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.     

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.     

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.     

Effect of storage on non‐enzymatic browning of liquid infant milk formulae

Furfural, hydroxymethylfurfural (HMF), furosine, lactulose, ascorbic acid and absorbance at 284 and 420 nm (A₂₈₄ and A₄₂₀) were all determined in two types of liquid infant formula prepared with different processing protocols. These browning indicators were used to assess the effects of storage and modified atmosphere on the shelf‐life of infant formulae. The study was carried out at 20 and 55 °C for 15, 30 and 90 days. At 20 °C, slight browning was observed and could be evaluated by furosine, furfural and total HMF indicators. At 55 °C, formula type A (pasteurised, spray‐dried and reconstituted) showed more browning in nitrogen storage conditions than did type B. Furfural, HMF, lactulose, A₂₈₄ and A₄₂₀ are useful indicators to control the extent of browning reactions in adverse storage conditions. © 2002 Society of Chemical Industry     

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.     

Kinetics of alkaline phosphatase and lactoperoxidase inactivation,and of beta-lactoglobulin denaturation in milk with different fat content

In the context of identifying intrinsic time temperature integrators (TTIs) for evaluating heat processing of milk, the extent to which milk fat content has an effect on alkaline phosphatase (ALP) and lactoperoxidase (Lpo) inactivation and on beta-lactoglobulin (beta-Ig) denaturation kinetics was studied. Inactivation and denaturation kinetics were analysed in whole, semi-skimmed and skimmed milk. In previous experiments (isothermal and non-isothermal heating conditions), heat inactivation of ALP and Lpo and heat denaturation of beta-Ig were found to follow first order kinetics. This allowed experimental design to be simplified. Data analysis was performed by non-linear regression and results were evaluated by construction of joint confidence regions. The possible effect of milk fat was illustrated by temperature time tolerance (TTT-) diagrams. Although initial ALP activity was lower in skimmed milk compared with semi-skimmed or whole milk, kinetics were comparable and fat content did not seem to substantially affect the ALP test result for pasteurized milk. Unlike ALP, Lpo inactivation and beta-Ig denaturation kinetics differed significantly in milk with different fat content. Differences between Lpo inactivation kinetics were relatively small and acceptable in the context of quantifying the process impact. Denaturation of beta-Ig, on the other hand, seemed to be enhanced at higher milk fat content (> 72 degrees C).     

Effects of overprocessing on heat damage of UHT milk

Formation of lactulose, furosine, galactosyl-|*beta*|-pyranone and lysinoalanine was studied in UHT milk samples produced by either direct or indirect heating on industrial plants and by indirect heating on a pilot plant. In particular, the effects of severe sterilization conditions, different proportions of milk recirculation, and storage of the finished product (23 °C for up to 90 days) have been investigated on the levels of the above molecules in UHT milk. An extensive increase of the values of all the indicators occurred when severe heat process was applied, but no direct relation was found between their levels and the nominal time–temperature conditions. Lactulose and furosine levels confirmed to be strictly correlated in UHT milk. In case of overheating or high proportion (60%) of milk recirculation, galactosyl-|*beta*|-pyranone formation was strongly enhanced, proving that also the advanced Maillard reaction takes place extensively, which is not detected by furosine value. Formation of lysinoalanine in UHT drinking milk on storage was pointed out for the first time. Lysinoalanine proved to be the most sensitive index of storage conditions among the four parameters studied. Data suggest that a realistic defence of UHT milk quality can be achieved only by fixing upper limits to heat damage parameters. Besides avoiding unjustified milk overheating, this approach may allow manipulations, like reprocessing expired milk, to be pointed out.     

Physical and Sensory Properties of Milk Chocolate Formulated with Anhydrous Milk Fat Fractions

Maximum additions of milk fat that produced temperable milk chocolates were anhydrous milk fat (AMF), middle-melting fraction (MMF) or low-melting fraction (LMF) up to 40 wt % total fat, and high-melting fraction (HMF) up to 35%. The solid fat content (SFC), melting point, melting enthalpy, instrumental and sensory hardness of milk chocolates decreased with increasing milk fat addition. No differences in sensory attributes sweetness, milk powder, chocolate, butter flavor or thickness of melt were observed. Chocolate with 40% MMF or LMF had greater milk flavor than that with 12.2% HMF. Onset of melt correlated (r = 0.96) with melting enthalpy. No differences between types of milk fat (AMF, HMF, MMF, LMF) were observed for any textural attribute assessed.     

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.     

Evaluation of heat and oxidative damage during storage of processed tomato products. I. Study of heat damage indices

The evolution of heat damage during storage of tomato pulp, puree and paste was studied by accelerated aging tests. Heat damage indices—5‐hydroxymethyl‐2‐furfural (HMF), furosine and colour changes (ΔE)—were evaluated for tomato products stored at 30, 40 and 50 °C for up to 90 days. Furosine and ΔE values increased following pseudo‐zero‐order kinetics, and the higher the solid content of the products, the higher were the rate constant values. HMF formation followed pseudo‐first‐order kinetics in tomato pulp and pseudo‐zero‐order kinetics in puree and paste samples. Data show that heat damage reactions in tomato products proceed even at room temperature, and the kinetic model provided can be used to predict changes occurring during shelf‐life. © 2002 Society of Chemical Industry     

Combined use of HMF and furosine to assess fresh honey quality

BACKGROUND: The quality of honey can be affected by practices such as adulteration, inadequate storage or the application of severe heat treatments. Because hydroxymehylfurfural (HMF) is an indicator of honey freshness and furosine (ε‐2‐furoylmethyl lysine) has proved to be a useful chemical indicator of the progress of the Maillard reaction in foods, the aim of this work was to assess their usefulness as indicators of fresh honey quality. The effect of heat treatment, storage and adulteration with different types of syrups on HMF and furosine content has been studied. RESULTS: In fresh honey, HMF and furosine values ranged from 0.9 to 14.6 mg kg^?1 of product and from 3.06 to 12.06 g kg^?1 of protein, respectively. Heating of honey samples with different pH (3.76 and 5.14) produced slight increases in HMF content and negligible changes were detected in furosine values. The storage of fresh honey for 2 years caused a high increase in the HMF level, reaching values above EU limits. However, furosine showed a different behavior depending on the type of honey sample. Adulteration assays using different syrups produced an increase in HMF and a decrease of furosine values by dilution effect. HMF content of adulterated honey samples with syrup of known origin did not exceed EU limits. CONCLUSION: These results show the influence of long periods of storage or adulteration, using different percentages of corn or invert sugar syrups, on HMF and furosine content of fresh honey. This seems to indicate that the combination of HMF and furosine may be useful for evaluating the quality of fresh honey. Copyright © 2009 Society of Chemical Industry     

Maillard Reaction in Microwave Cooking: Comparison of Early Maillard Products in Conventionally and Microwave-Heated Milk

The impact of microwave cooking on the formation of early Maillard products was investigated and compared with the effect of conventional cooking, using milk as a test system. Experiments were carried out at controlled temperatures of 80°C and 90°C, respectively, at holding times up to 420min. Furosine, hydroxymethylfurfural (HMF) and lactulose, which are all established indicators to estimate heat damage, were determined. The concentrations of all the heating indicators increased with increasing heating time. For example in the 90°C test series the furosine values rose from 34mglitre⁻¹ (0·5h) to 94mglitre⁻¹ (2h holding time) in the milk heated by microwaves and from 35mglitre⁻¹ (0·5h) to 96mg litre⁻¹ (2h) in the conventionally heated milk. None of the reaction products showed significant differences as between the microwave heating and conventional cooking methods.     

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.     

Survey of the furosine content in cheeses marketed in Spain

The furosine content in 53 samples of different cheese types (fresh, ripened with molds, artisanal hard-pressed, industrial hard-pressed, and processed) marketed in Spain was analyzed. The lowest furosine values were observed in artisanal hard-pressed cheeses (4.8 to 10.2 mg per 100 g of protein) and ripened with molds cheeses (4.2 to 12.8 mg per 100 g of protein). Industrial hard-pressed cheeses showed furosine values between 3.5 and 43.8 mg per 100 g of protein. Differences between samples may be attributed to the heat-treatment intensity given to cheese milk and to cheesemaking conditions. The highest contents of furosine were observed in processed cheeses (20 to 366.6 mg per 100 g of protein). A wide range of furosine content was found in fresh cheeses (17.9 to 73.6 mg per 100 g of protein), which could be due to the different amounts of dried milk added during the manufacture of cheeses.     

Distinguishing pasteurized, UHT and sterilized milks by their lactulose content

Commercial pasteurized, UHT and sterilized milk samples, and laboratory autoclaved milks, were analysed for lactulose by an enzymatic method. No lactulose was detected in the pasteurized milk. On the basis of the measured lactulose concentrations, the UHT and sterilized milk samples fell into five groups according to the type of process that they had received.
The lactulose concentrations in the laboratory autoclaved milks rose on storage, but this was not observed in the other milks.
It appears that pasteurized, UHT and sterilized milks can be differentiated by their lactulose content.     

HMF Formation during Heat-treatment of Milk-type Products as Related to Milkfat Content

Homogenized lactose/caseinate model systems and milk with different fat content were heated at 110 to 150 °C for up to 30 min. Free and total hydroxymethylfurfural (HMF) were measured by reverse-phase high-performance liquid chromatography. Multifactor analysis of variance was applied to determine whether milkfat content contributed to free and total HMF formation. There was a negative effect of milkfat on the formation of total HMF in both systems. However, free HMF formation was promoted by higher milkfat content in milk, but not in the lactose-caseinate model. Milkfat affected also the free and total HMF formation in commercial pasteurized milk, ultra heat-treated milk, and bottle-sterilized milk.     

Furosine is a useful indicator in pre‐baked breads

There is increasing demand for pre‐baked bread. Bakers can meet consumer requirements for breads of specific flavour and colour by pre‐baking an amount of bread in the morning and completing the baking process in the afternoon. This type of product is of special interest to sandwich bars, restaurants and large communities. In order to obtain an indicator of utility to monitor the processing of pre‐baked bread, the browning indicators furosine, hydroxymethylfurfural (HMF) and glucosylisomaltol were analysed in two independent assays of bread pre‐baked at 175 °C for between 5 and 30 min. No furosine was detected in raw or fermented dough. In the pre‐baking stage, furosine increased from 1.5‐ to 5‐fold between 5 and 30 min. The furosine values obtained in the two independent experiments were similar. HMF and glucosylisomaltol were only detected after 15 min, which is the time period commonly used for processing by the industry. Thus, among these indicators, furosine is the only one with utility for monitoring the pre‐baking process. On the other hand, a study of the baking of pre‐baked bread at 220 °C showed that HMF and glucosylisomaltol can be used to monitor the latter process. Copyright © 2004 Society of Chemical Industry     

Occurrence of furosine and hydroxymethylfurfural as markers of thermal damage in dehydrated vegetables

The presence of furosine and hydroxymethylfurfural (HMF) as markers of thermal damage in commercial dehydrated vegetables has been studied. Furosine was measured in all the analysed samples whereas HMF was detected only in garlic, onion, and tomato groups and some other individual vegetables. Furosine, as indicator of the first steps of the Maillard reaction, ranged from 1.12 to 923 mg/100 g protein (depending on the vegetable species and thermal treatment applied) and was well correlated with the browning development in not severely heat-treated samples. In addition, the results seem to indicate that reducing sugars play an important role in the formation of furosine in some vegetable species but not HMF at the conditions used for the dehydration process. The findings of this study show the usefulness of furosine as a quality indicator for sensitive control of the dehydration process in vegetables.     

Development of the Maillard reaction in foods cooked by different techniques. Intake of Maillard-derived compounds

Specific and non-specific Maillard reaction (MR) indices such as CIELab colour, browning measurement, furosine, hydroxymethylfurfural (HMF) and furfural, as well as the nutrient content, were analysed for commonly consumed dishes, to test the effects of different culinary treatment on dishes composed of the same ingredients. In addition, the consumption of early MR products (MRP), Amadori compounds, HMF and furfural from a normal serving of these dishes was calculated. As expected, recipes including frying, apart from their particular composition, led to significantly higher values of furosine and HMF, ranging from 4.40 to 175 and from 0.30 to 22.7 mg/kg, respectively; consequently they provided the highest levels of Amadori compounds and HMF intake (0.42–26.8 and 0.02–2.38 mg/serving, respectively). Even so, MRP intake/serving was not very high in comparison with levels reported in the bibliography on some individual foods typically studied in terms of MR development, suggesting that the culinary treatments used do not make a great contribution to the daily MRP consumption.