Effect of green tea flavonoids on Maillard browning in UHT milk

The ability of green tea flavonoids to control Maillard browning was investigated. Epicatechin (EC) and epigallocatechin gallate (EGCG) were added at levels of 0.l and 1.0 mmol/l to a glucose/glycine model system as well as into milk that was then thermally processed in a Microthermics processing system. Samples were assessed with (1) front-face fluorescence spectroscopy for Maillard browning, (2) Hunter L*, a*, and b*; and (3) sensory analysis. In the model gluocose/glycine system, EC and EGCG reduced Maillard fluorescence at the 0.1 mmol/l level, while fluorescence was negligible with added flavonoids at 1.0 mmol/l. When these flavonoids were added to milk, they reduced the production of Maillard associated fluorescence with UHT processing. EC and EGCG also reduced the ΔE (Total color difference) during thermal processing. Throughout shelf-life testing, these compounds reduced Maillard associated fluorescence in milk. Milk samples processed with these extracts were monitored by sensory analysis during extended storage. The sensory evaluation found the green tea milk samples to be of similar liking to the control milk. These flavonoids may be of use to the food industry to control Maillard browning.     

pH和加热时间对美拉德反应挥发性产物的影响

以葡萄糖一赖氨酸为原料,建立了最简单的美拉德反应模型,研究了pH和加热时间时美拉德反应挥发性产物的影响.结果发现,pH对产物种类有着至关重要的影响;而加热时间对反应产物的影响具有普遍性规律.以期为生产中食品体系工艺条件的优化提供理论参考和技术支持.     

乳及乳制品加工中的美拉德反应

针对乳及乳制品在加工和储藏过程中由于发生美拉德反应不仅使乳制品的营养物质受到破坏，还产生对人体有害的物质，在很大程度上影响的乳制品的质量，对乳制品中美拉德反应的历程，产生的标志物及其测定方法等进行了的综述。     

Monitoring of Maillard reactions in soy products

Zusammenfassung Der chemische Mechanismus der Maillard-Reaktionen und die Literatur der für die Untersuchung der frühen Maillard-Reaktion vorgeschlagenen analytischen Methoden werden kritisch gesichtet. Wir belegen die Anwendbarkeit unseres Verfahrens für die Verfolgung der frühen Maillard-Reaktionen durch die Erfassung der daran Teilnehmenden, der löslichen Raffinose-Oligosaccharide und der basischen Aminogruppen der Proteine, und zwar am Beispiel der Analyse von unterschiedlich denaturierten Sojaprodukten. Hierbei ist es zum ersten Mal gelungen, die quantitativen Zusammenhänge zwischen den Maillard-Reaktanten in einer natürlichen Matrix mit numerischen Daten zu stützen, wobei mit dieser Methode keine Korrekturfaktoren benötigt werden.

---

Monitoring of Maillard reactions in soy products

Summary Chemical mechanism and the analytical methods suggested in the literature for the analysis of early Maillard reactions are summarised and critically evaluated. The applicability of our method for the measurement of the Maillard reactions — the soluble raffinose oligosaccharides and the basic amino groups of proteins — are illustrated by following early Maillard reactions in differently denaturated soya bean samples. The quantitative relations of Maillard reactions taking place in natural matrices could be clarified by monitoring both of the reactants by means of methods not requiring correction factors.

     

Monitoring of Maillard reactions in soy products

Chemical mechanism and the analytical methods suggested in the literature for the analysis of early Maillard reactions are summarised and critically evaluated. The applicability of our method for the measurement of the Maillard reactions - the soluble raffinose oligosaccharides and the basic amino groups of proteins - are illustrated by following early Maillard reactions in differently denaturated soya bean samples. The quantitative relations of Maillard reactions taking place in natural matrices could be clarified by monitoring both of the reactants by means of methods not requiring correction factors.     

牦牛脱脂乳中酪蛋白受热处理温度及时间影响的研究

研究了随着加热温度(30～90℃)的上升及时间的延长(5～25min),牦牛脱脂乳的热稳定性、乳化性、浊度的变化,以及脱脂乳中存在的大量酪蛋白表面疏水性及平均粒径的改变.结果表明,加热温度的上升及加热时间的延长,导致牦牛脱脂乳的热稳定性下降、乳化性降低、浊度增大,酪蛋白表面疏水性及平均粒径总体呈增大的趋势,温度在70℃以上、加热时间大于15min时尤为明显.这一研究结果为牦牛乳酪蛋白的生产加工提供了一定的理论基础.     

牦牛脱脂乳中酪蛋白受热处理温度及时间影响的研究

研究了随着加热温度(30～90℃)的上升及时间的延长(5～25min),牦牛脱脂乳的热稳定性、乳化性、浊度的变化,以及脱脂乳中存在的大量酪蛋白表面疏水性及平均粒径的改变。结果表明,加热温度的上升及加热时间的延长,导致牦牛脱脂乳的热稳定性下降、乳化性降低、浊度增大,酪蛋白表面疏水性及平均粒径总体呈增大的趋势,温度在70℃以上、加热时间大于15min时尤为明显。这一研究结果为牦牛乳酪蛋白的生产加工提供了一定的理论基础。      

Maillard reactions of dextrins and starch

When dextrins or starch are heated with propyl-amine in neutral aqueous solution at 100–130° C a brown colouration is observed. From the reaction mixture 3-hydroxy-2-methyl-1-propyl-4(1H)-pyridone11, 1,4-dihy-dro-2-methyl-1-propyl-4-propylimino-3-pyridinol12 and 5-hydroxymethyl-1-propyl-pyrrol-2-aldehyde13 can be extracted with organic solvents and separated by HPLC. Enzymatic hydrolysis effects the release of 1(3-hydroxy-1-propyl-2-pyrrolyl)-1-ethanone10 from a glycosidically bound precursor.

---

Maillard Reaktionen von Dextrinen und Stärke

Zusammenfassung Erhitzt man Dextrine oder Stärke mit Propylamin in neutraler wäßriger Lösung auf 100–130 °C, so beobachtet man eine braune Färbung. Aus der Reaktionsmischung lassen sich 3-Hydroxy-2-methyl-1-propyl-4(1H)-pyridon11, 1,4-Dihydro-2-methyl-1-pro-pyl-4-propylimino-3-pyridinol12 und 5-Hydroxymethyl-1-propyl-pyrrol-2-aldehyd13 mit organischen Lösungsmitteln extrahieren und durch HPLC trennen. Nach enzymatischer Hydrolyse der wasserlöslichen Fraktion ist 1(3-Hydroxy-1-propyl-2-pyrrolyl)-1-ethanon10 isolierbar.

     

Maillard reaction kinetics in milk powder: Effect of water activity at mild temperatures

The kinetics of the Maillard reaction in skim milk powder was studied at a wide range of water activities (0.31–0.98) under storage at mildly elevated temperature conditions (37, 50 and 60 °C). The reaction rate was determined by the loss of available lysine content using the o-phthaldialdehyde method. Water activity affected the rate of loss of lysine above the glass transition temperature only at high water activity values. However, the mobility of the reactants seemed to play a role in damage to lysine, as the rate constant decreased considerably at temperatures close to the glass transition. Crystallization of lactose did not affect the rate constant values. Water activity did not influence the temperature-dependence of the reaction rate, although a significant increase in activation energy was observed in the vicinity of the glass transition temperature.     

微波加热下食品美拉德反应研究进展

微波加热作为一种高效、节能、环保的新型加热方式,在工业上的应用越来越广泛。微波加热下美拉德反应的早期反应程度更高,中期产物组成不同、挥发性芳香物质更丰富,晚期化合物的抗氧化性等生理活性显著增强,微波加热对美拉德反应产物有显著影响。文章主要介绍了微波加热下美拉德反应的影响因素、产物分析方法、产物类型及其在食品中的应用和研究进展。     

Effect of reaction pH on enolization and racemization reactions of glucose and fructose on heating with amino acid enantiomers and formation of melanoidins as result of the Maillard reaction

This study investigates the effect of reaction pH on enolization and racemization reactions of glucose and fructose on heating with amino acid enantiomers, can influence the formation of melanoidins as result of the Maillard reaction. Remarkable enolization reaction of sugars was observed in the course of the Maillard reaction. Especially, the degree of sugar enolization was increased as the pH levels increased, which was higher in fructose than glucose systems. Otherwise, enolization of sugars on heating with amino acid was higher in glucose than fructose systems. Formation of isomer in Glc/d-Lys, Fru/d-Asn and Fru/d-Lys were increased upon increase of pH levels. The relative amounts of isomers in Glc/l-Asn and Glc/d-Asn were decreased upon increase of pH levels. Browning development was dependent on the pH levels, being more significant for model systems apart from heated glucose solution alone. Browning development of fructose systems was higher than glucose-amino acid systems. The l- and d-isomers both showed different absorption in the UV–vis spectra and that these occur at similar shape. Every peak has a stable absorbance appeared in the range between 260 and 320 nm, characteristic of melanoidins.     

脂类对反应型香精风味形成影响的研究

根据3种不同原料所含主要脂肪酸及不饱和度的不同,通过反应所生成主要风味物质差异来进一步探讨反应型香精风味形成机理。     

乳制品中的Maillard反应标示物及其应用

乳制品中的Maillard反应标示物既可作为乳制品热处理程度的指标，还可用于不同热处理乳制品的鉴别。介绍了在评价乳制品热处理程度以及区分不同乳制品中常用的几种Maillard反应标示物。这些标示物包括糠氨酸、乳果糖、糠醛类化合物、荧光化合物等。此外，还介绍了可溶性乳清蛋白、碱性磷酸酶和乳过氧化物酶等热处理标示物，这些标示物与Maillard反应之间具有较好的相关性，也是评价乳制品热处理程度以及区分不同乳制品时常用的指标，可与Maillard反应标示物联合应用。     

Fluorescence associated with Maillard reaction in milk and milk-resembling systems

The progress of the Maillard reaction in milk and milk-resembling systems during heating was followed by monitoring free fluorescent intermediary compounds. Fluorescence intensity was examined over a wide temperature/time range (90–140 °C/0.5–30 min). Different kinetic behaviours were found in the presence or absence of amino groups in the system. Traces of fluorescence were detected when the lactose system without proteins was heated; the isomerization and degradation reactions of lactose could also generate fluorescent compounds. Fluorescence accumulation in the lactose system (without proteins) proceeded according to first-order reaction kinetics, whereas systems with lactose and casein, lactose and whey protein and milk fitted zero-order reaction kinetics. Apparent activation energies calculated were 61.3, 78.6, 59.6 and 83.9 kJ mol⁻¹ for lactose system, lactose/casein system, lactose/whey protein system and milk, respectively. Moreover, levels of intermediary fluorescent compounds in Spanish commercial milk (pasteurized, UHT-treated and in-bottle sterilized milk) have been studied.     

Demonstration and identification of a new Maillard compound in heated milk

By means of polarography a new Maillard product (5a) was detected in heated milk. The compound was isolated from a glycine/lactose mixture, which had been heated in buffer at pH 6,8, and then freeze dried by extraction with ethylacetate/methanol. According to its spectroscopic properties, 5a is 4-0-beta-D-galactopyranosyl-2-hydroxy-2-methyl-2H-pyran-3-(6H)-one. Though the amount of 5a formed during heat treatment of milk corresponds to the severity of heat stress, the usefulness of 5a as an indicator with respect to intensity of heat treatment is limited. 5a is rather rapidly converted to galactosyl isomaltol; also unknown peaks develop in the polarogram.     

Effect of pH at heating on the acid-induced aggregation of casein micelles in reconstituted skim milk

Reconstituted skim milk samples at pH between 6.5 and 7.1 (heating pH) were heated at 80°C, 90°C or 100°C for 30 min (heating temperature). The particle size of the casein micelles was measured at pH 4.75-7.1 (measurement pH) and at temperatures of 10°C, 20°C and 30°C (measurement temperature) using photon correlation spectroscopy. The particle size of the casein micelles, at a measurement pH of 6.7 and a measurement temperature of 20°C, was dependent on the heating pH and heating temperature to which the milk was subjected. The casein micelle size in unheated milk was about 215 nm. At a heating pH of 6.5, the casein micelle size increased by about 15, 30 and 40 nm when the milk was heated at 80°C, 90°C or 100°C, respectively. As the heating pH of the milk was increased, the size of the casein micelles decreased so that, at pH 7.1, the casein micelles were ∼20 nm smaller than those from unheated milk. Larger effects were observed as the heating temperature was increased from 80°C to 100°C. The size differences as a consequence of the heating pH were maintained at all measurement temperatures and at all measurement pH down to the pH at which aggregation of the micelles was observed. For all samples, size measurements at 10°C showed no aggregation at all measurement pH. Aggregation occurred at progressively higher pH as the measurement temperature was increased. Aggregation also occurred at a progressively higher measurement pH as the heating pH was increased. The particle size changes on heating and the aggregation on subsequent acidification may be related to the pH dependence of the association of whey proteins with, and the dissociation of κ-casein from the casein micelles as milk is heated.     

Effects of heating temperatures and addition of reconstituted milk on the heat indicators in milk

The objective of the present study was to evaluate the effect of heating temperatures and reconstituted milk on heat treatment indicators in milk by comparing the heat damage between raw milk and raw milk plus reconstituted milk (composite milk). The contents of lactulose, furosine, beta-lactoglobulin, and lactoperoxidase were determined after the heat indicators were heated to 65 to 115 °C for 15 s both in raw milk and composite milk. In the raw milk, the lactulose and furosine contents increased with increased heating temperature, while the beta-lactoglobulin content and lactoperoxidase activity decreased. The lactulose and furosine contents were increased after the addition of reconstituted milk. The reconstituted milk also significantly (P < 0.05) reduced the concentration of beta-lactoglobulin in the milk. Both heat treatment and an addition of reconstituted milk decreased the lactoperoxidase activity significantly (P < 0.05), and the lactoperoxidase activity was undetectable at 85 °C. The ratios of lactulose to furosine in pasteurized milk were higher than that in composite pasteurized milk. It is concluded that lactulose, furosine, and beta-lactoglobulin are suitable indicators of high heat pasteurization or raw milk, while lactoperoxidase may be used in monitoring mild heat pasteurization. Practical Application: Adequate heat treatment is necessary to destroy the microbes in raw milk. However, excessive heat treatment can result in inactivation of active compounds or loss of nutrients. The present study showed that the concentrations of lactulose, furosine, beta-lactoglobulin, and the activity of lactoperoxidase are sensitive to processing temperature and can serve as indicators of milk pasteurization.