Free radical scavenging capacity of Maillard reaction products as related to colour and fluorescence

The free radical scavenging activity of Maillard reaction products (MRPs) produced by heating glucose or lactose with lysine, alanine or glycine was estimated directly by means of a 2,2-diphenyl-1-picrylhydrazyl radical (DPPH·) method. Model systems of sugar (lactose and glucose) and amino acid (alanine, glycine, and lysine) were heated without pH control at 100°C up to 24 h. Fluorescence (347 and 415 nm), browning (absorbance at 420 nm), colour parameters in the CIELab scale, and free radical scavenging activity were determined. Browning is not directly related to the free radical scavenging properties of MRPs formed at prolonged heating conditions. This study shows that fluorescence measurement of heated sugar/amino acid systems is more effective than browning to follow the formation of MRPs with free radical scavenging activities. This approach could be applied to optimise the formation of natural antioxidants during food processing where browning is not desirable for consumers.     

苹果浓缩汁非酶褐变动力学及影响因素

通过检测苹果汁的色值(T440nm)、褐变指数(A420nnm)、氨基态氮、5- 羟甲基糠醛含量等指标研究加工过程对苹果汁褐变的影响以及在不同贮藏温度(5、20℃和37℃)下苹果浓缩汁(70.5°Brix)的非酶褐变速率。3 个贮藏温度下的苹果浓缩汁褐变速率均符合一级反应动力学模式,而且高温情况下褐变更明显。随着贮藏时间的延长,氨基态氮含量明显下降而5- 羟甲基糠醛含量上升,尤其是贮藏在37℃的苹果汁这一变化更明显。5- 羟甲基糠醛与果汁褐变效应呈指数关系,可以说明苹果汁在贮存中的褐变主因是发生美拉德反应,而且氨基态氮含量与果汁褐变效应的线性关系也验证了这一结论。在果汁的初始加工过程中,破碎、压榨、酶解、超滤、前巴氏杀菌等单元操作中美拉德反应并不明显;吸附操作可以去除果汁中的氨基态氮以及其他色素物质;而其他操作过程如浓缩和后巴氏杀菌则促进了美拉德反应,导致果汁氨基态氮含量明显下降。     

Role of sorbic acid in nonenzymic browning reactions in liquid and solid model food systems

Role of sorbic acid (SA) in browning development in model systems has been studied. In liquid model systems containing water-glycerol-glucose (WGG), water-glycerol-sucrose (WGS), 45% sucrose and 30% sucrose plus 15% glucose, SA degraded when stored at 37°C forming brown pigments. Addition of amino acids (glycine or lysine monohydrochloride) increased the rate of browning development while Cu²⁺ reduced SA degradation and browning development. In the absence of amino acids and SA, WGG and WGS systems did not brown appreciably.
In solid systems with SA adsorbed on microcrystalline cellulose, the maximum rate of browning occurred at 0.73 a_w , but maximum rate of SA loss was at 1.0 a_w . In all systems inclusion of amino acids reduced SA degradation but increased browning development. The rate of SA-induced browning was considerably higher than that caused by sugar-amino acid interactions.     

Browning of salted sun-dried fish

The lipid of traditional salted, sun-dried fish is highly susceptible to oxidation during processing and storage at tropical ambient temperatures (25–30°C), leading to browning and potential loss of nutritional and economic value of the product. Determinations of extractable fluorescence and soluble brown colour have been found to be relevant indicators of the high degree of lipid oxidation in such fish. Studies on model systems consisting of aerated fish oil and a range of components natural to fish confirmed that, at 25°C, the products of lipid oxidation reacted with phospholipids and amino acids to produce significant fluorescence. Similarly, proteins and amino acids interacted with lipid oxidation products to produce browning, although at 25°C, this only occurred in the presence of water. Temperatures above 50°C are required for the development of browning of aerated fish oil alone. The level of free amino acids in salted, sun-dried fish was found to decrease during storage which correlates with amino acid involvement in fluorescence and colour production. The fluorescence/colour can be related mechanistically to the development of lipid oxidation products and hence provides a realistic basis for their acting as indicators of extensive lipid oxidation.     

Review of non-enzymatic browning and antioxidant capacity in processed foods

Browning reactions represent an interesting research area for the implications in food technology, nutrition and health. The development of some non-enzymatic browning reactions, such as Maillard reaction, has been recently associated to the formation of compounds with strong antioxidant capacity. In this paper, the relation between colour changes due to non-enzymatic browning and the formation of compounds with antioxidant activity is discussed. Simple positive or complex correlation between colour and antioxidant properties can be found depending on composition and technological history of the product. Complex relations between these variables are generally obtained in multi-component and in formulated foods, where the simultaneous development of a number of reactions, interacting or prevailing Maillard reaction itself, can affect in opposite ways the overall antioxidant properties and colour of the product.     

Glycine Loss and Maillard Browning as Related to the Glass Transition in a Model Food System

The effects of water activity and the glass transition on the rate constants for glycine loss and brown pigment formation due to the Maillard reaction were evaluated in a model food system. Equimolar glucose and glycine were incorporated into amorphous polyvinylpyrrolidones of various molecular weights and moisture contents. Glycine loss and brown pigment formation were quantified during storage at 25°C. At constant water activity, rate constants were higher in systems with lower glass transition temperatures. Glycine rate constants decreased upon matrix collapse, but browning rate constants were not affected by collapse. Changes associated with the glass transition influence bimolecular reactions and should be considered during product formulation and shelf-life testing.     

Effect of glyceraldehyde on the kinetics of Maillard browning and inhibition by sulphite species

The kinetics of browning (A₄₇₀) are reported for glyceraldehyde+glycine and glucose+glycine+glyceraldehyde mixtures ([glucose]=0–1 mol l⁻¹; [glycine]=0–1 mol l⁻¹; [glyceraldehyde]=0–10 mmol l⁻¹; pH 5.5, [acetate buffer]=0.2 mol l⁻¹ with respect to acetate ion; 55°C). In the absence of glucose the rate of reaction depends only on glyceraldehyde concentration, whereas glycine is required for colour development. The rate of browning when all 3 reactants are present is much greater than calculated as the sum of the individual glyceraldehyde+glycine and glucose+glycine reactions. This synergistic behaviour is accompanied by the removal of the induction phase normally seen for the Maillard reaction, and a browning reaction whose kinetics depend on the concentrations of all 3 reactants. The apparent dissociation constant of the hydroxysulphonate of glyceraldehyde is 6.76×10⁻⁵ mol l⁻¹ (pH 5.5, 55°C, ionic strength≈0.2 mol l⁻¹). Theoretical calculations suggest that the conversion of glyceraldehyde to its hydroxysulphonate could contribute to the mechanism of the inhibition of Maillard browning by sulphite species.     

Causes of Browning in Pear Juice Concentrate During Storage

Pear juice was treated with cation exchange resin, PVPP, XAD-4, oxygen, and various resin combinations. Samples were concentrated and increases in browning measured during storage at 37°C. Analytical determinations included α-amino nitrogen, total phenolics, metal ions, ascorbic acid, and dehydroascorbic acid. While XAD-4 and PVPP were more effective in lowering phenolic content and reducing initial color, cation exchange treatment removed amino acids and was most effective in preventing browning and providing flavor stability. Addition of glycine to cation-exchange treated samples restored browning rates. Reductone formation during storage resulted in an apparent increase in ascorbic acid. It was concluded that Maillard browning reactions predominated during storage.     

Kinetics of the sulphite-inhibited browning of fructose.

Sulphite species, S(IV), inhibit the non-enzymic browning of fructose-amino acid mixtures. Inhibition of browning is accompanied by a loss of S(IV). The kinetics of the reaction of S(IV) in the system: fructose-glycine-S(IV) are described in detail; two distinct mechanisms have been identified. One involves only fructose in the rate determining step. The other requires fructose and both the glycine and S(IV). Some amines (e.g. taurine and ethanolamine) can markedly increase the rate of the S(IV)-independent step. Arginine and lysine are particularly effective for increasing the rate of reaction of S(IV) in the S(IV)-dependent reaction.     

Impact of lipid oxidation-derived aldehydes and ascorbic acid on the antioxidant activity of model melanoidins

As the heat-induced formation of antioxidants throughout the Maillard reaction is known, this study was undertaken to evaluate the impact of lipid oxidation-derived aldehydes and ascorbic acid in Maillard model systems on the resulting antioxidant activity. For this purpose, various fractions of melanoidin-like polycondensation products were obtained from mixtures of amino acids (glycine, lysine, arginine) and lipid oxidation-derived aldehydes (hexanal, (E)-2-hexenal), in the presence or absence of glucose or ascorbic acid. All fractions showed a significant radical scavenging capacity (DPPH assay) and ferric reducing power (FRAP assay). The activity varied according to the composition of the model system tested, although some similar trends were discovered in both assays applied. The presence of lipid oxidation products in the browning products augmented the antioxidant activity in specific cases. For instance, the combined presence of arginine, hexanal and glucose in heated model systems resulted in a significantly higher antioxidant capacity. With an exception of ascorbic acid-containing model systems, melanoidin-like polycondensation products possessed significantly stronger antioxidant activities than the corresponding unheated initial reactant mixtures. Water-soluble high molecular weight (>12kDa) and nonsoluble fractions comprised the major part of the antioxidants derived from amino acid/lipid oxidation product model systems, with or without glucose or ascorbic acid.     

Kinetics of the inhibition of ascorbic acid browning by sulphite.

Despite differences in the structures of aldoses and ascorbic acid, ASA, the non-enzymic browning of the latter involves intermediates similar to those found in Maillard browning. The kinetics of the sulphite-inhibited browning of ASA suggest that, under anaerobic conditions, the rate of reaction of sulphite species, S(IV), is of first order with respect to S(IV). The possibility that S(IV) could catalyse the hydrolysis of the lactone ring of ASA is considered by reference to D-glucono-delta-lactone. Evidence is presented to suggest that, under aerobic conditions, autoxidation of ASA leads to the oxidation of S(IV). The composition of melanoidins from ASA-glycine mixtures is compared with that from arabinose-glycine; the former contain 2 x 5 times more ASA-derived residues per glycine molecule than arabinose-derived residues per glycine molecule in the latter. The implications of these findings to the mechanism of ASA browning are discussed.     

美拉德反应产物的褐变、荧光吸收及抗氧化性的研究

采用以还原糖-氨基酸(木糖/葡萄糖分别与甘氨酸、赖氨酸、谷氨酰胺、半胱氨酸)模式美拉德反应(Maillard Reaction,MR)制备得到美拉德反应产物(MRPs),研究反应条件对MRPs的褐变程度、荧光吸收强度以及其抗氧化活性的影响,并分析MRPs的光学特征与抗氧化活性之间的联系。结果表明,还原糖和氨基酸的种类对MR的褐变强度有很大影响,其影响程度由强到弱分别为:Xly>Glc,Lys>Gly>Glu>Cys。随着反应时间的延长,各体系MRPs的褐变程度逐渐变强;而荧光吸收强度随着加热时间的延长而增强,然后在出现最大值后趋于平缓或者表现出下降的趋势。MRPs的抗氧化能力也随反应时间的延长而增强,抗氧化活性与褐变强度呈正相关,与荧光吸收特性没有表现出明显的关联。     

红枣干制过程中非酶褐变类型初探

为了探索红枣干制过程中非酶褐变类型,以新疆骏枣为原料,采用65℃热风干制的方式,研究红枣干制过程中总糖、还原糖、Vc、氨基态氮、5-羟甲基糠醛(5-HMF含量的变化规律,并进一步研究上述指标与红枣褐变度相关性。结果表明,随着干制时间的延长,红枣的总糖和5-HMF含量逐渐增加,还原糖、Vc、氨基态氮含量逐渐减少;氨基态氮、5-HMF与褐变度呈正相关(ρ0.05还原糖、Vc与褐变度显著负相关(ρ0.01推论美拉德反应和Vc氧化褐变可能是红枣干制过程中的主要褐变反应。     

Gas chromatographic determination of carbon dioxide in non-fat dry milk during non-enzymic browning reaction

Carbon dioxide formation in non-fat dry milk during accelerated non-enzymic browning reaction was determined by gas chromatography. Carbon dioxide content in the headspace of the sample bottle increased as the non-enzymic browning reaction increased. Non-fat dry milk containing added 0, 15 or 30 g kg^?1 lysine in the air-tight serum bottle was stored at 55, 65 or 75°C. The coefficients of variation for reflective spectroscopic brown colour measurement and GC carbon dioxide determination were 1.37% and 1.30%, respectively. The average correlation coefficient between brown colour development and carbon dioxide formation for the nine samples during storage was 0.96. The simple, fast and reproducible gas chromatographic carbon dioxide determination method could be used to study non-enzymic browning reactions in foods or to complement other analytical methods in measuring the non-enzymic browning reaction.     

Effects of zirconium and aluminium compounds and pH on the maillard reaction

The influence of aluminium and zirconium compounds and of pH changes on the development of non-enzymic browning on an incubated glucose-glycine system has been studied. The observed decrease in the browning rate is discussed in relation to pH effects on the ionisation of amino acids. A much smaller pH independent effect is also reported.     

Glucose Loss and Maillard Browning in Solids as Affected by Porosity and Collapse

The effects of porosity and collapse on the kinetics of glucose loss and brown pigment formation via the Maillard reaction were analyzed in solid low-moisture model food systems. Equimolar glucose and glycine were incorporated into amorphous polyvinylpyrrolidones having different porosities, ranging from high porosity to totally collapsed. Samples were equilibrated and stored in desiccators at water activity 0.33 or 0.44 and 25 °C. Glucose loss and brown pigment development were monitored for 3 months. Glucose loss rate constants were lower in collapsed systems compared to non-collapsed systems. The extent of porosity did not affect glucose loss rate constants. Collapse and porosity had minimal effects on the browning rate constants. Porosity and collapse affect chemical reactivity in low-moisture solids and should be considered during product development and shelf-life testing.     

储藏过程中百香果汁非酶褐变的研究

百香果汁在储藏过程中易发生非酶褐变,影响其品质。研究了储藏期间同非酶褐变相关的物质的变化规律及其与褐变的关系。结果显示,总糖、还原糖、氨基态氮和VC均随储藏温度升高或储藏时间延长而减少,褐变度及5-HMF含量则随储藏温度升高或储藏时间延长而增加,总酚含量变化不显著。因此,VC的氧化分解及Maillard反应是导致百香果汁储藏过程中非酶褐变的主要原因。     

Browning and Amino Acid Loss in Model Total Parenteral Nutrition Solutions

The kinetics of browning and amino acid loss due to the Maillard reaction was studied in model total parenteral nutrition (TPN) systems containing glucose and either lysine, tryptophan, and cysteine alone or in combination. Cysteine systems showed the highest molar rate of browning while lysine showed the slowest rate. The molar rate of browning with all amino acids combined was significantly less than that of the sum of the individual rates, indicating interactions or inhibition. TPN electrolytes had no significant effect on the browning rate. The amino acids showed an initial rapid pseudo-first-order decrease in concentration followed by an apparent recovery and stabilization at an equilibrium concentration of about 60-80% of the original level.     

Effect of pH on non-enzymatic browning reaction during γ-irradiation processing using sugar and sugar–glycine solutions

Effects of pH on the non-enzymatic browning reaction caused by γ-irradiation processing were investigated. The brown colour development of irradiated sugar–glycine solutions was greater in a buffer system than in deionized distilled water (DDW) with higher pH. Although browning of irradiated sugar solution without glycine was highly increased was in alkaline buffer, no browning was developed in DDW. The maximum browning of the solutions of sugar and sugar–glycine were observed at pH 10 and pH 8, respectively. The browning intensity was in the following order: sucrose ? fructose > glucose. Non-constant pH was observed in DDW (dropped pH between 1.58 and 2.03 units); however, the use of buffers was partially effective in keeping pH constant (pH dropped between 0.03 and 0.56 units). When the irradiated solutions of sugar with and without glycine were analyzed using reverse phase high performance liquid chromatography with diode-array detection (HPLC-DAD), three peaks were separated at 3.37 ± 0.04, 4.60 ± 0.02, and 2.53 ± 0.26 min, and the λ_max values of these peaks were the range 259–288 nm. The sum of the areas of these peaks at 260 nm increased with increasing pH. The results of this study indicated that conditions of the system, such as pH and media, can influence the non-enzymatic browning reaction during γ-irradiation.     

Chemical changes in powdered infant formulas during storage

Hydroxymethylfurfural (HMF), furosine (FUR), lactulose (LU), lysine loss, ascorbic acid and colour (ΔE) were determined in powdered infant formulas stored under nitrogen and oxygen conditions at 20°C and 55°CC during 15, 30 and 90 days. The indicators of the assay at 20°C showed similar behaviour in nitrogen or oxygen atmospheres. Changes in furosine and lysine loss after 90 days occurred under oxygen. Storage at 55°C produced considerable browning. Browning was always greater in nitrogen than in oxygen. Most of the studied parameters increased with the storage time and are useful in controlling the extent of browning in powdered infant formulas under adverse storage conditions.