Food preservation technologies: High Pressures

food preservation technology

Today, we are increasingly aware of the close relationship between food and health, we look for foods that are minimally processed, appetizing, easy to consume, and with functional properties. In recent years, important advances have been made in the field of food preservation and/or transformation technologies, different technologies from conventional thermal applications, so that we have achieved minimally processed foods with the same sensory and nutritional qualities, guaranteeing their food safety and preserving its bioactive compounds.

Food safety has to be taken into account in its entirety. We cannot pretend to obtain safe food for consumption if we are not capable of integrating under the same umbrella all those aspects that may influence the process of making that food. In this article, we are going to take into account aspects related to some of the technologies considered as new technologies for the preservation of food, technologies aimed at treating food in order to eliminate its altering and pathogenic microbiota, but we should not think that with the application of these new tools we have solved the problem of food safety of our products. Good handling practices, the proper design of the facilities and their condition, environmental control, the hygiene of the processing plants, the suitability of the materials … are some of the factors that we will necessarily have to take into account when it comes to establishing the plan for the food safety of our products.

In addition, the application of alternative conservation technologies to traditional pasteurization, among which the high hydrostatic pressures stand out, constitutes a revolution in the food industry, by obtaining safe products that preserve the functional, nutritional and sensory characteristics of fresh foods, with longer shelf life and greater guarantees of food safety. Reviewing the traditional methods (pasteurization, sterilization, freezing), we see that the most common for the preservation of products are based on temperature variations, both the application of heat and freezing. Thanks to these temperature gradients we achieve both the inactivation of microorganisms and the altering enzymes, but, on the contrary, we have problems of denaturation of proteins,

Pasteurization (a mild thermal process where pathogenic microorganisms are destroyed) requires a combination with another preservation process, usually refrigeration or freezing or the use of additives (acidulants, concentrated sugars, etc.). Regarding sterilization (drastic heat treatment that allows the destruction of vegetative forms and microbial spores), it involves substantial changes in the nutritional and sensory quality of foods: overcooking, changes in texture and taste, although sterile products that can keep at room temperature for up to two years. Freezing reduces the amount of available water, by solidifying and fixing part of it, which significantly slows down chemical and biochemical reactions and stops microbiological growth,

Among the new conservation technologies, we find some already introduced in the market due to the great advantages of their application (in the case of high pressures) and others in the advanced study (pulsed ultraviolet light, radiofrequency, ultrasound, ohmic heating, radiation, fluids supercritical, cold plasma, ozone …)

Radiofrequency: This is a technique where electrical energy is applied that is converted into electromagnetic waves that generate heat inside the product due to the oscillation of the dipoles (the water contained in food) and ionic depolarization (the mineral salts themselves of food). The main disadvantage of radio frequency dielectric heating is the lack of uniformity in the temperature distribution, leading to hot and cold spots.

High-voltage or high-intensity electrical pulses: It consists of the application of an electrical current in the form of very short pulses through a food placed between two electrodes. It is a non-thermal process since the treated foods are kept at room temperature, or in any case at temperatures below the pasteurization of the food. For this reason, the foods treated by this technology have sensory and nutritional properties more similar to those of the fresh product. The electrical pulses cause the destruction of the cell membrane of the microorganisms by electroporation without a significant contribution of heat.

Ohmic Heating

An ohmic heater, also known as a Joule heater, is an electrical heating device that uses a liquid’s own electrical resistance to generate heat. Together with the microbial inactivation derived from the heating itself, electroporation of cell membranes occurs. The main advantages of this technology are that the heating occurs quickly and is distributed evenly, no residual heat is transferred after the current is stopped, nor are incrustations on the heat transfer surface, and the maintenance cost of the equipment does not is high. Among the drawbacks is the difficulty to control, since a close match is required between the temperature and the electric field distribution.

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Radiation

Food, raw or processed, is exposed to ionizing radiation (high-energy electrons, X-rays, or gamma rays) or non-ionizing radiation (UV light). In any of the cases, free radicals are generated that ionize the organic molecules of the food, giving rise to damage fundamentally at the DNA level. The modifications that radiation causes in the color, flavor, aroma and other quality parameters are minimal. Microbiologically, molds and yeasts are more resistant to ionizing radiation than bacteria. At the nutritional and sensory level, the effects are highly dependent on the dose used.

 Ozone

Compared to traditional disinfectants (chlorine, chlorine dioxide, sodium chloride, sodium hypochlorite, calcium hypochlorite, peroxyacetic acid), ozonization has been shown to reduce the counts of the most common spoilage microorganisms and pathogens in food. The effectiveness of this treatment depends on the gas flow, the concentration, the temperature, the pH of the medium and the presence of organic matter.

Cold plasma

It is the fourth state of matter where there is no thermodynamic equilibrium between electrons and most of the gaseous atoms and molecules, which gives rise to an adiabatic system with a high content of kinetic energy at low temperatures, always below 70 ºC. Cold plasma is generated by subjecting a gas to a powerful electric field, partially ionizing said gas.

In addition, highly energetic species are generated capable of breaking covalent bonds and initiating numerous chemical reactions with technological implications, including the inactivation of microorganisms. Prolonged exposures inevitably deplete the content of antioxidant polyphenols. Currently, this technology is expensive and expensive and there are very few commercialized systems, focused on very specific applications.

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Supercritical carbon dioxide

This treatment includes liquid CO2, supercritical CO2 and highly pressurized CO2 (high pressurized carbon dioxide, HPCD) and has very attractive properties as a food preservation method due to its high antimicrobial capacity, its activity against altering enzymes, its low toxicity and easy elimination – just depressurize.

Ultrasound

The mechanisms through which ultrasound inactivates microorganisms are induced by cavitation, which leads to the weakening or rupture of bacterial cells. During cavitation, free radicals are also formed that chemically attack cells, in addition to producing hydrogen peroxide, a bactericide per se. Ultrasonic processing, alone or in combination with heat and/or pressure, is effective in inactivating microorganisms and better retaining bioactive compounds in liquid foods compared to conventional heat treatment. However, certain attributes such as flavor and color can be adversely affected by oxidative effect and cavitation. That is why the application of ultrasound, in the food industry, is basically used in cleaning and disinfection of facilities, such as the automatisms for the hygiene of hanging hooks in poultry slaughterhouses, cutting knives, wire mesh and metallic gloves …, obtaining very positive results, minimizing cleaning operator times and optimizing the consumption of water and chemical products. (ref. BETELGEUX HPC).

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High hydrostatic pressures

This technology uses water as a medium to uniformly transmit pressures between 100 and 1000 MPa to food at mild temperatures (5 – 25 ºC), which translates into a significant reduction in microbial load and an extension of shelf life. However, although most vegetative cells can be inactivated at relatively low pressures (200-400 MPa), bacterial spores are more resistant and require a combination of high pressure and temperature. This process has an impact only on non-covalent bonds (hydrogen, ionic and hydrophobic), with little impact on covalent bonds, which are associated with the sensory and nutritional properties of food. High-pressure processing is a non-thermal lethality process that respects the natural properties of the treated products. This technology, consisting of the transmission of isostatic pressures transmitted by water, is natural, clean and respectful with the environment, recycling the water used and requiring only electrical energy. Together with this, the use of this technology makes it possible to avoid the use of preservatives and additives in the manufacture of products.

The ability of high hydrostatic pressures to preserve food has been known since, in 1899, Hite pasteurized milk through pressurization, thus demonstrating the reduction of the microbial population thanks to the use of this technique. From this first study, years later, they began to study the effects of high pressures on other types of products, such as fruits, vegetables, and meat. However, the development of equipment that could apply high pressures on food for commercial purposes was not possible until the late 20th century.

Currently, there are companies dedicated to the manufacture of equipment for use in sectors such as beverages, dairy, meat, fishing and agriculture. These companies, Hyperbaric to be highlighted among them for having been one of the pioneers in the manufacture of this equipment, can design and produce customized equipment for each case, being able to adjust the equipment parameters (number of intensifiers, powers, times, cycles/hour…) based on real needs, adjusting your productivity to the maximum.

At the bacterial level, with the application of this technique, changes in the cell membrane, biochemical, morphological and genetic changes are achieved. The cell membrane is a particularly pressure-sensitive structure, responsible in many cases for the death of cells subjected to sufficient treatment conditions. A pressure of 300 MPa is enough to provoke the irreversible denaturation of the proteins and phosphoproteins that make up the cell membrane, modifying its permeability and the ion exchange being altered. At the biochemical level, high pressures destroy the tertiary and quaternary structure of enzyme proteins, which are maintained by weak non-covalent interactions. Since the biological activity of an enzyme depends on the three-dimensional configuration of its active center, any structural modification leads to the loss of enzyme activity. Likewise, high pressures also produce morphological changes in the vegetative cells of microorganisms. At the genetic level, high pressures inactivate the enzymes involved in DNA replication and transcription. Finally, comment that the sensitivity to this type of treatment of the microorganisms is not the same in all of them (bar resistance). This sensitivity is at the level both between microorganisms of different species, as well as microorganisms of the same species and between their different strains. Yeasts and most molds are especially sensitive to pressure. Eukaryotic cells are more sensitive to pressure than prokaryotes, and Gram-positive cells resist pressure better than Gram-negative cells.

High hydrostatic pressures constitute a processing technique that, as already mentioned, consists of subjecting the solid or liquid food already packed in its final flexible format to pressures of between 100 and 1000 MPa, (generally high pressures between 400 and 600 MPa / 4000 bar and 6000 bar) with water as the pressure transmitter vehicle, at a temperature in a range between 5 and 25ºC for a variable time ranging from a few seconds to 20 minutes, thus achieving the reduction of several logarithms of spoilage and pathogenic microorganisms in food. As an advantage over high-pressure heat treatments, the chemical components associated with the organoleptic qualities of food (amino acids, vitamins, volatile molecules), such as flavor,

The three critical parameters to control in the design of any high-pressure treatment are temperature, pressure and time. With regard to time, not only is the duration of treatment at the desired pressure important, but also the time required to achieve said pressure and the post-treatment decompression time to recover atmospheric pressure.

Stalwart International – One of the best Pressure vessel manufacturers in Vadodara

 

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