has hindered efforts to improve soybean seed quality. The metabolic and genetic bases of soybean seed composition remain elusive. We evaluated metabolic diversity in a soybean near-isogenic line (NIL) population derived from parents (JD12 and CMSD) with contrasting seed oil contents. Using GC-TOF/MS, we compared seed primary metabolites of high protein/low oil lines, low protein/high oil lines, and their parents. Principal-components analysis showed that metabolic profiles of all progeny lines could be discriminated based on protein and oil contents. Univariate analysis revealed wide variation and transgressive segregation of metabolites in the population. Twenty-eight annotated metabolites, in particular free asparagine, free 3-cyanoalanine, and L-malic acid, were correlated with seed protein content or seed oil content or seed protein and oil content. These results shed light on the metabolic and genetic basis of soybean seed composition.

Free asparagine concentrations in Canadian hard red spring wheat cultivars

The amino acid asparagine is considered the rate limiting precursor in the formation of acrylamide in cereal-based baked foods. However, there are no data on the quantity of this precursor in Canadian wheat. Wholemeal and white flour samples obtained from 30 Canadian hard red spring wheat grown in the Prairie provinces were analysed for asparagine content by liquid chromatography. The asparagine content varied from 302 to 965 and 116 to 336 μg g−1 for wholemeal and white flour, respectively. Therefore, wheat grown in Canada has similar asparagine levels to wheat grown in other parts of the world. Analysis of variance suggested that asparagine content is significantly affected by genotype (p &lt; 0.001), suggesting that breeding strategies could be investigated to produce cultivars with lower levels of this amino acid. Few significant correlations were observed between wheat and flour quality parameters and asparagine content, although there was a tendency towards weaker dough strength indices with increasing asparagine content.

Important factors to consider for acrylamide mitigation in potato crisps using pulsed electric fields

Abstract This preliminary study aimed to compare the application of pulsed electric field (PEF) with a traditional blanching as pre-treatments before frying for the mitigation of acrylamide content in potato crisps. Measuring the degree of cell disintegration index (po) and the changes in water electrical conductivity during washing of potato slices, PEF protocol and sample preparation scheme were optimized. Peeled potato slices (thickness 1.5 ± 0.2 mm) were subjected to PEF (1.5 kV/cm, pulse duration 10 μs, total treatment time 10 ms, pulse frequency 100 Hz) and to blanching (85 °C for 3.5 min) pre-treatments and then to washing in water, evaluating the reduction of acrylamide precursors (reducing sugars and free asparagine). After frying (175 °C, 3 min), product quality, in terms of colour, texture and acrylamide content were evaluated. Results showed that PEF promoted acrylamide precursors leaching followed by a reduction of the final acrylamide content of around 30%, significantly higher if compared to the reduction obtained with blanching, with only slight modifications of the final quality of the product, in terms of colour and texture. Industrial relevance The Commission Regulation (EU) 2017/2158 of 20 November 2017 has introduced new benchmark levels and mitigation strategies for the reduction of the presence of acrylamide in foods, directing food businesses to the research of measures to lower the acrylamide formation in foods. The actual industrial production process of fried potato crisps involves the use of many mitigation strategies, such as a blanching of raw potatoes. However, the traditional blanching treatment presents several practical drawbacks and leads to undesirable changes of the product quality. The application of PEF as a pre-treatment could reduce the acrylamide content in deep-fat fried potato crisps. This preliminary study gives important indications regarding the possibility of combining a PEF pre-treatment on raw potato slices with subsequent industrial processing steps for the production of potato crisps with low acrylamide concentration.

Effect of Asparaginase Enzyme in the Reduction of Asparagine in Green Coffee

Coffee is the most consumed beverage in the world, especially in Nordic countries. Its composition has substances considered to have high value for human health, such as chlorogenic and phenolic acids. However, the roasting of coffee can form substances such as acrylamide that are considered toxic and carcinogenic, depending on the time and the heat of roasting. However, there are some ways of reducing acrylamide formation during the processing of coffee beans. The reduction of its precursor asparagine is one of these ways. This can be achieved by the treatment of beans with the enzyme asparaginase. This study aimed to test the effectiveness of applying asparaginase (Acrylaway™) and evaluate the reduction of the amount of asparagine in Coffea arabica and C. canephora beans. The results showed the effectiveness of the enzyme in the reduction of free asparagine in green coffee beans of both species (C. arabica and C. canephora). Steam pretreatment was effective for the two species but required different times (30 min for C. arabica and 45 min for C. canephora). This can be attributed to the different chemical compositions found in the two species.

Evaluation of Asparagine Concentration as an Indicator of the Acrylamide Formation in Cereals Grown under Organic Farming Conditions

This study investigated the impact of organically grown cereals on the level of free asparagine (Asn) with simultaneous consideration of grain yields and flour qualities over three growing seasons in Germany. Additionally, the relation of free Asn and acrylamide (AA) was investigated. By including free Asn results of a second trial site, heritability of the trait free Asn was calculated. Free Asn was significantly influenced by species and within species by cultivars. Rye showed the highest free Asn amount, followed by einkorn, emmer, wheat, and spelt. Replacing rye with spelt would reduce free Asn by 85%. Cultivars differed in free Asn by up to 67% (wheat), 55% (spelt), and 33% (rye). Year significantly influenced free Asn levels. Heritability was high for wheat and spelt concerning locations, but regarding years, heritability was low for wheat but high for spelt and rye. For organically grown cereals, the relation between free Asn and AA formation has never been investigated. Across species and years, a correlation of R2 = 0.69 *** was found. Thus, free Asn can serve as an indicator for AA formation. In conclusion, the level of free Asn can be highly influenced by proper selection of species and cultivars.

Impact of Nitrogen and Sulfur Supply on the Potential of Acrylamide Formation in Organically and Conventionally Grown Winter Wheat

In a two-year field trial, the effect of nitrogen (N) and sulfur (S) fertilization was investigated on grain yield, grain quality parameters, formation of acrylamide (AA), and the precursor free asparagine (Asn) in organically and conventionally produced winter wheat cultivars. In both production systems, different types, amounts, and temporal distributions of N were tested. The the effect of S fertilizer types and amounts on free Asn was only tested in the conventional farming system. Within both cropping systems, grain yield and baking quality were significantly influenced by N treatment while the effect on free Asn was only minor. Especially within the organic farming system, increasing N fertilization levels did not increase free Asn significantly. A slight trend of increasing free Asn levels with an intensified N supply was observed, especially in the presence of crude protein contents of 14% or higher. However, only N amounts of 180 kg N ha−1 or higher increased the probability of high free Asn contents considerably, while N supply below that amount led to free Asn values similar to the unfertilized controls. The results indicated that good baking quality can be achieved without significantly increasing free Asn levels. In addition, cultivars affected the levels of free Asn significantly. Compared to cv. Bussard and Naturastar, cv. Capo exhibited the lowest AA formation potential at an N supply of 180 kg N ha−1 while simultaneously reaching a crude protein content &gt; 15% (conventional) and &gt; 12% (organic). Thus, it seems that cultivars differ in their ability to store and incorporate free Asn into proteins. Over all trials, a relation of free Asn and AA was shown by R2 = 0.77, while a relation of free Asn and protein was only R2 = 0.36. Thus, lowering free Asn by adjusting N treatments should not necessarily affect baking quality. S fertilization within conventional farming did not change the free Asn amount or crude protein significantly, probably due to the fact that soil was not sulfate-deficient. In summary, it was evident that free Asn amounts in wheat varied widely both within cultivars and between cropping systems. In order to clearly unravel genotypic differences and their interaction with environmental factors and especially N fertilization, further research is needed.

Development of LC-MS and LC-MS/MS Methods for Free Asparagine in Grains

New analytical methods for the determination of free asparagine （Asn）, which is a precursor of acrylamide, in grains were developed using LC-MS and LC-MS/MS. Asn was extracted from a sample with 5％ （w/v） aqueous trichloroacetic acid solution, appropriately diluted with 0.1％ （v/v） formic acid solution, and then analyzed by LC-MS or LC-MS/MS. HPLC separation was performed by isocratic elution on a Penta Fluoro Phenyl （PFP） column using 0.1％ （v/v） formic acid and acetonitrile mixture as the mobile phase. The calibration curve was linear in the range of 0.005-0.1 μg/mL. The mean recoveries from potato starch, non-glutinous rice flour and whole wheat flour ranged from 95.4 to 100.9％, repeatability （RSD） ranged from 0.9 to 6.0％, and within-laboratory reproducibility （RSDwr） ranged from 2.8 to 7.1％. Limits of quantitation （LOQs） were 7 mg/kg for potato starch, and 5 mg/kg for non-glutinous rice flour. In addition, an inter-laboratory study was performed in 10 laboratories using 5 kinds of grains （non-glutinous brown rice flour, corn flour, strong flour, whole wheat flour, and whole rye flour）, which naturally contained free asparagine. The HORRATR values ranged from 0.4 to 1.0. These results are within the range of the procedural manual of the Codex Alimentarius Commission, confirming the effectiveness of the developed procedures.

Screening of microorganisms producing a novel protein-asparaginase and characterization of the enzyme derived from Luteimicrobium album

A screening system using enrichment culture has been established with the aim of obtaining a novel enzyme for protein modification that has not been previously reported. This enzyme catalyzes deamidation of the side-chain amide group of asparagine in proteins. Enrichment culture of 390 soil samples was carried out with Z-Asn-Gly as the sole source of nitrogen, and the reaction product, Z-Asp-Gly, was detected in the culture supernatant of 102 strains. Strains with particularly high activity were Leifsonia sp., Luteimicrobium sp., Microbacterium sp., and Agromyces sp., all belonging to the class Actinobacteria. Of these, a protein-asparaginase (PA) was obtained from the culture supernatant of Luteimicrobium album 333B-h1, and its reactivity with different substrates and its basic enzymatic characteristics were investigated. Addition of the enzyme solution resulted in specific deamidation of only the asparagine residue in insulin chain B. The enzyme showed no reactivity with free asparagine or asparagine in low molecular weight peptides. It was demonstrated that the enzyme reacts with various protein substrates. In particular, proteins that have open structures, such as casein or gelatin, were good substrates. The activity and stability of PA at different temperatures and pH values were investigated. It was found that a temperature of 37°C and a roughly neutral pH are optimal conditions for the enzyme.

Reduction of acrylamide formation in fried potato chips by Aureobasidum pullulans L1 strain

Acrylamide is a potential carcinogenic molecule formed during food heat processing at high temperature (Maillard reaction). In the present study, the ability of the yeast Aureobasidium pullulans to deplete the acrylamide precursor free asparagine in fresh potatoes was investigated. A. pullulans applied before final frying changes the free amino acid composition of potatoes, decreasing the content of free asparagine by 16% and reducing acrylamide by 83% in fried potatoes. Potato browning was also reduced by yeast treatment without negative drawbacks on chip taste. This yeast, commonly used in fruit postharvest disease control, can therefore also be applied in potato and bakery industries to reduce food acrylamide content.

Mitigation measures for acrylamide reduction in dough-based potato snacks during their expansion by frying

ABSTRACTAcrylamide (AA) can occur in fried and baked food products which contain reducing sugars and free asparagine. Recently, the European Commission established mitigation measures and benchmark levels for the reduction of AA in food. The content of reducing sugars in raw materials and the temperature and time of the expansion process by frying were considered in this study of the preparation of dough-based potato snacks, mainly destined for children. Final moisture and bulk density were also evaluated. An increase from 0.15 to 1.0% in reducing sugar content, due to the addition of micro-ingredients in the dough, caused a remarkable AA increase of five- to six-fold. During frying at temperatures between 175 and 195°C, AA was produced after only a few seconds; the AA content was affected more by process time than by temperature. The best temperature/time conditions for expansion by frying were 185°C for 8 s.