Effects of fat, casein and lactose on high-pressure destruction of Escherichia coli K12 (ATCC-29055) in milk

Survivability of Escherichia coli O157:H7 ATCC 43888 and Enterococcus faecium ATCC 8459 in a Hydrocolloid Gel Bar Model and Macronutrient Bar Model in Response to Vacuum Microwave Drying and Storage

This study aimed to investigate the microbial safety of Vacuum Microwave Drying (VMD) and 30 days storage at 25 °C on survivability of Escherichia coli O157:H7 ATCC 43888 and Enterococcus faecium ATCC 8459 in a nutritionally minimal bar model and macronutrient bar model. Sodium alginate hydrocolloid gel bars were inoculated with each microorganism and underwent processing in a 2 kW VMD and subsequent storage at 25 °C for 10 days in sealed bags to determine the impact of VMD on bacteria without the influence of a nutritionally dense food matrix. Additionally, the effects of macronutrient concentration on organism survivability during processing and storage were tested using a peanut butter banana bar formulated to contain high carbohydrate, high protein, or high-fat content. The macronutrient bars were inoculated with each microorganism and underwent VMD with subsequent storage at 25 °C for up to 30 days in sealed bags. Results of the hydrocolloid gel model showed that in a nutritionally minimal food matrix, both microorganisms were susceptible to VMD with additional loss of each microorganism during storage. Results showed the entire loss of E. coli O157:H7 by day 10 of storage. In the macronutrient bar study, E. faecium had minimal susceptibility to VMD and storage at 30 days while E. coli O157:H7 had minimal susceptibility to VMD with greater susceptibility to storage for 30 days. There was a significant difference (p < 0.05) in log loss comparing E. coli O157:H7 VMD processed and unprocessed bars and minimal significance comparing E. faecium VMD processed and unprocessed bars. Water activity and moisture content at storage timepoints had no observed correlation with pathogen survivability in either study.

Radio frequency inactivation of Salmonella Typhimurium and Listeria monocytogenes in skimmed and whole milk powder

Milk powder is a convenient, shelf-stable food ingredient used in a variety of food products. However, pathogenic bacteria can be present and survive during prolonged storage, leading to outbreaks of foodborne diseases and product recalls. Radio frequency (RF) heating is a processing technology suitable for bulk treatment of milk powder, aiming at microbial inactivation. This study investigates the RF inactivation of Salmonella Typhimurium and Listeria monocytogenes in two types of milk powder; skimmed and whole milk powder. Specifically, the aims were to (i) examine the influence of the powder's composition on bacterial inactivation, (ii) evaluate the response of bacteria with different Gram properties (Gram positive and Gram negative) and (iii) verify the use of Enterococcus faecium as a surrogate for the two microorganisms for the specific RF process. In order to examine exclusively the influence of RF, a non-isothermal temperature profile was used, employing solely different RF energy levels to heat the product to the target temperatures. A log-linear model with a Bigelow-type temperature dependency was fitted to the experimental data. S. Typhimurium was less susceptible to RF treatments in comparison to L.monocytogenes, demonstrating a higher inactivation rate (k) and higher percentage of sublethal injury. A higher k was also observed for both microorganisms in the whole milk powder, indicating that the increased fat content and decreased levels of lactose and protein in the milk powder had an adverse impact on the microbial survival for both pathogens. The surrogate microorganism E. faecium successfully validated the microbial response of the two microorganisms to RF treatments. In general, a low heating rate RF-only process was successful in inactivating the two foodborne pathogens in skimmed and whole milk powder by 4 log(CFU/g).

Regulation of the Ice Ⅰ to Ice III high pressure phase transition meta-stability in milk and its bactericidal effects

This study was focused on a novel approach of creating perturbations under high pressure (HP) meta-stable Ice Ⅰ to Ice Ⅲ phase transition and its bactericidal effects. Experiments were carried out under subzero high pressure processing conditions using Escherichia coli suspended in milk, and the microbial inactivation before and after the meta-stable state regulation was compared. The phase transition position of unperturbed milk was 302 MPa/-37.5 °C. The volume change resulting from the phase transition was employed as the perturbation mechanism. Glucose (5 %, 20 %) and sodium chloride solutions (5 %, 20 %) were used as regulatory sources. Glucose solutions accelerated the phase change of the milk better than the sodium chloride solution and resulted in an optimum phase transition position of milk at 243 MPa/-30.6 °C. The induced perturbations accelerated meta-stable transformation and enhanced the microbial destruction. At 330 MPa/3s, compared to the unfrozen samples, the lethality of E. coli in the frozen-regulated samples significantly increased by 1.79 log. The relationship between the E. coli inactivation within the phase change pressure range and the pressure was not continuous, but a segmented one, both before and after meta-stable state regulation. A higher level of E. coli destruction was accomplished by a 5 min pressure-holding of frozen samples at 220 MPa and 280 MPa as compared to the one-pulse and two-pulses treatments without holding time. The maximum lethality of 6.73 log was achieved at 280 MPa/5 min in the frozen-regulated application.

Recent Progress in the Synergistic Bactericidal Effect of High Pressure and Temperature Processing in Fruits and Vegetables and Related Kinetics

BACKGROUND

Traditional thermal processing is a widely used method to ensure food safety. However, thermal processing leads to a significant decline in food quality, especially in the case of fruits and vegetables. To overcome this drawback, researchers are extensively exploring alternative non-thermal High-Pressure Processing (HPP) technology to ensure microbial safety and retaining the sensory and nutritional quality of food. However, HPP is unable to inactivate the spores of some pathogenic bacteria; thus, HPP in conjunction with moderate- and low-temperature is employed for inactivating the spores of harmful microorganisms. Scope and approach: In this paper, the inactivation effect of high-pressure and high-pressure thermal processing (HPTP) on harmful microorganisms in different food systems, along with the bactericidal kinetics model followed by HPP in certain food samples, have been reviewed. In addition, the effects of different factors such as microorganism species and growth stage, process parameters and pressurization mode, and food composition on microbial inactivation under the combined high-pressure and moderate/low-temperature treatment were discussed.

KEY FINDINGS AND CONCLUSIONS

The establishment of a reliable bactericidal kinetic model and accurate prediction of microbial inactivation will be helpful for industrial design, development, and optimization of safe HPP and HPTP treatment conditions.

Preservation of high pressure pasteurised milk by hyperbaric storage at room temperature versus refrigeration on inoculated microorganisms, fatty acids, volatile compounds and lipid oxidation

High pressure pasteurised (HPP) milk was stored by hyperbaric storage at room temperature (HS/RT) (50-100 MPa at 20 °C) and compared with refrigeration (RF), to assess the effect on two pathogens surrogates and a pathogenic, up to 120 days, and on fatty acids, volatile organic compounds (VOCs) and secondary lipid oxidation over 60 days. HS/RT (75-100 MPa) was able to inactivate at least 6.68/6.31/6.03 log CFU/mL of Escherichia coli/Listeria innocua/Salmonella Senftenberg (to below the detection limit), while RF resulted only in minor changes. Overall, fatty acids profile remained stable under HS/RT, although secondary lipid oxidation showed slightly higher values. In addition, both HS/RT and RF showed stable and similar VOCs profiles and off-flavour indicative compounds were not detected, except for the lowest pressure (50 MPa) after 40 days. HS/RT preserved HPP milk with enhanced microbial safety, shelf-life and quality compared to RF, being in addition quasi-energetically costless and more sustainable than RF.

Inactivating Food Microbes by High-Pressure Processing and Combined Nonthermal and Thermal Treatment: A Review

High-pressure processing (HPP) is a mild technology alternative to thermal pasteurization and sterilization of different food products. HPP has emerged to provide enormous benefits to consumers, i.e., mildly processed food and additive-free food. It effectively retains bioactive compounds and extends the shelf life of food commodities by inactivating bacteria, yeast, mold, and virus. The limitation of HPP in inactivating spores can be overcome by using other thermal and nonthermal processing sequentially or simultaneously with HPP. This review summarizes the applications of HPP in the fruits and vegetables, dairy, meat, fish, and poultry sector. It also emphasizes microbial food safety and the effectiveness of HPP in the load reduction of microorganisms. Comprehensive information about the synergistic effect of HPP with different techniques and their effectiveness in ensuring food safety is reported. The summarized data would be handy to interested researchers and industry personnel.

EFSA Panel on Biological Hazards (BIOHAZ Panel), Koutsoumanis K, Alvarez‐Ordóñez A, Bolton D, Bover‐Cid S, Chemaly M, Davies R, De Cesare A, Herman L, Hilbert F, Lindqvist R, Nauta M, Peixe L, Ru G, Simmons M, Skandamis P, Suffredini E, Castle L, Crotta M, Grob K, Milana MR, Petersen A, Roig Sagués AX, Vinagre Silva F, Barthélémy E, Christodoulidou A, Messens W, Allende A. The efficacy and safety of high-pressure processing of food

High-pressure processing (HPP) is a non-thermal treatment in which, for microbial inactivation, foods are subjected to isostatic pressures (P) of 400-600 MPa with common holding times (t) from 1.5 to 6 min. The main factors that influence the efficacy (log10 reduction of vegetative microorganisms) of HPP when applied to foodstuffs are intrinsic (e.g. water activity and pH), extrinsic (P and t) and microorganism-related (type, taxonomic unit, strain and physiological state). It was concluded that HPP of food will not present any additional microbial or chemical food safety concerns when compared to other routinely applied treatments (e.g. pasteurisation). Pathogen reductions in milk/colostrum caused by the current HPP conditions applied by the industry are lower than those achieved by the legal requirements for thermal pasteurisation. However, HPP minimum requirements (P/t combinations) could be identified to achieve specific log10 reductions of relevant hazards based on performance criteria (PC) proposed by international standard agencies (5-8 log10 reductions). The most stringent HPP conditions used industrially (600 MPa, 6 min) would achieve the above-mentioned PC, except for Staphylococcus aureus. Alkaline phosphatase (ALP), the endogenous milk enzyme that is widely used to verify adequate thermal pasteurisation of cows' milk, is relatively pressure resistant and its use would be limited to that of an overprocessing indicator. Current data are not robust enough to support the proposal of an appropriate indicator to verify the efficacy of HPP under the current HPP conditions applied by the industry. Minimum HPP requirements to reduce Listeria monocytogenes levels by specific log10 reductions could be identified when HPP is applied to ready-to-eat (RTE) cooked meat products, but not for other types of RTE foods. These identified minimum requirements would result in the inactivation of other relevant pathogens (Salmonella and Escherichia coli) in these RTE foods to a similar or higher extent.

High Hydrostatic Pressure Induced Changes in the Physicochemical and Functional Properties of Milk and Dairy Products: A Review

High-pressure processing (HPP) is a nonthermal technology used for food preservation capable of generating pasteurized milk products. There is much information regarding the inactivation of microorganisms in milk by HPP, and it has been suggested that 600 MPa for 5 min is adequate to reduce the number of log cycles by 5-7, resulting in safe products comparable to traditionally pasteurized ones. However, there are many implications regarding physicochemical and functional properties. This review explores the potential of HPP to preserve milk, focusing on the changes in milk components such as lipids, casein, whey proteins, and minerals, and the impact on their functional and physicochemical properties, including pH, color, turbidity, emulsion stability, rheological behavior, and sensory properties. Additionally, the effects of these changes on the elaboration of dairy products such as cheese, cream, and buttermilk are explored.

Effect of Low-Temperature-High-Pressure Treatment on the Reduction of Escherichia coli in Milk

Non-thermal processing of milk can potentially reduce nutrient loss, and a low-temperature-high-pressure (LTHP) treatment is considered as a promising alternative to thermal treatment, attracting considerable attention in recent years. The effect of LTHP treatment (−25 °C, 100–400 MPa) on the phase transition behavior of frozen milk was evaluated. The lethal and injured effects of different pressures and cycle numbers on E. coli in frozen milk were studied by using selective and non-selective enumeration media. Results from the gathered transient time–temperature–pressure data showed that pressures over 300 MPa could induce a phase transition from Ice I to Ice III. The treatment at −25 °C and 300 MPa could achieve a lethal effect similar to the two-cycle treatment of 400 MPa at room temperature. This meant that LTHP conditions can lower the operating pressure by at least 100 MPa or reduce the operation from two cycle to one cycle. Increasing the number of pressure cycles enhanced the lethal effects, which was not additive, but resulted in a transformation of part of the injured cells into dead cells. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) provided direct evidence for the breakdown of cell membrane and cell walls by phase transitions. Combined with a designed internal cooling device, the LTHP process can be expected to be a more attractive alternative to non-thermal processing for the dairy industry.