Alkaline phosphatase and microbial inactivation by pulsed electric field in bovine milk

The effects of pulsed electric field (PEF) treatments at field intensities of 25–37 kV cm^− 1 and final PEF treatment temperatures of 15 °C and 60 °C on the inactivation of alkaline phosphatase (ALP), Total Plate Count (TPC), Pseudomonas and Enterobacteriaceae counts were determined in raw skim milk. At 15 °C, PEF treatments of 28 to 37 kV cm^− 1 resulted in 24–42% inactivation in ALP activity and < 1 log reduction in TPC and Pseudomonas count, while the Enterobacteriaceae count was reduced by at least 2.1 log units to below the detection limit of 1 CFU mL^− 1. PEF treatments of 25 to 35 kV cm^− 1 at 60 °C resulted in 29–67% inactivation in ALP activity and up to 2.4 log reduction in TPC, while the Pseudomonas and Enterobacteriaceae counts were reduced by at least 5.9 and 2.1 logs, respectively, to below the detection limit of 1 CFU mL^− 1. Kinetic studies suggested that the effect of field intensity on ALP inactivation at the final PEF treatment temperature of 60 °C was more than twice that at 15 °C. A combined effect was observed between the field intensity and temperature in the inactivation of both ALP enzyme and the natural microbial flora in raw skim milk.Industrial relevanceMilk has been pasteurised to ensure its safety and extend its shelf life. However, the need for retaining heat-sensitive nutrient and sensory properties of milk has resulted in interest in the application of alternative technologies. The results of the current study suggest that PEF as a non-thermal process can be employed for the treatment of raw milk in mild temperature to achieve adequate safety and shelf life while preserving the heat-sensitive enzymes, nutrients and bioactive compounds.     

Microbial shelf-life of high-pressure-homogenised milk

The anti-bacterial effect of high pressure homogenisation (HPH) on milk is widely reported but the shelf-life of HPH-treated milk, as reported in this communication has not been studied thus far. Raw whole milk was homogenised at 200 or 250 MPa at 55 or 70 °C and counts of total bacteria (TBC), psychrotrophs, pseudomonads, coliforms, lactobacilli, Bacillus cereus and Staphylococcus aureus were determined throughout subsequent storage for 14 days at 4 °C. Immediately after HPH treatment, counts of all bacteria were below the level of detection but after storage for 14 days at 4 °C, TBC, psychrotroph and pseudomonad counts had reached ∼10⁸ cfu mL⁻¹ in all samples treated with HPH. The limited shelf-life obtained indicates that HPH of milk at these processing parameters it is not a suitable alternative to pasteurisation for extending the shelf-life of milk.     

Effect of thermosonication,pulsed electric field and their combination on inactivation of Listeria innocua in milk

The impact of thermosonication (TS) and pulsed electric field (PEF), individually and combined, on the survival of Listeria innocua 11288 (NCTC) in milk was investigated. TS (400 W, 160 s) without pre-heating reduced L. innocua by 1.2 log₁₀ cfu mL^?1, while shorter treatment times produced negligible inactivation, suggesting TS to be a hurdle rather than an effective standalone treatment. PEF (30 and 40 kV cm^?1, 50 μs) at 10 °C caused a reduction of L. innocua of 1.1 and 3.3 log cycles, respectively. The highest field strength (40 kV cm^?1) combined with TS (80 s) led to 6.8 log₁₀ cfu mL^?1 inactivation. Milk pre-heated to 55 °C (over 60 s) prior to TS followed by PEF (30 and 40 kV cm^?1) showed inactivation between 4.5 and 6.9 log₁₀ cfu mL^?1, the latter being comparable (P > 0.05) with thermal pasteurisation. The data indicate that TS followed by PEF represents a valid alternative for L. innocua inactivation in milk.     

Growth of Pseudomonas weihenstephanensis,Pseudomonas proteolytica and Pseudomonas sp. in raw milk: Impact of residual heat-stable enzyme activity on stability of UHT milk during shelf-life

One of the reasons for spoilage of UHT milk during shelf-life is the presence of residual proteolytic activity produced from Pseudomonas spp. during storage of raw milk. The aim of this study was to describe the product defects occurring in indirectly heated UHT milk during shelf-life, and to establish a correlation between proteolytic activity and onset of product spoilage. UHT milk was produced from raw milk incubated with different Pseudomonas strains, and examined over four months during storage at 20 °C. Inactivation kinetics of the peptidases were determined. In UHT milk, product defects occurred in the order: bitterness – particles – creaming – sediment – gelation in all the samples containing peptidases (apparent enzyme activity ≥ 0.03 pkat mL⁻¹). A linear correlation was found between proteolytic activity and onset of product defects, apart from onset of gelation.     

Numerical and experimental studies on a novel Steinmetz treatment chamber for inactivation of Escherichia coli by radio frequency electric fields

Radio frequency electric field (RFEF) is an emerging non-thermal food processing technology that is alternative to pulsed electric fields (PEF). A novel Steinmetz treatment chamber design, that increases homogeneity of the electric field distribution, has been proposed and constructed. The design was performed and evaluated via Multiphysics modelling. The model was validated by comparison with experimental measurements of outlet temperature, power consumption and current. Inactivation studies showed the influence of electric field intensity, temperature, and treatment time on the inactivation of Escherichia coli in saline water with electrical conductivities between 0.02 and 0.1 S m^− 1. A maximum inactivation of 3.6 log CFU mL^− 1 was obtained at 26.5 kV cm^− 1, 45 °C and 900 μs treatment time. An energy demand of 63 kJ kg^− 1 is required for 1 log reduction, when processing at 25 °C, for foods having 0.1 S m^− 1 conductivity at 20 °C, but energy consumption increases with the electrical conductivity.     

Partial renneting of pasteurised bovine milk: Casein micelle size,heat and storage stability

The effects of partial renneting at low temperature on the casein micelle (CM) size and the storage stability of milk were investigated. Low chymosin concentrations (≤ 0.03 IMCU mL^− 1) was applied to pasteurised skim milk at 4 °C and enzyme activity was terminated by thermal application at 60 °C/3 min and 85 °C/30 min, referred to as low heat (LHT) and high heat (HHT) treatment milk, respectively. The addition of rennet with concentrations of 0.01, 0.02 and 0.03 IMCU mL^− 1 for 15 min resulted in κ-casein hydrolysis of 10, 20 and 25%, respectively. Moreover, mean CM size of milk was reduced by up to 10 nm. For LHT milk, the renneted micelles appeared to be stable for up to 17 days, especially in response to the application of 0.01 IMCU mL^− 1 and at a storage temperature of 4 °C. Severe heating at 85 °C/30 min to inactivate the enzyme caused an increase in CM size.     

Comparison of the effect of pulsed electric field or high voltage electrical discharge for the control of sweet white must fermentation process with the conventional addition of sulfur dioxide

The present work discusses the efficiency of pulsed electrical treatments for the inactivation of yeasts. The application of pulsed electric fields (PEFs) and high voltage electrical discharges (HVEDs) as alternatives to sulfites, which are used as anti-microbial to stop the fermentation of sweet white wine, was investigated. The influence of sulfite concentration (from 0 mg·L^− 1 to 500 mg·L^− 1), PEF (from 4 kV·cm^− 1 to 20 kV·cm^− 1; from 0.25 ms to 6 ms) and HVED (40 kV/cm; 1 ms or 4 ms) treatments on the inactivation of total yeasts and non-Saccharomyces yeasts was determined. The addition of SO₂ (250 mg·L^− 1) resulted in 8 log total yeast reduction. The maximum yeast inactivation obtained with PEF and HVED was respectively 3 and 4 logs. The use of SO₂, HVED and PEF allows decreasing the non-Saccharomyces yeast level by 7, 5 and 4 logs respectively. However, the wine browning was less pronounced for the samples treated by PEF in comparison with HVED and SO₂ treatments. PEF seems to be the most suitable alternative technique to sulfite addition.     

Developing an antimicrobial packaging of ready-to-eat pomegranate arils based on vapors of brandy or distillery ethanol

Despite the increasing pomegranate consumption, the ready-to-eat (RTE) arils are highly perishable and this negatively impacts their commercialization. Nowadays, mild pre-packaging decontamination interventions (washing with sanitizing agents or exposure to ultraviolet light) in sequence or not with modified atmospheres packaging technologies are applied. Even though, the latter combination of methods provides them a shelf-life of 10–14 days at cold storage, several negative effects have been also reported (i.e., degradation of anthocyanins). Thus, the aim of the study was to evaluate the effect of alternative, mild antimicrobials such as the vapors of distillery ethanol and brandy on microbial, physical, textural, sensorial, and multispectral imaging attributes of RTE arils during storage at different temperatures in perforated bags. Lactic acid bacteria (LAB) and yeasts/moulds were the dominant spoilage microbiota of RTE arils, regardless of storage temperature and antimicrobial. Vapors produced by both volatile antimicrobials significantly inhibited (p < 0.05) the growth of LAB and yeasts/moulds, at all storage temperatures. For instance, at 4 °C, when population of TVC on controls was 6.9 log CFU g^− 1 (day 23), the respective counts on arils treated with distillery ethanol or brandy followed the order: 4.9 log CFU g^− 1 (1 mL of ethanol) > 3.9 log CFU g^− 1 (1 mL of brandy) > 2.2 log CFU g^− 1 (2 mL of ethanol) > 1.2 log CFU g^− 1 (2 mL of brandy). Moreover, arils exposed to distillery ethanol and brandy vapors showed lower weight loss (%) compared to controls, while the firmness was reduced, regardless of treatment and storage temperature. Color measurements and evaluation of multiple sensory attributes revealed that arils exposed to brandy vapors showed more intense red color and look fresher compared to controls for longer storage time. The latter observation was also validated by multispectral image analysis, since the results suggested that arils packaged with distillery ethanol or brandy maintained their anthocyanin and carotenoids content at higher levels than controls, at 4 °C. Thus, such preservation methods may open new perspectives on mild antimicrobial packaging in order to extend shelf-life of perishable minimally processed fruits, like pomegranate RTE arils.     

Effects of somatic cell counts in milk on physical and chemical characteristics of yoghurt

The quality of plain stirred yoghurt produced from whole milk with somatic cell counts (SCC) at low (147,000 cells mL⁻¹), intermediate (434,000 cells mL⁻¹) and high (1,943,000 cells mL⁻¹) levels was examined. Each milk treatment was obtained from selected cows, according to its SCC status and milk composition. Yoghurt samples were analysed on days 1, 10, 20 and 30 after production. Analyses included pH, acidity, fat, lipolysis (expressed as free fatty acids, FFA), proteolysis and apparent viscosity. Viscosity of high SCC yoghurt was higher (P<0.05) than the low SCC yoghurt on days 10, 20 and 30 of storage. High SCC yoghurt also had higher FFA content (P<0.05). SCC did not affect pH, acidity, fat content and proteolysis of the yoghurt (P>0.05). Results indicate that SCC in milk increases the lipolysis in the resulting yoghurt during storage for 30 d.     

Fate of enterotoxigenic Staphylococcus aureus in the presence of nisin-producing Lactococcus lactis strain during manufacture of Jben,a Moroccan traditional fresh cheese

The inhibitory effect of nisin-producing Lactococcus lactis subsp. lactis UL730 on the growth of enterotoxigenic Staphylococcus aureus J10 during manufacture of Jben, a Moroccan traditional fresh cheese prepared from recombined milk, was investigated.With an inoculum level of 10³ cfu mL⁻¹, S. aureus was absent in Jben four days after inoculation when the nisin-producing lactococcus was used as lactic starter. In contrast, it survived after that period, when the starter was non-nisin-producing. No staphylococcal thermonuclease was detected in all Jben samples made from milk inoculated with S. aureus at the level of 10³ cfu mL⁻¹.With a higher inoculum of 10⁵ cfu mL⁻¹, S. aureus was still present in Jben after manufacture and persisted during the storage of the product for 3 days in the laboratory, even when the starter used was nisin-producing. Staphylococcal thermonuclease and type C enterotoxin were detected in all Jben samples made from milk inoculated with 10⁵ cfu mL⁻¹. Thermonuclease and enterotoxin were already produced in the coagulum, at 24 h after milk inoculation with S. aureus.     

High-pressure and temperature effects on the inactivation of Bacillus amyloliquefaciens,alkaline phosphatase and storage stability of conjugated linoleic acid in milk

Milk rich in conjugated linoleic acid (CLA, 42 ± 3 mg g^− 1 fat) was used to evaluate the impact of high-pressure sterilization (HPS). The pressure, temperature and time needed to reduce 7-log of Bacillus amyloliquefaciens endospores were determined in the presence of nisin (4–64 mg L^− 1). In addition, the inactivation of alkaline phosphatase was evaluated. After HPS treatment, the remaining CLA and formation of hydroperoxides were monitored during storage up to 60 d at 25 °C. The addition of nisin (≥ 16 mg L^− 1) to milk significantly enhanced the inactivation of B. amyloliquefaciens (7-log reduction) after treatment at 600 MPa, 120 °C and 5 min of holding time. These conditions were selected to evaluate the impact of HPS on the CLA retention and hydroperoxides formation. Milk with the addition of nisin and treated with HPS delivered higher retention of CLA and a lower concentration of hydroperoxides compared with the UHT equivalent process (125 °C/15 s and 135 °C/10 s).Industrial relevanceHigh-pressure sterilization is a valuable alternative to produce superior quality milk products in cases where traditional thermal treatments have failed. This study evaluated the impact of processing conditions on the conjugated linoleic acid content at conditions where commercial sterilization has been achieved (7-log reduction of B. amyloliquefaciens). The outcomes of this study are considered as a step further for the development of high-pressure sterilized milk.     

Immunoglobulins,growth factors and growth hormone in bovine colostrum and the effects of processing

In colostrum collected 0–80 h postpartum the contents of immunoglobulins (Igs), transforming growth factor beta-2 (TGF-β2), insulin-like growth factor-1 (IGF-1) and growth hormone (GH) were analysed. Colostrum initially contained 90 mg mL⁻¹ IgG1, 2.8 mg mL⁻¹ IgG2, 1.6 mg mL⁻¹ IgA, 4.5 mg mL⁻¹ IgM, and these concentrations declined by 92%, 87%, 93% and 84%, respectively, in the samples collected later. Of the growth factors, colostrum initially contained 289–310 ng mL⁻¹ TGF-β2 and the concentration diminished to 66 ng mL⁻¹. The content of IGF-1 and GH postpartum decreased from 870 to 150 ng mL⁻¹, and from 0.17 to <0.03 ng mL⁻¹, respectively. Heat treatment and freeze-drying of colostral whey decreased the content of Igs to 75%, while the contents of IGF-1 and TGF-β2 were unaffected. A similar processing, including filtration steps reduced also the IGF-1 and TGF-β2 by 25%. IgM seems to be the most sensitive of the Igs to processing.     

Combined densification and pulsed electric field treatment for selective polyphenols recovery from fermented grape pomace

The aim of this study is to assess a new process for the valorization of fermented grape pomace using pulsed electric fields (PEF). The combination of densification and PEF treatment was applied on grape pomace of low relative humidity, without any addition of conductive liquid. The kinetics of extraction and the composition of polyphenols were evaluated throughout the subsequent hydro-alcoholic extraction at different temperatures.Optimal parameters of PEF treatment (field strength E = 1.2 kV·cm^− 1; energy input W = 18 kJ·kg^− 1; density ρ = 1.0 g·cm^− 3) increased the content of total polyphenols regardless of the temperature of extraction. The ratio of total anthocyanins to total flavan-3-ols at 20 °C was equal to 7.1 and 9.0 for control and PEF treated modalities, respectively. These results demonstrate the selective nature of PEF treatment in anthocyanin extraction, and thus reveal new possibilities to produce extracts with different biochemical compositions.Industrial relevanceThis study examines the feasibility of densification combined with PEF pre-treatment of relatively low humidity grape pomace for the enhancement of bioactive compounds extraction. The concentration of total phenolic compounds obtained after PEF treatment showed that the use of this technique is relevant for an industrial use, since solvent amount and extraction time can be reduced. Moreover, the selective nature of PEF opens the opportunity to produce extracts of different biochemical compositions. This process is an alternative to conventional pre-treatments of raw material (e.g. dehydration and grinding), which have impacts on product quality and are more energy consuming.     

Prediction of Shelf-Life of Pasteurized Milk and Other Fluid Dairy Products in 48 Hours

The objectives of this study were to provide early shelf-life information about various dairy products and to eliminate the need for flavor analysis to detect microbiological spoilage. Two combinations of milk and media volumes (5 and 20 ml) and two preincubation times (18 and 24 h) were evaluated. An improved impedance method to predict potential shelf-life of whole milk, skim milk, chocolate milk, and half and half was developed. A mixture of 20 ml of product and 20 ml of plate count broth, preincubated for 18 h at 18°C, followed by impedance testing at 21°C, gave consistent results in the least time. Traditionally the impedance method required the input of a taste panel for calibration of the impedance detection times to flavor-related shelf-life. A simpler method replaces flavor analysis by impedimetric determination of each sample's last day of use. Last day of use was defined as the day after the impedance detection time was ≤2.0 h. On this day, standard plate counts were usually in the 1.0 × 10⁶ to 1.0 × 10⁷ cfu/ml range, indicating spoilage. Correlation coefficients between impedance detection times and days to last day of use or Moseley plate counts were r = .89 and r = .71, respectively. A field trial at a commercial dairy research center verified that impedance detection times correlate very closely to flavor-related shelf-life and that last day of use determination is useful in replacing flavor analysis when necessary. This method provides potential shelf-life prediction within 48 h. The last-day-of-use concept allows users to calibrate the impedance method without a plate count procedure or taste panel.     

HPLC of proteose peptones for evaluating ageing of packaged pasteurized milk

The proteolysis of casein (CN) occurring in packaged pasteurized milk (PM) during refrigerated storage was studied with relation to hygienic and microbiological characteristics of starting raw milk. Six batches of raw milk having standard plate count (SPC) from 1.5×10⁴ to 2.5×10⁵ cfu mL⁻¹ and somatic cell count (SCC) from 1.6×10⁵ to 4.4×10⁵ units mL⁻¹ were pasteurized (73 °C for 15 s), packaged and stored at 4 °C for 12 days. Capillary zone electrophoresis of CN showed breakdown of β-CN in all PM samples during storage. An HPLC method for monitoring proteose peptones (PP) formation was developed. Level of PP in PM samples increased, with keeping time from 667–789 to 947–1383 mg L⁻¹ and PP formation was significantly (P<0.05) related to SCC of starting raw milk. Electrospray ionization–mass spectrometry showed that PP were mainly represented by PP-5 from either A¹ or A² variants of β-CN. Five commercial samples of PM were analysed for PP formation during 14-day storage at 4 °C. Commercial samples prepared by microfiltration process or bactofugation combined with pasteurization showed the slowest formation of PP. The effect of storage temperature on PP formation was evaluated by keeping a conventional PM sample at either 8 or 12 °C for 12 days. Proteolysis of all major CNs upon action of plasmin and bacterial proteinases was observed under these conditions. PP level thus proves to be a reliable analytical index for evaluating the ageing of packaged PM during refrigerated storage.     

Microbiological and physicochemical stability of raw,pasteurised or pulsed electric field-treated milk

Pulsed electric field (PEF) processing was investigated as an alternative dairy preservation technology that would not compromise quality yet maintain safety. PEF processing of raw whole milk (4% fat) was conducted at two processing conditions (30 kV/cm, 22 μs, at either 53 or 63 °C outlet temperature) and compared with two thermal treatments (15 s, at either 63 or 72 °C) and a raw milk control and replicated twice. Milk bottles (2 L) from each treatment were incubated for two weeks, at 4 and 8 °C, and assessed for total plate count, pH, colour, rennetability, plasmin activity and lipid oxidation. The microbial quality of the thermal (72 °C/15 s) and PEF (63 °C) were similar. A drop in pH occurred after a change in counts was observed. Rennetability was not different between the treatments. Short chain acids dominated the volatile profile of the milk samples. Concentration of volatiles derived from microbial activity, namely 2,3-butanedione, acetic acid and other milk lipid derived short chain free fatty acids (e.g. butanoic and hexanoic acids), followed the trend of microbial activity in milk samples.Industrial relevanceResearch on the application of PEF to control spoilage and pathogenic microorganisms and enzyme systems in milk spans a wide array of processing equipment and reaction conditions. While industrial scale PEF processing of liquid milk for preservation and improved quality seems generally possible, substantiation of lower thermal damage under safe and scalable PEF conditions is required to enable economic feasibility.     

Salmonella typhimurium resistance on pulsed electric fields associated with membrane fluidity and gene regulation

Effects of different growth temperatures on cytoplasmic membrane fluidity and phospholipids phase transition temperature (T_m) of Salmonella typhimurium and resistance to pulsed electric field (PEF) inactivation, as well as the expression of stress-related genes and fatty acid biosynthesis-associated genes were investigated. Results indicated that the PEF resistance of S. typhimurium increased as growth temperature increased. S. typhimurium cultivated at 10 °C exhibited the lowest PEF resistance with the reduction of 4.23 log₁₀ CFU/mL, while the reduction of 2.10 log₁₀ CFU/mL was found in S. typhimurium cultivated at 45 °C under the same PEF treatment, due to the up-regulation of the expression of fabA gene, which was characterized by the lowest T_m of membrane phospholipids and the greatest membrane fluidity. Although the expression of alternative sigma factors were altered by growth temperature, these genes were not essential for S. typhimurium to develop PEF resistance, suggesting that the PEF resistance modified by growth temperature could be caused by alterations in membrane fluidity.Industrial relevancePulsed electric fields (PEF) treatment has been widely applied in nonthermal pasteurization and increasingly focused on synergistic combinations with other techniques such as thermal treatment, sonication and antibacterial agents to improve the efficacy of PEF to inactivate micro-organisms. Our results indicated that S. typhimurium cultivated at relatively lower temperature was easily inactivated by PEF, due to the up-regulation of the expression of fabA gene, which was characterized by the lowest phase transition temperature of cytoplasmic membrane phospholipids and the greatest membrane fluidity. Therefore, the underlying mechanism of alterations in PEF resistance of S. typhimurium induced by growth temperature was explored to achieve better understanding of microbial inactivation by PEF.     

Effect of pulsed electric field (PEF)-treated kombucha analogues from Quercus obtusata infusions on bioactives and microorganisms

Pulsed electric field (PEF) is a promising non-thermal food preservation technology. The objective was to study inactivation of yeasts in PEF-treated kombucha analogues prepared from Quercus obtusata infusions. Fermentation conditions of infusions from Q. obtusata were time (7 days), sugar (10%), starting culture (10%), and inoculum (2.5%, at 25 °C). The PEF treatment considered using square waves, an electric field strength (37.3–53.4 kV/cm), PEF processing time (445.3–1979.2 μs), an output temperature (18.31 ± 0.98 °C), an input energy (21.2 - 136.5 KJ/L), and two feed flow rates (51.42 and 102.85 L/h). pH, °Brix, color determinations, microbiological testing, total phenolic, flavonoid content, DPPH test, and UPLC/ESI/MS/MS analysis were done. No changes at different PEF conditions were observed for pH and °Brix. Higher color changes were observed at higher specific energies. Acid-acetic bacteria were more sensitive to PEF than yeasts. Lower specific energies render products with higher polyphenolic content and antioxidant capacity.Industrial relevancePulse electric field is an interesting alternative to preserve kombucha analogues from oak leave infusions with minimal changes in physicochemical characteristics, antioxidant activity and bioactive compounds. The present work describes the effect of feed flow and specific energy on the several characteristics of fermented beverages, determining conditions for best processing.     

Characterization of bacteriocin ST8KF produced by a kefir isolate Lactobacillus plantarum ST8KF

Lactobacillus plantarum ST8KF, isolated from kefir, produced a 3.5 kDa bacteriocin (bacST8KF) active against Lb. casei, Lb. salivarius, Lb. curvatus and Listeria innocua. BacST8KF was sensitive to proteolytic enzymes, but stable between pH 2.0 and 10.0, and heat resistant (20 min at 121 °C). BacST8KF did not adsorb to the surface of the producer cell. Maximum activity (25,600 AU mL⁻¹) was recorded in MRS broth with glucose, in MRS broth with glucose replaced by sucrose, and in MRS broth with glucose, supplemented with KH₂PO₄ after 24 h at 30 °C. Tri-ammonium citrate and glycerol in excess of 5.0 g L⁻¹ repressed bacST8KF production. Production of bacST8KF increased from 800 AU mL⁻¹ after 3 h of fermentation in MRS broth at 30 °C to 12,800 AU mL⁻¹ after 9 h and to 51,200 AU mL⁻¹ after 27 h. These results suggest that bacST8KF may be a secondary metabolite and shows that its mode of activity is bacteriostatic.     

Effect of temperature on growth and metabolism of probiotic bacteria in milk

The growth and metabolism of six probiotic strains with documented health effects were studied in ultra-high temperature (UHT) treated milk supplemented with 0.5% (w/v) tryptone or 0.75% (w/v) fructose at different temperatures. The probiotic strains were Lactobacillus acidophilus La5, Lb. acidophilus 1748, Lb. johnsonii LA1, Lb. rhamnosus GG, Lb. reuteri SD 2112 and Bifidobacterium animalis BB12. Fermentation was followed for 48 h at 20, 30, 37 and 45 °C and the samples were analysed for pH, log cfu mL⁻¹, volatile compounds, organic acids and carbon dioxide. All six probiotic strains showed very different profiles of metabolites during fermentation, however, the two Lb. acidophilus strains were the most alike. All strains, except Lb. reuteri SD 2112, showed viable cell numbers above 6.5 log cfu mL⁻¹ after 48 h fermentation at 30, 37 and 45 °C. The probiotic strains produced different amounts of metabolic products according to temperature and fermentation time illustrating the importance of controlling these parameters.