Effect of Steam Baking on Acrylamide Formation and Browning Kinetics of Cookies

Abstract: Effects of baking method and temperature on surface browning and acrylamide concentration of cookies were investigated. Cookies were baked in natural and forced convection and steam‐assisted hybrid ovens at 165, 180, and 195 °C and at different times. For all oven types, the acrlyamide concentration and surface color of cookies increased with increasing baking temperature. Significant correlation was observed between acrylamide formation and browning index, BI, which was calculated from Hunter L, a, and b color values, and it showed that the BI may be considered as a reliable indicator of acrylamide concentration in cookies. Acrylamide formation and browning index in cookies were considered as the first‐order reaction kinetics and the reaction rate constants, k, were in the range of 0.023 to 0.077 (min^?1) and 0.019 to 0.063 (min^?1), respectively. The effect of baking temperature on surface color and acrylamide concentration followed the Arrhenius type of equation, with activation energies for acrylamide concentration as 6.87 to 27.84 kJ/mol; for BI value as 19.54 to 35.36 kJ/mol, for all oven types. Steam‐assisted baking resulted in lower acrylamide concentration at 165 °C baking temperature and lower surface color for all temperatures. Steam‐assisted baking is recommended as a healthy way of cooking providing the reduction of harmful compounds such as acrylamide for bakery goods, at a minimal level, while keeping the physical quality. Practical Application: The kinetics of acrylamide formation and browning of cookies will possibly allow definition of optimum baking temperatures and times at convectional and steam‐assisted baking ovens. The kinetic model can be used by developing baking programs that can automatically control especially a new home‐scale steam‐assisted hybrid oven producing healthy products, for the use of domestic consumers.     

Heat inactivation of exogenous proteinases from Pseudomonas fluorescens. I. Possibility of inactivation in milk

The inactivation reaction of the proteinase of a P. fluorescens strain of biotype I in milk was investigated at 130-150 degrees C, also in milk and in buffer with and without added CaCl2 at temperatures below 100 degrees C. The decline in activity corresponded to first order kinetics in the UHT region; Ea = 115 kJ/mol. D values were 290 (130 degrees C), 124 (140 degrees C) and 54 s (150 degrees C); therefore, the usual temperature time combinations of UHT treatment are not sufficient to achieve the required rates of inactivation. At temperatures below 80 degrees C, inactivation corresponded increasingly to second order kinetics with considerably higher reaction rates; at 55 degrees C, an inactivation reaction corresponding to that induced by UHT treatment could be achieved at a thermal stress lower by a factor of 500. This "low temperature inactivation" was observed in a further 20 strains representing the spectrum of P. fluorescens. The average rates of inactivation following heat treatment in milk for 20 min are 47% at 55 degrees C and 44% at 60 degrees C. This can be regarded as the most effective temperature range for the inactivation of the proteinases in milk. Clear connections can be seen between the biotype groups and the optimum temperature for inactivation: biotype group I ca. 55 degrees C, group II (with a few exceptions) less than or equal to 50 degrees C and group III greater than or equal to 60 degrees C. The inactivation reaction is systematically influenced by the proteins and Ca++ ions present in milk.     

Formation kinetics of hydroxymethylfurfural, lactulose and furosine in milk heated under isothermal and non-isothermal conditions

A detailed kinetic study of hydroxymethylfurfural, lactulose and furosine formation was performed upon heating milk at temperatures between 90 degrees C and 140 degrees C. In case of prolonged heating, formation kinetics could be described by a fractional conversion model. Considering only the first phase of the model, kinetics could be simplified to a pseudo-zero order model. A first assessment of kinetic parameters was made by isothermal experiments. Data were analysed using both a 2-step linear and a 1-step non-linear regression method. Only for furosine, did the global 1-step regression approach seem to give better results than the individual 2-step regression approach. Next, the estimated parameters k(ref) and Ea were re-evaluated under non-isothermal conditions by subjecting milk to a time variable temperature profile. Given the complexity of Maillard reaction, it seemed better to estimate kinetic parameters under non-isothermal conditions when using a simplified model. Formation of hydroxymethylfurfural, lactulose and furosine was characterized by an Ea value of 90.2 kJ/mol (k(110 degrees C) = 1.2 micromol/l, min), 99.1 kJ/mol (k(110 degrees C) = 51.5 mg/l, min) and 88.7 kJ/mol (k(110 degrees C) = 16.3 mg/100 g protein, min) respectively. Additionally, 90% joint confidence regions were constructed in order to obtain an accurate representation of the statistical confidence associated with the simultaneously estimated parameters.     

Lipid Oxidation. Part. 1. Effect of Free Carboxyl Group on the Decomposition of Lipid Hydroperoxide

Hydroperoxido butyl oleate was decomposed by heating in excess palmitic acid at 60–120 °C. The decomposition followed the kinetics of a first order reaction with formation of both monomeric and oligomeric secondary products. The proportions of oligomers slightly increased with increasing reaction temperature and decreased with increasing concentration of hydroperoxide. The activation energy was 70.4 kJ/mol ± 4.7 kJ/mol. The decomposition of hydroperoxides proceeded partially by monomolecular cleavage, partially by formation of esters with palmitic acid.     

Effect of temperature and/or pressure on lactoperoxidase activity in bovine milk and acid whey

At atmospheric pressure, inactivation of lactoperoxidase (LPO) in milk and whey was studied in a temperature range of 69-73 degrees C and followed first order kinetics. Temperature dependence of the first order inactivation rate constants could be accurately described by the Arrhenius equation, with an activation energy of 635.3 +/- 70.7 kJ/mol for raw bovine milk and 736.9 +/- 40.9 kJ/mol for diluted whey, indicating a very high temperature sensitivity. On the other hand, LPO is very pressure resistant and not or only slightly affected by treatment at pressure up to 700 MPa combined with temperatures between 20 and 65 degrees C. Both for thermal and pressure treatment, stability of LPO was higher in milk than in diluted whey. Besides, a very pronounced antagonistic effect between high temperature and pressure was observed, i.e. at 73 degrees C, a temperature where thermal inactivation at atmospheric pressure occurs rapidly, application of pressure up to 700 MPa exerted a protective effect. At atmospheric pressure, LPO in diluted whey was optimally active at a temperature of about 50 degrees C. At all temperatures studied (20-60 degrees C), LPO remained active during pressure treatment up to 300 MPa, although the activity was significantly reduced at pressures higher than 100 MPa. The optimal temperature was found to shift to lower values (30-40 degrees C) with increasing pressure.     

动力学模型预测板鸭货架寿命

研究不同温度下贮藏过程中板鸭的感官性质、细菌总数、酸价、水分含量、过氧化值及挥发性盐基氮(TVB-N值)随存放时间的变化规律,确定引起贮藏过程中板鸭品质下降的关键因子是板鸭中脂肪的氧化酸败,并建立了酸价、过氧化值与贮藏时间、贮藏温度之间的动力学模型,以预测板鸭在贮藏过程中的品质变化和货架期。并求出了酸价变化反应的Ea和K0分别为66.1kJ/mol和2.173×1010,过氧化物生成反应的Ea(活化能)和K0分别为103.96kJ/mol和1.016×1017。     

Unravelling the kinetics of the formation of acrylamide in the Maillard reaction of fructose and asparagine by multiresponse modelling

A kinetic model for the formation of acrylamide in a fructose–asparagine reaction system at initial pH 5.5 is proposed, based on an approach called multiresponse kinetic modelling. The formation of acetic acid and formic acid from the degradation of fructose and its isomer glucose was included in the proposed kinetic model. The kinetic model suggests that the effect of temperature on acrylamide formation with fructose is more due to the preceding steps with the formation of the Schiff base. The use of fructose and lower pH resulted in a higher yield of acrylamide (3%), suggesting that both can play an important role in acrylamide mitigation. Furthermore, these models have shown that, at high temperatures (120–200 °C), the Maillard reaction rapidly goes into the advanced stages, forming high amounts of organic acids and high molecular weight melanoidins. Overall, these mechanistic models provide more insight of the formation of acrylamide in a quantitative way.     

Baking kinetics of muffins in convection and steam assisted hybrid ovens (baking kinetics of muffin…)

Effects of oven type and baking temperature on acrylamide concentration, surface browning, temperature profiles and drying rates of muffins were investigated. Muffins were baked in convection and steam assisted hybrid ovens at 145, 160 and 175 °C for different baking times. For all oven types, the acrylamide concentration of muffins increased with increasing baking time and temperature (p < 0.05). The formation was considered as the first order reaction kinetics except for the lowest baking temperature at natural convection and steam assisted hybrid ovens. The reaction rate constant, k was found to be in the range of 0.027–0.078 (min⁻¹). For the forced convection oven, the effect of baking temperature on acrylamide concentration followed the Arrhenius type of equation; with activation energy of 36.35 kJ/mol. The minimum drying rate was observed by the steam assisted hybrid oven, at all conditions. Steam assisted baking resulted in lower acrylamide concentration at all baking temperatures, while providing the average moisture content not significantly different.     

Degradation Kinetics of Lycopene and Visual Color in Tomato Peel Isolated from Pomace

Kinetics of lycopene and visual color degradation of tomato peel was studied at selected temperatures (50–100°C). Models based on lycopene and Hunter (a?×?b) values of fractional conversion were applied to determine the kinetic parameters. The degradation of lycopene and Hunter color values adequately followed first order reaction model with R²?>?0.97. The temperature dependence of the rate constants was adequately modeled by the Arrhenius equation. The activation energies of lycopene and color parameters were 18.27 and 29.07 kJ/mol, respectively, indicating greater temperature sensitivity of visual color parameters. Correlation of lycopene content and Hunter (a?×?b) values showed that they can be used interchangeably with good accuracy.     

Role of precursors on the kinetics of acrylamide formation and elimination under low moisture conditions using a multiresponse approach – Part I: Effect of the type of sugar

The effect of type of sugar on the kinetics of acrylamide formation and elimination reactions was investigated under low moisture conditions using equimolar asparagine–sugar model systems, heated at temperatures between 120 and 200 °C. The monosaccharides glucose and fructose and the disaccharide sucrose were selected to study this effect. A mechanistic model was used as a basis for multiresponse modelling of the different responses measured (acrylamide, glucose, fructose, sucrose, asparagine, aspartic acid and melanoidins). In spite of the higher acrylamide yield per mol initial asparagine for sucrose over fructose to glucose, the kinetic parameters estimated for acrylamide formation revealed that the type of sugar, monosaccharide or disaccharide, had only a limited effect on this reaction. The corresponding activation energy, however, was significantly lower in case the disaccharide sucrose was added. An opposite trend was observed for the acrylamide elimination rate constant, being significantly higher for the system with sucrose, whereas the temperature dependence of this rate constant remained unaffected by the type of sugar available under the reaction conditions considered.     

Original article: Thermal dynamic properties of isoflavones during dry heating

Thermal stabilities of major soya isoflavones at different dry‐heating temperatures were determined in this study. The conversion of glucoside isoflavones to aglycone isoflavones was monitored as well. The thermal degradation of the isoflavones: glucoside form daidzin, glycitin, and genistin and aglycone form daidzein, glycitein, and genistein followed first‐order reaction kinetics at heating temperatures 100, 150, and 200 °C. The degradation rate constants of the six isoflavones were not significantly different at 100 °C. However, the constants increased with increasing heating temperature. The half‐life for the glucoside and aglycone isoflavones was from 144 to 169 min and 139 to 176 min at 100 °C, respectively. They decreased rapidly to 15.7–54.7 and 36.0–90.7 min when temperature increased to 150 °C. When heated at 200 °C, they further decreased to 5.8–6.0 and 15.7–21.2 min, respectively. The order of thermal stability from lowest to highest was glycitin < genistin < daidzin < glycitein < genistein < daidzein at temperature below 150 °C. However, their thermal stabilities were not different at 200 °C. The conjugated glucosides were cleaved from the isoflavones to produce their corresponding aglycones when heated at 150 °C or higher. The production of glycitein increased constantly and was the highest among the three aglycone isoflavones.     

赤藓糖醇对柠檬汁饮料中维生素C保护作用的研究

本文以柠檬汁饮料作为实验材料,采用调节温度的方法对维生素C的热降解进行动力学研究。在建立动力学模型的基础上,通过速率常数、反应活化能等动力学参数,来探究柠檬汁饮料中赤藓糖醇的加入对维生素C的保护作用。研究结果表明:柠檬汁饮料在贮藏过程中,维生素C对热不稳定,其热力学降解符合一级反应动力学模型;在本次实验中,1%~3%赤藓糖醇浓度的加入均有助于减缓维生素C的降解速率。其中,当赤藓糖醇添加浓度为2%时,维生素C降解反应活化能达到最大,为75.47kJ/mol,比对照高出了9.79kJ/mol。因此,赤藓糖醇在一定程度上能够起到对维生素C的保护作用。      

Dechlorination of lindane, dieldrin, tetrachloroethane, trichloroethene, and PVC in subcritical water

Pure water has been used to dechlorinate aliphatic organics without the need for catalysts or other additives. Dehydrohalogenation (loss of HCI with the formation of a double bond) occurred at temperatures as low as 105-200 degrees C for 1,1,2,2-tetrachloroethane, lindane (1,2,3,4,5,6-hexachlorocyclohexane, gamma-isomer), and dieldrin (1,2,3,4,10,10-hexachloro-6,7-epoxy-1,4,4a,5,6,7,8,8a-octahydro-endo, exo-1,4:5,8-dimethanonaphthalene). Complete loss of the parent compounds was achieved in less than 1 h at 150, 200, and 300 degrees C for 1,1,2,2-tetrachloroethane, lindane, and dieldrin, respectively. The initial dechlorination of lindane had an activation energy of 84 kJ mol(-1) with an Arrhenius pre-exponential factor of 1.5 x 10(6) s(-1). Dehydrohalogenation of lindane formed trichlorobenzenes, followed by subsequent hydrolysis and hydride/chloride exchange to form chlorophenols, lower chlorobenzenes, and phenol as the major final product. Reaction of poly(vinyl chloride) at 300 degrees C for 1 h formed aromatic hydrocarbons ranging from benzene to anthracene and a char residue with a ca. 1:1 carbon-to-hydrogen ratio (mol/mol). The residue contained <1 wt % of chlorine compared to 57 wt % chlorine in the original polymer. All compounds tested yielded chloride ion as the major product (at higher temperatures), indicating that complete dechlorination of some aliphatic organochlorines may be feasible.     

A RESEARCH NOTE EFFECT OF MOISTURE CONTENT AND INITIAL THIAMIN CONCENTRATION ON THIAMIN DEGRADATION KINETICS

The degradation kinetic parameters of thiamin in a pea puree system containing 80% (w/w) and 85% (w/w) water were studied at 110, 120, and 130C for three thiamin concentrations of 50, 200 and 260 mg B₁-HCl/100 g pea puree. Both moisture content and initial thiamin concentration had no significant effect on the degradation kinetics. The degradation followed a first order reaction with an average k_121C of 0.0114 min^−1. The temperature dependence was adequately described by the Arrhenius equation. The average activation energy was 25.2 kcal/mol.     

Effect of Water Activity and Temperature in Color and Chlorophylls Changes in Yerba Mate Leaves

The kinetics of chlorophylls (a and b) degradation were studied in yerba maté leaves at different temperatures (50 to 808C) and water activities (0.1 to 0.8). Chlorophyll changes followed a first order-kinetic reaction in all cases. Rate constant values were fitted to different models to describe temperature and water activity dependence. When an Arrhenius model was used, the activation energy was found to be dependant on water activity for chlorophyll a (80.4–99.7 kJ/mol), while for chlorophyll b activation energy showed only a little variation (88.1–89.5 kJ/mol). Color parameter a* underwent a great decrease while parameters L* and b* had only a little variation.     

红叶甜菜红色素降解动力学研究

研究了光照、pH、温度对色素降解特性的影响。研究表明红叶甜菜红色素稳定性受pH、温度、光的影响,光照强度越大红叶甜菜红色素保存率越低,在pH2~6范围内色素较稳定,统计分析发现pH2、pH4和pH6色素保存率在实验温度下无显著差异;红叶甜菜红色素的热降解遵循Arrhenius定律,遵循一级降解动力学方程,随温度升高半衰期缩短,pH2、pH4和pH6的活化能分别为67.02kJ/mol、67.12kJ/mol和67.76kJ/mol,pH2、pH4和pH6的色素溶液在对应温度下的半衰期和活化能无显著差异。     

Thermal Degradation Kinetics of Carotenoids and Visual Color of Papaya Puree

The degradation kinetics of carotenoids and visual color of papaya puree were investigated at selected temperatures (70 to 105°C). The concept of fractional conversion was applied to determine the kinetic parameters. The degradation of papaya color was based on change of Hunter a and b values and it was found that combination of Hunter (a × b) value adequately represented thermal color change. Degradation of carotenoids and visual color followed first order reaction kinetics. Dependence of the rate constant followed the Arrhenius relationship. The process activation energies for carotenoids and visual color were 20.56 and 32.59 kJ/mol respectively. Higher activation energy value indicated greater temperature sensitivity of visual color as compared to carotenoids. The degradation of pigment and visual color varied linearly. Visual color could therefore be used for on‐line quality control of papaya puree.     

Ascorbic acid degradation kinetics in mushrooms in a high-temperature short-time process controlled by a thermoresistometer

The degradation of ascorbic acid was studied in mushrooms heated at temperatures between 110 and 140°C, high-temperature short-time conditions, in a five-channel computer-controlled thermoresistometer. The kinetics parameters were calculated on the assumption that there are 2 degradation mechanisms, one aerobic (during the first few seconds of the process) and the other anaerobic. The 2 stages followed first-order reaction kinetics, with E_a=46.36 kJ/mol for aerobic degradation and E_a=49.57 kJ/mol for anaerobic degradation.     

Methanol oxidation using ozone on titania-supported vanadia catalyst

Ozone-enhanced catalytic oxidation of methanol has been conducted at mild temperatures of 100-250 degrees C using a V2O5/ TiO2 catalyst prepared by the sol-gel method. The catalyst was characterized using XRD, surface area measurements, and temperature-programmed desorption of methanol. The oxidation of methanol with ozone in the absence of a catalyst gave about 30% conversion at 100 degrees C. Methanol oxidation over a V2O5/TiO2 catalyst at 100 degrees C gave very little conversion with oxygen, whereas the conversion increased to 80% with ozone. Methanol, having an inlet stream concentration of 15 000 ppmv, can be completely oxidized to CO(x) with an ozone-to-methanol ratio of 1.2, a temperature of 150 degrees C, and a gas hourly space velocity (GHSV) of 60 000 h(-1). The apparent activation energy with ozone was calculated to be ca. 40 kJ/mol, which is much lower than that calculated with oxygen (60 kJ/mol). At low methanol conversion methyl formate was the main product, whereas higher conversions favored oxidation to CO(x). The results imply a consecutive reaction of adsorbed methanol species, favoring selectivity toward methyl formate at lower temperatures and ozone-to-methanol ratios and CO(x) at higher temperatures and ozone-to-methanol ratios. Langmuir-Hinshelwood kinetics was used to model the reaction with and without ozone in the feed. The model parameters were obtained using least-squares fit to a selected set of experimental data, and the model was subsequently compared to all experimental data obtained in this study.     

Contribution of protein-surface ion pairs of a hyperthermophilic protein on thermal and thermodynamic stability

Hyperthermophilic proteins possess many ion pairs on their surface. To reveal the role of the ion pairs, O6-methylguanine-DNA methyltransferase from Thermococcus kodakaraensis KOD1 (Tk-MGMT) was studied as a model protein. The maximum free-energy changes of the protein in 0.1 and 0.5 M NaCl at pH 7.0 were 61.7 kJ mol(-1) at 31.5 degrees C and 77.4 kJ mol(-1) at 39.7 degrees C, respectively. On the other hand, mid points of the thermal unfolding temperatures in 0.1 and 0.5 M NaCl at pH 7.0 were 94.8 degrees C and 90.1 degrees C, respectively. The results suggest that the protein-surface ion pairs contribute to thermal stability (Tm), rather than thermodynamic stability (DeltaG).