Effect of high-pressure processing on bacterial inactivation in açaí juices with varying pH and soluble solids content

This study evaluated microbial inactivation effects of high-pressure processing (HPP) applied to açaí juices formulated with varying pH and soluble solids content (SSC). Açaí juice with pH 4.3 and 2.9°Brix was initially inoculated with cocktails of 5 strains of E. coli O157:H7, Listeria monocytogenes or Salmonella spp. and processed at varying pressures (300, 400 and 600 MPa) and dwelling times (1 and 3 min) at 5 °C. The lethality at 400 MPa for 3 min was >6-log CFU/mL. Further inactivation was observed during storage under refrigeration in the populations of Salmonella spp. and L. monocytogenes. In order to study the influence of pH and SSC on inactivation of Salmonella spp. by HPP, pH of açaí juice samples was adjusted to a range between 4.0 and 5.5 and SSC was adjusted between 2.9 and 14.9°Brix. The ability of HPP to provide a 5-log reduction in the population of Salmonella spp. was reduced with increasing pH and SSC. Immediately after HPP the juices with pH 4.0 and 2.9°Brix presented >6-log reduction while the one with 8.9°Brix resulted in 5-log reduction. In one week of refrigerated storage (7 °C), the juices (pH 4.0–14.9°Brix and pH 4.5–2.9°Brix) also presented >6-log reduction in Salmonella spp. concentration. These results indicated that a less intense process (below commonly recommended commercial conditions - 600 MPa/3 min) could be applied for açaí juice thus assuring required safety, in addition to an extra microbial inactivation verified during refrigerated storage.Industrial relevanceOur results showed that viability of cells of pathogenic strains continues to fall after processing and that this effect can be reversed in higher pH and higher concentration of soluble solids. This observation can help the design of more efficient protocols for validation of HPP processing, leading to milder processing conditions that will allow reduction of maintenance and energy costs associated with HPP. In addition, our results help to clarify the criteria to be adopted in the microbiological validation of juices processed by high hydrostatic pressure.     

Inactivation of hepatitis A virus and a calicivirus by high hydrostatic pressure

Potential application of high hydrostatic pressure processing (HPP) as a method for virus inactivation was evaluated. A 7-log10 PFU/ml hepatitis A virus (HAV) stock, in tissue culture medium, was reduced to nondetectable levels after exposure to more than 450 MPa of pressure for 5 min. Titers of HAV were reduced in a time- and pressure-dependent manner between 300 and 450 MPa. In contrast, poliovirus titer was unaffected by a 5-min treatment at 600 MPa. Dilution of HAV in seawater increased the pressure resistance of HAV, suggesting a protective effect of salts on virus inactivation. RNase protection experiments indicated that viral capsids may remain intact during pressure treatment, suggesting that inactivation was due to subtle alterations of viral capsid proteins. A 7-log10 tissue culture infectious dose for 50% of the cultures per ml of feline calicivirus, a Norwalk virus surrogate, was completely inactivated after 5-min treatments with 275 MPa or more. These data show that HAV and a Norwalk virus surrogate can be inactivated by HPP and suggest that HPP may be capable of rendering potentially contaminated raw shellfish free of infectious viruses.     

Study of Antioxidant Capacity and Quality Parameters in An Orange Juice–Milk Beverage After High-Pressure Processing Treatment

The aim of this study was to obtain a beverage with a high content of bioactive compounds. Therefore, a mixture of orange juice and milk was prepared. The effect of high-pressure processing (HPP), four different pressures (100, 200, 300, and 400 MPa), four treatment times for each pressure (120, 300, 420, and 540 s) on antioxidant compounds, and quality parameters was studied. The effects of HPP treatment were compared with those of thermal treatment (90 °C for 15, 21 s and 98 °C for 15, 21 s). Ascorbic acid retention in the orange juice–milk beverage was higher than 91% in all cases after HPP. There was a significant increase (p < 0.05) in phenolic compounds at 100 MPa/420 s, however at 400 MPa/540 s, it was observed a non-significant decrease. Total carotenoid content was significantly higher in all samples treated by HPP when treatment time was 420 and 540 s. Color changes increased when pressure and treatment times were higher, with the highest difference appearing at 400 MPa/540 s, but HPP had a smaller effect on total color changes than thermal processing. A 5-log reduction of Lactobacillus plantarum CECT 220 was obtained in the orange juice–milk beverage after HPP (200 MPa, 300 s), and this was compared with treatment at 90 °C (15 s), the heat treatment most effective at preserving ascorbic acid.     

Equivalent processing for pasteurization of a pineapple juice–coconut milk blend by selected nonthermal technologies

Identifying equivalent processing conditions is critical for the relevant comparison of food quality attributes. This study investigates equivalent processes for at least 5-log reduction of Escherichia coli and Listeria innocua in pineapple juice–coconut milk (PC) blends by high-pressure processing (HPP), pulsed electric fields (PEF), and ultrasound (US) either alone or combined with other preservation factors (pH, nisin, and/or heat). The two blends (pH 4 and 5) and coconut milk (pH 7) as a reference were subjected to HPP at 300–600 MPa, 20°C for 0.5–30 min; PEF at an electric field strength of 10–21 kV/cm, 40°C for 24 µs; and US at 120 µm amplitude, 25 or 45°C for 6 or 10 min. At least a 5-log reduction of E. coli was achieved at pH 4 by HPP at 400 MPa, 20°C for 1 min; PEF at 21 kV/cm, 235 Hz, 40°C for 24 µs; and US at 120 µm, 45°C for 6 min. As L. innocua showed greater resistance, a synergistic lethal effect was provided at pH 4 by HPP with 75 ppm nisin at 600 MPa, 20°C for 5 min; PEF with 50 ppm nisin at 18 kV/cm, 588 Hz, 40°C for 24 µs; and US at 45°C, 120 µm for 10 min. The total soluble solids (11.2–12.4°Bx), acidity (0.47%–0.51% citric acid), pH (3.91–4.16), and viscosity (3.55 × 10⁻³–4.0 × 10⁻³ Pa s) were not significantly affected under the identified equivalent conditions. HPP was superior to PEF and US, achieving higher ascorbic acid retention and lower color difference in PC blend compared to the untreated sample.     

Inactivation of bacterial pathogens in human milk by high-pressure processing

Low-temperature, long-time (LTLT) pasteurization assures the safety of banked human milk; however, heat can destroy important nutritional biomolecules. High-pressure processing (HPP) shows promise as an alternative for pasteurization of breast milk. The purpose of this study was to investigate the efficacy of HPP for inactivation of selected bacterial pathogens in human milk. Human milk was inoculated with one of five pathogens (10(8) to 10(9) CFU/ml), while 0.1% peptone solution solutions with the same levels of each organism were used as controls. The samples were subjected to 400 MPa at 21 to 31 degrees C for 0 to 50 min or to 62.5 degrees C for 0 to 30 min (capillary tube method) to simulate LTLT pasteurization. Tryptic soy agar and selective media were used for enumeration. Traditional thermal pasteurization resulted in inactivation (> 7 log) of all pathogens within 10 min. In human milk and in peptone solution, a 6-log reduction was achieved after 30 min of HPP for Staphylococcus aureus ATCC 6538. After 30 min, S. aureus ATCC 25923 was reduced by 8 log and 6 log in human milk and peptone solution, respectively. Treatments of 4 and 7 min resulted in an 8-log inactivation of Streptococcus agalactiae ATCC 12927 in human milk and peptone solution, respectively, while Listeria monocytogenes ATCC 19115 required 2 min for an 8-log inactivation in human milk. Escherichia coli ATCC 25922 was inactivated by 8 log after 10 min in peptone solution and by 6 log after 30 min in human milk. These data suggest that HPP may be a promising alternative for pasteurization of human milk. Further research should evaluate the efficacy of HPP in the inactivation of relevant viral pathogens.     

Pressure assisted thermal pasteurization (PATP) of hypoallergenic and low protein ready-to-feed (RTF) infant formula fortified with bioactives: A novel approach

Infant Milk Formula (IMF) is an instant alternative to breastfeeding which is being investigated continuously to mimic the composition of human milk. Hypoallergenic IMF is recommended for infants who cannot tolerate cow milk due to allergy. Paediatric obesity resulted in burgeoning demand for low protein infant formula, especially in Asia. Beta-lactoglobulin (β-Lg), a major cow milk allergen to infants, is present in cow milk as 3–4 g/L, whereas, interestingly, it is absent in human milk. Besides, human milk contains Fe³⁺ binding lactoferrin (LF) and Ca²⁺ binding alpha-lactalbumin (α-Lac) about 10 and 3 times, respectively, higher than cow milk. Therefore, a mechanism to formulate a hypoallergenic IMF with low protein content could be the addition of LF and α-Lac and reducing β-Lg at the same time using an appropriate processing method. Hence, as a pragmatic approach, this study considered a pasteurized form of ready-to-feed (RTF) by applying Pressure Assisted Thermal Pasteurization (PATP) achieved from HPP of 600 MPa for 15 s applied at 57.1 °C to attain 72.3 °C after pressurization. In parallel, conventional HTST was also applied at 72 °C for both 15 and 30 s to compare PATP's effect. HTST and PATP retained >90% and > 75% LF respectively whereas PATP induced higher retention of α-Lac compared to HTST. However, HTST retained >60% β-Lg while PATP induced a high denaturation of β-Lg with 28% retention only. Moreover, both PATP and HTST induced around 5 log reduction of E. coli (ATCC 8739) in IMF. Therefore, the current investigation potentially indicates a route to develop a PATP-processed hypoallergenic and low protein RTF formula, a niche product.     

Production and quality improvement of Indian cottage cheese (Paneer) using high pressure processing

Paneer, a product of India similar to cottage cheese, was prepared from cow's milk heat-treated (90 °C/5 min) (HTMP) or high-pressure (HP) treated (500 MPa/15 min) (HPPMP) for achieving pasteurization. HTMP and HPPMP paneer samples were HP treated (500 MPa for 15 min) again after vacuum packaging to get HTMP/HPP and HPPMP/HPP samples, respectively. The third set of samples were obtained by dipping HTMP and HPPMP paneer samples in 2% lactic acid solution and then subjecting them to the same HP treatment and stamped as HTMP/LA/HPP and HPPMP/LA/HPP, respectively. All six types of vacuum-packed paneer were studied for changes in moisture, acidity, pH, color, texture, and microbiological quality during storage at 5 ± 1 °C and 25 ± 1 °C. High-pressure treatment of milk increased the yield of paneer significantly (P < 0.05) from 13.9 ± 0.59% (HTMP) to 18.2 ± 0.32% (HPPMP). Paneer treated with lactic acid and high-pressure treatment (HTMP/LA/HPP and HPPMP/LA/HPP) had higher textural stability than HTMP, HTMP/HPP, HPPMP, and HPPMP/HPP for up to 28 days, but had a reduced moisture content, higher acidity, and lower whiteness index. High-pressure treatment of vacuum-packed paneer (HTMP/HPP and HPPMP/HPP) led to the formation of a more compact paneer matrix (higher hardness), higher moisture expulsion, and yellowness (b*). Thus, high-pressure processing of paneer could pave paths for extending paneer shelf-life without any additives and thermal treatment.     

Inactivation of Listeria innocua and Escherichia coli in carrot juice by combining high pressure processing,nisin, and mild thermal treatments

This study explored the effectiveness of high pressure (200–500 MPa) alone or in combination with mild thermal treatments (35 and 50 °C) and nisin (25 and 50-ppm) on the inactivation of L. innocua and E. coli in carrot juice. Processing at 500 MPa at 20 °C for 2 min without nisin resulted in 4- and 5-log CFU/mL reduction of L. innocua and E. coli, respectively while incorporating 25-ppm nisin at same pressure and temperature rendered 7-log CFU/mL reduction. There was synergism between high pressure, nisin, and heat in all treatments to inactivate both microorganisms. After a 28-d of refrigerated storage, total plate counts were <2-log CFU/mL in carrot juice treated with combination of 300 MPa and 25-ppm nisin at 35 °C. All combinations resulted in less intense use of pressure, i.e. more energy efficient, cost effective processes while attaining high quality juices. The results of this study suggest that by using selected combinations of high pressure, nisin and mild temperatures, safe, clean-label, high-quality juices can be produced.Industrial relevanceThe results from this study show a synergistic effect on the inactivation of L. innocua and E. coli in carrot juice from the combined application of HPP, nisin, and mild temperatures. By replacing the use of HPP alone by these combinations will allow the use of reduced pressures over shorter period of times to process low-acid juices, lowering energy requirements and increasing throughput. This study will aid the beverage processing industry in the development of clean label juice products with fresh-like quality attributes and using considerable less energy to conventional processing.     

Processing methods of donor human milk evaluated by a blood plasma clotting assay

Donor human milk is the first alternative for preterm infants when mother's own milk is not available. Most available human milk banking guidelines recommend classical holder pasteurization to ensure safety by eliminating potential infectious microorganisms. Processing by heat treatment, however, negatively affects functionality and availability of bioactive components naturally present in human milk. Here we compared the effect of five different processing methods on the ability of human milk to induce blood plasma clotting, which was recently described as a bioactive function present in human milk. From thirty lactating women, milk samples were collected, and all milk samples were subjected to holder pasteurization (30 min at 62.5 °C), high-temperature-short-time pasteurization (15 s at 72 °C), high-pressure processing (5 min at 500 MPa), ultraviolet-C irradiation (4863 J/L), or thermo-ultrasonication (6 min at 60 W, at 40 °C). All methods significantly reduced the ability of milk to trigger blood plasma clotting compared to untreated milk, but ultraviolet-C irradiation and high-pressure processing were best at preserving this activity. Taken together, measuring the ability of milk to induce blood plasma clotting may offer a new tool to monitor the effect of human milk processing.     

High-pressure processing (HPP) of raw and dry-cured ham from experimentally infected pigs as a potential tool for the risk control of Toxoplasma gondii

Raw and dry-cured meats have been identified as a potential source of Toxoplasma gondii infection for humans. The present study evaluated the efficacy of an alternative non-thermal food-processing treatment, high hydrostatic pressure, on the viability of T. gondii bradyzoites in raw and dry-cured ham. Meat of pigs experimentally exposed to 4000 oocysts of T. gondii VEG strain was vacuum-packaged and subjected to high pressure processing (HPP). Tap water (6 °C ± 1 °C) was used as the pressure-transmitting fluid, and its temperature during HPP increased 2.7 °C per 100 MPa. The effect was evaluated by bioassay in mice followed by qPCR. In raw ham, 100–400 MPa/1 min did not inactivate T. gondii, whereas 600 MPa/20 min was effective. In dry-cured ham, 600 MPa for 3 or 10 min were not effective and a 20-min treatment was required to render the bradyzoites non-infectious for mice. Our results point toward the potential use of HPP as a tool for risk control of T. gondii and as a food safety guarantee.Industrial relevance textUnder real production conditions, the usual HPP treatments applied by the food industry to control L. monocytogenes and other pathogenic bacteria are 600 MPa of pressure and holding times of 3–10 min. Our study demonstrated, however, that longer treatment times are required to inactivate the parasite and, thus, to guarantee the safety of raw and dry-cured meats in order to reduce the public health risk of toxoplasmosis. Further research is needed to evaluate other HPP conditions, including pulsed cycles, for the inactivation of T. gondii in foods of animal origin.     

High pressure processing at ultra-low temperatures: Inactivation of foodborne bacterial pathogens and quality changes in frozen fish fillets

High pressure processing (HPP) at ultra-low temperatures was conducted against Listeria monocytogenes and Salmonella enterica in frozen pink salmon fillets. Quality changes, such as drip loss, color and odor attributes were recorded in non-inoculated pollock, pink salmon and tuna fillets. Pressures at 250 and 400 MPa were applied from 0.5 to 10 min. Reductions up to 3.5 log cfu/g were recorded for the treatments performed at −32 °C, in contrast to −50 °C where the reductions were only up to 1.5 log cfu/g. Higher pressure did not cause higher reduction. It was apparent that the main factor contributing to the bacterial inactivation is the phase transition of ice structure from I to III, in contrast to transition from I to II. Drip loss was not higher than the expected with HPP at temperatures above 0 °C, while color changes were negligible. Finally, the odor evaluation did not exhibit considerable differences between untreated and treated samples.Industrial relevanceHigh pressure processing at ultra-low temperatures is a promising treatment for bacterial inactivation and retention of quality attributes of frozen fish. Treatment at 250 MPa for only 3 min at temperatures just below −22 °C, which is feasible and affordable, caused a more than 3-log reduction against Listeria monocytogenes and Salmonella enterica, without affecting considerably the quality properties. Thus, the application of low pressure and shorter processing times gives a great potential for industrial application for frozen fish or fish that wouldn't be undesirable to freeze before pressurization.     

Coliphage as pressure surrogates for enteric viruses in foods

In this study the potential of using selected bacteriophages as pressure surrogates for hepatitis A virus (HAV) and Aichi virus (AiV) was investigated. The coliphages included, T₄, MS2, Qβ, λ imm 434, λ cI 857 and λ cI 857A. T₄ displayed similar pressure responses as HAV and was chosen for further study. The most pressure-resistant phage, MS2, was selected as a possible surrogate to estimate AiV inactivation by high pressure processing (HPP). HAV, AiV and their selected bacteriophage surrogates were treated at a range of pressures and times in three different media. All four were treated in phosphate-buffered saline (PBS), artificial seawater (ASW) or oyster slurry (OS) at 250, 400 or 500 MPa for 1, 5 or 10 min at 20 °C. While T₄ had similar pressure resistance to HAV under conditions of high (500 MPa) and lower pressure (250 MPa), inactivation trends were very different following treatment at 400 MPa and when the viruses were suspended in OS. MS2 showed similar resistance as AiV but at ambient treatment temperatures only. The highest levels of inactivation of MS2 were achieved at 60 °C and 500 MPa. AiV was eliminated at 60 °C for 5 min at ambient pressure, but > 3 log survived exposure to 60 °C at 500 MPa. This degree of protection by pressure may be important in determining the mechanisms of pressure and heat resistances in other viruses.Industrial relevanceGreater knowledge of the responses of viruses and their surrogates to high pressure will aid in the validation of new high pressure-processed food that may be at risk to contamination from HAV or other enteric viruses.     

Pressure-induced inactivation of bacteria through pressure-assisted thawing using a thermal buffer zone.

Effect of thermal buffer zone was examined on the microbial inactivation through a pressure-assisted thawing. A plastic bag of bacterial suspension enclosed with a thermal buffer zone was frozen at − 50 °C, and treated for 20 min with a pressure-assisted thawing in water of 4 °C. A reduction of 8-log cycle was obtained at 200 MPa for the stationary growth phase cells of Escherichia coli that was suspended in 1% skim milk and enclosed with wheat flour/water paste and two polytetrafluoroethylene plates. When 100% ethanol was used as a thermal buffer and the samples were pressured at 194 MPa in 1% skim milk, levels of E. coli and Listeria monocytogenes were reduced by 6-log cycle and 7-log cycle, respectively. Staphylococcus aureus decreased by 4-log cycle.Industrial relevanceThis work will contribute to new developments in the pressure processing of foods, since the use of a thermal buffer zone in pressure-assisted thawing was very effective in enhancing the level of pressure-induced microbial inactivation.     

Comparison of hydrostatic and hydrodynamic pressure to inactivate foodborne viruses

The effect of high hydrostatic pressure (HPP) and hydrodynamic pressure (HDP), in combination with chemical treatments, was evaluated for inactivation of foodborne viruses and non-pathogenic surrogates in a pork sausage product. Sausages were immersed in distilled water, 100-ppm EDTA, or 2% lactoferrin, and then inoculated with feline calicivirus (FCV), hepatitis A virus (HAV) or bacteriophage (MS2, phiX174, or T₄). Each piece was packaged individually and subjected to pressure by either HDP, HPP (500 MPa, 5 min, 4 °C), or control (no pressure). On sausages immersed in water, HPP and HDP significantly (P < 0.05) reduced titers of FCV by 2.89 and 2.70 log₁₀ TCID₅₀/ml, and HAV by log₁₀ 3.23 and 1.10, respectively, when compared to non-pressure-treated controls. Titers of T₄ (1.48 and 1.10 log₁₀ PFU/g) and MS2 (1.46 and 0.96 log₁₀ PFU/g) were also significantly reduced by HPP and HDP treatments, respectively, in combination with water. Inoculation of viruses and bacteriophage on a meat product may have protected viruses from complete inactivation by pressure treatments.

Industrial relevance

This is the first study to directly compare hydrostatic and hydrodynamic pressure technologies to inactivate microorganisms. This is also the first study to examine the inactivation of viruses and bacteriophages by pressure technology in a deli meat product. This study shows that viruses attached to meat surfaces may be protected from complete inactivation by hydrostatic and hydrodynamic pressure treatments, and these findings require more investigation into the survival of viruses in deli meat products.     

Effect of high hydrostatic pressure and high-pressure homogenisation on <Emphasis Type="Italic">Lactobacillus plantarum</Emphasis> inactivation kinetics and quality parameters of mandarin juice

The inactivation kinetics of Lactobacillus plantarum in a mandarin juice treated by thermal treatment (45–90 °C), high-pressure homogenisation (HPH) (30–120 MPa at 15 and 30 °C) and high-pressure processing (HPP) (150–450 MPa at 15, 30 and 45 °C) were fitted to different Weibullian equations. A synergic effect between pressure and temperature was observed in HPH and HPP treatments achieving 2.38 log cycles after 120 MPa at 30 °C for 10 s (final T of 45 °C) and 6.12 log cycles after 400 MPa at 45 °C for 1 min (final T of 60 °C), respectively. A combined treatment of 100 MPa at 15 °C for 10 s and 300 MPa at 15–30 °C for 1 min in HPH and HPP, respectively, was needed to the first logarithm microbial population decline. Weibull model accurately predicted microorganism inactivation kinetics after HPH and HPP processing when displaying single shoulder or tail in the survivor curves, whereas when a more complex trend was observed after thermal treatment, the double-Weibull equation was found more appropriate to explain such behaviour. Equivalent treatments that achieved the same degree of microbial inactivation (77 °C–10 s in thermal processing, 120 MPa–10 s at 30 °C in HPH processing and 375 MPa–1 min at 30 °C in HPP) were selected to study the effects on quality parameters. The application of dynamic pressure led to a decrease in sedimentable pulp, transmittance and juice redness, thus stabilising the opaqueness and cloudiness of mandarin juice. Pectin methyl esterase (PME) was found to be highly baroresistant to static and dynamic pressure. Carotenoid content remained unaffected by any treatment. This study shows the potential of high-pressure homogenisation as an alternative for fruit-juice pasteurisation.     

High-Pressure Processing for the Control of Lipolysis,Volatile Compounds and Off-odours in Raw Milk Cheese

Build-up of flavour compounds throughout ripening of raw milk cheeses may result in strong over-ripening notes during refrigerated storage. In order to control the formation of free fatty acids (FFAs) and volatile compounds, and the appearance of off-odours, raw milk cheeses were high-pressure-processed (HPP) 21 or 35 days after manufacture at 400 or 600 MPa. Ripening proceeded at 8 °C until day 60 and, afterwards, cheeses were held at 4 °C until day 240. The effect of HPP on the formation of FFAs and volatile compounds was dependent on pressure level and cheese age at the time of treatment. On day 60, acetic and propionic acids, branched-chain FFAs and short-chain FFAs showed the lowest (p?<?0.05) concentrations in cheeses treated at 400 or 600 MPa on day 21, while medium- and long-chain FFAs were at similar levels in all cheeses. HPP influenced significantly (p?<?0.05) 84 out of the 94 volatile compounds found in cheese. On day 60, the lowest (p?<?0.05) concentrations of acids, alcohols and esters were recorded for cheeses treated at 400 or 600 MPa on day 21, and the lowest (p?<?0.05) concentrations of ketones for cheeses treated at 400 MPa on days 21 or 35. On day 240, all HPP cheeses showed lower (p?<?0.05) concentrations of aldehydes, esters and, particularly, sulphur compounds than control cheese, which exhibited putrid and rancid off-odours from day 120 onwards. Principal component analysis combining FFAs and volatile compounds discriminated 240-day control cheese from 120-day control cheese and both from the rest of cheeses.     

Combined effects of high-pressure treatment and storage temperature on the physicochemical properties of caprine milk

The effects of high-pressure (HP) treatment (200–500 MPa for 25 min at 25 °C) combined with storage temperature (25 and 4 °C) on the physicochemical properties of raw caprine milk were studied. Storage of HP-treated and untreated milk samples at 25 °C considerably affected the changes in the conformation of milk proteins, which were reflected by changes in the protein sedimentation rate, gradual decreases in the soluble calcium and phosphorus contents, a slight decrease in pH, an insignificant decrease (P > 0.05) in viscosity, and a decrease in the casein hydration level of milk at the end of the storage time. In contrast, the HP-treated and untreated milk samples stored at 4 °C demonstrated different characteristics than the samples stored at 25 °C. These results could be due to calcium and phosphate association with caseins, which screen charges and reduce the repulsion of micelles during the storage time.     

Effects of high pressure,microwave and ultrasound processing on proteins and enzyme activity in dairy systems — A review

High-pressure processing (HPP), microwaves (MW) and ultrasound (US) are used for pasteurization with minimum heat input. They also alter physico-chemical properties of milk proteins and enzymes. This article aims at identifying the important changes in milk proteins imparted by these three processing technologies. HPP dissociates casein micelles at low pH (<6.7) and concentrations (<4% w/w), while β-LG is the most pressure sensitive whey protein due to the presence of free thiol groups. Milk enzyme activity is inhibited at higher pressures (>400 MPa). MW treatment denatures whey proteins rapidly, even below their thermal denaturation temperatures. High-power MW treatment (e.g. 60 kW) deactivates enzymes by denaturing them. However, low-power controlled MW irradiation (e.g. 30 W) improves enzyme activity. Ultrasound can homogenize protein aggregates in dairy systems and cause whey protein denaturation. Sonication under applied pressure and heat (e.g. 3.5 kg/cm², 126.5 °C) causes enzyme inhibition while mild sonication conditions can improve enzyme activity.Industrial relevanceHPP, MW and US are gaining popularity in the dairy industry due to their ability to pasteurize and functionalize dairy streams with minimal heat input. This review offers insights into how these technologies can be used in isolation or in combination to alter milk proteins and enzyme activity for different academic and industrial applications. However, to fully understand the potential of HPP, MW and US treatment on dairy systems, further research is required in several areas including health related nutritional changes in milk and milk products caused by these technologies.     

Effect of high‐pressure treatments on microbial loads and physicochemical characteristics during refrigerated storage of raw milk Serra da Estrela cheese samples

This work studied the effect of high pressure processing (HPP) at 400, 500 and 600 MPa during 10, 5 and 3 min, respectively, on samples ewe cheese manufactured from raw milk, during storage (100 days) at 5 °C. Total aerobic mesophilic and lactic acid bacteria were slightly affected, decreasing by about 1.0 and 0.82 log CFU g^?1, respectively, immediately after HPP treatment at 600 MPa for 3 min, while Enterobacteriaceae, yeasts and moulds, and Listeria innocua were reduced to below the quantification limits. Lactic acid bacteria decreased further during storage, showing increasing inactivation as the pressure level increased. Physicochemical parameters (water activity, moisture content, pH and titratable acidity) were generally not affected by HPP, while lipid oxidation increased throughout storage, with HPP samples showing lower values (50–66%) at 100 days of storage. The results indicated that HPP has potential to improve cheese microbial safety and shelf‐life, with a lower lipid oxidation level than nonpressurised cheese.