Nonenzymic browning. XI. Effect of free amino groups on browning reactions in lipid-protein mixtures.

The course of browning was more rapid in mixtures of polyunsaturated fatty acid esters with casein that in those of the same lipids with formaldehyde-treated casein or with an inert inorganic substrate (barium sulphate or sodium sulphate). On the contrary, the content of oxidation products (peroxides and aldehydes) was much higher in lipids mixed with formaldehydetreated casein or with inorganic substrates. The results obtained with albumin were similar. The ratio of red to yellow pigments was higher in mixtures with non-treated casein than in the other two investigated reaction mistures. Brown pigments contained only low per centages of nitrogen.     

Nonenzymic browning XIII. Effect of an antioxidant on the discoloration of lipid-protein mixtures.

Higher concentrations of butylated hydroxyanisole inhibited the autoxidation of mixtures of unsaturated cod liver oil fatty acid esters with model proteins. The rate of discoloration was far less efficiently affected by the antioxidant because the antoixidant did not prevent the further transformation into brown pigments of colourless precursors, mainly carbonyl lipid oxidation products, already present in the lipid fraction before the addition of antioxidant. The antioxidant also did not influence the pigments already formed.     

Nonenzymic browning. VIII. Autoxidation and browning reactions of phosphatidylethanolamine

Summary Polyenoic fatty acids bound in phosphatidylethanolamine from egg yolk are easily oxidized at 40° C. Hydroperoxides formed as primary reaction products are rapidly decomposed to colourless nonperoxidic derivatives. The secondary reaction products turn rapidly to brown pigments. The blocking of amino groups of phosphatidylethanolamine corresponds to about half of total oxidation products. Some nitrogen-free brown pigments are obviously formed as well. More than one third of the end products remain colourless or slightly coloured.

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Zusammenfassung Die in Phosphatidylathanolamin von Eigelb gebundenen mehrfach ungesättigten Fettsäuren werden bei 40° C leicht autoxydiert. Die als primary Oxydationsprodukte gebildeten Hydroperoxide werden schnell zersetzt durch die Einwirkung der primären Aminogruppen unter Bildung von farblosen sekundären Zersetzungsprodukten, die durch weitere schnelle Reaktionen in gefärbte Stoffe übergehen. Etwa eine Hälfte der oxydierten Fettsäuren reagiert unter Blockierung der Aminogruppe des Colamins. Einige stickstofffreie braune Stoffe werden ebenfalls gebildet. Mehr als ein Drittel der Endprodukte bleibt farblos oder nur schwach gefärbt.

     

Nonenzymic browning XV. Effect of unsaturation on browning reactions of oxidized lipids with protein

Summary The amount of pigments produced by interaction of oxidized lipids with albumin and the intensity of coloration increase with increasing degree of unsaturation of the lipid fraction.

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Nichtenzymatische Bräunung XV. Einfluß der Ungesättigkeit auf die Bräunungsreaktionen oxydierter Lipide mit Protein

Zusammenfassung Die Menge der braunen Produkte der Wechselwirkung zwischen oxydierten Lipiden und Albumin und die Intensität der Verfärbung nehmen mit der zunehmenden Ungesättigkeitsstufe des Lipidanteils zu.

     

Nonenzymic browning. 4. Browning reactions of 2-furfuraldehyde with protein

Summary The binding of aldehyde on free amino groups of protein takes place during the heating of 2-furfuraldehyde with casein. The reaction is of the 1^st order, but becomes a 0 order reaction (with respect to amino groups) in the first reaction stage in case of sufficient excess of 2-furfuraldehyde. Multifold excess of 2-furfuraldehyde is necessary for the complete blocking of free amino groups. The condensation product is transformed by heating to higher temperatures, especially above 100° C, to deep brown coloured polymer products. A free amino group and also another functional group of protein are necessary for the formation of brown pigments. The reaction with other proteins is similar to that of casein.

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Zusammenfassung Während der Erhitzung von 2-Furfural mit Casein wird das Aldehyd an die freien Äminogruppen des Proteins gebunden. Die Reaktion ist 1. Ordnung, sie kann eine O. Ordnung werden (im Bezug mit Aminogruppen), wenn 2-Furfural in einem genügenden Über-schuß zu Beginn der Reaktion vorhanden ist. Ein mehrfacher Überschuß an 2-Furfural ist für die vollkommene Blockierung der Aminogruppen notwendig. Das Kondensationsprodukt wird durch Erhitzung unter höheren Temperaturen, besonders über 100° C, in tiefbraune Polymerderi vate überführt. Eine freie Aminogruppe und noch eine weitere Funktionsgruppe des Proteins sind für die Bildung der braunen Produkte notwendig. Die Reaktion verläuft mit anderen Eiweißstoffen in ähnlicher Weise wie mit Casein.

     

Nonenzymic browning. XII. Maillard reactions in green coffee beans on storage.

During storage of green coffee beans at increased temperature and at constant humidity reducing sugars present in original beans react with free amino acids with formation of colourless unstable products. Additional reducing sugars and free amino acids are produced by hydrolysis of polysaccharides and proteins, respectively. The second stage of storage is characterized by only slight changes in the content of free amino acids and sugars but by intensive browning reactions. This latter stage was characterized by deterioration of sensory quality of coffee beverage, especially of its odour. Lysine combined in protein was involved in browning reactions via colourless intermediary products.     

Nonenzymic browning of cauliflower on storage.

The nonenzymic browning of cauliflower homogenate was evaluated during storage at temperatures ranging between 40 degrees and 80 degrees C. In these accelerated tests, the reflectometric measurement was more sensitive and more reliable than the measurement of colour intensity of ethanolic extracts. The browning followed the kinetics of a first order reaction at higher temperatures and that of a zero order reaction at lower temperatures. The activation energy depended considerably on the reaction temperature. The rate of browning was only slightly affected by the addition of ferrous ions both in the absence and in the presence of oxygen. Results of model experiments show that the most important reaction under experimental conditions was probably the reaction of free amino-acids and other amine derivatives with quinones produced by oxidation of natural polyphenolic compounds. Red primary condensation products were transformed into brown pigments by subsequent secondary reactions.     

Nonenzymic browning reactions in boiled grape juice and its models during storage

Reaction orders, rate constants and activation energies were evaluated for 5-hydroxymethyl furfural (HMF) accumulation and brown pigment formation (BPF) in pekmez and its model systems stored at 55, 65 and 75°C over 10 days at pH 4.0. The model systems and their compositions were decided by considering the major pekmez components. Accumulation of HMF and BPF were the highest in pekmez and they were the smallest in model 1. ANOVA showed that the effects of temperature on both accumulation of HMF and BPF were significant (p<0.05). Results obtained from non-linear regression analysis indicated that reaction order was 0.5 for 5-HMF accumulation and was zero for brown pigment formation in the model systems. Reaction orders were zero for both HMF accumulation and BPF in pekmez. Calculated activation energies for HMF and brown pigment formation were in the range of 49.7–103 kJ mol⁻¹ and 116–132 kJ mol⁻¹ respectively.     

Nonenzymic browning of cauliflower on storage

European Food Research and Technology - The nonenzymic browning of cauliflower homogenate was evaluated during storage at temperatures ranging between 40° and 80° C. In these accelerated...     

Nonenzymic browning. 3. Browning reactions during heating of fish oil fatty acid esters with protein

Summary During heating of mixtures of methyl esters of polyunsaturated fish oil fatty acids and albumen under simulated conditions of roasting and frying of fish, peroxides present in the lipidic fraction are rapidly decomposed and form both liposoluble and insoluble brown pigments with free amino groups of albumen. Small amounts of lipids in the mixture have already great effect on the development of colour. The reaction is very rapid at the temperatures above 100° C, and the brown pigments are not decomposed by prolonged heating.

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Zusammenfassung Gemische der Methylester von polyungesättigten Fischölfettsäuren mit Albumin wurden unter simulierten Bedingungen des Röstens und Fritürens erhitzt. Die in der lipidischen Fraktion anwesenden Peroxide werden schnell zersetzt und bilden fettlösliche sowie auch unlösliche stickstoffhaltige braune Produkte mit den freien Aminogruppen des Albumins. Geringe Lipidmengen haben schon einen merkbaren Einfluß auf die Farbentwicklung. Die Reaktion tritt sehr schnell bei Temperaturen > 100° C ein und die braunen Produkte ändern sich auch während einer längeren Erhitzung nicht wesentlich.

     

Nonenzymic browning. XIV. Reaction of phospholipids with 1,4-benzoquinone.

Phosphatidylethanolamine reacts with 1,4-benzoquinone with the formation of a red unstable intermediary product consisting of one phosphatidylethanolamine residue and one 1,4-benzoquinone residue. The secondary reaction products are purple, violet, and reddish brown. Consequently, the absorption maximum shifts from 430 nm to 490 nm during the reaction. Finally, brown macromolecular end-products are formed. Phospholipids derived from choline, such as phosphatidylcholine, lysophosphatidylcholine, sphingomyelin, contribute only a little to the browning reactions, in comparison with phospholipids containing a primary amino-group (phosphatidylethanolamine, lysophosphatidylethanolamine, phosphatidylserine). The browning of a natural mixture of egg phospholipids depends on the content of derivatives containing a primary amino-group.     

Nonenzymic browning. VI. Browning produced by oxidized polyunsaturated lipids on storage with protein in presence of water

Summary Oxidized methyl esters of polyunsaturated fish oil fatty acids were stored with casein soaked in water at 4 and at 60° C. The more oxidized sample was less completely extracted from the reaction mixture because it was bound in higher degree in insoluble products of browning reactions. Changes taking place at 4° and 60° C differed more in the reaction rate than in the reaction mechanisms. The soluble and the insoluble pigments were formed approximately at relatively equal rates. Prolonged storage increased the intensity of browning and also produced a bathochrome shift connected with increased dominant wavelength and saturation, this behaviour being evidently due to the prolongation of conjugated double bond system by further reaction of primary browning products.

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Zusammenfassung Oxydierte Methylester polyungesättigter Fischölfettsäuren wurden mit dem in Wasser gequollenen Casein bei 4° C und 60° C gelagert. Die stärker oxydierte Probe war weniger quantitativ aus dem Reaktionsgemisch extrahiert, da diese Lipide in größerem Maße in der Form unlöslicher Produkte gebunden wurden. Die bei 4° C und bei 40° C verlaufenden Prozesse unterschieden sich mehr durch die Reaktionsgeschwindigkeit als durch die Reaktionsmechanismen. Die löslichen und die unlöslichen gefärbten Produkten wurden mit verhältnismäßig gleichen Geschwindigkeiten gebildet. Während der längeren Lagerung nahm die Bräunungsintensität zu und eine bathochrome Verschiebung zeichnete sich durch eine Zunahme der vorwiegenden Wellenlänge und Abnahme der Farbenreinheit aus. Sie wurde durch eine Verlängerung des konjugierten Doppelbindungssytems durch weitere Reaktionen der primären Bräunungsprodukten verursacht.

     

Nonenzymic browning during storage of white hard grape pekmez (Zile pekmezi)

Effects of storage period on hydroxymethylfurfural, pH and colour were studied in white hard grape pekmez (Zile pekmezi), a Turkish traditional product. Pekmez samples were stored at 20 °C for 8 months. Analysis of variance revealed significant differences in hydroxymethylfurfural, pH, L, a and b values (P<0.01) based on storage time.     

Enzymatic browning reactions in apple and apple products

This review examines the parameters of enzymatic browning in apple and apple products that is, phenolic compounds, polyphenoloxidases, and other factors (ascorbic acid and peroxidases), both qualitatively and quantitatively. Then the relationships between intensity of browning and the browning parameters are discussed, including a paragraph on the methods used for browning evaluation. Finally, the different methods for the control of browning are presented.     

Some formaldehyde reaction products in non-enzymatic browning reactions

Summary The volatiles isolated from the glycine-glyoxal model system were analysed and two compounds derived from formaldehyde (arising from the Strecker degradation of glycine) were identified. The structure of the two compounds, i.e., 2,4,6-trioxaheptane and 2,4,6,8-tetraoxanonane, was confirmed by the analysis of the reference compounds isolated from the commercial formaldehyde solution and analysed by gas chromatography/mass spectrometry and¹H-NMR spectrometry. The above compounds (the reaction products of formaldehyde oligomers with methanol) are described, for the first time, as minor volatiles in non-enzymatic browning reactions.

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Einige Reaktionsprodukte von Formaldehyd in nicht-enzymatischen Bräunungsreaktionen

Zusammenfassung Es wurden aus einem Modellsystem Glycin-Glyoxal flüchtige Stoffe isoliert und zwei Verbindungen, abgeleitet vom Formaldehyd (der durch die Streckersche Reaktion der Degradierung von Glycin entsteht) identifiziert. Die Struktur dieser zwei Verbindungen 2,4,6-Trioxaheptan und 2,4,6,8-Tetraoxanonan wurde durch die Analyse der Referenzverbindungen aus der Lösung von Formaldehyd des Handels bestätigt. Die Analyse wurde mit der Methode MGC/MS and¹H-NMR Spektrometrie vorgenommen. Die oben angeführten Verbindungen (Reaktionsprodukte von Oligomeren von Formaldehyd mit Methanol) wurden zum erstenmal als flüchtige Stoffe in den Reaktionen der nicht-enzymatischen Bräunung beschrieben.

     

Non-enzymic browning reactions of ascorbic acid and their inhibition. The production of 3-deoxy-4-sulphopentosulose in mixtures of ascorbic acid, glycine and bisulphite ion

The inhibition of browning of ascorbic acid-glycine mixtures by bisulphite ion has been studied at pH 3.0. Glycine enhances the formation of coloured products from ascorbic acid but it is not involved in the stages leading to the formation of 3-deoxy-pentosulose as a reactive intermediate in browning. One of the actions of bisulphite on the browning reaction is to interrupt the sequence of events leading from reactive carbonylic intermediates, such as 3-deoxypentosulose, to other reactive intermediates and ultimately to coloured products. The reaction of bisulphite with 3-deoxypentosulose or its dehydration product 3,4-dideoxypentosulos-3-ene can give rise to 3-deoxy-4-sulphopentosulose. This product has been isolated from a model system where it accounted for one third of the reacted bisulphite.