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.     

Heat-induced and other chemical changes in commercial UHT milks

The properties of commercial directly and indirectly heated UHT milks, both after heating and during storage at room temperature for 24 weeks, were studied. Thermally induced changes were examined by changes in lactulose, furosine and acid-soluble whey proteins. The results confirmed previous reports that directly heated UHT milks suffer less heat damage than indirectly heated milk. During storage, furosine increased and bovine serum albumin in directly heat-treated milks decreased significantly. The changes in lactulose, alpha-lactalbumin and beta-lactoglobulin were not statistically significant. The data suggest that heat treatment indicators should be measured as soon as possible after processing to avoid any misinterpretations of the intensity of the heat treatment.     

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.     

Formation of hydroxymethylfurfural and furosine during the storage of jams and fruit-based infant foods

Simultaneous formation of hydroxymethylfurfural (HMF) and furosine (Fu) during the storage of three batches of jam samples (one commercial and two laboratory prepared) and one of fruit-based infant food (commercial), at 20 and 35 °C during 12 months, was investigated to evaluate the reliability of the combination of both parameters as quality indicators. In general, the concentration of both indicators increased with time and temperature of storage, formation of furosine being less temperature dependent than that of HMF. HMF was proved to be a good indicator of the severity of heating during manufacture and/or inadequate temperature during prolonged storage, whereas furosine may be a useful indicator of the storage conditions. The combination of both indicators can afford important information on the quality of jams and fruit-based infant foods during processing and storage.     

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.     

Heat damage evaluation in ultra-high pressure homogenized milk

The evaluation of heat damage in ultra-high pressure homogenized (UHPH)-treated samples has been studied by analyzing different thermal indicators such as compounds that absorb at 340 nm, hydroxymethylfurfural, free sulphydryl content, furosine, lactulose and whey protein denaturation. Milk was treated at 200 and 300 MPa with inlet temperature of 30 and 40 °C and was compared to high-pasteurized milk (PA; 90 °C, 15 s) and to commercial UHT, in bottle-sterilized and pasteurized milks. UHPH samples were differentiated from PA milk, basically by the determination of absorbance at 340 nm and β-Lactoglobulin denaturation. Both parameters indicated a reduced thermal effect in UHPH samples over PA milk. Comparison of UHPH samples with UHT and sterilized milks showed an increase of all heating indicators when severe heat process was applied. Overall, in spite of the increase of temperature during UHPH treatments, heat damage was lower compared to PA milk, suggesting the potential of this technology as an alternative to pasteurization.     

Evaluation of tracers for the authentication of thermal treatments of milks

For regulatory purposes, several methods have been proposed for defining biochemical tracers to identify heat treatments to which milks may be submitted. However, none of these methods is universal whereas they are usually restricted to one or two categories of treated milks and are not able to discriminate any unknown sample arriving in a control laboratory. Therefore, Arilait-Recherches and Syndilait (Syndicat National des Laits de Consommation) decided to undertake a study in order to define an efficient discrimination approach applicable to commercial milk samples. About 200 commercial samples were tested, produced in several plants where they received the standard heat treatments here-applied. Five types of heat treatments were studied: pasteurisation, high pasteurisation, direct UHT, indirect UHT, and sterilisation. In order to estimate the effect of storage on long-term storage milks, samples were submitted to two storage conditions: 90 days at 25 °C and 90 days at 35 °C. The selected tracers were: furosine; lactulose; native α-lactalbumin; denaturised α-lactalbumin; percent of denaturised α-lactalbumin; FAST index, tryptophan fluorescence, β-lactoglobulin, and lactoperoxidase: altogether 5000 measurements were collected. Analysis of variance clearly demonstrates that no tracer can be selected to universally discriminate milks from all these technologies. The only possible authentication technique must be based on a multivariate approach. The application of factorial discriminant analysis by combining at least five tracers, gives a possible solution to this question. Most discriminative tracers are those which globally measure the structural modifications of the milk protein rather than those which specifically quantify the metabolites of the Maillard reaction.     

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.     

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.     

热处理对牛乳成分的影响以及热敏感指标的变化研究进展

热加工可以有效杀灭生牛乳中的各种致病微生物,但也会对牛乳成分产生影响。随着热处理温度的升高,乳清蛋白变性和凝集、乳糖异构化和降解、美拉德反应等理化反应会依次发生,这些反应中活性成分(例如碱性磷酸酶和乳清蛋白)的减少或反应产物的生成(例如乳果糖和糠氨酸)都可作为热加工强度的标识。本文对牛乳的热加工条件、牛乳在受热情况出现的理化变化以及相应的热敏感成分的变化进行综述。     

复原乳鉴别指标探讨

选择适宜的鉴别指标,确定并完善复原乳的鉴定方法,不但可为质量监督检验机构的检测和监督工作提供技术支持．而且可有效保护消费者的利益。可以通过检测牛奶在长时间贮藏过程中产生的荧光物质．或检测牛奶中脂肪酸组成分的变化来鉴别鲜奶与复原乳,但难以排除某些干扰因素的影响。近年来复原乳鉴定指标的研究热点主要集中在奶制品经热处理后其中的热损害产物。有两种化学反应产物可用来评价：（1）降解产物：热不稳定组分的降解、变性、失活,如乳清蛋白或酶;（2）新形成物质：如乳果糖或美拉德反应的产物。目前国际上通常用糠氨酸和乳果糖作为评估热处理和贮存对奶制品质量影响的指标。然而各指标也不可避免的存在一定的局限性,因此可能需要不止一个指标来进行综合评价。     

前表面荧光法在牛奶美拉德反应检测中的应用

在热处理中,牛奶中的乳蛋白容易与乳糖发生美拉德反应,使牛奶的色泽、风味、营养等发生变化。与传统化学检测法相比,前表面荧光法具有快速灵敏、前处理简便等优点。为了评估前表面荧光法在检测牛奶美拉德反应程度上的准确性和适用性,本文对比了不同热处理下牛奶的美拉德反应的荧光图谱和美拉德产物的含量,分析了指标间的相关性。并以前表面荧光法和羟甲基糠醛含量建立模型对商业乳品进行预测,结果良好,为荧光检测的工业应用提供理论依据。结果显示,前表面荧光法可应用于牛奶前中期美拉德产物的无损检测。     

The influence of enzymatic cross‐linking of proteins on the Maillard reaction in milk

The influence of transglutaminase (TGase) on the Maillard reaction was investigated in skimmed milk samples during heat treatment. TGase‐treated and control samples were heated at 80, 120 and 140 °C for 1, 5, 15, 30, 40 and 60 min. Compared with the TGase‐treated samples heated at 80 and 120 °C, the sample heated at 140 °C showed a larger decrease in furosine concentration. It was also found that TGase did not affect the formation of hydroxymethylfurfural and lactulose at 120 °C, whereas their concentrations increased in the presence of TGase at 140 °C. It was concluded that blockage of lysine residues via enzymatic cross‐linking of milk proteins had a limited effect on the Maillard reaction.     

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.     

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     

Chemical modifications of casein occurring during industrial manufacturing of milk protein powders

The effect of milk acidification at different pH levels applied during the processing of various types of milk protein powders was first evaluated in the experimental samples of caseins, caseinates and milk protein concentrates. The absence of inorganic colloidal phosphorus was detected when milk was acidified to pH 4.60, whereas low levels (0.36–0.72 g/100 g of protein) were detected when mild milk acidification occurred. The extent of protein glycation and the occurrence of protein cross-linking were assessed in the same samples by measuring their furosine (5.7–427 mg/100 g of protein) and lysinoalanine (0.4–35.2 mg/100 g of protein) levels, respectively. In addition to heat treatments, the contents of these markers strictly depend on the presence of lactose and consequently on the effectiveness of the washing step applied during processing before drying to remove non-protein soluble components. The determination of these chemical markers in the samples permitted the identification of different technological conditions applied in the manufacturing of commercial milk protein powders with the same class.     

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     

Evaluation of furosine,lactulose and acid-soluble β-lactoglobulin as time temperature integrators for whipping cream samples at retail in Austria

Three heat load indicators, i.e., furosine, lactulose and acid-soluble β-lactoglobulin, were determined in whipping cream samples purchased from Austrian market (n = 33), as well as commercial samples obtained directly from one Austrian dairy company (one brand, n = 25). Furosine contents were 47.8 ± 14.0, 72.2 ± 36.6, and 172.5 ± 17.7 mg 100 g⁻¹ protein, and β-lactoglobulin contents were 143 ± 91, 195 ± 150, and 89 ± 31 mg L⁻¹ for retailed pasteurised, extended shelf life (ESL), and ultra-high temperature (UHT) cream samples, respectively. Lactulose concentrations (analysed enzymatically) were 29 ± 10, 56 ± 41, and 201 ± 24 mg L⁻¹ for pasteurised, ESL and UHT cream samples, respectively. Linear correlation obtained for furosine and lactulose concentrations indicated that these indicators can reliably assess the heat load of pasteurised, ESL and UHT cream samples, whereas β-lactoglobulin was definitely not appropriate to discriminate between these heating categories.     

Changes in phosphoglyceride composition during storage of ultrahigh-temperature milk, as assessed by 31P-nuclear magnetic resonance: possible involvement of thermoresistant microbial enzymes

Soluble phosphoglycerides were studied in ultrahigh-temperature (UHT) milk by 31P-nuclear magnetic resonance. It was shown that, during storage of UHT milk, manufactured from raw milk with poor microbial quality, glycerophosphocholine and glycerophosphoethanolamine disappeared in parallel with an increase in alpha-glycerophosphate (GP). Storage at 10, 20, and 30 degrees C showed a faster transformation as the temperature increased. UHT milk samples manufactured from raw milks with better microbial quality and submitted to severe heat processes did not display changes in phosphoglycerides during storage. Screening of commercial UHT milks showed variations regarding the presence of GP, while in pasteurized milk samples, the appearance of GP occurred when the commercial life had been exceeded. Inoculation of sterile milk with Pseudomonas fluorescens NCIB9046 and incubation at 10 degrees C supported that changes in phosphoglycerides could be the consequence of a phosphodiesterase activity of bacterial origin, able to survive UHT processing. A similar behavior was observed between this activity and proteolytic activity. The potential application of the detection of these compounds as spoilage predictor indices is discussed.