Pressure-assisted Thermal Sterilization Research Articles

Effect of pressure-assisted thermal sterilization combining with ε-polylysine on Bacillus subtilis spore proteins, nucleic acids and other intraspore substances

Pressure-assisted thermal sterilization (PATS) is a new technology to inactivate bacterial spores and ensure food safety. Little has been known about the effects of PATS combining with ε-PL on the spore’s nucleic acid, enzymes and other key substances. This study aimed to investigate the inactivation effect of PATS combining with ε-PL on the spores of B. subtilis. The spores were treated with pressure 600 MPa at 25 °C, 65 °C and 75 °C, and ε-PL at 0.1% and 0.3%. After treatment, the survival rate of B. subtilis spores, leakage of nucleic acid and protein, the change in the cell membrane ATPase activity, the leakage of dipicolinic acid, and the damage on protein and nucleic acid of the spores were determined. The results showed that PATS combining with ε-PL inactivated more spores, and significantly increased the release of protein and nucleic acid compared to the control. ATPase activity reached the lowest value after the treatment of 600 MPa/75 °C combining with 0.3% ε-PL. The release of dipicolinic acid from the spores was increased by 600 MPa/75 °C combining with 0.3% ε-PL as compared with 600 MPa/75 °C treatment alone. FTIR analysis showed that a combination of PATS with ε-PL changed the spectral features of B. subtilis functional groups of proteins and nucleic acids. The PATS treatments when combined with ε-PL were found to shift the symmetric and antisymmetric stretching vibrational absorption peaks of phosphodiester group in nucleic acid molecules (P=O). This change suggested that the combined treatment denatured nucleic acid. The combined treatment also changed the protein from an ordered state to a disordered state, and decreased protein stability. The results improved our understanding on the principle of spore inactivation by PATS combining with ε-PL.

Pressure-Assisted Thermal Sterilization and Storage Stability of Avocado Puree in High Barrier Polymeric Packaging

Pressure-Assisted Thermal Sterilization and Storage Stability of Avocado Puree in High Barrier Polymeric Packaging

Effect of Hurdle Approaches Using Conventional and Moderate Thermal Processing Technologies for Microbial Inactivation in Fruit and Vegetable Products.

Thermal processing of packaged fruit and vegetable products is targeted at eliminating microbial contaminants (related to spoilage or pathogenicity) and extending shelf life using microbial inactivation or/and by reducing enzymatic activity in the food. The conventional process of thermal processing involves sterilization (canning and retorting) and pasteurization. The parameters used to design the thermal processing regime depend on the time (minutes) required to eliminate a known population of bacteria in a given food matrix under specified conditions. However, due to the effect of thermal exposure on the sensitive nutrients such as vitamins or bioactive compounds present in fruits and vegetables, alternative technologies and their combinations are required to minimize nutrient loss. The novel moderate thermal regimes aim to eliminate bacterial contaminants while retaining nutritional quality. This review focuses on the “thermal” processing regimes for fruit and vegetable products, including conventional sterilization and pasteurization as well as mild to moderate thermal techniques such as pressure-assisted thermal sterilization (PATS), microwave-assisted thermal sterilization (MATS) and pulsed electric field (PEF) in combination with thermal treatment as a hurdle approach or a combined regime.

Assessing the Pressure’s Direct Contribution to the Efficacy of Pressure-Assisted Thermal Sterilization

Assessing the Pressure’s Direct Contribution to the Efficacy of Pressure-Assisted Thermal Sterilization

Pressure-assisted thermal sterilization of avocado puree in high barrier polymeric packaging

The aim of this study was to examine the influence of pressure-assisted thermal sterilization (PATS) on properties of polymeric packaging and packaged avocado puree. High pressure of 600 MPa and initial vessel temperature of 90 °C were used over 5 min processing time. We used two high barrier film pouches: Film A-(PE/PA6//EVOH//PA6/PE) and film B-(AlOx-coated PET//AlOx-coated PET//PA//CPP). Oxygen transmission rates (OTR) changed from 0.16 ± 0.07 to 3.24 ± 0.52 cm3/m2.day for film A after processing while OTRs were not detected for film B. Water vapor transmission rates (WVTR) changed from 3.72 ± 0.06 to 4.97 ± 0.14 g/m2.day for film A and 0.11 ± 0.02 to 0.62 ± 0.0.6 g/m2.day for film B. The dissolved oxygen in packaged avocado puree reduced from 21% to 3% after PATS for both films. Reduced oxygen level in packaged avocado may help extend its shelf life. Dielectric properties and X-ray diffraction helped explain PATS induced changes in film barrier properties. The total chlorophyll, greenness, and lightness decreased significantly (p < 0.05) after PATS. The thiobarbituric acid activity reduced after PATS. PATS showed potential to produced shelf-stable avocado puree; however, shelf-life studies are needed to further develop PATS process.

Applications of novel processing technologies to enhance the safety and bioactivity of milk.

Bioactive compounds in food can have high impacts on human health, such as antioxidant, antithrombotic, antitumor, and anti-inflammatory activities. However, many of them are sensitive to thermal treatments incurred during processing, which can reduce their availability and activity. Milk, including ovine, caprine, bovine, and human is a rich source of bioactive compounds, including immunoglobulins, vitamins, and amino acids. However, processing by various novel thermal and non-thermal technologies has different levels of impacts on these compounds, according to the studies reported in the literature, predominantly in the last 10 years. The reported effect of these technologies either covers microbial inactivation or the bioactive composition; however, there is a lack of comprehensive compilation of studies that compare the effect of these technologies on bioactive compounds in milk (especially, caprine and ovine) to microbial inactivation at similar settings. This research gap makes it challenging to conclude on the specific processing parameters that could be optimized to achieve targets of microbial safety and nutritional quality at the same time. This review covers the effect of a wide range of thermal and non-thermal processing technologies including high-pressure processing, pressure-assisted thermal sterilization, pulsed-electric field treatment, cold plasma, microwave-assisted thermal sterilization, ultra-high-pressure homogenization, ultrasonication, irradiation on the bioactive compounds as well as on microbial inactivation in milk. Although a combination of more than one technology could improve the reduction of bacterial contaminants to meet the required food safety standards and retain bioactive compounds, there is still scope for research on these hurdle approaches to simultaneously achieve food safety and bioactivity targets.

High pressure-assisted thermal sterilization of low-acid fruit and vegetable purees: Microbial safety, nutrient, quality, and packaging evaluation

The objective of this study was to assess the influence of pressure-assisted thermal sterilization (PATS) on nutrients and quality of pumpkin, butternut squash, pea, beetroot, and purple potato purees. PATS processing parameters included preheating of purees at 98 °C for 5 min and pressurizing at 600 MPa in a vessel set at 90 °C for 5 min. Colorimetric temperature sensors, two types of Bacillus amyloliquefaciens spores, total aerobic and anaerobic plate count, HPLC, as well as spectrometer and spectrophotometer were utilized. The colorimetric temperature sensor based on its color value when extrapolated suggested the purees' temperature reached 122 °C. Thus, at least 9-log10 reduction of B. amyloliquefaciens spores was achieved in a purple potato puree, and no detectable aerobic and anaerobic microorganisms were found after PATS in all purees. Vitamin C showed 3–14% reduction after PATS. Total chlorophyll and β-carotene did not vary significantly (p > 0.05) after PATS, while betalains and anthocyanin were sensitive and decreased significantly. Interestingly, total color change (ΔE) of pumpkin, butternut squash, and beetroot purees ranged between 2.5 and 3.4 below the threshold (ΔE = 6) value that can be observed by the naked eyes. EVOH-based packages did not show any visual deformation, but their oxygen and water vapor transmission rates increased significantly (p < 0.05) after PATS. The present research suggests that PATS can be used to produce safe and high-quality shelf-stable fruit and vegetable products.

Application of High Pressure with Homogenization, Temperature, Carbon Dioxide, and Cold Plasma for the Inactivation of Bacterial Spores: A Review.

Formation of highly resistant spores is a concern for the safety of low-acid foods as they are a perfect vehicle for food spoilage and/or human infection. For spore inactivation, the strategy usually applied in the food industry is the intensification of traditional preservation methods to sterilization levels, which is often accompanied by decreases of nutritional and sensory properties. In order to overcome these unwanted side effects in food products, novel and emerging sterilization technologies are being developed, such as pressure-assisted thermal sterilization, high-pressure carbon dioxide, high-pressure homogenization, and cold plasma. In this review, the application of these emergent technologies is discussed, in order to understand the effects on bacterial spores and their inactivation and thus ensure food safety of low-acid foods. In general, the application of these novel technologies for inactivating spores is showing promising results. However, it is important to note that each technique has specific features that can be more suitable for a particular type of product. Thus, the most appropriate sterilization method for each product (and target microorganisms) should be assessed and carefully selected.

Processing of baby food using pressure-assisted thermal sterilization (PATS) and comparison with thermal treatment

ABSTRACTCurrently baby food is sterilized using retort processing that gives an extended shelf life. However, this type of heat processing leads to reduction of organoleptic and nutrition value. Alternatively, the combination of pressure and heat could be used to achieve sterilization at reduced temperatures. This study investigates the potential of pressure-assisted thermal sterilization (PATS) technology for baby food sterilization. Here, baby food (apple puree), inoculated with Bacillus subtilis spores was treated using PATS at different operating temperatures, pressures and times and was compared with thermal only treatment. The results revealed that the decimal reduction time of B. subtilis in PATS treatment was lower than that of thermal only treatment. At a similar spore inactivation, the retention of ascorbic acid of PATS-treated sample was higher than that of thermally treated sample. The results indicated that PATS could be a potential technology for baby food processing while minimizing quality deterioration.

Prediction of temperature distribution in a horizontal high pressure food processing vessel and its impact on process uniformity

The temperature distributions in HPP vessels should be of particular concern for pressure assisted thermal sterilization (PATS) processes because in PATS temperature plays a major role in microbial inactivation. Numerical simulations were carried out to predict thermal transport in a horizontal HPP vessel with and without insulation. The results showed that the temperature of water added to compensate for the compression of water in the pressure vessel and the addition of insulation on the inner surface of vessel had significant impact on the temperature distribution and on the predicted inactivation of Clostridium botulinum spores. It was concluded that adding insulation to the vessel lead to higher temperature levels but more non-uniform temperature distribution as compared with without insulation. It was also observed that the water added to compensate for compression did not impact the flow pattern in the vessel significantly due to low inlet velocity but the temperature of added water had a significant impact on the temperature and Clostridium botulinum spore inactivation distributions. The temperature distribution was close to uniform when the temperature of the inlet water was the same as the initial temperature for the process. Practical applications The results obtained from this research will be useful in the evaluation of process performance in terms of process validation and process filing with regulatory agencies to develop guidelines for producing high pressure processed foods using PATS, which are safe to consume. The results will also be important for food processors and equipment manufacturers to understand the effects of non-uniform thermal treatment on foods processed using PATS.

Multi-pulsed high hydrostatic pressure inactivation of microorganisms: A review

Multi-pulsed high hydrostatic pressure (mpHHP) treatment, which has been applied for two decades, is broadly more effective than the classical or single-pulsed HHP (spHHP) for inactivation of viruses, yeasts, bacterial cells, and fungal and bacterial spores. The effectiveness of the mpHHP treatment could be increased with a smart choice of pressure, initial and target temperature, pulse number, pulse holding time, and compression and decompression rates. The effectiveness of the mpHHP treatment is well documented and at the moment it seems that it is not feasible to apply the mpHHP treatment commercially for the food industry. However, with the availability of new technologies it may be possible to speed up the HHP processing by decreasing compression and decompression rates and to produce repeated pulses of high pressure. The mpHHP treatment could be very beneficial to the food industry and could replace the pressure-assisted thermal sterilization (PATS) with lower pressure and temperature values. Most of the studies have shown that the mpHHP treatment could be used to inactivate the microrganisms in foods at lower pressure values than the spHHP treatment for the same amount of holding time but for a longer processing time (including the compression and decompression periods of the pulses). The mpHHP treatment has a potential to sterilize the food products with the help of developing technology if the optimization between pressure, temperature, number of pulses, pulse holding time and compression and decompression rates could be possible. • This contribution compiles the studies about the mpHHP inactivation of microorganisms. • The mpHHP treatment inactivates the viruses, yeasts, bacteria and spores effectively. • Pulse number, pulse holding time, and compression and decompression rates are important factors during the mpHHP treatment.

High-pressure Processing: Kinetic Models for Microbial and Enzyme Inactivation

High-pressure processing (HPP) has become the most widely accepted nonthermal food preservation technology. The pressure range for commercial processes is typically around 100–600 MPa, whereas moderate temperature (up to 65 °C) may be used to increase microbial and enzymatic inactivation levels. However, these industrial processing conditions are insufficient to achieve sterilization since much higher pressure levels (>1,000 MPa) would be required to inactivate bacterial endospores and enzymes of importance in food preservation. The next generation of commercial pressure processing units will operate at about 90–120 °C and 600–800 MPa for treatments defined as pressure-assisted thermal processing or pressure-assisted thermal sterilization if the commercial food sterilization level required is achieved. Most published HPP kinetic studies have focused only on pressure effects on the microbial load and enzyme activity in foods and model systems. Published work on primary and secondary models to predict simultaneously the effect of pressure and temperature on microbial and enzymatic inactivation kinetics is still incomplete. Moreover, few references provide a detailed and complete analysis of the theoretical, empirical, and semiempirical kinetic models proposed to predict the level of microbial and enzyme inactivation achieved. This review organizes these published kinetic models according to the approach used and then presents an in-depth and critical revision to define the modeling research needed to provide commercial users with the computational tools needed to develop and optimize pasteurization and sterilization pressure treatments.

Pressure-assisted thermal sterilization effects on gas barrier, morphological, and free volume properties of multilayer EVOH films

Pressure-assisted thermal sterilization (PATS) alters the morphology and free volume distributions of polymers leading to a decrease in gas-barrier properties of polymer packaging materials, and hence compromising the quality and shelf life of PATS processed foods. Two multilayer ethylene–vinyl alcohol (EVOH) films, intended for high pressure applications, were investigated to understand the influence of free volume characteristics and film morphology on gas-barrier properties of PATS processed EVOH films. X-ray diffraction (XRD) and positron annihilation lifetime spectroscopy (PALS) were applied to investigate film morphology and free volume characteristics, respectively. Film A was comprised of polyethylene terephthalate (PET)/EVOH/polypropylene (PP). Film B consisted of PET laminated to a co-extruded structure of PP/tie/Nylon6/EVOH/Nylon6/tie/PP. Both oxygen and water vapor transmission rates increased in the two films after the selected treatments. However, the increase in film A is much larger which can be understood from the change in free volume distributions measured by positron lifetime and overall crystallinity observed from X-ray diffraction. This work shows that PALS and XRD are suitable tools to reason out the gas-barrier changes in multilayer EVOH films after PATS treatment.

Effect of pressure-assisted thermal sterilization on conjugated linoleic acid (CLA) content in CLA-enriched milk

Conjugated linoleic acid (CLA) has been recently studied for its health-promoting and disease-preventing properties. The objective of this study was to evaluate the effect of pressure (100–600 MPa), temperature (60–120 °C) and treatment time (0–14 min) on CLA content in milk and anhydrous milk fat (AMF) rich in CLA. In milk treated up to 14 min at 100 MPa, CLA was stable (> 80% of retention), regardless of the temperature. In contrast, only 3.4 ± 2% of CLA was retained at 600 MPa and 120 °C. For AMF, CLA retention was considerably higher (40.2 ± 2%) than that obtained for milk. The presence of free metal ions in milk might catalyze CLA degradation. When the antioxidant catechin (1 g/kg) was used, CLA retention increased significantly (> 90%) in milk and AMF, regardless of the experimental conditions. Previous research led by Dr. John Kennelly resulted in CLA-enriched milk by manipulating the diet of dairy cattle. CLA in milk suffers significant losses in terms of its biological activity during processing at high temperatures like UHT. High consumption of CLA products has been associated with many health benefits. This study provided new data on CLA retention with and without an antioxidant at pressure-assisted thermal sterilization (PATS) conditions and confirmed the role of catechin in reducing oxidative damage by PATS treatments. Milk rich in CLA can be treated with PATS to deliver shelf-stable milk while CLA activity is preserved.

The Impact of High Pressure and Temperature on Bacterial Spores: Inactivation Mechanisms of Bacillus subtilis above 500 MPa

High-pressure thermal sterilization (HPTS) is an emerging technology to produce shelf stable low acid foods. Pressures below 300 MPa can induce spore germination by triggering germination receptors. Pressures above 500 MPa could directly induce a Ca+2-dipicolinic acid (DPA) release, which triggers the cortex-lytic enzymes (CLEs). It has been argued that the activated CLEs could be inactivated under HPTS conditions. To test this claim, a wild-type strain and 2 strains of Bacillus subtilis spores lacking germinant receptors and one of 2 CLEs were treated simultaneously from 550 to 700 MPa and 37 to 80 C (slow compression) and at 60 to 80 C up to 1 GPa (fast compression). Besides, an additional heat treatment to determine the amount of germinated cells, we added TbCl3 to detect the amount of DPA released from the spore core via fluorescent measurement. After pressure treatment for 120 min at 550 MPa and 37 °C, no inactivation was observed for the wild-type strain. The amount of released DPA correlated to the amount of germinated spores, but always higher compared to the belonging cell count after pressure treatment. The release of DPA and the increase of heat-sensitive spores confirm that the inactivation mechanism during HPTS passes through the physiological states: (1) dormancy, (2) activation, and (3) inactivation. As the intensity of treatment increased, inactivation of all spore strains also strongly increased (up to -5.7 log10), and we found only a slight increase in the inactivation of one of the CLE (sleB). Furthermore, above a certain threshold pressure, temperature became the dominant influence on germination rate. The continuous increase of high-pressure (HP) research over the last several decades has already generated an impressive number of commercially available HP pasteurized products. Furthermore, research helped to provoke the certification of a pressure-assisted thermal sterilization process by the U.S. FDA in February 2009. However, this promising sterilization technology has not yet been applied in industrial settings. An improved understanding of spore inactivation mechanisms and the ability to calculate desired inactivation levels will help to make this technology available for pilot studies and commercialization at an industrial scale. Moreover, if the synergy between pressure and elevated temperature on the inactivation rate could be identified, clarification of the underlying inactivation mechanism during HP thermal sterilization could help to further optimize the process of this emerging technology.

An Update on High Hydrostatic Pressure, from the Laboratory to Industrial Applications

High hydrostatic pressure has become an industrial reality, and although there are still many aspects under research, today it is possible to buy high-pressurized products in many countries. Indeed, pasteurization of food products using elevated pressure at room temperature has been accepted by regulatory agencies for commercial use. The quality displayed in such products includes better nutritional retention, fresh-like flavor, improved color, texture, and taste, and extended shelf life compared to thermally pasteurized products. There are several applications of high hydrostatic pressure (HHP) use today in processing fruits, vegetables, meats, seafood, dairy and egg products, including the intelligent combination of pressure, temperature, and time to generate specific characteristics in certain products. One of the biggest challenges in high-pressure application is in the sterilization of low-acid foods with combined elevated pressure (600–800 MPa), moderate temperatures (30–90 °C), and short processing times (less than 5 min). Combined pressure and temperature, also known as pressure-assisted thermal sterilization (PATS), was recently approved by the FDA in 2009 for commercial sterilization. This manuscript is an update of the state-of-the-art in high-pressure technology, showing the advances achieved in past years and its most recent applications today in food processing. Inactivation of different microorganisms and the potential use of mathematical models to describe and validate the process are also mentioned, including using PATP to achieve sterilization parameters. Facts pertaining to equipment and operation costs are included as well to show that as a new technology, high-pressure use would likely require high initial investment. However, given the productivity and capability of this technology to enhance food quality, it may well deserve this initial investment, as many food companies have indicated in their annual cost reports.

Pressure-assisted thermal sterilization of soup

The overall efficiency of an existing scale-up pressure-assisted thermal sterilization (PATS) unit was investigated with regards to inactivation of Geobacillus stearothermophilus spores suspended in pumpkin soup. The PATS unit is a double pipe heat exchanger in which the soup is pumped into its inner high pressure tube and constrained by two high pressure valves, while steam is continuously passed through the annular region to heat the content. The technology is based on pressure generation by thermal expansion of the liquid in an enclosure. In this work, the addition of an air line to push the treated liquid food out of the existing PATS unit has improved the overall quality of the treated samples, as evidenced by achieving higher log reduction of the spores. Compared with thermal processing, the application of PATS shows the potential for lowering the thermal treatment temperature, offering improved food quality.

Stability of peptide amides under high pressure

The effects of pressure on two-model peptide amides have been analysed since the modifications in those groups are usually related to changes in protein/peptide functionality. Pressure accelerated the hydrolysis at the C-terminal amide of the dipeptide H-Leu-Gly-NH2, producing the diketopiperazine cLG that might have a biological role. Furthermore, pressure accelerated the deamidation of the asparagine residue in the oligopeptide H-Val-Pro-Gly-Val-Gly-Asn-Gly-Val-Pro-Gly-Val-Gly-OH containing an Asn-Gly sequence, probably via a cyclic imide intermediate, producing a peptide with aspartic acid. The reported pressure-induced modifications in amide groups were slow under the considered conditions (600–800 MPa, 60–80 °C). Effects under parameters closer to pressure-assisted thermal sterilization remain to be investigated.

Effect of High-Pressure Processing at Elevated Temperatures on Thiamin and Riboflavin in Pork and Model Systems

High-pressure/high-temperature properties of vitamins in food are important with respect to the new pressure-assisted thermal sterilization method utilizing pressure-induced adiabatic temperature changes. Riboflavin, thiamin, and thiamin monophosphate (TMP) stabilities were assayed in the temperature range from 25 to 100 degrees C under normal pressure (0.1 MPa) and high pressure (600 MPa) in acetate-buffered (pH 5.5) model solutions, some with added fructose, hemoglobin, or ascorbic acid. Thiamin and riboflavin stabilities were also assayed in minced fresh pork fillet and in rehydrated pork reference material with and without pressure treatment at 600 MPa in the temperature range from 20 to 100 degrees C. In pork, the vitamins proved to be sufficiently stabile for high-pressure/high-temperature processing. Under similar conditions, vitamin decay in model solutions was up to 30 times faster, especially that of TMP. Thus, it appears that it may not be possible to draw conclusions for the pressure behavior of real food matrices from the results of investigations in food models. A further consequence is that caution is necessary when supplementing foods with synthetic B vitamins preceding high-pressure/high-temperature processing.