Kinetics of hydroxymethylfurfural,lactulose and furosine formation in milk with different fat content

In the context of the general applicability of hydroxymethylfurfural (HMF), lactulose and furosine as time-temperature integrators (TTIs) for thermal processing of milk, the influence of milk fat content was studied. Formation kinetics were analysed for milk with fat content of 4.0 +/- <0.1%. In previous experiments, it was observed that, under isothermal and non-isothermal heating conditions, formation of the three chemical compounds could be described by pseudo-zero order kinetics. Since the kinetic model was known, the experimental design could be simplified. Data were analysed by a non-linear regression procedure and results were evaluated by construction of joint confidence regions and temperature time tolerance (TTT-) diagrams. Formation kinetics of HMF and lactulose was not affected by milk fat content. Regarding furosine, significant differences were observed between kinetic parameters in whole, semi-skimmed and skimmed milk. The observed differences however were negligible in the context of process impact evaluation.     

Confidence intervals for modeling anthocyanin retention in grape pomace during nonisothermal heating

ABSTRACT:  Degradation of nutraceuticals in low- and intermediate-moisture foods heated at high temperature (>100 °C) is difficult to model because of the nonisothermal condition. Isothermal experiments above 100 °C are difficult to design because they require high pressure and small sample size in sealed containers. Therefore, a nonisothermal method was developed to estimate the thermal degradation kinetic parameter of nutraceuticals and determine the confidence intervals for the parameters and the predicted Y (concentration). Grape pomace at 42% moisture content (wb) was heated in sealed 202 × 214 steel cans in a steam retort at 126.7 °C for > 30 min. Can center temperature was measured by thermocouple and predicted using Comsol software. Thermal conductivity (k) and specific heat ( C_p ) were estimated as quadratic functions of temperature using Comsol and nonlinear regression. The k and C_p functions were then used to predict temperature inside the grape pomace during retorting. Similar heating experiments were run at different time–temperature treatments from 8 to 25 min for kinetic parameter estimation. Anthocyanin concentration in the grape pomace was measured using HPLC. Degradation rate constant ( k _{110 °C}) and activation energy ( E_a ) were estimated using nonlinear regression. The thermophysical properties estimates at 100 °C were k = 0.501 W/m °C, Cp = 3600 J/kg and the kinetic parameters were k _{110 °C}= 0.0607/min and E_a = 65.32 kJ/mol. The 95% confidence intervals for the parameters and the confidence bands and prediction bands for anthocyanin retention were plotted. These methods are useful for thermal processing design for nutraceutical products.     

Influence of seasonal variation on kinetics of time temperature integrators for thermally processed milk

In the context of identifying intrinsic time temperature integrators (TTIs) for evaluating thermal processing of milk, the possible influence of seasonal variation in milk composition on the applicability of alkaline phosphatase (ALP), hydroxymethylfurfural (HMF), lactulose and furosine for process impact assessment was studied. Hereto inactivation and formation kinetics of these indicators were analysed in milk samples collected over a one year period. Based on previous research (isothermal and non-isothermal heating conditions) it was assumed that thermal inactivation of ALP followed first order kinetics, and formation of HMF, lactulose and furosine could be described by pseudo-zero order kinetics. This allowed the use of a simplified experimental design to obtain the kinetic parameters. Based on 90% joint confidence regions, kinetic parameter values differed significantly between different batches of milk for all four indicators. Additionally, variable ALP activities and HMF concentrations were observed in the raw milk samples. Nevertheless, the observed differences did not seem to restrict the applicability of the selected TTIs as illustrated by the construction of temperature time tolerance (TTT-) diagrams. Through these diagrams, use of the TTIs implied an uncertainty of approximately 2 degrees C between equivalent processes.     

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.     

Use of different thermal indices to assess the quality of pasteurized milks

 Lactoperoxidase activity and lactulose, furosine and undenatured whey protein contents were determined in Spanish commercial milks labelled as pasteurized (group A) and high-temperature pasteurized (group B), in order to assess their quality. Three samples of group A and all of the samples of group B were lactoperoxidase negative. Most samples of group A had measurable amounts of lactulose, even though their concentrations of undenatured β-lactoglobulin were higher than 2600 mg/l. In general, samples of group B showed higher lactulose and furosine and lower undenatured whey protein contents. High levels of furosine and lactulose accompanied by high levels of undenatured β-lactoglobulin could indicate the addition of milk heated at high temperatures, whereas high levels of furosine and relatively low levels of lactulose may have been due to the presence of reconstituted milk powder. Received: 29 June 1998     

Use of different thermal indices to assess the quality of pasteurized milks

 Lactoperoxidase activity and lactulose, furosine and undenatured whey protein contents were determined in Spanish commercial milks labelled as pasteurized (group A) and high-temperature pasteurized (group B), in order to assess their quality. Three samples of group A and all of the samples of group B were lactoperoxidase negative. Most samples of group A had measurable amounts of lactulose, even though their concentrations of undenatured β-lactoglobulin were higher than 2600 mg/l. In general, samples of group B showed higher lactulose and furosine and lower undenatured whey protein contents. High levels of furosine and lactulose accompanied by high levels of undenatured β-lactoglobulin could indicate the addition of milk heated at high temperatures, whereas high levels of furosine and relatively low levels of lactulose may have been due to the presence of reconstituted milk powder.     

维生素C在婴儿配方乳粉加工、冲调模拟体系中的热降解动力学

对婴儿配方乳粉在加工、冲调过程中氧化型维生素C(DHAA)、还原型维生素C(AA)及总量维生素C(AA+DHAA,以VC表示)的热降解动力学进行研究。结果表明:加工模拟体系中,AA及VC符合动力学一级反应,活化能分别为46.49 kJ/mol和39.69 kJ/mol。冲调模拟过程中,温度对AA和VC的降解符合零级反应模型,对DHAA的降解符合一级反应模型,反应活化能分别为16.71,19.50,12.04 kJ/mol。     

Purification and thermostability of beta-galactosidase (lactase) from an autolytic strain of Streptococcus salivarius subsp. thermophilus

beta-Galactosidase from an autolytic strain of Streptococcus salivarius subsp. thermophilus was purified 109-fold to near homogeneity. The yield of purified enzyme was 41% and the specific activity was 592 o-nitrophenyl beta-D-galactopyranoside U/mg at 37 degrees C. Two isozymes were present, but only one subunit was detected, having a mol. wt of 116,000. Enzyme stability was 37-83 times greater in milk than in buffer in the range 60-65 degrees C. At 60 degrees C the half-life in milk was 146 min. Denaturation in buffer was first-order, but in milk the overall reaction order with respect to enzyme concentration was approximately 0.5. The activation energy for denaturation was 453 kJ/mol in milk and 372 kJ/mol in buffer. In milk the activation energy for lactose hydrolysis was 35.1 kJ/mol.     

Assessment of quality and technological characterization of lactose-hydrolyzed milk

The intensity and sequence of heat and hydrolytic treatments as well as storage stability of lactose-hydrolyzed milk was assessed during processing and storage in 15 different commercial samples by monitoring the glycidic fraction (glucose, lactose and galactose) and selected thermal treatment markers (furosine, lactulose and fructose). The use of an additional indicator (fructose) together with classical process indicators (lactulose and furosine), was useful to better understand the quality of this dietetic milk and the processing procedures utilized. The results confirmed the high reactivity of lactose-hydrolyzed milk to the Maillard reaction and the more limited chemical stability of this milk typology when stored at 20 °C. In addition, a wide variability in the quality of commercial samples of lactose-hydrolyzed milk was found, which underlines the necessity to establish definite thresholds for this milk to defend both consumers and product quality.     

DEVELOPMENT OF SUCROSE INVERSION KINETICS UNDER CONTINUOUS FLOW CONDITIONS

Reaction kinetic data for the acid hydrolysis of sucrose were generated during continuous flow thermal treatment. Predicted levels of hydrolysis were calculated using batch-generated kinetic parameters and the equivalent point method of thermal evaluation. Actual and simulated levels of hydrolysis were linearly correlated (r > 0.98). Evaluation of hydrolysis data for isothermal and non-isothermal operations, using the equivalent point method supported first order kinetics, and yielded Arrhenius parameters resembling batch generated values. Experimental activation energy, Ea, values ranged from 100.2 to 119.7 kJ/mole, which is in agreement with literature values which range from 99 to 106 kJ/mole.     

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.     

Guideline for proper usage of time temperature integrator (TTI) avoiding underestimation of food deterioration in terms of temperature dependency: A case with a microbial TTI and milk

Time-temperature integrators (TTIs) can be used to predict food deterioration. However, underestimation of the magnitude of deterioration is not desirable. This study aims to establish guidelines in terms of temperature dependency (Arrhenius activation energy, Ea) to avoid such underestimation by proper use of TTIs. A case study was executed with a microbial TTI and milk. The Ea of the TTI color change was 106 kJ/mol and those of milk deterioration factors aerobic mesophilic bacteria count, lactic acid bacteria count, ln lactic acid %, and pH were 101, 107, 122, and 145 kJ/mol, respectively. The deterioration factors with values of Ea larger than that of TTI, ln lactic acid %, LAB, and pH, were found to be underestimated as compared to their actual levels by prediction from TTI color change, leading to potential consumption of deteriorated milk.     

Kinetic Parameters for Thermal Degradation of Green Asparagus Texture by Unsteady-state Method

An unsteady-state method was developed for estimating texture degradation during heating-cooling of green asparagus spears. The method used a mathematical model of heat transmission for time-temperature history estimation, and a nonlinear regression of texture measurements of asparagus spears to estimate kinetic parameters. The specific heat, conductivity and convective coefficient of green asparagus were determined experimentally and used in the mathematical model for temperature estimation. Values obtained were Ea = 76.19±0.13 kJ/mol and k_1158°C= 0.00528±0.00005 s^-1. Good agreement was found between predicted and observed texture values. The method was compared with the classical steady-state method. The mathematical model and kinetic parameters estimated could be used to design and evaluate thermal processes for green asparagus.     

Effect of protein and temperature on cutting time prediction in goats' milk using an optical reflectance sensor

An objective method for determining the coagulum cutting time is needed to improve consistency and processing efficiency of goats' cheese. A fibre optic sensor was used to measure the backscatter of near-infrared radiation at 880 nm during the coagulation of skimmed goats' milk for the purpose of predicting coagulum cutting time. A randomised block design, replicated three times, was used to test the effect of three protein concentrations (3, 5 and 7% (w/w)) on diffuse reflectance parameters for cutting time prediction of milk coagulated at five different temperatures (20, 25, 30, 35 and 40 degrees C) to assure a wide range of coagulation rates. The inclusion of a protein term in the existing algorithms was essential to reduce the standard error of prediction to under 6.2 min. An algorithm including a time-based parameter and a protein term, Tcut=beta0 T2min (1 + gamma% Protein) was found to predict cutting time with a SEP of 2.42 min and an R2 of 0.98. Gamma was considered constant (gamma=-0.0674, goats' milk) representing the protein effect on beta0. Algorithms using response-based parameters (such as change in reflectance ratio) and the composition parameter protein required additional regression parameters such as temperature and an intercept term to predict the cutting time with the same precision as algorithms using only time-based parameters. Time-based parameters were found to decrease proportionally with increasing temperature and decreasing protein concentration. Response-based and mixed-based parameters were found to decrease with decreasing temperature. Reflectance ratio at cutting time did not significantly change with protein concentration for skimmed goats' milk. The activation energy of kappa-casein hydrolysis was calculated based on changes in reflectance profile parameters and was found to be in the range 63-72 kJ mol(-1).     

Immobilized α-amylase from Bacillus licheniformis: a potential enzymic time—temperature integrator for thermal processing

Biphasic and nth-order models were tested as to their usefulness to fit experimental inactivation data of Bacillus licheniformis α-amylase, immobilized on glass beads, and were discussed with respect to their suitability to characterize the considered enzymic system as a time—temperature integrator (TTI) to evaluate heat processes. Both isothermal and non-isothermal inactivation experiments were carried out. Model (kinetic) parameters (rate constant k, activation energy E_A and reaction order n) were estimated using a non-linear regression procedure. The results obtained, especially the activation energy of about 293 kJ mole^–1, indicated a potential use of this system as a TTI for heating processes in the temperature range of 96–108°C.     

Characterization of industrial processed milk by analysis of heat-induced changes

Summary Thermal indicators in milk, which had been subjected to one of the six industrial processes of thermization, pasteurization, direct and indirect UHT-sterilization, pre-sterilization and in-bottle sterilization, were studied. The following three indices of heat damage were analyzed by high performance liquid chromatography (HPLC), hydroxymethylfurfural (HMF), lactulose and acid-soluble β-lactoglobulin(β-LG). Average amounts found were 1710 mg/l of β-LG and 2.49 μmol/l of HMF in pasteurized milk. In UHT milk, the amounts for direct and indirect processes were 389 and 322 mg/l of β-LG, 12.0 and 250 mg/l of lactulose and 5.6 and 8.7 μmol/l of HMF. In sterilized milk the amounts were 1120 mg/l of lactulose and 22 μmol/l of HMF, without any detectable presence of undenatured whey proteins. On the basis of the time/temperature profiles, a sterilization factor, expressed as seconds, was defined for each thermal treatment. By applying discriminant analysis each industrial process could be classified independently at the 95% confidence level (pasteurization, UHT-treatment and in-bottle sterilization), but direct-UHT treated milk could not be discriminated from indirect-UHT milk, nor thermized milk from raw bulk milk. The simultaneous application of several heat-induced parameters improves the classification of industrial processed milks, and is therefore a useful tool for optimization of the processing conditions.     

Inactivation kinetics of alkaline phosphatase and lactoperoxidase, and denaturation kinetics of beta-lactoglobulin in raw milk under isothermal and dynamic temperature conditions

A detailed kinetic study of alkaline phosphatase, lactoperoxidase and beta-lactoglobulin was carried out in the context of identifying intrinsic time-temperature indicators for controlling the heat processing of milk. The heat inactivation or denaturation of alkaline phosphatase, lactoperoxidase and beta-lactoglobulin under isothermal conditions was found to follow first order kinetics. Experimental results were analysed using both a two step linear regression and a one step non-linear regression method. Results obtained using the two statistical techniques were comparable, but the 95% confidence interval for the predicted values was smaller when the one step non-linear regression method was used, indicating its superiority for estimating kinetic parameters. Thermal inactivation of alkaline phosphatase and lactoperoxidase was characterized by z values of 5.3 deg C (D60 degrees C = 24.6 min) and 4.3 deg C (D71 degrees C = 38.6 min) respectively. For the denaturation of beta-lactoglobulin we found z values of 7.9 deg C (D7.5 degrees C = 49.9 min) in the temperature range 70-80 degrees C and 24.2 deg C (D85 degrees C = 3.53 min) in the range 83-95 degrees C. Dref and z were evaluated under dynamic temperature conditions. To estimate the statistical accuracy of the parameters, 90% joint confidence regions were constructed.     

Thermal kinetics of color degradation of mulberry fruit extract

The effects of temperature and pH on color degradation kinetics of the mulberry fruit extract were investigated. The absorbance at 510 nm was decreased with increase of heating time, but that at 420 nm was increased with the increase of heating time at 100 degrees C. The change of the browning index (A510/A420) was increased with increase of pH and was lower at pH 2.0 than that at pH 5.0. The browning index variation was adequately described by both the first-order and the zero-order kinetic. However, the zero-order kinetic model was proposed because of the better fit. According to the Arrhenius model, the activation energies for the browning index in the range of 80-100 degrees C for the four different pH values were 30.68 kJ/mol for pH 2.0, 35.87 kJ/mol for pH 3.0, 42.67 kJ/ mol for pH 4.0, and 43.49 kJ/mol for pH 5.0.     

采用动力学模型预测河蟹调味汁货架期

以河蟹边角料为原料,加工成河蟹调味汁。为了能够迅速、准确预测常温（25 ℃）环境下河蟹调味汁的货架期,将河蟹调味汁置于37、45、55 ℃下贮藏,以加速变质。以总挥发性盐基氮含量为指标建立一级动力学模型,货架期的预测值通过动力学模型和阿伦尼乌斯方程来确定。结果表明：阿伦尼乌斯方程中的活化能（Ea）为29.28 kJ/mol,指前因子（k0）为1.443×103,河蟹调味汁在25 ℃环境下的货架期为183 d。