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  • 1
    Language: English
    In: Journal of agricultural and food chemistry, 10 April 2013, Vol.61(14), pp.3494-500
    Description: Thermal treatment of an aqueous solution of D-galacturonic acid at pH 3, 5, and 8 led to rapid browning of the solution and to the formation of carbocyclic compounds such as reductic acid (2,3-dihydroxy-2-cyclopenten-1-one), DHCP (4,5-dihydroxy-2-cyclopenten-1-one), and furan-2-carbaldehyde, as degradation products in weak acidic solution. Studies on their formation revealed 2-ketoglutaraldehyde as their common key intermediate. Norfuraneol (4-hydroxy-5-methyl-3-(2H)-furanone) is a typical alkaline degradation product and formed after isomerization. Further model studies revealed reductic acid as an important and more browning active compound than furan-2-carbaldehyde, which led to a red color of the model solution. This red-brown color is also characteristic of thermally treated uronic acid solutions.
    Keywords: Food Handling ; Maillard Reaction ; Models, Chemical ; Hexuronic Acids -- Chemistry
    ISSN: 00218561
    E-ISSN: 1520-5118
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  • 2
    Language: English
    In: Food Chemistry, 01 October 2017, Vol.232, pp.450-454
    Description: Heating aqueous -glucose model reactions with -glutamine and -alanine yielded similar colored solutions. However, size-exclusion chromatography (SEC) revealed that both non-enzymatic browning reactions proceeded differently. Due to a fast occurring cyclization of -glutamine to pyroglutamic acid, the typical amino-carbonyl reaction was slowed down. However, -glutamine and -alanine model reactions showed the same browning index. Closer investigations could prove that -pyroglutamic acid was able to influence non-enzymatic browning reactions. SEC analyses of -glucose model reactions with and without -pyroglutamic acid revealed an increase of low molecular colored compounds in the presence of -pyroglutamic acid. Polarimetric measurements showed a doubling of -glucose mutarotation velocity and HPLC analyses of -fructose formation during thermal treatment indicated a tripling of aldose-ketose transformation in the presence of -pyroglutamic acid, which are signs of a faster proceeding non-enzymatic browning process. 2-Pyrrolidone showed no such behavior, thus the additional carboxylic group should be responsible for the observed effects.
    Keywords: Non-Enzymatic Browning Reaction ; D-Glucose ; L-Alanine ; L-Glutamine ; L-Pyroglutamic Acid ; Size-Exclusion Chromatography ; Polarimetry ; Carboxylic Group Catalysis ; Chemistry ; Diet & Clinical Nutrition ; Economics
    ISSN: 0308-8146
    E-ISSN: 1873-7072
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  • 3
    Language: English
    In: Journal of agricultural and food chemistry, 07 November 2018, Vol.66(44), pp.11806-11811
    Description: In this study, α-dicarbonyl compounds consisting of a backbone with six carbon atoms resulting from the Maillard reaction of d-fructose with γ-aminobutyric acid were determined. The reaction was carried out under mild reaction conditions at 50 °C and water contents between 0 and 90%. A thus far unknown α-dicarbonyl compound was found as the main product in the first 24 h at water contents below 50%. After isolation of its stable quinoxaline derivative, it was possible to identify the compound as 2-deoxy-d- glycero-hexo-3,4-diulose (2-deoxyglucosone). For the first time, the four C-α-dicarbonyl compounds, 1-deoxyglucosone, 2-deoxyglucosone, 3-deoxyglucosone, and 4-deoxyglucosone, could be identified in the Maillard reaction of a hexose at the same time. This indicates the formation of a 2,3-eneaminol from the Schiff base of d-fructose and the formation of 2-amino-2-deoxy-3-ketose as an alternative to the Heyns product.
    Keywords: 2-Amino-2-Deoxy-3-Ketose ; 2-Deoxyglucosone ; 4-Deoxyglucosone ; Amadori Product ; C6-Α-Dicarbonyl Compounds ; Maillard Reaction ; Deoxyglucose -- Chemistry ; Fructose -- Chemistry ; Gamma-Aminobutyric Acid -- Chemistry
    ISSN: 00218561
    E-ISSN: 1520-5118
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  • 4
    Language: English
    In: Journal of agricultural and food chemistry, 27 March 2013, Vol.61(12), pp.3090-6
    Description: The degradation reaction of thermally treated 3-deoxy-d-erythro-hexos-2-ulose and methylglyoxal, both key intermediates in Maillard chemistry, was investigated. Different analytical strategies were accomplished to cover the broad range of formed products and their different chemical behavior. These involved HPLC-DAD and accordingly LC/MS analysis of the quinoxaline derivates, GC/MS analysis of the acetylated quinoxalines, and GC-FID analysis of the decyl ester of acetic acid. As a main degradation product of 3-deoxy-d-erythro-hexos-2-ulose, 5-(hydroxymethyl)furfural could be identified. At alkaline pH values, 3-deoxy-d-erythro-hexos-2-ulose generated various acids but no colored products. In contrast, thermal treatment of methylglyoxal yielded high molecular weight, brownish products. A dimer of methylglyoxal, first precursor for aldol-based polymerization of methylglyoxal, could be clearly identified by GC/MS.
    Keywords: Hot Temperature ; Maillard Reaction ; Ketoses -- Chemistry ; Pyruvaldehyde -- Chemistry
    ISSN: 00218561
    E-ISSN: 1520-5118
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  • 5
    Language: English
    In: Journal of agricultural and food chemistry, 30 December 2015, Vol.63(51), pp.10973-9
    Description: The influence of different polyphenolic compounds (PPs) on the Maillard reaction in a d-glucose/l-alanine model system with or without metal ions was studied under various reaction conditions. At temperatures up to 100 °C the PPs showed pro-oxidative effects due to their reducing effects on metal ions. This can be explained by a combined redox cycling mechanism of metals and PPs that promotes oxidation in the Maillard reaction. The antioxidative capacities of the PPs were measured with three different assays and correlated directly with their pro-oxidative effects on d-glucosone formation. The degree of the pro-oxidative effect depended not only on the PPs' reducing potential and their antioxidative ability but also on their concentration, the temperature, and the pH value of the model system. At low pH values and temperatures, the PPs were more stable and therefore showed an increased pro-oxidative tendency. In contrast, some of the used PPs were almost completely degraded at temperatures of 130 °C, and the formed polymers were able to complex metal ions. In the absence of these catalyzing ions, the oxidation ratio of d-glucose to d-glucosone was decreased.
    Keywords: Maillard Reaction ; Antioxidative Influence ; D-Glucosone ; Oxidation ; Polyphenol ; Pro-Oxidative Influence ; Hot Temperature ; Alanine -- Chemistry ; Antioxidants -- Pharmacology ; Glucose -- Chemistry ; Metals -- Chemistry ; Polyphenols -- Pharmacology
    ISSN: 00218561
    E-ISSN: 1520-5118
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  • 6
    Language: English
    In: Journal of agricultural and food chemistry, 02 April 2014, Vol.62(13), pp.2837-44
    Description: The antioxidant capacity of two 1,2-dicarbonyl compounds, 1-deoxy-d-erythro-hexo-2,3-diulose (1-deoxyglucosone) and d-arabino-hexo-2-ulose (d-glucosone), was investigated. Both compounds are key intermediates of the Maillard reaction, and both possess a reductone-like structure. The reductive potential of the reductones was measured with the trolox equivalent antioxidant capacity (TEAC) assay and the Folin-Ciocalteu reagent (FCR) assay. Their antioxidant capacity set them apart from their precursors and other typical Maillard reaction products. Using electron paramagnetic resonance (EPR) spectroscopy, the special radical scavenging behavior of 1-deoxyglucosone and d-glucosone was measured. Both exhibited a slow, but constant, scavenging ability over the course of several hours, even days. It was postulated that this characteristic behavior is caused by the isomeric composition and the transformation to the particular antioxidant form. Reaction mixtures of 1-deoxyglucosone showed a correlation between the decrease of antioxidant properties and the decomposition of 1-deoxyglucosone.
    Keywords: Antioxidants -- Chemistry ; Ketoses -- Chemistry
    ISSN: 00218561
    E-ISSN: 1520-5118
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  • 7
    Language: English
    In: Journal of agricultural and food chemistry, 22 July 2015, Vol.63(28), pp.6457-65
    Description: Thermal treatment of aqueous solutions of D-galacturonic acid and L-alanine at pH 3, 5, and 8 led to rapid and more intensive nonenzymatic browning reactions compared to similar solutions of other uronic acids and to Maillard reactions of reducing sugars. The hemiacetal ring structures of uronic acids had a high impact on browning behavior and reaction pathways. Besides reductic acid (1,2-dihydroxy-2-cyclopenten-1-one), 4,5-dihydroxy-2-cyclopenten-1-one (DHCP), furan-2-carboxaldehyde, and norfuraneol (4-hydroxy-5-methyl-3-(2H)-furanone) could be detected as typical products of nonenzymatic uronic acid browning reactions. 2-(2-Formyl-1H-pyrrole-1-yl)propanoic acid (FPA) and 1-(1-carboxyethyl)-3-hydroxypyridin-1-ium (HPA) were identified as specific reaction products of uronic acids with amine participation like l-alanine. In contrast, the structurally related D-galacturonic acid methyl ester showed less browning activity and degradation under equal reaction conditions. Pectin-specific degradation products such as 5-formyl-2-furanoic acid and 2-furanoic acid were found but could not be verified for d-galacturonic acid monomers alone.
    Keywords: 3-Hydroxypyridine ; Maillard Reaction ; Colored Compounds ; D-Galacturonic Acid ; D-Galacturonic Acid Methyl Ester ; D-Glucuronic Acid ; L-Alanine ; Nonenzymatic Browning ; Pyrrole-2-Carboxaldehyde ; Maillard Reaction ; Amino Acids -- Chemistry ; Hexuronic Acids -- Chemistry
    ISSN: 00218561
    E-ISSN: 1520-5118
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  • 8
    Language: English
    In: Food Chemistry, 15 August 2012, Vol.133(4), pp.1456-1465
    Description: ► Temperature and radiation influence flavonol glycosides in kale structure-dependent. ► Establishment of compound–climate relationship for flavonol aglycones and glycosides for the first time. ► Low temperature induce antioxidant relevant quercetin glycosides. The winter crop kale has a complex profile of different glycosylated and acylated flavonol glycosides which may be affected by global warming. To the best of our knowledge, compound–climate relationships for flavonol aglycones and flavonol glycosides were established for the first time. The investigated 10 major flavonol glycosides responded structure-dependent in the investigated temperature range between 0 and 12 °C and the photosynthetic active radiation range between 4 and 20 mol m d , e.g. the decrease in temperature led to an increase in sinapic acid monoacylated and diacylated quercetin glycosides, while the sinapic acid monoacylated kaempferol glycosides showed a maximum at 4.5 °C. Furthermore, the hydroxycinnamic acid residues and the different number of glucose moieties in the 7- position affected the response of kaempferol triglucosides. Consequently, global warming would result in lower concentrations of antioxidant-relevant quercetin glycosides in winter crops, suggesting a production at e.g. higher altitudes due to lower temperature.
    Keywords: Kale ; Flavonol Aglycones ; Flavonol Glycosides ; Temperature ; Radiation ; Chemistry ; Diet & Clinical Nutrition ; Economics
    ISSN: 0308-8146
    E-ISSN: 1873-7072
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  • 9
    Language: English
    In: Food Chemistry, 01 January 2012, Vol.130(1), pp.1-8
    Description: ► Thermal breakdown of individual glucosinolates in broccoli sprouts was studied. ► The structure of the glucosinolate had great impact on the thermal stability. ► Sulphur containing aliphatic glucosinolates were unequally stable according to the oxidation state of the sulphur. ► Basic medium increased thermal breakdown. Glucosinolates are secondary plant metabolites occurring in vegetables. Food processing significantly reduces glucosinolate content, among other things due to thermal degradation. As there is only little information about thermal glucosinolate breakdown, the influence of the chemical structure as well as the influence of different pH to thermal degradation of individual glucosinolates was studied by analysing desulphoglucosinolates with HPLC-DAD. Thermal degradation was forced by heating broccoli sprouts at 130 °C in dry medium, whereas the influence of the pH was studied by cooking at 100 °C in aqueous medium Within each group of glucosinolates differences in thermal degradation were revealed. Within the sulphur containing aliphatic glucosinolates the oxidative state of the sulphur atom as well as the side chain length influenced the reactivity. Among the indole glucosinolates great differences in stability were observed. A hydroxyl function in the side chain generally seems to destabilise glucosinolates. Glucosinolates were most stable towards thermal treatment in neutral and slightly acidic medium, whereas they degraded more rapidly in basic medium.
    Keywords: Glucosinolates ; Thermal Degradation ; Ph Influence ; Structural Influence ; Roasting ; Cooking ; Broccoli Sprouts ; Chemistry ; Diet & Clinical Nutrition ; Economics
    ISSN: 0308-8146
    E-ISSN: 1873-7072
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  • 10
    Language: English
    In: Food Chemistry, 01 June 2013, Vol.138(2-3), pp.857-865
    Description: ► Three kale cultivars were subjected to thermal treatment and investigated. ► During boiling, total phenolic content and total antioxidant activity remain unchanged. ► HPLC-online-TEAC revealed distinct changes in composition and activity of the flavonols. ► Degradation products compensate the loss of the antioxidant activity of the original compounds. Generally, boiling of vegetables is assumed leading to lower nutritional values because of leaching effects and activity loss of bioactive compounds. Kale ( var. ) reveals a great diversity of flavonoids, which have been shown to be good antioxidants. As vegetables are mainly consumed cooked, the influence of boiling on kale’s flavonoids and their antioxidant activity was investigated. Therefore, three kale cultivars were cooked at 100 °C for 2 and 4 h prior to analysis. The total phenolic content (TPC) and the total antioxidant activity (TEAC assay and EPR spectrometry) of each cultivar were determined and revealed no change, independent of cooking time, although kale samples visually altered. Using the HPLC–UV/Vis-online-TEAC approach, distinct changes in composition and antioxidant activity of the flavonoids were detectable. Thus, it was observable, that the antioxidant activities of the reaction products compensated the “loss” of the antioxidant activity of the original compounds of the uncooked material.
    Keywords: Curly Kale ; Flavonol Glycosides ; Thermal Stability ; Epr Spectrometry ; Online-Teac ; Folin-Ciocalteu Assay ; Degradation Reaction ; Boiling ; Chemistry ; Diet & Clinical Nutrition ; Economics
    ISSN: 0308-8146
    E-ISSN: 1873-7072
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