Ultra-high Temperature Treatment Research Articles

Experimental and molecular dynamics simulation study on the mechanism of β-lactoglobulin self-aggregation induced by ultra-high temperature

Ultra-high temperature (UHT) treatment effectively prevents milk spoilage, yet it can cause protein aggregation, thereby impacting milk stability. β-Lactoglobulin (β-Lg) is a thermally unstable whey protein, but the mechanism of its self-aggregation induced by UHT treatment remains unclear. Herein, experimental approaches and molecular dynamics simulations were performed to elucidate β-Lg aggregation under UHT. The physicochemical properties of the aggregates were initially characterized after different UHT treatments. Size exclusion chromatography and multi-angle static light scattering showed β-Lg aggregates with molecular weights from 20 to 900 kDa and particle sizes from 100 to 350 nm, with bead string and irregular morphologies. Multispectroscopy showed that UHT treatment caused the unfolding of the β-Lg. Molecular dynamics simulations further observed hydrogen bond disruption and β-barrel opening, enhancing the electrostatic interactions and hydrophobicity of β-Lg surfaces, leading to non-covalent aggregation. Furthermore, SDS-PAGE confirmed the involvement of disulfide bonds in aggregate formation, and mass spectrometry identified the disruption of original disulfide bonds under UHT, promoting intermolecular disulfide bonding involving residues Cys119, Cys121, and Cys160. These findings provide a comprehensive understanding of β-Lg aggregation under UHT conditions, which is essential for improving the stability and quality of UHT-treated milk products.

Effect of ultra-high temperature treatment on the rolled pure molybdenum for nuclear thermal propulsion

Molybdenum (Mo)-based uranium dioxide (UO2) fuel is considered one of the most promising fuel forms for deep-space exploration. The rolling process has been proposed for the preparation of Mo matrix due to its excellent performance. However, there has been limited research on the ultra-high temperature stability of Mo matrix used in nuclear thermal propulsion (NTP). Therefore, in this study, annealing experiments were carried out on rolled Mo plates within a relatively wide temperature range of 1200 to 2300 °C for 1 h to investigate the effects of temperature on the phase composition, microstructure, and mechanical property. The results showed that, despite the body-centered cubic structure of the Mo plates remaining unchanged without undergoing phase transition after high-temperatures, the intensity of the crystal diffraction peaks experienced a significant increase. The preferred growth orientation shifted from the (110) direction at lower temperatures to the (200) direction at 2300 °C. The grain shape of the rolled Mo plates changed from elongated to equiaxed after annealing, and the grain size increased from the initial 1 μm to tens of microns. No discernible surface pores or fracture bubbles were observed when annealed at 1200 to 2100 °C. However, subsequent annealing at 2300 °C revealed a proliferation of polyhedral bubbles, ranging in size from tens of nanometers to several microns, distributed both in grain boundaries and within grains. Nevertheless, there is no apparent change in the density from 1200 to 2300 °C. Bright-field TEM micrographs show that after annealing at 2300 °C, the dislocation density is significantly reduced, and the dislocation shape evolves from screw dislocation to long and straight line. In addition, the Vickers hardness value of the rolled Mo plates undergoes a significant decrease, from 247.1 to 199.6 Hv, after annealing at 1200 °C. Subsequently, in the temperature range of 1200 to 2300 °C, a gradual decline in the hardness value is observed. This work will deepen our understanding of the high-temperature resistance of rolled Mo plates and provide data to support their applications in ultra-high-temperature conditions.

Bioactive Peptides in Dairy Milk: Highlighting the Role of Melatonin.

Melatonin, an endogenous indolamine derived from tryptophan, is primarily synthesized by the pineal gland in mammals and regulated by a complex neural system. Its release follows a circadian rhythm, which is crucial for regulating physiological processes in response to light-dark cycles in both humans and animals. In this review, we report that the presence of this hormone in bovine milk, with significant differences in concentration between daytime and nighttime milking, has increased interest in milk as a natural source of bioactive molecules. Melatonin lowers cortisol levels at night, reduces body temperature and blood pressure, coinciding with decreased alertness and performance, acts as an antioxidant and anti-inflammatory agent, modulates the immune system, offers neuroprotective benefits, and supports gastrointestinal health by scavenging free radicals and reducing oxidative stress in dairy cows. Many factors influence the release of melatonin, such as the intensity of artificial lighting during nighttime milking, the frequency of milkings, milk yield, and genetic differences between animals. Nocturnal milking under low-intensity light boosts melatonin, potentially reducing oxidative damage and mastitis risk. Additionally, ultra-high temperature (UHT) treatment does not significantly affect the melatonin content in milk. However, further research on its stability during milk processing and storage is crucial for ensuring product efficacy. In some countries, nighttime milk with naturally elevated melatonin content is already commercialized as a natural aid for sleep. Thus, naturally melatonin-rich milk may be a promising alternative to synthetic supplements for promoting better sleep and overall well-being.

Age Gelation in Direct Steam Infusion Ultra-High-Temperature Milk: Different Heat Treatments Produce Different Gels.

To investigate the gelation process of direct ultra-high-temperature (UHT) milk, a pilot-scale steam infusion heat treatment was used to process milk samples over a wide temperature of 142-157 °C for 0.116-6 s, followed by storage at 4 °C, 25 °C, and 37 °C. The results of the physicochemical properties of milk showed that the particle sizes and plasmin activities of all milk samples increased during storage at 25 °C, but age gelation only occurred in three treated samples, 147 °C/6 s, 142 °C/6 s, and 142 °C/3 s, which all had lower plasmin activities. Furthermore, the properties of formed gels were further compared and analyzed by the measures of structure and intermolecular interaction. The results showed that the gel formed in the 147 °C/6 s-treated milk with a higher C* value had a denser network structure and higher gel strength, while the 142 °C/6 s-treated milk had the highest porosity. Furthermore, disulfide bonds were the largest contributor to the gel structure, and there were significant differences in disulfide bonds, hydrophobic interaction forces, hydrogen bonds, and electrostatic force among the gels. Our results showed that the occurrence of gel was not related to the thermal load, and the different direct UHT treatments produced different age gels in the milk.

Physiochemical properties, volatile compounds and consumer acceptance of novel ultra-high temperature milk during storage

Ultra-high temperature (UHT) treatment, achieved through direct heating (D-UHT) and indirect heating (ID-UHT), imparts a long shelf-life to milk, allowing for non-refrigerated distribution. This study investigates the impact of a novel D-UHT method (155 °C, 0.5 s) on milk properties, volatile compounds, and consumer acceptance, contrasting it with traditional ID-UHT. Compared to ID-UHT, D-UHT milk showed smaller particle size (0.63–0.65 μm) and reduced whey protein denaturation (43.11–61.54 %). No statistically significant difference in consumer overall liking scores was observed between D-UHT and ID-UHT milk samples (from 5.3 to 5.9; P > 0.05). Emoji-check-all-that-apply analysis revealed a more positive attitude towards D-UHT milk before 1-month storage. Identification of 36 volatile compounds, including 18 aroma-active compounds, in the milk samples facilitated characterization through principal component analysis. The profile of D-UHT milk after a 1-month storage period closely resembled that of raw milk. Our findings suggest that novel D-UHT milk may offer enhanced nutrition and consumer acceptance within the first month, attributed to lower heat exposure and a volatile compound profile resembling raw milk.

Changes in nutritional and technological properties of heat-treated milk and cream at dairy production scale during storage

Changes in nutritional and technological properties during storage of milk and cream subjected to different heat treatments at dairy production scale (high-temperature-short-time pasteurisation, extended shelf-life treatment and ultra-high temperature treatment) were investigated. Results indicate a decrease in pH with longer storage times, whereas no changes in ionic calcium concentration occurred during shorter storage. Vitamin losses ranged from 1 to 22% for different heat treatments and more pronounced effects of vitamin degradation was observed with more intense heat treatment and longer storage times. Vitamin B12 concentration tended to decrease more over time than vitamins B1, B2 and E and more losses in vitamin concentration were found after storage than after heat treatment. Significant effects on physical stability and colour changes in milk and cream were observed during prolonged storage. This suggests that larger changes in nutritional and technological quality of heat-treated milk and cream at dairy production scale occur during longer storage times.

Selenium Decipher: Trapping of Native Selenomethionine-Containing Peptides in Selenium-Enriched Milk and Unveiling the Deterioration after Ultrahigh-Temperature Treatment.

Selenopeptide identification relies on databases to interpret the selenopeptide spectra. A common database search strategy is to set selenium as a variable modification instead of sulfur on peptides. However, this approach generally detects only a fraction of selenopeptides. An alternative approach, termed Selenium Decipher, is proposed in the present study. It involves identifying collision-induced dissociation-cleavable selenomethionine-containing peptides by iteratively matching the masses of seleno-amino acids in selenopeptide spectra. This approach uses variable-data-independent acquisition (vDIA) for peptide detection, providing a flexible and customizable window for secondary mass spectral fragmentation. The attention mechanism was used to capture global information on peptides and determine selenomethionine-containing peptide backbones. The core structure of selenium on selenomethionine-containing peptides generates a series of fragment ions, namely, C3H7Se+, C4H10NSe+, C5H7OSe+, C5H8NOSe+, and C7H11N2O2Se+, with known mass gaps during higher-energy collisional dissociation (HCD) fragmentation. De-selenium spectra are generated by removing selenium originating from selenium replacement and then reassigning the precursors to peptides. Selenium-enriched milk is obtained by feeding selenium-rich forage fed to cattle, which leads to the formation of native selenium through biotransformation. A novel antihypertensive selenopeptide Thr-Asp-Asp-Ile-SeMet-Cys-Val-Lys TDDI(Se)MCVK was identified from selenium-enriched milk. The selenopeptide (IC50 = 60.71 μM) is bound to four active residues of the angiotensin-converting enzyme (ACE) active pocket (Ala354, Tyr523, His353, and His513) and two active residues of zinc ligand (His387 and Glu411) and exerted a competitive inhibitory effect on the spatial blocking of active sites. The integration of vDIA and the iteratively matched seleno-amino acids was applied for Selenium Decipher, which provides high validity for selenomethionine-containing peptide identification.

Ultra-High Temperature Treatment of Liquid Infant Formula, Systemic Immunity, and Kidney Development in Preterm Neonates.

Ready-to-feed liquid infant formulas (IFs) are increasingly being used for newborn preterm infants when human milk is unavailable. However, sterilization of liquid IFs by ultra-high temperature (UHT) introduces Maillard reaction products (MRPs) that may negatively affect systemic immune and kidney development. UHT-treated IF without and with prolonged storage (SUHT) are tested against pasteurized IF (PAST) in newborn preterm pigs as a model for preterm infants. After 5 days, blood leukocytes, markers of systemic immunity and inflammation, kidney structure and function are evaluated. No consistent differences between UHT and PAST pigs are observed. However, SUHT increases plasma TNFα and IL-6 and reduces neutrophils and in vitro response to LPS. In SUHT pigs, the immature kidneys show minor upregulation of gene expressions related to inflammation (RAGE, MPO, MMP9) and oxidative stress (CAT, GLO1), together with glomerular mesangial expansion and cell injury. The increased inflammatory status in SUHT pigs appears unrelated to systemic levels of MRPs. SUHT feeding may impair systemic immunity and affect kidney development in preterm newborns. The systemic effects may be induced by local gut inflammatory effects of MRPs. Optimal processing and length of storage are critical for UHT-treated liquid IFs for preterm infants.

The behavior of cathepsin D during milk processing and its contribution to bitterness in a model fresh cheese

The bovine endopeptidase cathepsin D was investigated regarding its temperature-dependent inactivation and ability to form bitter peptides within a spiked model fresh cheese. Cathepsin D was found to be more susceptible than other milk endogenous peptidases to temperature treatments in skim milk. Inactivation kinetics revealed decimal reduction times of 5.6 min to 10 s in a temperature range from 60 to 80°C. High temperature and ultra-high temperature (UHT) treatments from 90 to 140°C completely inactivated cathepsin D within 5 s. A residual cathepsin D activity of around 20% was detected under pasteurization conditions (72°C for 20 s). Therefore, investigations were done to estimate the effect of residual cathepsin D activity on taste in a model fresh cheese. The UHT-treated skim milk was spiked with cathepsin D and acidified with glucono-δ-lactone to produce a model fresh cheese. A trained bitter-sensitive panel was not able to distinguish cathepsin D-spiked model fresh cheeses from the control model fresh cheeses in a triangle test. Model fresh cheese samples were also analyzed for known bitter peptides derived from casein fractions using a HPLC-tandem mass spectrometry (MS) approach. In accordance with the sensory evaluation, the MS analyses revealed that the bitter peptides investigated within the cathepsin D-spiked model fresh cheese were not found or were below the limit of detection. Even though cathepsin D may be present during the fermentation of pasteurized milk, it does not seem to be responsible for bitter peptide formation from milk proteins on its own.

Effect of vat pasteurization, ultra-high temperature sterilization, retort sterilization and homogenization on soluble proteins in donor human milk detected via proteomics

Donor human milk (DHM) is recommended for preterm infants when a parent's own milk is unavailable or insufficient. To ensure microbiological safety, DHM is processed by donor milk processing companies using vat pasteurization (Vat-PT), ultra-high temperature (UHT) sterilization or retort (RTR) sterilization with and without homogenization. These processes may differentially affect the bioactive proteins in DHM. LC-MS/MS-based proteomics was applied to compare the detection of proteins in the soluble fraction of DHM after Vat-PT, UHT sterilization, RTR sterilization and homogenization in comparison with raw DHM (referred to herein as intact protein survival or retention). Protein retention (based on protein counts and abundances) was higher after Vat-PT than after UHT, and retention was higher after UHT sterilization than after RTR sterilization. Homogenization further decreased protein retention (based on protein counts and abundances) in both UHT- and RTR-treated samples. Representative DHM proteins including lactoferrin, lysozyme, immunoglobulins and caseins had higher retention after Vat-PT (5–57% decrease) than UHT (25–82% decrease) and RTR (54–88% decrease) treatments. These results will guide DHM processing to preserve bioactive proteins and potentially improve infant outcomes.

Changes in the physiochemical, flavor and stability of whey protein solutions during UHT processing and storage: a review

A growing product on the worldwide dairy market is ultra-high temperature (UHT) milk, which can be kept at room temperature for 6 to 9 months. As the milk undergoes either direct or indirect UHT treatment at 140 ℃ for a few seconds, could kill the majority of bacteria and heat-resistance enzymes. The whey protein in milk will experience a series of physiochemical reactions such as denaturation, proteolysis, age gelation, sedimentation and Maillard after UHT treatment and following storage. The aims of this review were to screen occurred reactions in whey protein, allocate the generated flavor and analysis the volatile compounds. This review explained the mechanisms of the physiochemical reactions, and analysed the related flavor and relevant compounds of the flavor. Also, proposing several suggestions to improve UHT milk quality and find out suitable treatment conditions to prevent or minimize the effects of UHT on whey proteins.

Proteolytic activity and heat resistance of the protease AprX from Pseudomonas in relation to genotypic characteristics

AprX is an alkaline metalloprotease produced by Pseudomonas spp. and encoded by its initial gene of the aprX-lipA operon. The intrinsic diversity among Pseudomonas spp. regarding their proteolytic activity is the main challenge for the development of accurate methods for spoilage prediction of ultra-high temperature (UHT) treated milk in the dairy industry. In the present study, 56 Pseudomonas strains were characterized by assessing their proteolytic activity in milk before and after lab-scale UHT treatment. From these, 24 strains were selected based on their proteolytic activity for whole genome sequencing (WGS) to identify common genotypic characteristics that correlated with the observed variations in proteolytic activity. Four groups (A1, A2, B and N) were determined based on operon aprX-lipA sequence similarities. These alignment groups were observed to significantly influence the proteolytic activity of the strains, with an average proteolytic activity of A1 > A2 > B > N. The lab-scale UHT treatment did not significantly influence their proteolytic activity, indicating a high thermal stability of proteases among strains. Amino acid sequence variation of biologically-relevant motifs in the AprX sequence, namely the Zn2+-binding motif at the catalytic domain and the C-terminal type I secretion signaling mechanism, were found to be highly conserved within alignment groups. These motifs could serve as future potential genetic biomarkers for determination of alignment groups and thereby strain spoilage potential.

Thermal stabilisation of cocoa fruit pulp — Effects on sensory properties, colour and microbiological stability

To improve cocoa pulp’s shelf-life, preservation processes are necessary while maintaining the quality of the pulp. We applied pasteurisation and UHT-treatment and investigated different quality parameters: dry matter content, water activity, total soluble solids, colour and peroxidase activity. Both technologies inactivated peroxidase successfully. The colour of the pasteurised pulp was similar to the fresh, while UHT-treated pulp was more brownish. The sensory properties were investigated in detail by descriptive analysis and the identification of aroma-active volatile organic compounds. Fresh pulp revealed the highest aroma intensity for attribute unripe banana-like, whereas UHT-treated pulp scored highest in the intensity of attribute tropical fruit-like. Pasteurised pulp showed strong similarities to the fresh pulp. Fresh cocoa pulp exhibited 74 aroma-active regions identified by GC-MS/O. UHT-treated and pasteurised pulp accounted for 66 and 60 aroma-active regions, respectively. Five identified substances were only found in the fresh and pasteurised pulp, namely: δ-carene, 1-pentanol, 3-(methylthio)propanol, phenol and δ-undecalactone. Similarly, fresh and UHT-treated pulp shared ten exclusive odorants, such as decanal, geraniol, and δ-nonalactone. The pasteurised and UHT-treated pulp shared two compounds, δ–decalactone and 5-(hydroxymethyl)furfural. Furthermore, the thermally treated pulps could be stored at 4 °C and 23 °C for 24 weeks without observing a significant growth of microorganisms. The rate of non-enzymatic browning was higher in samples stored at 23 °C compared to those stored at 4 °C, leading to higher browning indices. We demonstrated that pasteurisation and ultra-high temperature treatment are suitable technologies for the stabilisation of cocoa fruit pulp. These resulted in prolonged shelf-lifes and minimal changes in the sensory prorperties of the treated pulps, characterised by a reduction in the aroma diversities. This work provides important insights for the thermal stabilisation of further side-streams.

High-pressure treatment enhanced aromatic compound concentrations of melon juice and its mechanism.

The flavor deterioration blocks the development of melon juice. The effects of ultra-high temperature (UHT) and high pressure (HP) treatments on the aromatic compound concentrations of melon juice and their mechanisms were explored with fresh juice as the control. A total of 57 volatile compounds were identified by gas chromatography-tandem mass spectrometry analysis. β-ionone was shown to be the major aromatic component of melon juice for the first time. The HP at 200 MPa for 20 min increased the total volatile concentration of melon juice by 1.54 and 3.77 times the control and UHT, respectively. Moreover, the sum concentration of a major aromatic component in the HP treatment was 1.49 and 5.94 times higher than that of the control and UHT, respectively. The HP treatment raised the concentration of volatile and aromatic components of melon juice by reducing their surface tension.

Stacking order reduction in multilayer graphene by inserting nanospacers

Toward macroscopic applications of graphene, it is desirable to preserve the superior properties of single-layer graphene in bulk scale. However, the AB-stacking structure is thermodynamically favored for multilayer graphene and causes strong interlayer interactions, resulting in property degradation. A promising approach to prevent the strong interlayer interaction is the staking order reduction of graphene, where the graphene layers are rotated in-plane to form a randomly stacking structure. In this study, we propose a strategy to effectively decrease the stacking order of multilayer graphene by incorporating nanospacers, cellulose nanofibers, or nano-diamonds (NDs) in the formation process of porous graphene sponges. We conducted an ultrahigh temperature treatment at 1500 °C with ethanol vapor for the reduction and structural repair of graphene oxide sponges with different concentrations of the nanospacers. Raman spectroscopy indicated an obvious increase in the random-stacking fraction of graphene by adding the nanospacers. The x-ray diffraction (XRD) analysis revealed that a small amount of the nanospacers induced a remarkable decrease in ordered graphene crystalline size in the stacking direction. It was also confirmed that a layer-number increase during the thermal treatment was suppressed by the nanospacers. The increase in the random-stacking fraction is attributed to the efficient formation of randomly rotated graphene through the ethanol-mediated structural restoration of relatively thin layers induced by the nanospacers. This stacking-order-reduced graphene with bulk scale is expected to be used in macroscopic applications, such as electrode materials and wearable devices.

Structural and functional changes of bioactive proteins in donor human milk treated by vat-pasteurization, retort sterilization, ultra-high-temperature sterilization, freeze-thawing and homogenization.

BackgroundDonor human milk should be processed to guarantee microbiological safety prior to infant feeding, but this process can influence the structure and quantity of functional proteins.ObjectiveThe aim of this study was to determine the effect of thawing, homogenization, vat-pasteurization (Vat-PT), retort sterilization (RTR) and ultra-high-temperature (UHT) processing on the structure of bioactive proteins in donor milk.MethodsPooled donor milk was either not treated (Raw) or treated with an additional freeze-thaw cycle with and without homogenization, Vat-PT, RTR with and without homogenization, and UHT processing with and without homogenization. Overall protein retention was assessed via sodium-dodecyl sulfate (SDS-PAGE), and the immunoreactivity of 13 bioactive proteins were assessed via enzyme-linked immunosorbent assay (ELISA).ResultsFreeze-thawing, freeze-thawing plus homogenization and Vat-PT preserved all the immunoglobulins (sIgA/IgA, IgG, IgM) in donor milk, whereas RTR and UHT degraded almost all immunoglobulins. UHT did not alter osteopontin immunoreactivity, but Vat-PT and retort decreased it by ~50 and 70%, respectively. Freeze-thawing with homogenization, Vat-PT and UHT reduced lactoferrin's immunoreactivity by 35, 65, and 84%, respectively. Lysozyme survived unaltered throughout all processing conditions. In contrast, elastase immunoreactivity was decreased by all methods except freeze-thawing. Freeze-thawing, freeze-thawing plus homogenization and Vat-PT did not alter polymeric immunoglobulin receptor (PIGR) immunoreactivity, but RTR, RTR plus homogenization and UHT increased detection. All heat processing methods increased α-lactalbumin immunoreactivity. Vat-PT preserved all the growth factors (vascular/endothelial growth factor, and transforming growth factors β1 and β2), and UHT treatments preserved the majority of these factors.ConclusionDifferent bioactive proteins have different sensitivity to the treatments tested. Overall, Vat-PT preserved more of the bioactive proteins compared with UHT or RTR. Therefore, human milk processors should consider the impact of processing methods on key bioactive proteins in human milk.

Ultra-High Temperature Treatment and Storage of Infant Formula Induces Dietary Protein Modifications, Gut Dysfunction, and Inflammation in Preterm Pigs.

Ready-to-feed liquid infant formula is increasingly used for preterm infants when human milk is unavailable. These formulas are sterilized by ultra-high temperature treatment, but heating and storage may reduce bioactivity and increase formation of Maillard reaction products with potential negative consequences for immature newborns. Using preterm pigs as a model for sensitive newborn infants, the study tests the intestinal responses of feeding experimental liquid formula within 5 days. A pasteurized formula (PAST) with the same nutrient composition but less protein modifications serves as control to ultra-high temperature-treated formula without (UHT) and with prolonged storage (SUHT). Relative to PAST, UHT contains lower levels of lactoferrin and IgG. Additional storage (40°C, 60 days, SUHT) reduces antimicrobial capacity and increases non-reducible protein aggregates and Maillard reaction products (up to 13-fold). Pigs fed SUHT have more diarrhea and show signs of intestinal inflammation (necrotizing enterocolitis) compared with pigs fed PAST and UHT. These clinical effects are accompanied by accumulation of Maillard reaction products, protein cross-links, and inflammatory responses in the gut. The results demonstrate that feeding UHT infant formulas, particularly after prolonged storage, adversely affects gut maturation and function in preterm pigs used as a model of preterm infants.

Two-year survey of aflatoxin M1 in milk marketed in Albania, and human exposure assessment

Aflatoxin M1 (AFM1), a metabolite of aflatoxin B1 (AFB1), is detected in milk obtained from ruminants fed AFB1-contaminated feedstuff. Considering the potential risk of aflatoxin exposure for human health, the AFM1 content in milk and dairy products is regularly monitored. A survey on AFM1 contamination in milk from retail markets consumed in Albania was conducted in 2019–2020. A total of 119 cow milk samples, subjected to pasteurization and ultra-high temperature (UHT) treatment, were collected, and the AFM1 content was analyzed using a commercial enzyme-linked immunosorbent assay kit. AFM1 was detected in 62 of the 119 milk samples (52.10%). AFM1 contamination in pasteurized milk was higher than that in UHT milk samples (59.68% and 43.86%, respectively). Although the mean AFM1 concentration for the analyzed samples was 0.022 μg kg−1, the maximum AFM1 content of 0.217 μg kg−1 was found in milk samples collected in the autumn of 2019. Seven milk samples (5.88%) contained AFM1 at levels exceeding the European Union maximum residue permitted level. Overall, milk samples from 2019 had greater AFM1 contamination (81.36%) than those from 2020 (23.33%). The Human Exposure Assessment revealed that the Average Daily Dose (ADD) for adults was 0.082–0.096 ng kg−1 body weight (bw)/day. Also, the ADD was considerably higher in 2019 than in 2020 with no significant difference between the seasons.

Milk lipids characterization in relation to different heat treatments using lipidomics

Heat treatment is an important processing technique related to milk quality and nutritional value in the dairy industry. In this study, changes in milk lipids in response to different heat treatments were comprehensively characterized using a lipidomic approach. Ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) were used to identify and quantify 29 classes and 788 different lipids. In general, heat treatment promoted milk lipid hydrolysis and oxidation; in particular, ultra-high temperature (UHT) treatment resulted in more phospholipid hydrolysis than did pasteurization and extended shelf-life (ESL) treatment. Heat treatment resulted in further lipid oxidation reactions and a reduction in the amount of mild oxidation products. Moreover, the levels of lysophospholipids and free fatty acids (including oxidized free fatty acids) can be used to distinguish UHT-treated milk. In turn, oxidized phosphatidylcholine, oxidized phosphatidylethanolamine, ether-linked phosphatidylethanolamine, diacylglycerol, triacylglycerol, and oxidized triacylglycerol can be used to differentiate raw, pasteurized, and ESL milk. These biomarkers can potentially be used in the dairy industry to monitor the degree and method of heat treatment of milk.

Effect of ultra-high temperature treatment on microstructures and mechanical properties of TRISO particles

Tristructural-isotropic (TRISO) fuel particles have long been widely used in high temperature gas-cooled reactors (HTGR), where their high temperature mechanical integrity and ability to retain fission products even in the accident conditions are the critical safety issues. In the present work, TRISO particles were subjected to ultra-high temperature thermal treatments at 1900, 2000, and 2200 °C, respectively, which were much higher than the projected accident temperature (1620 °C). Phase compositions and microstructures of the samples before and after thermal treatments were studied by X-ray diffraction (XRD), Raman spectroscopy, and Scanning Electron Microscopy (SEM). Nano hardness and Young's modulus of the SiC layer in TRISO particles were studied by nano indentation technique, and crushing strength of the TRISO particles was evaluated by mechanical crush tests. The results show that, there were no obvious temperature effects on phase composition and microstructure, except for SiC layer in the sample thermal treated at 2200 °C, in which many pores caused by SiC decomposition were observed. The nano hardness and Young's modulus values of SiC layer in the as-received and thermally treated TRISO particles were similar within the experimental error. On the other hand, the crushing strength of the thermally treated TRISO particles decreased greatly as compared with the as-received particles, but the crack propagation mode changed from through-the-particle to deflection inside the buffer PyC layer or between buffer PyC and inner PyC (IPyC) layers. The change of crack propagation mode could probably due to the shrinkage of PyC layers due to anisotropy at high temperature and ordering of graphitization of IPyC layers, which probably weakened the interfacial bonding between the IPyC and the buffer PyC layers. The results of this study provide a database reference for the performance of TRISO particles under ultra-high temperature operation and even accident conditions.