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Lotte Bach Larsen - One of the best experts on this subject based on the ideXlab platform.
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relationship between casein micelle size protein composition and stability of UHT Milk
International Dairy Journal, 2021Co-Authors: Marije Akkerman, Valentin Rauh, John Sørensen, Lotte Bach Larsen, Lene Buhelt Johansen, Nina Aagaard PoulsenAbstract:Abstract Casein (CN) micelle size has been suggested as important for stability of ultra-high temperature (UHT) treated Milk. Therefore, full fat Milk samples were pooled according to native CN micelle size (small, intermediate and large CN micelles), homogenised and UHT treated, and stored at 20 °C or 40 °C for up to 6 months to study storage stability. Small average CN micelle size was associated with higher relative content of κ-CN B and glycosylated κ-CN. Processing increased particle size in the skimmed Milk, resulting in comparable sizes, regardless of initial size. Major changes in physicochemical properties were observed for all Milk pools directly after processing and during storage, greater at elevated storage temperature. Interestingly, Milk with small CN micelles before processing displayed significantly less formation of sediment during storage compared with Milk with intermediate or large CN micelles, suggesting that inherent variation in Milk quality is important for UHT Milk stability.
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Maillard reaction progress in UHT Milk during storage at different temperature levels and cycles
International Dairy Journal, 2018Co-Authors: Anne Vuholm Sunds, Valentin Maximillian Rauh, John Aasted Sørensen, Lotte Bach LarsenAbstract:Abstract Elevation and fluctuation in storage temperature of UHT Milk can result in chemical reactions that may affect quality; hence understanding changes related to shelf-life conditions is of high value for the dairy industry in improvement of storage stability and quality control. A study on progress of Maillard related quality parameters was thus carried out on skimmed and full fat UHT Milk stored for 24 weeks at various temperatures. All three stages of Maillard reaction were possible to describe in Arrhenius plots, and data obtained provided temperature sensitivities and kinetics, with the intermediate phase being the most temperature sensitive. Fluctuations in temperature are often encountered during export and storage of UHT products, therefore temperature cycles were included to somehow simulate real life conditions. The effect of temperature cycles was most pronounced at higher temperatures resulting in increased reaction rates and revealed different temperature dependencies of the Maillard reaction.
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correlation between sensory properties and peptides derived from hydrolysed lactose UHT Milk during storage
International Dairy Journal, 2017Co-Authors: Soren Drudheydary Nielsen, Therese Jansson, Valentin Rauh, John Sørensen, Ulrik Kraemer Sundekilde, Nina Eggers, Henrik J Andersen, Sidsel Jensen, Hanne Christine Bertram, Lotte Bach LarsenAbstract:Abstract The effects of storage conditions on the shelf-life of hydrolysed-lactose ultra-high-temperature (UHT) Milk was evaluated using proteomics. Lactose content was initially reduced to approximately 40% by ultra- and nanofiltration before hydrolysis. Increased peptide and amino acid levels were observed in the Milk over a seven-month storage period at room temperature. Potentially bitter peptides (Q-value > 1400 cal mol −1 ) increased in levels from 86 to 116 days of storage, which coincided with the shelf-life (three months) of this Milk, as found by sensory analysis. Sensory descriptive analysis was used to describe the sensory characteristics of the Milk during storage. Bitterness intensity significantly increased over time and was correlated with the level of peptides released via either enzymatic (proteolytic side activity of the enzyme used in lactose hydrolysis) or non-enzymatic pathways (heat and storage induction). This study reveals a relationship between proteolysis and decreased shelf-life of hydrolysed-lactose UHT Milk compared with conventional UHT Milk.
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protein lactosylation in UHT Milk during storage measured by liquid chromatography mass spectrometry and quantification of furosine
International Journal of Dairy Technology, 2015Co-Authors: Valentin Rauh, Marie Paulsson, Lotte Bach Larsen, Lene Buhelt Johansen, Richard Ipsen, Mette Bakman, Marianne HammershojAbstract:The initial stage of the Maillard reaction, protein lactosylation, occurs during heat treatment of Milk and continues during subsequent storage. We compared the initial lactosylation as well as the rate of lactosylation of Milk proteins during storage in UHT Milk subjected to direct or indirect heat treatment using liquid chromatography (LC) coupled with electrospray injection mass spectrometry (ESI-MS). Furosine content was used as an overall marker to allow for a quantitative correlation of lactosylation measured by LC-ESI-MS in the UHT Milks. Protein lactosylation increased during the storage period of 6months at 20 degrees C. Both the initial extent and the rate of lactosylation positively correlated with the number of lysine residues in the different proteins. An exponential or linear correlation with furosine concentration could be established for major and minor lactosylated proteins, respectively. (Less)
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chemical and proteolysis derived changes during long term storage of lactose hydrolyzed ultrahigh temperature UHT Milk
Journal of Agricultural and Food Chemistry, 2014Co-Authors: Therese Jansson, Lotte Bach Larsen, Morten Rahr Clausen, Ulrik Kraemer Sundekilde, Nina Eggers, Colin Ray, Henrik J Andersen, Hanne Bak Jensen, Hanne Christine BertramAbstract:Proteolytic activity in Milk may release bitter-tasting peptides and generate free amino terminals that react with carbohydrates, which initiate Maillard reaction. Ultrahigh temperature (UHT) heat treatment inactivates the majority of proteolytic enzymes in Milk. In lactose-hydrolyzed Milk a β-galactosidase preparation is applied to the Milk after heat treatment, which has proteolytic side activities that may induce quality deterioration of long-term-stored Milk. In the present study proteolysis, glycation, and volatile compound formation were investigated in conventional (100% lactose), filtered (60% lactose), and lactose-hydrolyzed (<1% lactose) UHT Milk using reverse phase high-pressure liquid chromatography–mass spectrometry, proton nuclear magnetic resonance, and gas chromatography–mass spectrometry. Proteolysis was observed in all Milk types. However, the degree of proteolysis was significantly higher in the lactose-hydrolyzed Milk compared to the conventional and filtered Milk. The proteins most pr...
Jun Wang - One of the best experts on this subject based on the ideXlab platform.
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occurrence of tetracyclines sulfonamides sulfamethazine and quinolones in pasteurized Milk and UHT Milk in china s market
Food Control, 2014Co-Authors: Yi Zhang, N. Zheng, Rongwei Han, Baodong Zheng, S S Zheng, Jun WangAbstract:This study examines 94 samples of ultra high temperature (UHT) Milk and 26 samples of pasteurized Milk from China's top dairy brands (I, II, III, IV), using the ELISA method to assess their contamination with tetracyclines, sulfonamides, sulfamethazine and quinolones. All of the samples were collected from China's market in September 2010. The percentage of UHT Milk samples containing detectable levels of tetracyclines, sulfonamides, sulfamethazine and quinolones were 0%, 20.2%, 7.4% and 95.7%, respectively, and 7.7%, 15.4%, 0% and 61.5%, respectively, in pasteurized Milk samples. The maximum concentrations of the tetracyclines, sulfonamides, sulfamethazine and quinolones in all liquid Milk samples were 47.7 μg kg−1, 20.24 μg kg−1, 14.62 μg kg−1 and 20.49 μg kg−1, respectively. None of the samples exceeded the maximum residue levels (MRLs) set by China, the European Union (EU) and the Codex Alimentarius Commission (CAC). However, because of the high detection rates of some veterinary drug residues in the liquid Milk, stringent control measurements for these residues need to remain in effect, in order to guarantee that the Milk is safe for people to drink.
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Occurrence of aflatoxin M1 in UHT Milk and pasteurized Milk in China market
Food Control, 2013Co-Authors: N. Zheng, P. Sun, Jun Wang, Y.p. Zhen, R.w. HanAbstract:In the present study, the contamination of aflatoxin M1 (AFM1) in 153 UHT Milk samples collected in July and September 2010, and 26 pasteurized Milk samples collected in September 2010, were assessed using the ELISA method. The AFM1 was detected in 54.9% of UHT Milk samples with a concentration of 0.006–0.160 μg/L. Moreover, 96.2% of pasteurized Milk samples tested positive for AFM1 with concentration levels of 0.023–0.154 μg/L. The occurrence of AFM1 in all positive samples was far below China's national legal limit of 0.5 μg/L. Meanwhile, the AMF1 content in 20.3% of UHT Milk samples and 65.4% of pasteurized Milk samples exceeds the European Union's legal limit of 0.05 μg/L.
Therese Jansson - One of the best experts on this subject based on the ideXlab platform.
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Effect of green tea catechins on physical stability and sensory quality of lactose-reduced UHT Milk during storage for one year
International Dairy Journal, 2019Co-Authors: Therese Jansson, Valentin Rauh, Sandra S. Waehrens, John Sørensen, Mikael Agerlin Petersen, Wender L P Bredie, Bente Danielsen, Marianne N. LundAbstract:Abstract Ultra-high temperature (UHT) processed lactose-reduced Milk containing added green tea extract (GTE) at two concentrations (0.1% and 0.25%) was stored at 22 ± 2 °C for one year. The effect of GTE addition on physical stability, protein binding, and sensory quality was evaluated. Sedimentation in skim Milk and creaming of full fat Milk were inhibited by addition of GTE. The formation of Maillard-related flavour compounds was inhibited during storage as determined by dynamic headspace GC–MS. Using Western blot analysis, Milk proteins were found to be highly conjugated to polyphenols. Addition of GTE before UHT treatment resulted in increased bitterness and astringency in UHT Milk and this remained during storage. Even though GTE addition improved the physical stability and inhibited Maillard reactions in the Milk, the taste and flavour contribution from GTE was dominating throughout storage, and alternative sources of polyphenols should be explored for increasing shelf-life stability of long-life Milk.
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correlation between sensory properties and peptides derived from hydrolysed lactose UHT Milk during storage
International Dairy Journal, 2017Co-Authors: Soren Drudheydary Nielsen, Therese Jansson, Valentin Rauh, John Sørensen, Ulrik Kraemer Sundekilde, Nina Eggers, Henrik J Andersen, Sidsel Jensen, Hanne Christine Bertram, Lotte Bach LarsenAbstract:Abstract The effects of storage conditions on the shelf-life of hydrolysed-lactose ultra-high-temperature (UHT) Milk was evaluated using proteomics. Lactose content was initially reduced to approximately 40% by ultra- and nanofiltration before hydrolysis. Increased peptide and amino acid levels were observed in the Milk over a seven-month storage period at room temperature. Potentially bitter peptides (Q-value > 1400 cal mol −1 ) increased in levels from 86 to 116 days of storage, which coincided with the shelf-life (three months) of this Milk, as found by sensory analysis. Sensory descriptive analysis was used to describe the sensory characteristics of the Milk during storage. Bitterness intensity significantly increased over time and was correlated with the level of peptides released via either enzymatic (proteolytic side activity of the enzyme used in lactose hydrolysis) or non-enzymatic pathways (heat and storage induction). This study reveals a relationship between proteolysis and decreased shelf-life of hydrolysed-lactose UHT Milk compared with conventional UHT Milk.
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chemical and proteolysis derived changes during long term storage of lactose hydrolyzed ultrahigh temperature UHT Milk
Journal of Agricultural and Food Chemistry, 2014Co-Authors: Therese Jansson, Lotte Bach Larsen, Morten Rahr Clausen, Ulrik Kraemer Sundekilde, Nina Eggers, Colin Ray, Henrik J Andersen, Hanne Bak Jensen, Hanne Christine BertramAbstract:Proteolytic activity in Milk may release bitter-tasting peptides and generate free amino terminals that react with carbohydrates, which initiate Maillard reaction. Ultrahigh temperature (UHT) heat treatment inactivates the majority of proteolytic enzymes in Milk. In lactose-hydrolyzed Milk a β-galactosidase preparation is applied to the Milk after heat treatment, which has proteolytic side activities that may induce quality deterioration of long-term-stored Milk. In the present study proteolysis, glycation, and volatile compound formation were investigated in conventional (100% lactose), filtered (60% lactose), and lactose-hydrolyzed (<1% lactose) UHT Milk using reverse phase high-pressure liquid chromatography–mass spectrometry, proton nuclear magnetic resonance, and gas chromatography–mass spectrometry. Proteolysis was observed in all Milk types. However, the degree of proteolysis was significantly higher in the lactose-hydrolyzed Milk compared to the conventional and filtered Milk. The proteins most pr...
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lactose hydrolyzed Milk is more prone to chemical changes during storage than conventional ultra high temperature UHT Milk
Journal of Agricultural and Food Chemistry, 2014Co-Authors: Therese Jansson, Lotte Bach Larsen, Morten Rahr Clausen, Ulrik Kraemer Sundekilde, Nina Eggers, Steffen Nyegaard, Colin Ray, Anja Sundgren, Henrik J Andersen, Hanne C BertramAbstract:The enzymatic hydrolysis of lactose to glucose and galactose gives rise to reactions that change the chemistry and quality of ambient-stored lactose-hydrolyzed ultra-high-temperature (UHT) Milk. The aim of the present study was to investigate and compare chemical changes in lactose-hydrolyzed and conventional UHT Milk during a 9 month ambient storage period. Several complementary analyses of volatiles, free amino acids, acetate, furosine, and level of free amino terminals were concluded. The analyses revealed an increased level of free amino acids and an increased formation rate of specific compounds such as furosine and 2-methylbutanal in lactose-hydrolyzed UHT Milk compared to conventional UHT Milk during storage. These observations indicate more favorable conditions for Maillard and subsequent reactions in lactose-hydrolyzed Milk compared to conventional UHT Milk stored at ambient temperature. Furthermore, it is postulated that proteolytic activity from the lactase-enzyme preparation may be responsible...
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volatile component profiles of conventional and lactose hydrolyzed UHT Milk a dynamic headspace gas chromatography mass spectrometry study
Dairy Science & Technology, 2014Co-Authors: Therese Jansson, Lotte Bach Larsen, Morten Rahr Clausen, Nina Eggers, Colin Ray, Anja Sundgren, Henrik J Andersen, Sidsel Jensen, Hanne C BertramAbstract:Lactose-hydrolyzed Milk gains still increasing market share, and understanding the chemical characteristics of lactose-hydrolyzed Milk products is important for the dairy industry. The aim of the present study was to identify and compare volatile compounds of commercial lactose-hydrolyzed and conventional ultra-high temperature (UHT) Milk. For this purpose, the volatile compounds of lactose-hydrolyzed (<1% lactose), conventional (100% lactose), and filtered (60% lactose) UHT-treated Milk were extracted using dynamic headspace sampling and analyzed by gas chromatography-mass spectrometry (GC-MS). A total of 24 volatile compounds were identified including ketones, aldehydes, and sulfides. Overall, principal component analysis (PCA) showed grouping of the different Milk types, with loadings indicating a higher concentration of ketones in conventional versus lactose-hydrolyzed UHT Milk, but PCA also indicated a marked batch-to-batch variation. Elucidation of individual volatile compounds detected also revealed that the content of ketones in general was higher in conventional UHT Milk than in lactose-hydrolyzed Milk; however, no significant differences in the volatile compound profiles could be identified between the various Milk types as a result of the batch-to-batch variation. The present study highlights a useful analytical method based on dynamic headspace sampling and GC-MS to profile volatiles important for the flavor characteristics of lactose-hydrolyzed and conventional UHT Milk. In addition, the present study reveals that a considerable batch-to-batch variation exists in industrially produced batches of lactose-hydrolyzed UHT Milk, which must be considered an important challenge for the dairy industry.
Hilton C. Deeth - One of the best experts on this subject based on the ideXlab platform.
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the effect of UHT processing and storage on Milk proteins
2020Co-Authors: Hilton C. DeethAbstract:UHT Milk is produced by a high-temperature process and is stored at room temperature, which can be up to 50°C, for several months. Both of these factors cause considerable changes to the Milk proteins. Many of the changes have little or no effect on the organoleptic and nutritional attributes of the product. Such changes include whey protein denaturation, lactosylation, deamidation, and polymerization. However, other changes such as proteolysis can cause flavor and textural defects. Defects include bitterness, gelation, sedimentation, and fat separation. This chapter explores the several changes that occur in the proteins in UHT Milk during both processing and storage and discusses ways in which the adverse changes can be minimized or prevented.
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UHT Milk contains multiple forms of αs1 casein that undergo degradative changes during storage
Food Chemistry, 2012Co-Authors: John W Holland, Hilton C. Deeth, Rajesh Gupta, Paul F AlewoodAbstract:Milk proteins are susceptible to chemical changes during processing and storage. We used proteomic tools to analyse bovine αS1-casein in UHT Milk. 2-D gels of freshly processed Milk αS1-casein was presented as five or more spots due to genetic polymorphism and variable phosphorylation. MS analysis after phosphopeptide enrichment allowed discrimination between phosphorylation states and genetic variants. We identified a new alternatively-spliced isoform with a deletion of exon 17, producing a new C-terminal sequence, K164SQVNSEGLHSYGL177, with a novel phosphorylation site at S174. Storage of UHT Milk at elevated temperatures produced additional, more acidic αS1-casein spots on the gels and decreased the resolution of minor forms. MS analysis indicated that non-enzymatic deamidation and loss of the N-terminal dipeptide were the major contributors to the changing spot pattern. These results highlight the important role of storage temperature in the stability of Milk proteins and the utility of proteomic techniques for analysis of proteins in food.
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Improved Shelf Life Estimation of UHT Milk by Prediction of Proteolysis
Journal of Food Quality, 2011Co-Authors: P. D. Button, H. Roginski, Hilton C. Deeth, H M CravenAbstract:During growth in raw Milk, many psychrotrophic bacteria produce proteases that can retain activity following ultra-high temperature (UHT) treatment. In this study, casein and skim Milk powder assays for detecting very low levels of protease in UHT Milk were optimized, and the suitability of azocasein and fluorescein isothiocyanate-casein (FITC-casein) as substrates was investigated. The strongest correlations of protease activity with proteolysis in stored UHT Milk were observed when FITC-casein was used as substrate in the assays. Assays using casein and FITC-casein as substrates yielded the highest activities. To determine sensitivity, crude protease was added at low concentrations to UHT Milk, and the Milk was assayed for progress of proteolysis over 12 months and for protease activity using the casein and FITC-casein assays. With long assay incubation times, the FITC-casein assay was more sensitive than the casein assay and may be suitable for detecting very low levels of protease activity and predicting progress of proteolysis in stored UHT whole Milk.
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cross linking of proteins and other changes in UHT Milk during storage at different temperatures
Australian Journal of Dairy Technology, 2008Co-Authors: Jasim M S Alsaadi, Hilton C. DeethAbstract:Many chemical changes take place in UHT Milk during storage. In this work UHT Milk was stored at different temperatures (5°C, 20°C, 37°C and 45°C) for 12 weeks and assessed for pH, browning, proteolysis and protein changes by HPLC, PAGE and lysinoalanine determination. There was a greater decrease in pH and increase in browning, due to Maillard reactions, and proteolysis in samples stored at 37°C and 45°C than in samples stored at 5°C and 20°C; these changes were positively related to both time and temperature of storage. The RP-HPLC chromatogram of the proteins in the UHT Milk samples stored at 45°C changed considerably during storage and at the end of 12 weeks' storage was completely different from that of a sample stored at 5°C, indicating that considerable change takes place in the proteins of samples stored at elevated temperature. Lysinoalanine concentration, an indicator of covalent, non-disulfide cross-linking of proteins, increased with storage temperature and time. The cross-linking was also observed by reduced SDS-PAGE from which the percentages of cross-linked Milk proteins were estimated to be 1.1%, 1.3%, 7.0% and 36.8% after 12 weeks' storage at 5°C, 20°C, 37°C and 45°C, respectively.
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Diagnosing the cause of proteolysis in UHT Milk
LWT - Food Science and Technology, 2003Co-Authors: Nivedita Datta, Hilton C. DeethAbstract:Proteolysis of UHT Milk during storage at room temperature is a major factor limiting its shelf-life through changes in its flavour and texture. The latter is characterised by increases in viscosity leading in some cases to gel formation. The enzymes responsible for the proteolysis are the native Milk alkaline proteinase, plasmin, and heat-stable, extracellular bacterial proteinases produced by psychrotrophic bacterial contaminants in the Milk prior to heat processing. These proteinases react differently with the Milk proteins and produce different peptides in the UHT Milk. In order to differentiate these peptide products, reversed-phase HPLC and the fluorescamine method were used to analyse the peptides soluble in 12% trichloroacetic acid (TCA) and those soluble at pH 4.6. The TCA filtrate showed substantial peptide peaks only if the Milk was contaminated by bacterial proteinase, while the pH 4.6 filtrate showed peptide peaks when either or both bacterial and native Milk proteinases caused the proteolysis. Results from the fluorescamine test were in accordance with the HPLC results whereby the TCA filtrate exhibited significant proteolysis values only when bacterial proteinases were present, but the pH 4.6 filtrates showed significant values when the Milk contained either or both types of proteinase. A procedure based on these analyses is proposed as a diagnostic test for determining which type of proteinase - Milk plasmin, bacterial proteinase, or both - is responsible for proteolysis in UHT Milk. © 2003 Swiss Society of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.
Frederic Gaucheron - One of the best experts on this subject based on the ideXlab platform.
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Proteolysis of casein micelles by heat-stable protease secreted by Serratia liquefaciens leads to the destabilisation of UHT Milk during its storage
International Dairy Journal, 2017Co-Authors: François Baglinière, Julien Jardin, Antônio Fernandes De Carvalho, Frederic Gaucheron, Maria Cristina Dantas VanettiAbstract:Abstract Serratia liquefaciens is a psychrotrophic species, frequently found in raw Milk, which secretes Ser2, a heat-resistant protease. Involvement of this species in UHT Milk destabilisation was investigated in the present study. Microfiltered Milk was inoculated independently with strains S. liquefaciens L53 or L64. Then, UHT treatment was performed and stability of the corresponding UHT Milk was investigated during three months of storage. The residual proteolytic activity of strain L53 led to destabilisation of UHT Milk, with sedimentation and formation of aggregates. Hydrolysis of casein micelles was confirmed by the increase in the content of non-casein nitrogen and the identification of numerous peptides coming from the four caseins using mass spectrometry. For strain L64, no visual and biochemical alteration were found. This study showed that Ser2 resists UHT treatment and could be a cause of UHT Milk destabilisation; however, this destabilisation by S. liquefaciens was strain-dependent.
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Ser2 from Serratia liquefaciens L53: A new heat stable protease able to destabilize UHT Milk during its storage
Food Chemistry, 2017Co-Authors: François Baglinière, Gaëlle Tanguy, Rafael Locatelli Salgado, Marielle Harel-oger, Benoît Robert, Julien Jardin, Maria Cristina Dantas Vanetti, Florence Rousseau, Frederic GaucheronAbstract:Abstract The heat-stable protease Ser2 is secreted by the species Serratia liquefaciens, a psychrotrophic bacteria frequently found in raw Milk. To understand the physicochemical modifications of casein micelles induced by Ser2 and to confirm its implication in UHT Milk destabilization, the enzyme was purified and added to microfiltered raw Milk before UHT treatment. UHT Milk destabilization was investigated during 90 days of storage. A visual destabilization appeared after 8 days of storage with the presence of sediment. Zeta potential increase and formation of aggregates were observed during the storage. Using tandem mass spectrometry, numerous released peptides from the four caseins were identified at the end of storage. Caseins were hydrolyzed in the preferential order β- > αs1- > κ- > αs2. No specific peptidic hydrolysed bond was detected. The present study confirmed that the presence of the protease Ser2 in raw Milk can be one of the main causes of UHT Milk destabilization.
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Proteolysis of Milk proteins by AprX, an extracellular protease identified in [i]Pseudomonas[/i] LBSA1 isolated from bulk raw Milk, and implications for the stability of UHT Milk
International Dairy Journal, 2015Co-Authors: Aurélie Matéos, François Baglinière, Julien Jardin, Frederic Gaucheron, Muriel Guyard, Annie Mourot, Gérard Humbert, Jean-luc GaillardAbstract:UHT Milk made from Milk contaminated by Pseudomonas LBSA1 destabilised during storage. Sedimentation of UHT Milk was observed; zeta potential of casein micelles decreased, while contents of noncasein nitrogen and non-protein nitrogen increased. Pseudomonas LBSA1 produced an extracellular protease that hydrolysed caseins but not whey proteins; this was identified as AprX, a thermoresistant protease belonging to the serralysin family. This protease showed a broad range of pH activity (pH 6 to pH 10) and an optimal temperature of activity of 40 C. Peptides released from purified aS1-, b- and kcaseins were determined by tandem mass spectrometry. The identified cleavage sites did not reveal a strong specificity of the extracellular protease. However, the presence of basic or aromatic amino acid residues in the P1 position had a positive influence on cleavage in comparison with acidic amino acid residues or proline.
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Effects of storage temperature on physico-chemical characteristics of semi-skimmed UHT Milk
Food Hydrocolloids, 2008Co-Authors: Isabelle Gaucher, Daniel Mollé, Valérie Gagnaire Soumet, Frederic GaucheronAbstract:Storage of UHT Milk results in physico-chemical changes, which can sometimes lead to aggregation or sedimentation of Milk. In this study, close attention was paid to the reactions occurring in semi-skimmed UHT Milk during 6 months of storage at 4, 20 and 40 1C. Overall Milk characterization revealed the development of the Maillard reaction and proteolysis which led to acidification of the Milk. One hundred eighty-one peptides were identified by mass spectrometry for the freshly processed UHT Milk and the Milks stored 6 months at 4, 20 and 40 1C. The cleavage sites gave information concerning the possible actors of proteolysis. Plasmin, cathepsins B, D and G, elastase and proteases from Pseudomonas fluorescens B52 were thus found to be potential contributors to enzymatic proteolysis. Non-enzymatic proteolysis induced by heat-treatment and storage was also observed. Despite these modifications, Milk particles (casein micelles and homogenized fat globules) did not exhibit many changes in zeta-potential, except for the last storage time at 40 1C where a decrease of the absolute value of about -3mV was observed. The decrease in size in Milks stored at 20 and 40 1C was only about 20nm after 6 months. Similarly, storage of UHT Milk showed that the higher the storage temperature the lower the heat stability and the higher the phosphate stability. Storage leads to physico-chemical changes in Milk and, although some reactions such as acidification and proteolysis are known to be destabilizing, some of them are probably stabilizing to counterbalance the negative effects.
