Ultra-high Temperature Treatment Research Articles

IMPROVED SHELF LIFE ESTIMATION OF UHT MILK BY PREDICTION OF PROTEOLYSIS

During growth in raw milk, many psychrotrophic bacteria produce proteases that can retain activity following ultra-high temperature (UHT) treatment. In this study, casein and skim milk powder assays for detecting very low levels of protease in UHT milk were optimized, and the suitability of azocasein and fluorescein isothiocyanate-casein (FITC-casein) as substrates was investigated. The strongest correlations of protease activity with proteolysis in stored UHT milk were observed when FITC-casein was used as substrate in the assays. Assays using casein and FITC-casein as substrates yielded the highest activities. To determine sensitivity, crude protease was added at low concentrations to UHT milk, and the milk was assayed for progress of proteolysis over 12 months and for protease activity using the casein and FITC-casein assays. With long assay incubation times, the FITC-casein assay was more sensitive than the casein assay and may be suitable for detecting very low levels of protease activity and predicting progress of proteolysis in stored UHT whole milk.

The effect of native and modified konjac on the physical attributes of pasteurized and UHT-treated skim milk

The aim of the current study was to examine the influence of addition of mechanically modified konjac glucomannan, on the physical properties of pasteurized and ultra-high-temperature (UHT) treated skim milk. The effect of adding modified konjac (0–0.12%, w/w) on the viscosity and stability of skim milk, following pasteurization or UHT treatment, was investigated. It was possible to add modified konjac at levels up to 0.12% (w/w) without phase separation, as compared to <0.03% (w/w) native konjac. Addition of modified konjac increased the viscosity of pasteurized and UHT skim from ∼2.0 to 3.6 mPa s, with UHT samples having increased stability to sedimentation during simulated storage. The addition of modified konjac had little effect on particle size or colour of the skim milk post heating. Addition of modified konjac could provide a mechanism to enhance the physical properties of both pasteurized and UHT-treated skim milk.

Proteolysis of casein micelles by Pseudomonas fluorescens CNRZ 798 contributes to the destabilisation of UHT milk during its storage

Among the incriminating factors in the destabilisation of ultra-high-temperature (UHT) milk during storage, the heat-resistant proteases of Pseudomonas are considered to play a role. The objective of this work was to study the consequences of contamination of raw skim milk with Pseudomonas fluorescens CNRZ 798 on the stability of the corresponding UHT milk during storage. After 92 days, milk destabilisation was determined by the presence of a gelled sediment and low value to phosphate test (2.4 mL for control against 0 mL of phosphate solution for milk contaminated before UHT treatment) and the presence of aggregates. For the UHT control milk and UHT milk manufactured from raw skim milk contaminated with P. fluorescens, an increase in the size of the casein micelles (205 and 332 nm, respectively), a decrease in the zeta potential (−16.6 and −14.0 mV, respectively) and decrease in the level of hydration (2.00 and 1.55 g of water per gramme of dried pellet, respectively) were detected. The increase in pH 4.6-soluble nitrogen and trichloroacetic acid-soluble nitrogen content for UHT milk previously contaminated were ten- and fivefold higher than those for control milk, respectively. The trichloroacetic acid-soluble nitrogen fraction of the milk contaminated before treatment contained 118, 22, 4 and 9 peptides from β-, αs1-, αs2- and κ-caseins in comparison to only 22, 19, 6 and 4 peptides for the control milk. This study showed that destabilisation of UHT milk was due to proteolysis of casein micelles.

Efficacy of UV light treatment for the microbiological decontamination of chicken, associated packaging, and contact surfaces.

UV light was investigated for the decontamination of raw chicken, associated packaging, and contact surfaces. The UV susceptibilities of a number of Campylobacter isolates (seven Campylobacter jejuni isolates and three Campylobacter coli isolates), Escherichia coli ATCC 25922, and Salmonella enterica serovar Enteritidis ATCC 10376 in liquid media were also investigated. From an initial level of 7 log CFU/ml, no viable Campylobacter cells were detected following exposure to the most intense UV dose (0.192 J/cm(2)) in liquid media (skim milk subjected to ultrahigh-temperature treatment and diluted 1:4 with maximum recovery diluent). Maximum reductions of 4.8 and 6.2 log CFU/ml were achieved for E. coli and serovar Enteritidis, respectively, in liquid media. Considerable differences in susceptibilities were found between the Campylobacter isolates examined, with variations of up to 4 log CFU/ml being observed. UV treatment of raw chicken fillet (0.192 J/cm(2)) reduced C. jejuni, E. coli, serovar Enteritidis, total viable counts, and Enterobacteriaceae by 0.76, 0.98, 1.34, 1.76, and 1.29 log CFU/g, respectively. Following UV treatment of packaging and surface materials, reductions of up to 3.97, 4.50, and 4.20 log CFU/cm(2) were obtained for C. jejuni, E. coli, and serovar Enteritidis, respectively (P < 0.05). Overall, the color of UV-treated chicken was not significantly affected (P ≥ 0.05). The findings of this study indicate that Campylobacter is susceptible to UV technology and that differences in sensitivities exist between investigated isolates. Overall, UV could be used for improving the microbiological quality of raw chicken and for decontaminating associated packaging and surface materials.

Steam condensation dynamics in annular gap and multi-hole steam injectors

In direct UHT (Ultra high temperature) treatment, milk is pumped through a closed system where it is preheated, high temperature heated, cooled, homogenised and packed aseptically [1].Continuous direct steam injection is used to quickly raise the temperature of a product, either for pure heating or for a sterilization process. The injector can be of either annular gap type (also called ring nozzle steam injector), or multi hole type. In this study we have analyzed the details of the condensation process by visualizations and by mapping the temperature fields. It was found that steam condensation in steam injectors is an intense process with heat transfer rates in the order of 1 MW/(m2 K). The steam is always condensed at the equilibrium temperature and the turbulence created in the condensation zone mixes the hot condensate and heated product with the cold product. The efficiency of this turbulent transport determines the sufficient heat transfer area and thus the size of the steam/product interface. If the condensation rate is faster than the steam addition rate the condensation process is unstable which results in detachments, fluctuations, noise and vibrations.

The effect of hydrogen peroxide on the growth of thermophilic lactic starter and acid gelation of UHT milk

The influence of H 2O 2 pre-treatment (10–250 mg L −1) of ultra-high temperature treated (UHT) milk devoid of lactoperoxidase activity on the growth of thermophilic starter in the process of yoghurt production was studied using isothermal batch microcalorimetry and dynamic rheological measurements. Typical dual-peak power-time curves of diauxic growth of starter bacteria in milk were registered. Even the lowest concentrations of H 2O 2 added into milk 1 h before inoculation hindered the growth of thermophilic bacteria, retarded the onset of milk gelation, and resulted in formation of weaker gels. UHT milk samples treated with H 2O 2 and subsequently with catalase showed certain bacteriostatic influence of H 2O 2 pre-treatment on the second exponential growth phase. However, hardly any difference in gelation and no changes in rheological characteristics of mature gels in milk free of residual H 2O 2 due to catalase treatment prior to inoculation in comparison with H 2O 2-free control samples were observed.

Assessment of aflatoxin M1 levels in selected dairy products in north‐western Iran

The purpose of this survey was to evaluate the natural occurrence and content of aflatoxin M1, AFM1, in dairy products marketed in Urmia. During September 2007, 40 samples of pasteurised milk, 40 samples of ultra high temperature‐treated (UHT) milk, 40 samples of creamy cheese and 40 samples of Iranian Feta cheese were collected from different supermarkets in Urmia city. AFM1 contents were determined by the competitive enzyme‐linked imunosorbent assay (ELISA) technique. All milk samples analysed showed a mean of AFM1 concentrations lower than the permissible level of 50 ng/kg in Iran (23.22 and 19.53 ng/kg in pasteurised milk and UHT milk respectively). The mean levels of AFM1 contamination were 43.31 ng/kg in Feta cheeses and 21.96 ng/kg in creamy cheeses. The potential risk of human exposure to aflatoxin M1 via consumption of milk and milk products is well known. Dairy products must therefore be evaluated for aflatoxin and kept free from fungal contamination as much as possible.

Changes in lipopolysaccharide‐ related endotoxicity of food‐borne pathogens in response to safety treatments practised in South Africa

PurposeThis paper aims to evaluate the influence of pasteurization, ultra high temperature (UHT) treatment and sodium benzoate preservation on the LPS‐related endotoxicity of food‐borne pathogens Escherichia coli, Salmonella enteritidis and Pseudomonas aeruginosa.Design/methodology/approachThe paper sees that selected bacteria were subjected to laboratory simulations of commercially used heat treatments. In the case of sodium benzoate preservation, the bacteria were grown in the presence of a sub‐lethal dose of this preservative. Cells and debris were subjected to LPS extraction, GC‐MS analyses and endotoxicity measurement with the chromogenic Limulus Amebocyte Lysate (LAL) assay.FindingsThe heat treatments and preservation method influenced the LPS‐related toxicity of each organism in a different manner. Increases in LPS‐related toxicity were noted in the LPS liberated from UHT‐treated E. coli and S. enteritidis and pasteurized E. coli and P. aeruginosa. Toxicity of the membrane associated LPS of UHT‐treated E. coli and pasteurized S. enteritidis was also elevated. Sodium benzoate resulted in E. coli cells with LPS with related toxicity levels almost double compared to that of the control cells. S. enteritidis LPS also demonstrated an increase in toxicity, while that of P. aeruginosa was rendered less toxic.Practical implicationsToxicity could still be detected even after sterilization treatments like UHT, suggesting that viability and toxicity are not necessarily connected and that the toxicity of LPS molecules that remain in food products after treatment should be considered. Although ingestion of LPS originating from Gram‐negative bacteria is a fairly new concept, the effect that these toxins might have on members of society with compromised immune systems and individuals suffering from gastrointestinal diseases cannot be ignored.Originality/valueThe paper introduces a unique insight into food safety treatment‐induced toxicological changes related to LPS originating from food‐borne organisms, a factor that is currently unexplored in the South African food industry.

ENZYME INACTIVATION ON APPLE JUICE TREATED BY ULTRAPASTEURIZATION AND PULSED ELECTRIC FIELDS TECHNOLOGY

ABSTRACT Apple juice was pasteurized by an ultra-high temperature treatment (UHT) at 115, 125 and 135C for 3 and 5 s, and compared with a high-voltage pulsed electric field treatment (PEF) at ranges between 33 and 42 kV/cm with frequencies of 150, 200, 250 and 300 pulses per second (pps). Enzyme inactivation and physicochemical properties of the treated juices were compared using a nontreated sample as control. The UHT treatment was more efficient in enzyme inactivation, reducing 95% the residual activity of polyphenoloxidase at the maximum temperature and time. However, a PEF treatment at 38.5 kV/cm and 300 pps combined with a temperature of 50C achieved a 70% reduction of residual PFO activity. In terms of quality characteristics as a function of physicochemical properties, color, pH, acidity and soluble solids were all less affected by PEF than by UHT when compared with the untreated juice. PRACTICAL APPLICATIONS Apple juice is a popular beverage worldwide and it is consumed nearly as much as orange juice. Consumers prefer fresh-squeezed fruit juices with high nutrient value and fresh-like sensory attributes. Enzymatic browning negatively impacts appearance, nutritive value and flavor of fruit juices. The use of ultra-high temperature processing is efficient in microbial control, as well as in enzyme inactivation. Any thermal processing may, however, decrease the overall quality of the treated juices. Pulsed electric field processing provides a potential alternative to thermal pasteurization of fruit juices.

Kinetics of Maillard reactions in model infant formula during UHT treatment using a static batch ohmic heater

The impact of an ultrahigh temperature (UHT) treatment on amodel infant formula (IF) was examined by assessing the advancement of Maillard reactions during a thermal treatment by ohmic heating. The heating and holding steps of the heat treatment were carried out in a static batch ohmic heater equipped with a nitrogen counter-pressure system, allowing the reaching of five temperature levels from 100 to 140 °C. A heat treatment was characterised by monitoring a holding time at a given temperature. Samples were taken during heating and holding steps and analysed for early Maillard reaction products (MRPs), such as furosine, advanced MRPs, such as advanced glycated end products (AGEs) and carboxymethyllysine (CML), and final MRPs such as melanoidins. The results show that Maillard reactions in model IF are highly dependent from time-temperature treatment. In compliance with other classical heating techniques, the selected chemical markers followed a pseudo-zero order of reaction under isothermal conditions. However, the contribution of the heating step can be significant as MRPs could be detected from the first seconds of the UHT treatment.

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.

Competence of the housefly, Musca domestica, as a vector of Microsporum canis under experimental conditions

The role of Musca domestica Linnaeus as a vector of the dermatophyte Microsporum canis was investigated under experimental laboratory conditions. About 400 4-day-old M. domestica flies were divided into two groups. Group A consisted of about 200 infected flies and group B comprised about 200 uninfected flies that were used as controls. Each trial was run three times. Flies from group A were fed for 24 h with a solution of ultra-high temperature-treated (UHT) milk containing about 10(6) colony-forming units (CFU) per mL of M. canis (infected milk inoculum [IMI]). The control group (group B) was fed with only UHT milk spiked with a teaspoon of honey. Microsporum canis was detected from faeces, vomitus, external surfaces and internal organs of 20 adult flies, eggs, first-, second- and third-stage (L1, L2, L3) larvae and pupae of each group, as well from 20 adult newly emerged flies (NEFs; from infected generations only). Samples were collected at 2, 4, 6 and 24 h post-infection (p.i.) (i.e. the times at which IMI was available) and on 2, 5, 7 and 8 days p.i. from adult flies, faeces and vomitus. Eggs, L1, L2, L3 and pupae were processed as soon as they appeared. Equivalent samples were taken from group B. All the samples were individually cultured. Microsporum canis was not isolated from the control group, from eggs, larvae, pupae or NEFs, or from faeces and vomitus, although it was detected on the body surface (26.2%) and internal organs (26.9%) of adult flies. The highest positivity for M. canis was detected on flies within the first 6 h p.i. (i.e. 57.2% on the body surface and 71.6% in the internal organs). No M. canis was isolated at 24 h p.i., but it was isolated from the body surface only at 2 and 5 days p.i. The results presented provide evidence that M. domestica transmits M. canis mechanically with its outer body surface for up to 5 days p.i., but does not do so through its vomitus and faeces or transovarially. The role played by M. domestica in the epidemiology of human and animal dermatophytoses is discussed.

Ultra High Temperature Treatment, but Not Pasteurization, Affects the Postprandial Kinetics of Milk Proteins in Humans

Although the chemical and physical modifications to milk proteins induced by technological treatments have been characterized extensively, their nutritional consequences have rarely been assessed in humans. We measured the effect of 2 technological treatments on the postprandial utilization of milk nitrogen (N), pasteurization (PAST) and ultra high temperature (UHT), compared with microfiltration (MF), using a sensitive method based on the use of milk proteins intrinsically labeled with 15N. Twenty-five subjects were studied after a 1-wk standardization of their diet. On the day of the investigation, they ingested a single test meal corresponding to 500 mL of either MF, PAST, or UHT defatted milk. Serum amino acid (AA) levels as well as the transfer of 15N into serum protein and AA, body urea, and urinary urea were determined throughout the 8-h postprandial period. The kinetics of dietary N transfer to serum AA, proteins, and urea did not differ between the MF and PAST groups. The transfer of dietary N to serum AA and protein and to body urea was significantly higher in UHT than in either the PAST or MF group. Postprandial deamination losses from dietary AA represented 25.9 ± 3.3% of ingested N in the UHT group, 18.5 ± 3.0% in the MF group, and 18.6 ± 3.7% in the PAST group (P < 0.0001). The higher anabolic use of dietary N in plasma proteins after UHT ingestion strongly suggests that these differences are due to modifications to digestive kinetics and the further metabolism of dietary proteins subsequent to this particular treatment of milk.

Ultra High Temperature treatment, but not pasteurization, affects the postprandial kinetics of milk proteins in humans1,2

Ultra High Temperature treatment, but not pasteurization, affects the postprandial kinetics of milk proteins in humans1,2

Automated fluorimetry in quality control of pasteurized and ultra-high temperature-treated starch soup

Summary Automated monitoring of the microbiological quality of heat-processed foods by the resazurin reduction test was applied to microtitration plate incubator-fluorimeter technology. The appearance and disappearance of the fluorescing peak of resorufin was monitored on microtitration trays. Pasteurized or ultra-high temperature-treated starch-based soup was used as the model food system. Bacillus subtilis spores (ultra-high temperature treatment) and vegetative cells of Enterococcus faecalis (pasteurization) were inoculated into the soup before the heat treatment at levels which resulted in some survival. The timing of appearance of maximum fluorescence correlated with the number of bacteria in pre-incubated samples. Automated resazurin-reduction fluorimetry was compared with conventional plating, turbidometry and microcolony count by the direct epifluorescent filter technique. The results of the resazurin test correlated well with those of all the other methods tested. Fluorimetry had the advantage that the results could be read within 1–5h and the reproducibility was superior to the other methods.

Development of matrix lysis for concentration of gram positive bacteria from food and blood

The development of a fast, reliable and inexpensive protocol for the concentration of bacteria from food by the removal of fat, carbohydrates and proteins that is compatible with downstream alternative DNA-based quantification methods is described. The protocol was used for dairy products, cooked and smoked fish and meat, carbohydrate-rich cooked products, ready-to-eat sauces, egg and blood. Lysis resulted in pellets of reasonable size for further processing. Starch, plant materials, fungi, tissues such as sinew, and chalaza could not be dissolved. Using L. monocytogenes, S. aureus and B. cereus as model organisms, microscopic analysis of the remaining bacterial pellets revealed that the recovered bacteria remained physically intact, albeit that the viability of the cells was compromised. Using real-time PCR, 7.3 CFU of L. monocytogenes were detected in artificially contaminated ultra-high temperature treated (UHT) milk and raw milk.

Prion Protein in Milk

BackgroundPrions are known to cause transmissible spongiform encephalopathies (TSE) after accumulation in the central nervous system. There is increasing evidence that prions are also present in body fluids and that prion infection by blood transmission is possible. The low concentration of the proteinaceous agent in body fluids and its long incubation time complicate epidemiologic analysis and estimation of spreading and thus the risk of human infection. This situation is particularly unsatisfactory for food and pharmaceutical industries, given the lack of sensitive tools for monitoring the infectious agent.Methodology/Principal FindingsWe have developed an adsorption matrix, Alicon PrioTrap®, which binds with high affinity and specificity to prion proteins. Thus we were able to identify prion protein (PrPC)–the precursor of prions (PrPSc)–in milk from humans, cows, sheep, and goats. The absolute amount of PrPC differs between the species (from µg/l range in sheep to ng/l range in human milk). PrPC is also found in homogenised and pasteurised off-the-shelf milk, and even ultrahigh temperature treatment only partially diminishes endogenous PrPC concentration.Conclusions/SignificanceIn view of a recent study showing evidence of prion replication occurring in the mammary gland of scrapie infected sheep suffering from mastitis, the appearance of PrPC in milk implies the possibility that milk of TSE-infected animals serves as source for PrPSc.

Preface

Preface

Bacillus sporothermodurans and other highly heat-resistant spore formers in milk

A recent example of a micro-organism causing undesired growth in consumer milk is Bacillus sporothermodurans producing highly heat-resistant spores (HRS) which may survive ultra-high temperature (UHT) treatment or industrial sterilization. Molecular typing showed a heterogeneous group of farm isolates (non-HRS strains), but a clonal group of UHT isolates from diverse European countries and other continents (HRS-clone) suggesting a common source. During a survey of Belgian dairy farms for the presence of potentially highly heat-resistant spore formers, high numbers of these spores were detected in filter cloth, green crop and fodder samples. The strain collection showed a high taxonomic diversity with 18 potentially new species and with Bacillus licheniformis and Geobacillus pallidus as predominating species overall. Seventeen B. sporothermodurans isolates were identified, mainly originating from feed concentrate. Heat resistance studies showed the UHT resistance of B. sporothermodurans spores present in industrially contaminated UHT milk, but a lower heat resistance of laboratory-grown strains (HRS and non-HRS). Hydrogen peroxide, used as sanitizer in the dairy industry, was found to induce higher heat resistance of laboratory-grown B. sporothermodurans strains to a certain level. This indicates that sublethal stress conditions may affect the heat resistance. By transmission electron microscopy, structural differences at the spore level were found between HRS and non-HRS strains. The data indicate that the attainment of extreme heat resistance is rather multifactorial.

Plasmin activity in direct-steam-injection UHT-processed reconstituted milk: Effects of preheat treatment

Ultra-high-temperature (UHT)-processed reconstituted milk that is subjected to a minimal preheat treatment during the direct-steam-injection heating process may have a shortened shelf-life as a result of plasmin-mediated proteolysis. Some manufacturers apply a preheat treatment before UHT treatment (140 °C for 4 s) with the aim of prolonging the shelf-life. Preheat treatments are, however, often arbitrary in terms of temperature and holding time. The aim of the current work was to determine guidelines for the minimum preheat treatment that will effectively inhibit or prevent plasmin-type enzyme activity in UHT milk. A selected range of preheat treatments was applied to milk preparations reconstituted from several batches of low-heat skim milk powder. Increased plasmin-type proteolysis was observed after intermediate preheat treatments at ⩾80 and <90 °C. Effective inhibition of plasmin-type proteolysis was obtained by preheating at 90 °C for 30 or 60 s.