Ultra-high Temperature Milk Research Articles

Comparative study on the microstructure and functional properties of casein in goat milk processed by different methods

SummaryThis work compared the thermal stability, microstructure and functional properties of casein (CN) in goat milk processed by different methods, including homogenisation, low‐temperature long‐time (LTLT), high‐temperature short‐time (HTST), ultrapasteurisation (UP) and ultrahigh temperature (UHT) treatment. The greatest development of CN‐whey protein complexes was observed in LTLT goat milk and the least in HTST goat milk. The CN micelles in LTLT, UP and UHT milk were more obviously changed than the CN micelles in HTST milk, and the random coil content increased significantly after the homogenisation, UP and UHT treatments. The homogenisation had a significant effect on the functional properties of CN. In addition, the most obvious changes in the properties of CN were observed in LTLT and UHT goat milk. The results suggested that homogenisation, pasteurisation and UHT can cause effective changes in the functional properties of CN in goat milk that facilitate its application in the milk industry.

Relationship between casein micelle size, protein composition and stability of UHT milk

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.

Effect of Homogenization Pressure on Plasmin Activity and Mechanical Stress-Induced Fat Aggregation of Commercially Sterilized Ultra High Temperature Milk during Storage.

Commercially sterilized ultra high temperature (UHT) milk was manufactured at different homogenization pressures (20, 25, and 30 MPa), and changes in fat particle size, mechanical stress-induced fat aggregation, plasmin activity, and lipid oxidation were monitored during ambient storage of the UHT milk for up to 16 wk. The particle sizes of milk fat globules were significantly decreased as homogenization pressure increased from 20 to 30 MPa (p<0.05). The presence of mechanical stress-induced fat aggregates in milk produced at 20 MPa was significantly higher than for UHT milk produced at either 25 or 30 MPa. This difference was maintained all throughout the storage. There were no significant differences in plasmin activity, trichloroacetic acid (12%, w/v) soluble peptides, and the extent of lipid oxidation. Based on these results, an increase of homogenization pressure from 20 (the typical homogenization pressure employed in the Korea dairy industry) to 25–30 MPa significantly decreased mechanical stress-induced fat aggregation without affecting susceptibility to lipid oxidation during storage.

Establishing an untargeted-to-MRM liquid chromatography–mass spectrometry method for discriminating reconstituted milk from ultra-high temperature milk

The counterfeit use of reconstituted milk to simulate fresh milk in some countries is largely driven by profiteering; hence, establishing a robust market-surveillance method is an important objective. In this study, an untargeted metabolomics approach that uses ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC–Q-TOF-MS) was established to discover biomarkers that can be used to classify UHT and reconstituted milk. Furthermore, 36 positive- and 24 negative-ionization mode features were selected as candidate markers to establish a UPLC–tandem mass spectrometry (UPLC–MS/MS) multiple reaction monitoring (MRM) method. The support vector machine (SVM) method was used to process the responses of the selected potential markers, and 100% classifiability was observed. The marker metabolites could be divided into three categories by hierarchical clustering analysis: peptides, lipids, and nucleic acids. The results suggest that the untargeted-to-MRM metabolomics method is an effective tool for distinguishing between UHT and reconstituted milk.

Digestion patterns of proteins in pasteurized and ultra-high temperature milk using in vitro gastric models of adult and elderly

Abstract The objective of the current study was to investigate gastric digestibility of milk proteins in an in vitro model of the elderly considering their altered physiological capabilities reported in vivo. Commercial pasteurized and ultra-high temperature (UHT) milks were exposed to in vitro models of the adult and elderly and their protein degradation patterns were investigated during digestion using liquid chromatography-mass spectrometry (LC-MS). Our results showed significant differences in the gastric digestion of milk proteins between the adult and elderly models in pasteurized and UHT milks. For the pasteurized milk, the relative mean abundance of larger peptides (>30 amino acids) was 2.5 fold higher after 60 min in the elderly model than the adult model. The digestion of caseins in the UHT milk in the elderly model occurred with a lower rate under the first 30 min of hydrolysis. Similarly, immunoglobulins showed at least 3 times more effective gastric digestion in the pasteurized milk.

Comparative Genome Analysis of Bacillus sporothermodurans with Its Closest Phylogenetic Neighbor, Bacillus oleronius, and Bacillus cereus and Bacillus subtilis Groups.

Bacillus sporothermodurans currently possesses one of the most highly heat-resistant spores (HRS), which can withstand ultra-high temperature (UHT) processing. Determination of multiple whole genome sequences of B. sporothermodurans provided an opportunity to perform the first comparative genome analysis between strains and with B. oleronius, B. cereus, and B. subtilis groups. In this study, five whole genome sequences of B. sporothermodurans strains, including those belonging to the HRS clone (SAD and BR12) normally isolated from UHT milk, were compared with the aforementioned Bacillus species for gene clusters responsible for heat resistance. In the phylogenomic analysis, B. sporothermodurans, with its closest phylogenetic neighbor, B. oleronius, clustered with B. thermoamylovorans and B. thermotolerans. Heat shock proteins GrpE, GroES, GroEL, and DnaK presented identical sequences for all B. sporothermodurans strains, indicating that differences in functional efficiency are not involved in the thermal resistance variations. However, comparing all species evaluated, B. sporothermodurans exhibited a different gene configuration in the chromosomal region of the heat shock protein GrpE. Furthermore, only B. sporothermodurans strains presented the stage II sporulation protein P gene located in this region. Multisequence alignment and phylogenetic analysis of the ClpB protein showed differences for HRS and non-HRS strains. The study identified ClpC, ClpE, and ClpX as the three ATPases putatively involved in protein disaggregation in B. sporothermodurans. Bacillus sporothermodurans exhibits high homology with other Bacillus species in the DnaK, DnaJ, GroEL, and GroES cluster of genes involved in heat resistance. The data presented here pave the way to select and evaluate the phenotypic effects of genes putatively involved in heat resistance.

Identification of Pseudomonas jessenii and Pseudomonas gessardii as the most proteolytic Pseudomonas isolates in Iranian raw milk and their impact on stability of sterilized milk during storage.

Identification of the most proteolytic Pseudomonas strains that can produce heat-resistant proteases and contribute to the Ultra High Temperature (UHT) milk destabilization is of great interest. In the present study, among the 146 Pseudomonas isolates that encoded the aprX gene, five isolates with the highest proteolytic activity were selected and identified based on 16S rRNA, rpoD and gyrB gene sequences data. The identification results were confirmed by phylogenetic analysis based on multilocus sequence analysis and identified the representative isolates as P. jessenii (two isolates) and P. gessardii (three isolates). Casein zymography demonstrated the ability of these species to produce heat-resistant enzymes, AprX, with molecular mass of about 48 kDa during storage at 7° C for 72 h. In sterilized milk samples, the residual activity of AprX caused a considerable enhancement in the degree of protein hydrolysis, non-protein nitrogen and non-casein nitrogen contents of the samples during a two-month storage. This enhancement was slightly higher in samples containing enzyme produced by P. jessenii compared to P. gessardii ones, resulting in earlier onset of sterilized milk destabilization. Hence, this study revealed that P. jessenii and P. gessardii can play a considerable role in deterioration of Iranian commercial long-life milk.

Investigation of the Applicability of Raman Spectroscopy as Online Process Control during Consumer Milk Production

Online detection of product defects using fast spectroscopic measurements is beneficial for producers in the dairy industry since it allows readjustment of product characteristics or redirection of product streams during production. Raman spectroscopy has great potential for such application due to the fast and simple measurement. Its suitability as online sensor for process control was investigated at typical control points in consumer milk production being raw milk storage, standardization, and heat treatment. Additionally, the appropriateness of Raman spectroscopy to act as indicator for product application parameters was investigated using the example of barista foam. To assess the suitability of a pure online system, the merit of Raman spectra was evaluated by a principal component analysis (PCA). Thereby, proteolytic spoilage due to the presence of extracellular enzymes of Pseudomonas sp. was detected and samples based on the applied heat treatment (extended shelf life (ESL) and ultra-high temperature (UHT)) could be separated. A correlation of the content of free fatty acids and foam stability with spectra of the respective milk samples was found, allowing a prediction of the technofunctional quality criterion “Barista” suitability of a UHT milk. The results underlined the suitability of Raman spectroscopy for the detection of deviations from a defined product standard of consumer milk.

Flavor Characteristics of Low Temperature Long Time (LTLT) and Ultra High Temperature (UHT) Milk

Flavor Characteristics of Low Temperature Long Time (LTLT) and Ultra High Temperature (UHT) Milk

A Survey of 61 Veterinary Drug Residues in Commercial Liquid Milk Products in China

To investigate the drug residue status in commercial liquid milk products in China, 190 samples, including ultrahigh temperature milk (n = 168) and pasteurized milk (n = 22) samples, were collected in 2019. Milk samples were analyzed for the presence of any of the 61 veterinary drugs in them by using a screening assay combined with an ultraperformance liquid chromatography-tandem mass spectrometry analysis. Ten (5.26%) samples were found positive for β-lactams, tetracyclines, and aminoglycosides, and six (3.16%) samples were confirmed residual for penicillin G (n = 6; 3.16%), tetracycline (n = 1; 0.53%), and oxytetracycline (n = 1; 0.53%), with the maximum concentration of 2.85, 40.64, and 12.35 μg kg-1, respectively. Drug residue detection rate in group II (4.55%; the local city domestic brands) was higher than that in group I (2.70%; the major brands of China) and group III (2.78%; the imported brands into China) and higher in domestic samples (3.39%) than that in imported samples (2.78%), and higher in pasteurized milk samples (9.09%) than in ultrahigh temperature milk samples (2.38%). All drug residue levels were far below the regulated maximum residue limits. However, based on some veterinary drug residues detected in the samples, there is a potential veterinary drug risk in liquid milk products in the Chinese market, and this situation deserves the attention of governments and consumers.

Investigation of caprine milk serum proteome and glycated proteome changes during heat treatment using robust ion mobility time-of-flight proteomic techniques

For microbial safety, thermal processing is applied during caprine milk processing, which affects the stability of proteins, specially the whey proteins. Therefore, this study evaluated the changes of glycated serum proteome in caprine milk products using a robust ion mobility time-of-flight proteomic technique, without glycated peptides enrichment. In total, 302 proteins were identified in whey and 41 lactosylation sites from 16 proteins. The number of identified whey proteins decreased from 202 to 194, 178 and 186 in pasteurised milk (PM), spray-dried milk (SDM) and ultra-high temperature (UHT) milk serum, respectively, as the heating intensity increased. Nevertheless, lactosylation sites increased 16 in raw milk to 20 in PM, 25 in UHT and 27 in SDM serum. Moreover, major whey proteins contained the highest number of lactosylation sites as expected. The results of this study may contribute to measurement of the quality of caprine milk after industrial processing.

Trapping of Carbonyl Compounds by Epicatechin: Reaction Kinetics and Identification of Epicatechin Adducts in Stored UHT Milk.

The kinetics of the reaction between epicatechin and various carbonyl compounds typically formed in cooked and stored foods were evaluated in model systems at pH 7.4 and 37 °C, and the corresponding reaction products in stored ultrahigh temperature (UHT) milk-added epicatechin were identified by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The rate constants for the reactions of carbonyl compounds with epicatechin decreased in the following the order: methylglyoxal; 1.6 ± 0.2 M-1 s-1 > glyoxal; (5.9 ± 0.3) × 10-2 M-1 s-1 ≥ 5-(hydroxymethyl)furfural; (4.0 ± 0.2) × 10-2 M-1 s-1 ≥ acetaldehyde; (2.6 ± 0.3) × 10-2 M-1 s-1 ≥ phenylacetaldehyde; (2.1 ± 0.2) × 10-2 M-1 s-1 ≥ furfural; (4.3 ± 0.1) × 10-3 M-1 s-1 > 2-methylbutanal and 3-methylbutanal; ∼0 M-1 s-1. Reaction products generated by epicatechin and methylglyoxal, glyoxal, 5-(hydroxymethyl)furfural, and acetaldehyde were detected in UHT milk samples by incubating milk samples with epicatechin at 37 °C for 24 h. The lack of reaction between epicatechin and phenylacetaldehyde, furfural, 2-methylbutanal, and 3-methylbutanal in stored UHT milk may be due to their slow reaction rates or low concentration in stored UHT milk. It is demonstrated that epicatechin traps 5-(hydroxymethyl)furfural, acetaldehyde, glyoxal, and methylglyoxal and may thereby reduce off-flavor formation in UHT milk during storage both by trapping of precursors (methylglyoxal and glyoxal) for off-flavor formation and by direct trapping of off-flavors.

Prevalence and Antimicrobial Resistance of Bacillus cereus in Milk and Dairy Products

Objective: To investigate the prevalence of Bacillus cereus in milk and dairy products along with detection of its antibiotic sensitivity. Design: Descriptive study. Samples: One hundred and fifty samples of market milk, ultra high temperature milk packs (UHT), condensed milk, Milk powder, Damietta cheese, Kariesh cheese and Ras cheese. Procedures: Samples were examined for isolation and identification of Bacillus spp. via direct and indirect isolation, molecular examination and antimicrobial resistance. Further molecular examination was carried out in 46 isolates to detect hblA, hblC, hblD, nheA, nheB and nheC genes Results: The prevalence of B. cereus by direct isolation was 52%, 13.3 %, 10%, 8%,44%, 0 % and 16% in market milk, ultra high temperature milk packs (UHT) , condensed milk , Milk powder, Damietta cheese, Kariesh cheese and Ras cheese, respectively, whereas its prevalence by indirect isolation was 64%, 20%, 20%, 48%, 52%, 40% and 36% in market milk, ultra high temperature milk packs (UHT) , condensed milk , Milk powder, Damietta cheese, Kariesh cheese and Ras cheese, respectively. B. cereus isolates were 100% resistant to colistin (CT), ampicillin (AM) and amoxicillin (AML). However, 83.01% were resistant to ampicillin-sulbactum (SAM), 67.9% resistant to streptomycin (S), 45.2% resistant to spiramycin (SP), 35.8% resistant to lincomysin (MY), 22.6% resistant to tetracyclin (TE), and 5.6% resistant to erythromycin (E). A prevalence of 58.6% for hblA, hblC and hblD was recorded, while a prevalence of 86.9%, 93.4% and 89.1% for nheA, nheB and nheC was recorded. Conclusion and clinical relevance: This study provides data on prevalence, contamination level and antibiotic sensitivity of B. cereus in milk and its products, suggesting a potential risk to health and the dairy industry.

Prevalence and Antimicrobial Resistance of Bacillus cereus in Milk and Dairy Products

ABSTRACT Objective: To investigate the prevalence of Bacillus cereus in milk and dairy products along with detection of its antibiotic sensitivity. Design: Descriptive study. Samples: One hundred and fifty samples of market milk, ultra high temperature milk packs (UHT), condensed milk, Milk powder, Damietta cheese, Kariesh cheese and Ras cheese. Procedures: Samples were examined for isolation and identification of Bacillus spp. via direct and indirect isolation, molecular examination and antimicrobial resistance. Further molecular examination was carried out in 46 isolates to detect hblA, hblC, hblD, nheA, nheB and nheC genes Results: The prevalence of B. cereus by direct isolation was 52%, 13.3 %, 10%, 8%,44%, 0 % and 16% in market milk, ultra high temperature milk packs (UHT) , condensed milk , Milk powder, Damietta cheese, Kariesh cheese and Ras cheese, respectively, whereas its prevalence by indirect isolation was 64%, 20%, 20%, 48%, 52%, 40% and 36% in market milk, ultra high temperature milk packs (UHT) , condensed milk , Milk powder, Damietta cheese, Kariesh cheese and Ras cheese, respectively. B. cereus isolates were 100% resistant to colistin (CT), ampicillin (AM) and amoxicillin (AML). However, 83.01% were resistant to ampicillin-sulbactum (SAM), 67.9% resistant to streptomycin (S), 45.2% resistant to spiramycin (SP), 35.8% resistant to lincomysin (MY), 22.6% resistant to tetracyclin (TE), and 5.6% resistant to erythromycin (E). A prevalence of 58.6% for hblA, hblC and hblD was recorded, while a prevalence of 86.9%, 93.4% and 89.1% for nheA, nheB and nheC was recorded. Conclusion and clinical relevance: This study provides data on prevalence, contamination level and antibiotic sensitivity of B. cereus in milk and its products, suggesting a potential risk to health and the dairy industry.

Genetic Organization of the aprX-lipA2 Operon Affects the Proteolytic Potential of Pseudomonas Species in Milk.

Psychrotolerant Pseudomonas species are a main cause of proteolytic spoilage of ultra-high temperature (UHT) milk products due to the secretion of the heat-resistant metallopeptidase AprX, which is encoded by the first gene of the aprX-lipA2 operon. While the proteolytic property has been characterized for many different Pseudomonas isolates, the underlying aprX-lipA2 gene organization was only described for a few strains so far. In this study, the phylogenomic analysis of 185 Pseudomonas type strains revealed that the presence of aprX is strongly associated to a monophylum composed of 81 species, of which 83% carried the aprX locus. Furthermore, almost all type strains of known milk-relevant species were shown to be members of the three monophyletic groups P. fluorescens, P. gessardii, and P. fragi. In total, 22 different types of aprX-lipA2 genetic organizations were identified in the genus, whereby 31% of the species tested carried the type 1 operon structure consisting of eight genes (aprXIDEF prtAB lipA2). Other genetic structures differed from type 1 mainly in the presence and location of genes coding for two lipases (lipA1 and lipA2) and putative autotransporters (prtA and prtB). The peptidase activity of 129 strains, as determined on skim milk agar and in UHT-milk, correlated largely with different aprX-lipA2 gene compositions. Particularly, isolates harboring the type 1 operon were highly proteolytic, while strains with other operon types, especially ones lacking prtA and prtB, exhibited significantly lower peptidase activities. In conclusion, the phylogenomic position and the aprX-lipA2 gene organization specify the proteolytic potential of Pseudomonas isolates. In addition, however, an interplay of several environmental factors and intrinsic traits influences production and activity of AprX, leading to strain-specific proteolytic phenotypes.

Iodine contents in conventional ultra-high temperature (UHT) processed cow milk: Changes over the year and regional differences. Implications for epidemiological studies on iodine nutritional status

Background and objectivesUltra-high temperature (UHT) processed cow milk is the milk most commonly consumed in Southwest Europe. The study objectives were: 1) to describe the pattern followed by iodine concentration (IC) in conventional UHT milk over the year, and 2) to find out any differences in IC in this type of milk depending on its geographical origin. Material and methodsBricks of conventional UHT cow milk of commercial brands available in food stores in Vitoria-Gasteiz (Araba/Álava), Basque Country (Spain) were bought for 12 consecutive months, and their ICs were measured using high performance liquid chromatography (HPLC). ResultsMedian (P25-P75) IC in UHT milk (n = 489) was 190 (159–235) µg/L. IC in milk showed great changes over the year, reaching peak values between January and May (241 [201−272] µg/L), and minimal levels between July and November (162 [134–185] µg/L) (P < 0.0001). The IC of milk packed in Germany was significantly lower than that of milks packed in Spain and France, 119 (106–156) µg/L versus 189 (159–229) µg/L and 205 (176–243) µg/L respectively (p < 0.0001). ConclusionsConventional UHT cow milk is a very important nutritional source of iodine, but its IC is highly variable. Knowledge of the pattern followed by IC in milk over the year is of great interest for planning epidemiological studies on iodine nutritional status in schoolchildren and for interpretation of their results.

Prevalence of Milk Fraud in the Chinese Market and its Relationship with Fraud Vulnerabilities in the Chain.

This study aimed to assess the prevalence of ultra-high-temperature (UHT) processed milk samples suspected of being adulterated on the Chinese market and, subsequently, relate their geographical origin to the earlier determined fraud vulnerability. A total of 52 UHT milk samples purchased from the Chinese market were measured to detect possible anomalies. The milk compositional features were determined by standardized Fourier transform-infrared spectroscopy, and the detection limits for common milk adulterations were investigated. The results showed that twelve of the analysed milk samples (23%) were suspected of having quality or fraud-related issues, while one sample of these was highly suspected of being adulterated (diluted with water). Proportionally, more suspected samples were determined among milks produced in the Central-Northern and Eastern areas of China than in those from the North-Western and North-Eastern areas, while those from the South were in between. Combining the earlier collected results on fraud vulnerability in the Chinese milk chains, it appears that increased fraud prevalence relates to poorer business relationships and lack of adequate managerial controls. Since very few opportunities and motivations differ consistently across high and low-prevalence areas, primarily the improvement of control measures can help to mitigate food fraud in the Chinese milk supply chains.

The role of key process steps on microstructural organisation of fat globules and lipid profiles in UHT milk processed in a pilot plant unit

Microscopy was applied to explore changes in fat globules and gas chromatography was used to determine the fatty acid distribution in different lipid classes in ultra-high temperature (UHT) milk processed in a pilot plant. Four milk samples were collected at key steps during UHT-milk production. Second-stage homogenisation significantly decreased fat globule size and disrupted the original milk fat globule membrane (MFGM) organisation. Pasteurisation applied before homogenisation increased the adsorption of casein micelles to the newly formed MFGM. The final UHT treatment for 4 s at 137 °C exacerbated the damage to MFGM causing disruption of fat globules. Damaged fat globules in UHT milk were more prone to aggregation and entrapment in the protein network compared with fat globules in commercial UHT milk. The significant modifications of milk microstructure and lipid composition suggested processes applied in commercial dairy plants might contribute to destabilisation of UHT milk during shelf life.

Multifuntional Gold Nanoparticles for the SERS Detection of Pathogens Combined with a LAMP-in-Microdroplets Approach.

We developed a droplet-based optofluidic system for the detection of foodborne pathogens. Specifically, the loop-mediated isothermal amplification (LAMP) technique was combined with surface-enhanced Raman scattering (SERS), which offers an excellent method for DNA ultradetection. However, the direct SERS detection of DNA compromises the simplicity of data interpretation due to the variability of its SERS fingerprints. Therefore, we designed an indirect SERS detection method using multifunctional gold nanoparticles (AuNPs) based on the formation of pyrophosphate generated during the DNA amplification by LAMP. Towards this goal, we prepared multifunctional AuNPs involving three components with key roles: (1) thiolated poly(ethylene glycol) as stabilizing agent, (2) 1-naphthalenethiol as Raman reporter, and (3) glutathione as a bioinspired chelating agent of magnesium (II) ions. Thus, the variation in the SERS signal of 1-naphthalenethiol was controlled by the aggregation of AuNPs triggered by the complexation of pyrophosphate and glutathione with free magnesium ions. Using this strategy, we detected Listeria monocytogenes, not only in buffer, but also in a food matrix (i.e., ultra-high temperaturemilk) enabled by the massive production of hotspots as a result of the self-assemblies that enhanced the SERS signal. This allowed the development of a microdroplet-LAMP-SERS platform with isothermal amplification and real-time identification capabilities.

Development and application of a multiple reaction monitoring mass spectrometry method for absolute quantification of lysinoalanine and lanthionine in dairy products

Next to the widely studied glycation and Maillard reaction cascade, the heat treatment of milk during production of long shelf-life products may induce side reactions where serine, phosphoserine, glycoserine, cysteine or cystine can be converted into dehydroalanine, which in turn can further react with lysine, histidine or cysteine to yield lysinoalanine (LAL), histidinoalanine (HAL) or lanthionine (LAN) cross-links. The nutritional value, digestibility and functionality of the proteins may be affected by the introduction of covalent cross-links, modified amino acid residues and eventually aggregation. In this study, a liquid chromatography triple quadrupole based method was developed to directly quantify LAL and LAN using multiple reaction monitoring. The method was validated and applied to investigate the content of these cross-links in different dairy products. The level of LAL and LAN was below quantification in raw milk and pasteurised milk, but increasing amounts were measured in ultra-high temperature milk and micellar casein isolate.