UHT Treatment Research Articles

Insight into protein cross-linking and casein polymerization in pre- and post-hydrolyzed lactose-free UHT milk during long-term storage

During processing and storage of both conventional and lactose-hydrolyzed UHT milk (LHM), aggregation of milk proteins occurs. Protein aggregation can inter alia occur via non-reducible covalent cross-links derived from either Maillard or dehydroalanine (DHA) pathways. To study this further in relation to processing method and lactase enzyme purity, LHM was produced using 3 different lactase preparations, with lactase enzymes added in a dairy setting either before (pre-hydrolysis) or after (post-hydrolysis) UHT treatment. The prepared LHM types were subsequently stored at either 25°C or 35°C for up to one year. Mass spectrometry was used to absolutely quantify the level of furosine, N-ɛ-(carboxymethyl)lysine (CML) and N-ɛ-(carboxyethyl)lysine (CEL), lanthionine (LAN) and lysinoalanine (LAL) in these products using a newly developed method on Triple Q for these processing-induced markers. The results showed higher levels of Maillard related processing markers in pre-hydrolyzed LHM compared with post-hydrolyzed LHM and conventional UHT milk which, on the other hand, contained higher concentrations of DHA-derived cross-links. Proteomics of collected particles from asymmetrical flow field-flow fractionation (AsFlFFF) in combination with gel electrophoresis indicated presence of intra-micellar cross-links during storage, for especially larger particles involving αS1- and αS2-caseins.

Advantages of UHT in retaining coconut milk aroma and insights into thermal changes of aroma compounds

Coconut milk products are susceptible to bacterial damage, necessitating sterilization methods that often compromise nutrient and aroma integrity. This study investigates the effects of different thermal sterilisation methods on coconut milk aroma using headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS) and headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS). We assessed the impact of pasteurisation (PAS, 70 °C, 25 min), high-temperature sterilisation (HTS, 121.1 °C, 15 min), and ultra-high temperature sterilisation (UHT, 130 °C, 5 s) through clustered heat maps and correlation analyses. Significant differences were observed (p < 0.05), with 37 and 52 substances detected by HS-GC-IMS and HS-SPME-GC-MS, respectively, identifying 12 key aroma compounds. UHT treatment primarily reduced 8 acids, maintaining a compositional structure and sensory profile similar to raw coconut milk. PAS and HTS treatments decreased the sensory intensity of overall coconut milk aroma, creamy, and floral notes, correlating with the presence of 2-heptanol, nonanal, 4-methylvaleric acid, and 2-tridecanone. These methods increased cooked notes, associated with 5-methyl-3-heptanone, 3-butyn-1-ol, hydroxyacetone, and acetoin. Rancidity was linked to acids such as isobutyric acid, isovaleric acid, and heptanoic acid, with high temperatures effectively reducing these compounds. Prolonged temperature changes in PAS and HTS accelerated lipid oxidative degradation and the Maillard reaction, involving free fatty acids in the formation of alcohols, aldehydes, esters, and lactones. These findings provide a theoretical basis for studying coconut milk flavour deterioration.

Exploration of dynamic interaction between β-lactoglobulin and casein micelles during UHT milk process

The protein aggregation induced by UHT treatment shortens the shelf life of UHT milk. However, the mechanism of β-Lg induced casein micelle aggregation remains unclear. Herein, the dynamic interaction between β-Lg and casein micelles during UHT processing was investigated by experimental techniques and molecular dynamics simulations. Results showed that β-Lg decreased the stability of casein micelles, increased their size and zeta potential. Raman and FTIR spectra analysis suggested that hydrogen and disulfide bonds facilitated their interaction. Cryo-TEM showed that the formation of the casein micelle/β-Lg complex involved rigid binding, flexible linking, and severe cross-linking aggregation during UHT processing. SAXS and MST demonstrated β-Lg bound to κ-casein on micelle surfaces with a dissociation constant (Kd) of 3.84 ± 1.14 μm. Molecular docking and dynamic simulations identified the interacting amino acid residues and clarified that electrostatic and van der Waals forces drove the interaction. UHT treatment increased hydrogen bonds and decreased total binding energy. The non-covalent binding promoted the formation of disulfide bonds between β-Lg and casein micelles under heat treatment. Ultimately, it was concluded that non-covalent interaction and disulfide bonding resulted in casein micelle/β-Lg aggregates. These findings provided scientific insights into protein aggregation in UHT milk.

Differences in development of volatiles and bitter peptides between pre- and post-hydrolysed lactose-free UHT milk during storage

Lactose-hydrolysed UHT milk (LHM) has a limited shelf life, especially due to early browning and off-flavour development. This study aimed to directly compare the development in colour, volatile and bitter peptide formation in pre- (lactase addition prior to UHT treatment) and post-hydrolysed (lactase addition after UHT treatment) milk using three different lactases and stored at 25 or 35 °C for up to one year. Pre-hydrolysed milk exhibited more pronounced browning than post-hydrolysed milk. Furthermore, level of Maillard related compounds like acetic acid and furfural were higher in pre-hydrolysed milk compared to post-hydrolysed milk, whereas post-hydrolysed milk was higher in Strecker aldehyde related volatile organic compounds (VOCs). After storage, level of bitter peptides was higher in post-hydrolysed milk using more impure lactases. Generally, lower VOC concentrations and bitter peptides were observed for LHM produced by more pure lactases suggesting higher purity lactases can aid in the development of ambient long-life LHM.

Destabilization of ultra-instantaneous ultra-high-temperature sterilized milk stored at different temperatures

Ultra-instantaneous UHT (UI-UHT, > 155°C, < 0.1 s) treated milk exhibits higher retention of active protein than regular UHT milk. However, UI-UHT products demonstrate increased susceptibility to destabilization during storage. This study aimed at monitoring the destabilizing process of UI-UHT milk across different storage temperatures and uncovering its potential mechanisms. Compared with regular UHT treatment, ultra-instantaneous treatment markedly accelerated the milk's destabilization process. Aged gel formation occurred after 45 d of storage at 25°C, while creaming and sedimentation were observed after 15 d at 37°C. To elucidate the instability mechanism, measurements of plasmin activity, protein hydrolysis levels, and proteomics of the aged gel were conducted. In UI-UHT milk, plasmin activity, and protein hydrolysis levels significantly increased during storage. Excessive protein hydrolysis at 37°C resulted in sedimentation, while moderate hydrolysis and an increase in protein particle size at 25°C resulted in aged gel formation. Proteomics analysis results indicated that the aged gel from UI-UHT milk contained intact caseins, major whey proteins, and their derived peptides. Furthermore, specific whey proteins including albumin, lactotransferrin, enterotoxin-binding glycoprotein PP20K, and MFGM proteins were identified in the gel. Additionally, MFGM proteins in UI-UHT milk experienced considerable hydrolysis during storage, contributing to fat instability. This study lays a theoretical foundation for optimizing UI-UHT milk storage conditions to enhance the quality of liquid milk products.

Impact of hydrolysis method and lactase preparation on proteolysis and glycation in long-term stored lactose-hydrolysed UHT milk

Shorter shelf-life of lactose-hydrolysed UHT milk (LHM) can be linked to lactase purity both due to unwanted proteolytic activity and Maillard reactions. To study this, pre- and post-hydrolysed milk was added one of three types of lactase enzymes of increasing purity (A, B and C), and stored for up to 1 year at 25 or 35 °C. Proteolytic side-activities in post-hydrolysed milk depended on lactase purity, with lactase A causing the highest proteolysis. The lowest proteolytic activity occurred with lactase C in both pre- and post-hydrolysed milk. LHM with lactase A exhibited proteolysis in C-terminal regions of major milk proteins, particularly in post-hydrolysed milk, which also showed endopeptidase activity. Glycation initiated by UHT treatment was higher in pre-hydrolysed milk than in post-hydrolysed milk, but subsequent storage led to similar glycation levels in both. Therefore, using post-hydrolysis with highly purified lactases, proteolytic side-activities can be lowered and glycation can be delayed.

Interaction of alkaline and acid treatment on the removal of proteinaceous mineral-enriched dairy fouling from UHT treatment

CIP processes in milk processing plants are frequently oversized to reliably meet hygienic and safety requirements. Cleaning follows a fixed protocol, but the exact mechanisms and intermediate products are often unknown. This study presents an experimental approach to elucidate the interaction between alkaline and acidic treatment with special regard to the impact of acid on proteinaceous deposits. The protein containing fouling layers become yellowish in colour by acidic treatment; this is attributed to the xantho-proteic reaction and no efficient removal is thereby achieved. In contrast, the removal is efficient if an efficient initial alkaline treatment step is performed. An efficient initial alkaline treatment step was identified as crucial for the further course of cleaning and a short alkaline treatment soaked the entire soil, which enabled an efficient subsequent acidic removal. Lower concentrations of HNO3 demonstrate more efficient cleaning than higher ones, suggesting an optimum acid concentration during CIP.

Prior denaturation and aggregation of whey proteins: is this a useful strategy for increasing the content of these proteins in UHT high-protein dairy beverages?

UHT treatments applied to dairy products have been associated with modifications on the proteins’ structure that may trigger the occurrence of fouling, sedimentation and/or gelation. These issues are particularly relevant regarding formulated whey protein-rich dairy beverages. In this context, this study aimed to evaluate the impact of a two steps preheating treatment coupled with homogenization (pretreatment) prior to UHT treatment to allow an increase of whey protein concentration in UHT high-protein dairy beverage. The pretreatment was applied to 10% w/w protein formulated beverages displaying casein (CN) to whey protein (WP) ratios of 40:60 and 30:70. The pretreated beverages were compared with non-pretreated beverage containing 50CN:50WP ratio. The applied pretreatment induced the denaturation of around 97.8–99.4% of WP. After UHT treatment, despite the higher concentration of WP, pretreated beverages displayed similar particle size distribution and equivalent or lower sedimentation level than the non-pretreated samples. The present study reveals the potential of the pretreatment for allowing the increase of WP content in UHT treated high-protein beverages. The results reinforce the rationalization of process development as a useful strategy for producing stable high-protein products.

Influence of storage time on protein composition and simulated digestion of UHT milk and centrifugation presterilized UHT milk in vitro

The centrifugation presterilizing UHT (C-UHT) sterilization method removes 90% of the microorganism and somatic cells from raw milk using high-speed centrifugation following UHT treatment. This study aimed to study the changes in protein composition and plasmin in the UHT and C-UHT milk. The digestive characteristics, composition, and peptide spectrum of milk protein sterilized with the 2 technologies were studied using a dynamic digestive system of a simulated human stomach. The Pierce bicinchoninic acid assay, laser scanning confocal microscope, liquid chromatography-tandem mass spectrometry, and AA analysis were used to study the digestive fluid at different time points of gastric digestion in vitro. The results demonstrated that C-UHT milk had considerably higher protein degradation than UHT milk. Different processes resulted during the cleavage of milk proteins at different sites during digestion, resulting in different derived peptides. The results showed there was no significant effect of UHT and C-UHT on the peptide spectrum of milk proteins, but C-UHT could release relatively more bioactive peptides and free AA.

Quantitative microbial spoilage risk assessment of plant-based milk alternatives by Geobacillus stearothermophilus in Europe

Geobacillus stearothermophilus is one of the predominant spoilers of UHT-treated food products, due to its extremely heat-resistant spores. However, the surviving spores should be exposed to temperature higher than their minimum growth temperature for a certain time to germinate and grow to spoilage levels. Considering the projected temperature increase due to climate change, the events of non-sterility during distribution and transportation are expected to escalate. Hence, the aim of this study was to build a quantitative microbial spoilage risk assessment (QMRSA) model to quantify the risk of spoilage of plant-based milk alternatives within Europe. The model consists of four main steps: 1. Initial contamination of raw materials 2. Heat inactivation of spores during UHT treatment 3. Partitioning 4. Germination and outgrowth of spores during distribution and storage. The risk of spoilage was defined as the probability of G. stearothermophilus to reach its maximum concentration (Nmax = 107.5 CFU/mL) at the time of consumption. The assessment was performed for North (Poland) and South (Greece) Europe, and the risk of spoilage was estimated for the current climatic conditions and a climate change scenario. Based on the results, the risk of spoilage was negligible for the North European region, while the risk of spoilage in South Europe was 6.2 × 10−3 95% CI (2.3 × 10−3;1.1 × 10−2) under the current climatic conditions. The risk of spoilage was increased for both tested countries under climate change scenario; from zero to 1.0 × 10−4 in North Europe, risk multiplied 2 or 3 in South Europe depending on air conditioning implementation at consumer’s place. Therefore, the heat treatment intensity and the use of insulated trucks during distribution were investigated as mitigation strategies and led to significant reduction of the risk. Overall, the QMRSA model developed in this study can support risk management decisions of these products by quantify the potential risk under current climatic conditions and climate change scenarios.

Peptidomic Fingerprints of Stored UHT Milk Inoculated with Protease Extracts from Different Pseudomonas Strains Relative to aprX Expression and Visible Spoilage

Lately, concern about the protease AprX produced by Pseudomonas has increased in the dairy industry due to its ability to survive UHT treatment and spoil UHT milk. Efficient prediction methods for UHT milk spoilage are currently lacking, mainly due to high diversity in proteolytic potential between Pseudomonas strains. The present study aimed to gain more insight into the variability between Pseudomonas strains regarding proteolytic potential by comparing their proteolytic capability with their aprX expression levels and differences in peptide formation. The variability in aprX expression levels in four Pseudomonas strains were related to physical stability, milk proteolysis and peptidomic cleavage patterns of milk proteins in a storage experiment of UHT milk inoculated with protease extracellular extracts and stored for 45 days at 20 °C. A positive relationship was observed between the relative expression of aprX and milk proteolysis during storage, with the strain Pseudomonas panacis DSM 18529 showing the highest level in both parameters. This strain was the only strain to show visual gelation, which occurred after 21 days. The peptide formation analysis showed a similar protein hydrolysis pattern between strains and high hydrolysis of αs1-caseins during long-term spoilage putatively due to the activity of AprX was observed.

Exploration of interaction between α-lactalbumin and β-lactoglobulin under dUHT treatment and storage: Experimental and molecular dynamics study

Direct ultra-high temperature (dUHT) milk is considered as the next generation of liquid milk product because it keeps more nutritional ingredients and better flavor than UHT milk. However, sedimentation and age gelation are urgent problems to develop dUHT milk. The role of whey protein interaction in the destabilization of dUHT milk is rarely reported. In this study, the interaction between α-lactalbumin (α-La) and β-lactoglobulin (β-Lg) was investigated by thermodynamics, spectroscopy and silico approach at 75 °C (preheat), 145 °C (dUHT) and 37 °C (storage). The results showed that α-La could interact with β-Lg via hydrophobicity along with exothermic reaction. During dUHT and storage, the average molecular weight (MW) distribution of α-La/β-Lg complexes increased from 20.3 kDa to 274.4 kDa. The particle size increased from 135.53 ± 5.26 nm to 153.50 ± 3.83 nm and the zeta potential decreased from −27.80 ± 5.90 mV to −7.73 ± 2.65 mV. Fibrous cluster-like protein bridges promoted the formation of α-La/β-Lg aggregates. The interaction mechanism between α-La and β-Lg was explored by molecular docking and dynamics simulations. It was found that heat treatment reduced the binding free energy of α-La and β-Lg and promoted the formation of α-La/β-Lg complexes. Electrostatic and van der Waals were the main energy contributors to the binding. UHT treatment increased the number of hydrogen bonds and weakened the hydrophobic interaction. These findings indicate that the interaction between α-La and β-Lg forms aggregates during heat treatment and storage, which help to optimize process and storage of dUHT milk.

PH-dependent sedimentation and protein interactions in ultra-high-temperature-treated sheep skim milk

Sheep milk is considered unstable to UHT processing, but the instability mechanism has not been investigated. This study assessed the effect of UHT treatment (140°C/5 s) and milk pH values from 6.6 to 7.0 on the physical properties of sheep skim milk (SSM), including heat coagulation time, particle size, sedimentation, ionic calcium level, and changes in protein composition. Significant amounts of sediment were found in UHT-treated SSM at the natural pH (∼6.6) and pH 7.0, whereas lower amounts of sediment were observed at pH values of 6.7 to 6.9. The proteins in the sediment were mainly κ-casein (CN)-depleted casein micelles with low levels of whey proteins regardless of the pH. Both the pH and the ionic calcium level of the SSM at all pH values decreased after UHT treatment. The dissociation levels of κ-, β-, and αS2-CN increased with increasing pH of the SSM before and after heating. The protein content, ionic calcium level, and dissociation level of κ-CN were higher in the SSM than values reported previously in cow skim milk. These differences may contribute to the high amounts of sediment in the UHT-treated SSM at natural pH (∼6.6). Significantly higher levels of κ-, β-, and αS2-CN were detected in the serum phase after heating the SSM at pH 7.0, suggesting that less κ-CN was attached to the casein micelles and that more internal structures of the casein micelles may have been exposed during heating. This could, in turn, have destabilized the casein micelles, resulting in the formation of protein aggregates and high amounts of sediment after UHT treatment of the SSM at pH 7.0.

Assessment of structures in phosphocaseinate dispersions by A4F, NMR and SAXS: The impact of demineralization and heat treatment on viscosity

The present work aims to better understand the relation between heat treatment (Ultra High Temperature - UHT), partial demineralization of casein micelles (CMs) dispersions and their corresponded rheological properties. A multiscale analysis (SAXS, solid state NMR and Asymmetrical Flow Field Flow Fractionation (A4F)), has been used. Different samples with different levels of calcium/phosphorous demineralization (up to −30% of calcium content) have been studied before and after UHT treatment. The present data show that CM dispersions, displaying a mild demineralization, display an important decrease in viscosity after UHT. NMR shows that, during UHT, mild demineralized samples display stronger calcium/phosphorus intake than both, the non-demineralized and the strong demineralized ones. SAXS and A4F show that UHT-dependent calcium intake, in mild demineralization dispersions, seems to be responsible for a transformation of large casein aggregates into small and denser ones. This decrease of the large aggregates is probably the main reason of the UHT-dependent decrease in viscosity. These data show that a sample with a rather small amount of demineralization can have a quite important susceptibility to UHT in terms of viscosity.

Immunogold Labeling of Milk Proteins at Transmission Electron Microscopy.

Milk intended for human consumption is subjected to technological treatments to ensure its safety and storage stability. These treatments deeply modify some of its structural and nutritional characteristics. Principal modifications involve proteins that partly adsorb onto the membrane of milk fat globules upon homogenization or whey proteins that undergo denaturation and aggregation during thermal treatments. Transmission electron microscopy is a powerful approach to investigate milk ultrastructure, due to its high-resolution power. Immunogold labeling of β-lactoglobulin and β-casein proteins represents a sophisticated approach to examine their structure and localization following technological processes such as homogenization and UHT treatment. However, liquid milk is a very challenging matrix because of its complex multiphasic nature. To preserve both ultrastructure and antigenicity, and to obtain an efficient labelling in liquid milk samples, some precautions shall be adopted in fixation, embedding, and labeling steps as here reported.

Maillard reaction products and amino acid cross-links in liquid infant formula: Effects of UHT treatment and storage

The formation of Maillard reaction products, including Amadori compounds (determined as furosine), advanced glycation end products (AGEs), α-dicarbonyl and furfural compounds, as well as amino acid cross-links (lysinoalanine and lanthionine) was investigated in direct (DI) and indirect (IN) UHT-treated experimental liquid infant formula (IF) during storage at 40 °C. IN-IF had higher concentrations of all investigated compounds compared to DI-IF and low pasteurized IF. IN UHT treatment induced significantly higher concentrations of α-dicarbonyl compounds (glyoxal, methylglyoxal, 3-deoxyglucosone and 3-deoxygalactosone) compared to DI, which facilitated increased formation of AGEs (N-Ɛ-(carboxymethyl)lysine, methylglyoxal- and glyoxal-derived hydroimidazolones) in unstored IFs. During storage for 6 months, concentrations of furosine and AGEs increased while α-dicarbonyl compounds decreased. Principal component analysis indicated that differences between IN-IF and DI-IF disappeared after 2 months of storage. IN-IF had higher concentrations of lysinoalanine and lanthionine and lower concentrations of available lysine and arginine than DI-IF indicating higher loss of protein quality in IN-IF.

Effect of incorporation of Generally Regarded as Safe (GRAS) carbohydratederivatives on quality attributes of skim milk

Reducing the fat content of dairy products adversely affects their flavour, texture and mouthfeel which consequently affect the consumer acceptance of skim milk. It was observed in the present study that pasteurized toned milk (3% fat, 8.5% SNF) had better sensory properties and higher viscosities than pasteurized skim milk, showing the importance of fat in consumer acceptance of milk samples. In commercial practice, skim milk is therefore traded only upon UHT treatment as it was much better in sensory properties than pasteurized skim milk. Since carbohydrate derivatives are usually used as fat mimetics, Inulin fruitafit text and fruitafit HD and polydextrose were added at different levels (0-2.5%) to skim milk to improve its quality attributes. It is observed that incorporation of a 1% level of polydextrose in combination with either of inulins (@ 1%) had improved viscosity and sensory properties. The rheological properties of such milk were comparable to that of toned milk and better than that of UHT skim milk. The quality of the skim milk added with carbohydrate derivatives was not affected by the normal processing treatments, such as homogenisation, pasteurization, boiling and sterilization. The gross constituents such as fat, protein, lactose and ash contents did not differ much with the control skim milk sample. The pH, acidity, and color (measured as % reflectance) of the skim milk samples added with the derivative were within the normal range. The samples were heat-stable, had high MBR time and when packed in LDPE pouches and stored at 50C kept well for two days. After appropriate approvals from the Food Safety and Standards Authority of India (FSSAI) pasteurised skim milk added with GRAS carbohydrate derivatives can be commercialised with improved consumer acceptance and affordability.

The effect of extracellular protease secreted by Pseudomonas fluorescens W3 on the quality of UHT milk

The heat-resistant protease produced by psychrotrophic bacteria is harmful to the quality of UHT milk, and the complex structure formed by fat and protein also affects the hydrolysis of protein by protease. The protease secreted by Pseudomonas fluorescens W3 was added to whole milk and skimmed milk before UHT treatment to analyze its effect on the quality of two kinds of UHT milk. During the preservation of UHT milk, increases in proteolysis, viscosity, hardness, sediment content, zeta potential, and particle size were observed. Extracellular protease reduced the whiteness, pH, and cohesiveness of UHT milk during the storage. The protease secreted by P. fluorescens W3 was easier to hydrolyze casein than whey protein, and κ-casein of casein was easily hydrolyzed by the protease. Milk fat accelerated the hydrolysis of casein by protease secreted by P. fluorescens W3, which led to a faster decline in the quality of whole UHT milk. Novelty impact statement Pseudomonas fluorescens W3 can secrete a thermostable protease AprX with a molecular weight of about 45 kDa. The protease AprX has stronger hydrolysis ability on κ-casein than other caseins. Fat can promote the activity of protease AprX, so whole milk is more susceptible to the damage of protease AprX.

UHT treatment and storage of liquid infant formula affects protein digestion and release of bioactive peptides

Ready-to-feed liquid infant formulas (IF) were subjected to direct (D) or indirect (ID) ultra-high-temperature (UHT) treatment and then stored at 40 °C under aseptic conditions for 60-120 days simulating global transportation which accelerates the Maillard reaction. Low pasteurized and unstored IF (LP) was included as a control for the UHT treatments. Simulated infant in vitro digestion was conducted. SDS-PAGE indicated that protein aggregate formation correlated with thermal treatment, being greatest after 60 days of storage. Limited protein digestion was observed after pepsin treatment for 2 h. Beta-lactoglobulin (β-Lg), alpha-lactalbumin (α-La) and protein aggregates remained undigested after 2 h of pepsin digestion in LP and D, but less β-Lg and α-La remained in ID. The digestion of β-Lg and α-La was enhanced in D and ID stored for 60 days, but aggregates remained undigested. After pepsin and pancreatin digestion, large amounts of β-Lg remained undigested in the LP, but digestion increased after UHT treatment (ID > D) and increased further after storage for 60 and 120 days, indicating that heat treatment and storage facilitate the digestion of unaggregated proteins. No aggregates remained after pancreatin digestion of LP, D, ID and D stored for 60 days, but were present in ID stored for 60 days. Aggregates were mainly disulphide-linked, but dityrosine linkages were detected in D and ID stored for 120 days. LC-MS/MS indicated limited proteolysis arising from endogenous milk proteases prior to in vitro digestion, being highest in D. Peptide numbers increased following pepsin and further during pancreatin digestion (β-casein > β-Lg > β-La), and released β-Lg peptides, typically 5-8 amino acids in length, contained several bioactivities, e.g., dipeptidyl-peptidase IV (DPP-IV) and angiotensin converting enzyme (ACE) inhibition.

Influence of Ultra-Heat Treatment on Properties of Milk Proteins.

Milk can be considered one of the primary sources of nutrients for the mammalian neonate. Therefore, milk and milk-based products, such as infant formula, whey protein isolate, different varieties of cheese, and others are prepared to meet the nutritional requirements of the consumer. Due to its significant nutritional components and perishable nature, a variety of pathogenic microorganisms can grow and multiply quickly in milk. Therefore, various heat treatments can be employed for the improvement of the shelf life of milk. In comparison to pasteurized milk, due to excessive and severe heating, UHT milk has a more cooked flavor. During storage, changes in the physicochemical properties of milk can lead to off-flavors, undesirable browning, separation of fat, sediment formation, or gelation during the subsequent storage. Several important factors such as processing parameters, time-temperature abuse (storage condition), and packaging type also influence the quality characteristics and consumer acceptance of the milk; however, the influence of heat treatments on milk protein is inconstant. The major protein modifications that occur during UHT treatment are denaturation and aggregation of the protein, and chemical modifications of its amino acids. These UHT-induced protein alterations can change digestibility and the overall biological influence of the intake of these proteins. Therefore, this review is focused on the influence of UHT on the physicochemical and structural attributes of milk proteins during storage. There are many indications of milk proteins present in the UHT milk, and milk products are altered during processing and storage.