Non-enzymatic Browning Reactions Research Articles

Ratio of Maltose to Maltulose and Furosine as Quality Parameters for Infant Formula

Nonenzymic browning reactions in commercial infant formulas were evaluated through their furosine content as well as the isomeric disaccharides formed during processing. Lactulose was observed only in samples containing appreciable amounts of lactose, whereas maltulose was present in all samples due to the isomerization of maltose. Because formation of maltulose depends on the initial amount of maltose present, the ratio maltose/maltulose was used for comparative purposes. The ratio maltose/maltulose varied within a wide range, 27-167; therefore, low values in maltose/maltulose ratio may indicate severe processing conditions during manufacture, whereas high values may indicate mild processing conditions. Variable amounts of furosine content in samples with similar maltose/maltulose ratios may be attributed to different conditions used during storage. Levels of furosine higher than those reported for milk powder were detected in most studied samples. Determination of both furosine and maltose/maltulose ratio would yield information retrospectively about the heat treatment applied during processing and the storage conditions of commercial infant formula.

Effect of pH control on the intermediates and melanoidins of nonenzymatic browning reaction

The effect of pH control on the intermediates and melanoidins of nonenzymatic browning reaction was investigated. A solution of glucose (36.03 g/l) and lysine (36.53 g/l) was refluxed by heating for 24 h with the pH controlled at pH 7.0 by three methods: running the reaction in 2 mol/l phosphate buffer (buffer-melanoidin), adding a sodium hydroxide solution through a pH stat (pH stat-melanoidin) or initial pH control with NaHCO 3 at the start of reaction (NaHCO 3-melanoidin). The three resulting model melanoidins were monitored by pH, color intensity, reducing activity, gel permeation chromatography (GPC), and electrofocusing. The color intensity and reducing activity in the buffer- and pH stat-melanoidins were both higher than those of the NaHCO 3-melanoidin. The two intermediates, 5-hydroxymethyl-pyrrole-2-aldehyde and lysylpyrraline, were produced in the early stage of the reaction and are likely to have been incorporated in the melanoidin formation during heating. Electrofocusing showed that the melanoidins prepared under pH control were separated into 14 bands in the pI range of 3.5–4.85, and that the NaHCO 3-melanoidin consisted of 30 bands in the pI range of 3.5–8.35. The bands with pI of more than 4.85 were formed during the stage of decreasing pH in the reaction solution and disappeared after freezing preservation at −20°C for 6 months.

Effect of thermal processing on the quality loss of pineapple juice

Three indexes, namely colorimetric Hunter parameters ( L, a, b and Δ E), hydroxymethylfurfural (HMF) and brown pigment formation, were monitored to determine the quality loss of pineapple juice at temperatures ranging from 55 to 95 °C. The changes in a and b values followed first order kinetics while Δ E fitted well to a combined model which described both non-enzymatic browning reaction and destruction of carotenoid pigment. For browning indexes, HMF and brown pigment formation increased linearly with heating time and could be explained using zero order reaction kinetics. The results suggested that processing temperature had a significant effect on the color change of pineapple juice. The dependence of the rate constant on temperature was represented by an Arrhenius equation.

Loss of o-phthaldialdehyde reactivity during storage of infant cereals

A fluorimetric method was used to determine the o-phthaldialdehyde (OPA) reactivity of amino groups for the assessment of non-enzymatic browning reactions in products with a prolonged shelf-life. The studies were conducted in four commercial infant cereals: wheat-based ‘7-cereals’ and ‘8-cereals’, and gluten-free ‘rice cereal’ and ‘rice-corn cereal’. The cereals were monitored at 28°C for 4 or 16 weeks, or under high water activity (0.65) conditions at 25°C or 55°C for 1, 2, 3 or 4 weeks. OPA reactivity gradually decreased during storage under all temperature, time and water activity conditions, with especially marked losses under conditions of greatest heat intensity and high water activity. According to the present results, the determination of OPA reactivity offers a simple, rapid and reliable method to evaluate non-enzymatic browning.

Note. Hydrolysis of Onion and Kinetics of Non-Enzymatic Browning of its Hydrolysate

Enzymatic hydrolysis of onion was performed by three different commercial enzyme products (Econase, Rapidase and Viscozyme) for preparation of onion hydrolysates. The hydrolysis yield was determined through the analysis of reducing and total sugar contents in final hydrolysates. Total sugar contents after 2 h-hydrolysis with Econase, Rapidase and Viscozyme were 59.6, 64.1 and 62.2 mg/mL, respectively, and reducing sugar contents of 28.5, 42.7 and 35.9 mg/mL in the same order. According to these results Rapidase was more suitable for the hydrolysis of onion than the other enzymatic products. The effect of temperature on non-enzymatic browning reaction kinetics of the onion hydrolysate was determined. The browning index variation was adequately described by both the first- and the zero-order kinetic. However, the zero-order kinetic model was preferred because its fitting was higher. The values of kinetic constants were 0.081 (60 C), 0.185 (70 C), 0.270 (80 C) and 0.377 (90 C). According to the Arrhenius model, the activation energy for browning index in the range 60–90 C was 21.9 kJ/mol.

Effect of the pyrrole polymerization mechanism on the antioxidative activity of nonenzymatic browning reactions.

The present investigation was undertaken to study how the antioxidative activity (AA) of nonenzymatic browning reactions is changing at the same time that the browning (by the pyrrole polymerization mechanism) is being produced. The antioxidative activities of eight model pyrroles (pyrrole, 1-methylpyrrole, 2,5-dimethylpyrrole, 1,2,5-trimethylpyrrole, 2-acetylpyrrole, 2-acetyl-1-methylpyrrole, pyrrole-2-carboxaldehyde, and 1-methyl-2-pyrrolecarboxaldehyde) as well as the browning reaction of 2-(1-hydroxyethyl)-1-methylpyrrole (HMP) and the dimer (DIM) produced during HMP browning were determined. The results obtained suggest that the AAs observed in nonenzymatic browning reactions are the result of the AAs of the different oxidized lipid/amino acid reaction products formed. Thus, the different pyrrole derivatives produced in these reactions had different AAs, and the highest AAs were observed for alkyl-substituted pyrroles without free alpha-positions. Because some of these pyrrole derivatives are implicated in nonenzymatic browning production and this browning production implies the loss of hydroxyl groups and the transformation of some pyrroles with one type of substitution into others, changes in AA during browning production were observed, and the resulting DIM derivative was more antioxidant than HMP or higher polymers. These results explain the AA observed in fatty acid/protein mixtures after slight oxidation and suggest that, when the pyrrole polymerization mechanism is predominant, slightly browned samples may be more antioxidant than samples in which nonenzymatic browning has been highly developed.

Maillard reaction products in tissue proteins: new products and new perspectives.

The chemical modification of protein by nonenzymatic browning or Maillard reactions increases with age and in disease. Maillard products are formed by reactions of both carbohydrate- and lipid-derived intermediates with proteins, leading to formation of advanced glycation and lipoxidation end-products (AGE/ALEs). These modifications and other oxidative modifications of amino acids increase together in proteins and are indicators of tissue aging and pathology. In this review, we describe the major pathways and characteristic products of chemical modification of proteins by carbohydrates and lipids during the Maillard reactions and identify major intersections between these pathways. We also describe a new class of intracellular sulfhydryl modifications, Cys-AGE/ALEs, that may play an important role in regulatory biology and represent a primitive link between nonenzymatic and enzymatic chemistry in biological systems.

Kinetics of chemical marker formation in whey protein gels for studying microwave sterilization

The kinetics of 4-hydroxy-5-methy-3(2H)-furanone (M-2) formation in a model food system (20% whey protein gel) was determined for studying cumulative time–temperature effects in high-temperature-short-time processes. M-2 was formed from d-ribose and amines through non-enzymatic browning reactions and enolization under low acid conditions (pH > 5). The order of the reaction for M-2 formation was determined by non-linear regression analysis and further confirmed by graphical method. M-2 formation followed a first-order kinetics and the rate constant temperature dependence was described using an Arrhenius relationship. The reaction rates and activation energy were determined using two-step, multi-linear and non-linear regression analyses. This study also demonstrated the use of M-2 formation in determining the cumulative heating effect in a model food system subjected to 915 MHz microwave heating.

Browning of white chocolate during storage

Browning is one of the main problems that limit the shelf-life of confectionery products manufactured with white chocolate. Several parameters that indicate both fat alteration and non enzymatic reactions were measured in a white chocolate substitute and almonds panned with white chocolate. In both goods, the browning phenomenon was related to the surface of the product. In the white chocolate substitute there were strong differences in non-enzymatic browning indicators between the surface and the inside of the tablet but no important differences between the indicators of the state of the fat. In panned almonds, both non-enzymatic browning indicators and fat indices increased with storage. Fat indices did not show a marked alteration of the fat. Non-enzymatic browning parameters increased at different rates. Evidently, non-enzymatic browning reactions are responsible for the browning problems of white chocolate.

Recent Advances in the Studies of Bread Baking Process and Their Impacts on the Bread Baking Technology

In bread-making, baking process is one of the key steps to produce the final product qualities including texture, color and flavor, as a result of several thermal reactions such as nonenzymatic browning reaction, starch gelatinization, protein denaturalization and so on. These thermal reactions are dominated by heat and mass transfer mechanisms inside an oven chamber as well as inside the dough pieces. Mathematical models have been developed to ac-count for the heat and mass transfer phenomena and their consequent impacts on the product qualities. These studies have made the complicated baking process more clearly understood and predictable. As a result, baking process conditions can be optimized. In addition, new baking techniques and oven designs have been proposed in order to im-prove product qualities with better process economics.

Thermal analysis, state transitions and food quality

Thermal properties of food systems are important in understanding relationships between food properties and changes in food quality. Concentrated food systems (low-moisture and frozen foods) are seldom in an equilibrium state and they tend to form amorphous, non-crystalline structures. Several glass transition-related changes in such foods affect stability, e.g., stickiness and caking of powders, crispness of snack foods and breakfast cereals, crystallisation of amorphous sugars, recrystallisation of gelatinised starch, ice formation and recrystallisation in frozen foods and rates of non-enzymatic browning and enzymatic reactions. Relationships between glass transition, water plasticisation and relaxation times can be shown in state diagrams. State diagrams are useful as stability or quality maps and in the control of rates of changes in food processing and storage.

Role of oxidized lipids in nonenzymic browning reactions

Different lipid oxidation products, such as free radicals, hydroperoxides and aldehydes, react with free amine groups of proteins and with free amino acids, forming yellow intermediary products which polymerize into dark brown macromolecules. The intermediary products are imines, pyridine derivatives and even aldolization products with low nitrogen content. The nutritional value of brown products is very low.

Interactions between phospholipids, saccharides and oxidized lipids in non-enzymic browning reactions

In addition to browning products analogous to those occurring in oxidizing lipids, other types of browning reactions were observed that produced by intermolecular or intramolecular interactions between amine groups of phospholipids and hydroperoxides or their carbonylic degradation products. Primary amine groups of phosphatidylethanolamine, phosphatidylserine and the respective lysophospholipids react with oxidized acyl chains of phospholipids, forming yellow or red oxidation products. Polyunsaturated imines (Schiff bases) are formed, which rapidly turn brown. The presence of amine groups accelerates browning reactions, slowly on storage, rapidly on heating.

Effect of Equivalent Thermal Treatments on the Color and the Antioxidant Activity of Tomato Puree

ABSTRACT: The influence of different heat treatments on color and antioxidant properties of tomato purees was investigated. The treatments were designed to produce the same total thermal effect against spoilage microorganisms. Although the development of nonenzymatic browning reactions occurred by increasing process temperature, no changes in redness were observed in the heated samples, due to the “masking” effect of lycopene. Also, the heat treatments had equivalent effect on the chain‐breaking activity of the aqueous and lycopene tomato fractions. However the redox potential values increased as the heating temperature increased. All data together showed that the thermal resistance constant z values for color and chain‐breaking activity were close to 10°C, but lower than 10°C for reducing properties.

Structural and functional characterization of pronyl-lysine, a novel protein modification in bread crust melanoidins showing in vitro antioxidative and phase I/II enzyme modulating activity.

Application of an in vitro antioxidant assay to solvent fractions isolated from bread crust, bread crumb, and flour, respectively, revealed the highest antioxidative potential for the dark brown, ethanol solubles of the crust, whereas corresponding crumb and flour fractions showed only minor activities. To investigate whether these browning products may also act as antioxidants in biological systems, their modulating activity on detoxification enzymes was investigated as a functional parameter in intestinal Caco-2 cells. The bread crust and, in particular, the intensely brown, ethanolic crust fraction induced a significantly elevated glutathione S-transferase (GST) activity and a decreased phase I NADPH-cytochrome c reductase (CCR) activity compared to crumb-exposed cells. Antioxidant screening of Maillard-type model mixtures, followed by structure determination, revealed the pyrrolinone reductones 1 and 2 as the key antioxidants formed from the hexose-derived acetylformoin and N(alpha)-acetyl-L-lysine methyl ester or glycine methyl ester, chosen as model substances to mimic nonenzymatic browning reactions with the lysine side chain or the N terminus of proteins, respectively. Quantitation of protein-bound pyrrolinone reductonyl-lysine, abbreviated pronyl-lysine, revealed high amounts in the bread crust (62.2 mg/kg), low amounts in the crumb (8.0 mg/kg), and the absence of this compound in untreated flour. Exposing Caco-2 cells for 48 h to either synthetically pronylated albumin or purified pronyl-glycine (3) significantly increased phase II GST activity by 12 or 34%, respectively, thus demonstrating for the first time that "pronylated" proteins as part of bread crust melanoidins act as monofunctional inducers of GST, serving as a functional parameter of an antioxidant, chemopreventive activity in vitro.

Characterization of fumonisin B(1)-glucose reaction kinetics and products.

The reaction of fumonisin B(1) with the reducing sugar D-glucose can block the primary amine group of fumonisin B(1) and may detoxify this mycotoxin. A method to separate hundred milligram quantities of fumonisin B(1)-glucose reaction products from the excess D-glucose with a reversed-phase C(18) cartridge was developed. Mass spectrometry revealed that there were four primary products in this chain reaction when fumonisin B(1) was heated with D-glucose at 65 degrees C for 48 h: N-methyl-fumonisin B(1), N-carboxymethyl-fumonisin B(1), N-(3-hydroxyacetonyl)-fumonisin B(1), and N-(2-hydroxy, 2-carboxyethyl)-fumonisin B(1). The N-(1-deoxy-D-fructos-1-yl) fumonisin B(1) (fumonisin B(1)-glucose Schiff's base) was detected by mass spectrometry when fumonisin B(1) was heated with D-glucose at 60 degrees C. The nonenzymatic browning reaction of fumonisin B(1) with excess D-glucose followed apparent first-order kinetics. The activation energy, E(a), was 105.7 kJ/mol. Fumonisin B(1) in contaminated corn could precipitate the nonenzymatic browning reaction with 0.1 M D-glucose at 60 and 80 degrees C.

Continuous Evolved Gas Analysis and Thermal Analysis in Micro-scale Roasting of Foods

In roasting processes of foods, non-enzymatic browning reactions lead to the formation of water and carbon dioxide. Continuous monitoring of the evolution of moisture and carbon dioxide would offer an interesting tool for determining reaction kinetics of non-enzymatic browning and optimising roasting processes. Isothermal and dynamic heating of small specimens of hazelnuts in a differential scanning calorimeter which was linked to a non-dispersive IR gas analyser presents a possibility to simulate roasting processes on a micro-scale. Formation of water and carbon dioxide was dependant on the initial moisture content of the hazelnuts, heating rate and composition of gas atmosphere (nitrogen vs. oxygen). Depending on the heating conditions, evolution of carbon dioxide is not only caused by degradation of amino acids and sugars but also by lipid oxidation.

TOXICOLOGY AND ANTIOXIDANT ACTIVITIES OF NON-ENZYMATIC BROWNING REACTION PRODUCTS: REVIEW

This article summarizes toxicity and antioxidative activity of non-enzymatic browning reaction products. The subject focuses on the formation and toxicity testing of mutagenic Maillard reaction products (MPRs) formed in food model systems and in actual foods. The MRPs have also been investigated for nutritional, physiological, and biological activities. The antioxidant properties of MRPs are also reviewed in terms of protection potential against oxidative damage associated with a wide variety of diseases such as diabetes and cancer, and pathological conditions such as aging.

Article

Spray-drying is a rapid dehydration method allowing production of high quality dairy powders. In dehydration and subsequent powder handling and storage, however, both chemical and physical changes, such as caking, lactose crystallisation, and nonenzymatic browning, may impair powder characteristics and result in loss of powder quality. Many of these changes are related to the physical state of lactose, as rapid removal of water in spray drying results in the formation of low- moisture, amorphous, noncrystalline structures of lactose and other milk components. The amor- phous components may exist as solid-like glasses or highly supercooled, viscous liquids. The forma- tion of amorphous, glassy lactose during spray drying allows production of a free-flowing powder. High temperatures or residual water contents at the later stages of the drying process, however, may cause stickiness, caking, browning, and adhesion of the powder particles to the processing equip- ment. The glass transition of amorphous lactose occurs in the vicinity of room temperature at a water content of about 6.8 g (g × 100) -1 of lactose corresponding to an equilibrium relative humidity of 37% and 0.37 a w (water activity). At higher water contents, as the glass transition of amorphous lactose is well below storage temperature, dairy powders become sticky and the amorphous lactose may exhibit time-dependent crystallisation. Crystallisation of amorphous lactose may also release sorbed water from the amorphous material, which enhances other deteriorative changes, such as the nonenzymatic browning reaction. Amorphous lactose in dairy powders encapsulates milk fat, which, as a result of lactose crystallisation, is released and becomes susceptible for rapid oxidation. The glass transition and water activity are, therefore, important factors controlling processability, handling properties and stability of dairy powders.

Effects of pH on Caramelization and Maillard Reaction Kinetics in Fructose‐Lysine Model Systems

ABSTRACT: The nonenzymatic browning reactions of fructose and fructose‐lysine aqueous model systems were investigated at 100 °C between pH 4.0 and pH 12.0 by measuring the loss of reactants and monitoring the pattern of UV‐absorbance and brown color development. At all the pH values tested, the loss of fructose was lower in the presence than in the absence of lysine. And, in lysine‐containing fructose solution, the sugar disappeared more rapidly than the amino acid. Lysine was moderately lost below pH 8.0. Caramelization of fructose, which accounted for more than 40% of total UV‐absorbance and 10 to 36% of brown color development, may therefore lead to overestimating the Maillard reaction in foods.