Indirect Ultra-high Temperature Research Articles

Physicochemical properties of fluid milk with different heat treatments and HS-GC-IMS identification of volatile organic compounds

To improve understanding of the effects of industrial heating processes on its physiochemical and flavour properties, fluid milk was evaluated for protein denaturation and flavour volatiles after high-temperature short-time (HTST), indirect ultra-high temperature (IND-UHT) and direct ultra-high temperature with direct steam infusion (INF-dUHT) treatments. Protein denaturation was evaluated by particle size, free sulphydryl content, fluorescence spectra, native whey protein retention rate and microstructure. Volatile organic compounds (VOCs) were compared by headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). HTST treatment exerted the lowest negative effect on the aggregation and denaturation of native whey proteins including α-lactalbumin, β-lactoglobulin and lactoferrin, followed by INF-dUHT. IND-UHT caused the most severe denaturation of native whey proteins. HTST-treated milk was characterised by a high level of low molecular weight ketones and INF-dUHT milk possessed the greatest abundance of aldehydes, whereas IND-UHT milk exhibited the highest contents of high molecular weight methyl ketones, which contributed to an unpleasant aroma.

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.

EFFECT OF ULTRA HIGH TEMPERATURE PROCESSING ON THE VISCOSITY OF WHOLE BOVINE MILK FORTIFIED WITH ZINC, FERROUS AND MAGNESIUM

Age gelation is a main defect in Ultra-high temperature (UHT) processed milk. It is a process with two stages which distinguished by loss of viscosity. It can be followed by measuring the apparent viscosity of the milk. A control (T0) and four whole milk (fat 3.85%) samples fortified with Zinc (T1), Ferrous (T2) and Magnesium (T3) individually and collectively (T4) was processed by indirect heating UHT system at 145 ºC for six seconds. The UHT-processed milk samples were filled aseptically into Gamma ray pre-sterilized PET containers in a laminar flow cabinet sterilized shortly before filling by UV. The samples stored at 30 ºC for 60 days to investigate at 15 days intervals the effect of processing on apparent viscosity and appearance of the fortified milk and compared to control UHT milk (T0). Results recorded during 60 days of storage showed a slight rise in viscosity in all samples. No changes in appearance have been observed during the storage period. UHT Zinc-milk has shown at all intervals insignificant increase. Only after 30 days of storage, milk-fortified with ferrous showed a significant increase in viscosity measured by spindle speed of 30 rpm (SS30). Significant increases (p≤0.05) in viscosity were recorded within the fortified UHT-milk samples. Appearance and apparent viscosity can be adopted to follow gel forming in fortified milk with some minerals.

Age Gelation, Sedimentation, and Creaming in UHT Milk: A Review.

Demand for ultra-high-temperature (UHT) milk and milk protein-based beverages is growing. UHT milk is microbiologically stable. However, on storage, a number of chemical and physical changes occur and these can reduce the quality of the milk. These changes can be sufficiently undesirable so as to limit acceptance or shelf life of the milk. The most severe changes in UHT milk during storage are age gelation, with an irreversible three-dimensional protein network forming throughout, excessive sedimentation with a compact layer of protein-enriched material forming rapidly at the bottom of the pack, and creaming with excessive fat accumulating at the top. For age gelation, it is known that at least two mechanisms can lead to gelation during storage. One mechanism involves proteolytic degradation of the proteins through heat-stable indigenous or exogenous enzymes, destabilizing milk and ultimately forming a gel. The other mechanism is referred to as a physico-chemical mechanism. Several factors are known to affect the physico-chemical age gelation, such as milk/protein concentration, heat load during processing (direct compared with indirect UHT processes), and milk composition. Similar factors to age gelation are known to affect sedimentation. There are relatively few studies on the creaming of UHT milk during storage, suggesting that this defect is less common or less detrimental compared with gelation and sedimentation. This review focuses on the current state of knowledge of age gelation, sedimentation, and creaming of UHT milks during storage, providing a critical evaluation of the available literature and, based on this, mechanisms for age gelation and sedimentation are proposed.

Sedimentation in UHT milk

Sediment from ultra-high temperature (UHT) processed milk was composed of κ-casein depleted casein micelles, with low levels of denatured whey protein. Direct UHT was more prone to sediment formation than indirect UHT. In direct UHT milk samples, at low pH (<∼pH 6.65) and/or high ionic calcium levels (>∼1.5 mm), the unstable κ-casein-depleted casein micelles were prone to calcium-mediated aggregation and high sedimentation levels. Sedimentation in direct UHT milk samples could be reduced by increasing the pH with alkali or reducing the ionic calcium with chelators. Tri-sodium citrate was effective as it reduced ionic calcium levels and increased pH. Decreasing the pH by adding acid or increasing the ionic calcium level by adding of calcium salts markedly increased sedimentation. In indirect UHT milk samples, higher levels of denatured whey proteins were associated with the casein micelles and this may stabilise these micelles, reducing their propensity to aggregate and sediment.

Life cycle assessment of emerging technologies: The case of milk ultra-high pressure homogenisation

Milk is becoming a key food commodity as population grows and demand increases. The treatment of milk to extend its shelf life is thus an important step in avoiding losses and optimizing resource use. The drawbacks of the most common treatments for shelf stable milk are the loss of nutritional values and high energy consumption. Ultra-high pressure homogenisation (UHPH) is an emerging technology relying on dynamic pressure up to 400 MPa. The combination of high pressure, temperature, shear, cavitation and impingement can provide commercially sterile milk of higher quality and longer shelf life. A life cycle assessment was performed comparing this emerging technology to the common thermal treatment: indirect ultra-high temperature sterilisation combined with non-aseptic homogenisation. The results show that high-pressure based processing has a lower environmental burden compared to the high-temperature based processing, already at pilot-scale, and this difference is primarily due to the lower electricity consumption. Additionally, upscaling considerations were made using power laws and scenario analysis to simulate future full-scale applications of UHPH. The upscaling shows that a decrease in carbon footprint up to 88% is achievable with improvements in efficiency. UHPH could, therefore, represent a substitute for existing practices considering its technological readiness level and potential synergies when integrated into industrial scale production lines.

Milk reversibility following reduction and restoration of pH

The pH of skim milk was adjusted from 6.67 to between 6.00 and 5.45 before being restored with NaOH. Ionic calcium was higher after pH restoration but this did not result in instability during indirect ultra high temperature and in‐container sterilisation. Ionic calcium of pH restored milk increased with increased holding time but the pH restored milk remained stable to in‐container sterilisation. The viscosity of the milk was not affected by pH reversal. However, pH‐restoration reduced rennet coagulation time but milk was still stable when subjected to high temperature treatment. Properties of the soluble phase were measured at high temperature by dialysis.

Comparative Studies on the Chemical and Cell-Based Antioxidant Activities and Antitumor Cell Proliferation Properties of Soy Milk Manufactured by Conventional and Commercial UHT Methods

The aims of this work were to compare antiproliferation, antioxidant activities and total phytochemicals and individual isoflavone profiles in soy milk processed by various methods including traditional stove cooking, direct steam injection, direct ultrahigh temperature (UHT), indirect UHT, and a two-stage simulated industry method, and a selected commercial soy milk product. Various processing methods significantly affected total saponin, phytic acid, and total phenolic content and individual isoflavone distribution. The laboratory UHT and the two-stage processed soy milk exhibited relatively higher total phenolic content, total flavonoid content, saponin and phytic acid than those processed by the traditional and steam processed methods. Thermal processing caused obvious intertransformation but did not cause severe degradation except for breaking down of aglycons. Thermal processing significantly increased antioxidant capacities of soy milk determined by chemical analyses, but decreased cellular antioxidant capacities as compared to the raw soy milk. The raw and all processed soy milk exhibited antipoliferative activities against human HL-60 leukemia cells, AGS gastric tumor cells, and DU145 prostate cancer cells in a dose-dependent manner. The raw soy milk, but not the processed soy milk, exhibited a dose-dependent antiproliferative effect against colorectal adenocarcinoma Caco-2 cells. Taken together, these results indicate that various thermal processing methods change not only phytochemcials but also potential health-promoting effects of soy milk.

Isoflavones, Flavan-3-ols, Phenolic Acids, Total Phenolic Profiles, and Antioxidant Capacities of Soy Milk As Affected by Ultrahigh-Temperature and Traditional Processing Methods

The objectives of this work were to assess antioxidant activities and phenolic compounds of soy milk as affected by traditional and ultrahigh-temperature (UHT) processing. Three soybean varieties were processed into raw soy milk and then cooked soy milk by indirect and direct UHT methods (both at 143 degrees C for 60 s) and traditional cooking (stove cooking and steam injection) methods (both at 100 degrees C for 20 min). Total phenolic content (TPC), total flavonoid content (TFC), phenolic acids, isoflavones, flavan-3-ols, and anthocyanins were quantified. DPPH free radical scavenging activity, ferric reducing antioxidant power (FRAP), and oxygen radical absorbance capacity (ORAC) were analyzed. As compared to the raw soy milk, all thermal processing significantly (p < 0.05) reduced TPC values and significantly (p < 0.05) increased TFC values for all soybean varieties. All processing methods significantly (p < 0.05) increased DPPH and FRAP values in the soy milk processed from yellow soybean varieties Proto and IA 2032. UHT processing increased their ORAC values, but traditional and steam processing reduced their ORAC values. However, in the case of the soy milk from black soybean, all processing reduced ORAC values as compared to the raw soy milk. None of processing affected total phenolic acids, chlorogenic, and trans-cinnamic acid, as well as (+)-catechin. However, all processing significantly (p < 0.05) affected contents of total isoflavones and individual isoflavones. Thermal processing caused significant (p < 0.05) increases in 7-O-beta-glucosides and acetylglucosides, but caused significant (p < 0.05) decreases in malonylglucosides and aglycones. Indirect UHT processing transformed more isoflavones from malonylglucosides into 7-O-beta-glucosides than the direct UHT did.

Oxidative stability of UHT milk as influenced by fatty acid composition and packaging

Control milk and milk enriched with unsaturated fatty acids (3.3% fat) were heated using an indirect ultra-high temperature treatment, then stored at 20 °C in containers from different packaging materials: glass (no exposure to light), high density polyethylene (HDPE) packaging with light barrier (3-HDPE; no exposure to light) and monolayer HDPE (1-HDPE; 1000 lx). The decrease in antioxidant content and the formation of oxidation products were monitored over three months. For milk stored in 1-HDPE packaging, the available antioxidants were consumed at the same rate for both milk types, suggesting that oxidation is initiated in the serum phase. After depletion of these antioxidants, oxidation products were formed according to the fatty acid profile. When using a light barrier in the packaging, no oxidation products could be detected over three months.

Elimination of Trypsin Inhibitor Activity and Beany Flavor in Soy Milk by Consecutive Blanching and Ultrahigh-Temperature (UHT) Processing

Soy foods contain significant health-promoting components but also may contain beany flavor and trypsin inhibitor activity (TIA), which can cause pancreatic disease if present at a high level. Thermal processing can inactivate TIA and lipoxygenase. Ultrahigh-temperature (UHT) processing is relatively new for manufacturing soy milk. Simultaneous elimination of TIA and soy odor by UHT processing for enhancing soy milk quality has not been reported. The objective was to determine TIA in soy milk processed by traditional, steam injection, blanching, and UHT methods and to compare the products with commercial soy milk products. Soybean was soaked and blanched at 70-85 degrees C for 30 s-7.5 min. The blanched beans were made into base soy milk. The hexanal content of the base soy milk was determined by gas chromatography to determine the best conditions for further thermal processing by indirect and direct UHT methods at 135-150 degrees C for 10-50 s using the Microthermics processor. Soy milk was also made from soaked soybeans by traditional batch cooking and steaming methods. Eighteen commercial products were selected from the supermarket. Residual TIA in soy milk processed by the traditional and steam injection to 100 degrees C for 20 min was approximately 13%. Blanching could inactivate 25-50% of TIAs of the raw soy milk. The blanch conditions of 80 degrees C and 2 min were selected for UHT processing because these conditions produced blanched soy milk without hexanal, indicating a complete heat inactivation of lipoxygenases. The TIA decreased with increased temperature and time of UHT heating. The maximal trypsin inhibitor inactivation was achieved by UHT direct and indirect methods with residual activities of approximately 10%. Some commercial soy milk products contained high TIAs. The results are important to the food industry and consumers. Kinetic analysis showed that heat inactivation (denaturation) of TIA, under the continuous processing conditions of the Microthermics processor, followed first-order reaction kinetics, and the activation energy of the inactivation was 34 kJ/mol.

The Effects of Mass Flow Rate in an Indirect Ultra-High Temperature Processing System

The Effects of Mass Flow Rate in an Indirect Ultra-High Temperature Processing System

Effect of Preheating on Fouling of a Pilot Scale UHT Sterilizing Plant by Recombined, Reconstituted and Fresh Whole Milks

The principal aim of this study was to confirm and extend previous findings on the effects of milk preheating on fouling of UHT (ultra-high temperature) sterilizing plants by recombined whole milks. A comprehensive replicated experiment was carried out to examine the effects of preheat treatment on fouling by milk recombined from skim milk powder (SMP) and milk fat, milk reconstituted from whole milk powder (WMP), and fresh milk. Within each replicate the SMP, the WMP and the fresh milk were all derived from the same batch of milk. Fouling rates were measured in the high-temperature section of a pilot-scale indirect UHT plant. The effects of preheating conditions were compared as follows: UHT preheating conditions (recombined and fresh milk): 75°C × 11 s, 85°C × 147 s, and 95°C × 147 s; evaporator preheating conditions for skim milk powder manufacture: 75°C × 2 s, 85°C × 155 s, and 95°C × 155 s. The evaporator preheating conditions in whole milk powder manufacture (95°C × 33 s) were not varied. In all cases it was found that the more severe was a preheat treatment, whether evaporator preheating or UHT preheating, the higher was the fouling rate. The results, which are discussed in relation to previous findings for both recombined milks and fresh milk, suggest that the preheating of previously homogenized whole milks exacerbates fouling.

Quantification of Proteins in Dairy Products Using an Optical Biosensor

Two recent techniques using optical immunosensor technology were developed for the quantification of milk proteins in dairy products. The first application is the simultaneous quantification of the 3 major caseins (alpha(s1), beta, and kappa). This assay consists of a 2-step sandwich strategy, with 2 monoclonal antibodies directed against the N- and C-terminal extremities of each of the caseins, respectively. This strategy permits only intact caseins to be quantified, and not their degradation products. The technique is fast (10 min), sensitive (detection limit about 0.87 microg/mL), and has been applied successfully to raw and drinking milks. In the second application, the severity of the heat treatment sustained by a milk of unknown origin is determined by quantifying separately the native and heat-denatured forms of alpha-lactalbumin with specific monoclonal antibodies. The technique allows discrimination of the different heat treatments studied (pasteurization, direct and indirect ultra-high temperature, sterilization), is fast (4 min), repeatable, fully automated, and requires no pretreatment of the milk sample.

Effect of extraction methods and UHT treatment conditions on the level of isoflavones during soymilk manufacture

The objective of this study was to compare the effect of hot and cold grinding as well as the effect of direct and indirect ultra high temperature (UHT) treatment conditions on the level of isoflavones during the manufacture of soymilk. Soymilks were manufactured from dehulled soybeans by hot grinding or cold grinding processes. After inactivation of lipoxygenase at 85 °C, the resulting slurries were decanted and supernatants were held at 120 °C for 80 s to inactivate the trypsin inhibitor. The decanted soya bases were cooled and subjected to different temperature/time regimes by direct and indirect UHT treatments. Samples were drawn at different points in the processing operation and a reversed phase high performance liquid chromatography method was used to determine the concentration of isoflavones. Results showed that hot grinding caused a higher extraction of isoflavones into the soymilk than the cold-grinding process. However, direct or indirect heating in the UHT process did not significantly influence the concentration of isoflavones.

Proteolysis and storage stability of UHT milk as influenced by milk plasmin activity, plasmin/β-lactoglobulin complexation, plasminogen activation and somatic cell count

Little residual plasmin activity was found in both low and high somatic cell count (SCC) milk which had been subjected to indirect ultra-high temperature (UHT) treatment (138 °C × 2.4s) and subsequently stored at 20 °C. Milk with elevated SCCs showed definite sedimentation after 150 d storage but did not gel. Addition of potassium iodate to the milk before UHT treatment led to considerably increased plasmin activity during subsequent storage, indicating the protective influence of potassium iodate on the thermal stability of plasmin. These milk samples underwent significant decrease in pH on storage, did not gel, and urea-PAGE electrophoresis showed them to have almost complete breakdown of β-casein but incomplete hydrolysis of αs1-casein. When plasminogen was added to milk immediately after UHT treatment, it was readily activated to plasmin. Activation occurred more rapidly in the high SCC milk, suggesting the presence of cell-associated heat-stable plasminogen activators. UHT milk with added plasminogen showed definite gelation at 150 and 180d storage and gelation was more pronounced in the high SCC milk. Samples to which plasmin was added immediately after UHT treatment showed proteolysis patterns similar to those with added potassium iodate and showed slight gelation. Low levels of proteolysis appeared to be linked to the onset of gelation.

Optimization of the forewarming process with respect to deposit formation in indirect ultra high temperature plants and the quality of milk

SummaryThe influence of preheating intensity was examined on deposit formation in an indirect ultra high temperature (UHT) plate heat exchanger and on some quality parameters of the UHT treated milk, such as taste, proteinase inactivation and protein destabilization during storage. Response surface methods were used to define the relationship between the forewarming conditions and the responses. More intense forewarming reduced the fouling rate in the UHT plate section, resulting in longer operation times. While a greater inactivation of the proteinase(s) in the milk was obtained, the taste of the UHT milk was adversely affected, as well as the physical stability during storage owing to higher sedimentation. An optimum temperature/time range for the preheating process could be defined within the temperature/time range of 76–80 °C/40–70 s at which adverse effects were minimal, and positive effects were maximized.

Dynamic viscosities of milk and cream from 70 to 135 °C

SummaryThe dynamic viscosities of non-homogenized and homogenized (2-stage) whole and half skim-milk and cream, of unhomogenized skim-milk and of water-diluted milks were measured at temperatures between 70 and 135 °C; this range includes those temperatures used in ultra-high-temperature (UHT) treatments. A tube viscometer was used at the outlet of a continuous flow indirect heater. Above 85 °C the mean residence time of a milk or cream at the test temperature was 3–6 s.An equation relating viscosity μ and temperature θ of the form In μ = aθ2+bθ+c was derived for each product.It proved possible to relate μ, θ and fat content (0·03–15·5%) in a single equation which was appropriate for all the homogenized milks and creams as well as the non-homogenized skim-, half skim- and whole milk; the equation is considered valid for these products under conditions of indirect UHT sterilization. Viscosity values calculated with the equation, even those relating to temperatures as low as 50 °C, were comparable with those reported in the literature.