Packaging Requirements for HP Treatment.
Food products need to be packed in a flexible container prior to HP processing in a batch system, to compensate for potential volume reductions in the food inside the package as well as the collapse of the head space.
Several factors need to consider for high pressure processing.
Considering that the packaging material should be flexible enough to transmit pressure and withstand a volume change, glass, metal, and paper are excluded. Polymeric materials, including polyethylene terephthalate, polyethylene,
, ethylene vinyl alcohol copolymer, and their combinations are usually used as the packaging materials for HP treatment.
To improve the barrier properties of the polymeric films, they are occasionally coated with extremely thin layers (a few nanometers thick) of inorganic compounds such as aluminum oxide and silicon oxide, or metalized by the deposition (approximately 0.01 mm thick) of a thin layer of aluminum.
Moreover, packaging materials that are oxygen impermeable and opaque to light may be developed especially for keeping the fresh color and flavor of certain HP-treated foods.
Effect of High-Pressure Processing on microorganisms.
The high pressure affects the microorganisms in a similar manner to that described for chemical components of food. Denaturation of proteins, which are essential to many of the functions of the bacterial cell, has a major impact on the survival of microorganisms. This can eventually lethally damage the cell if a sufficient amount of pressure is applied. The recovery of bacterial cell is, thus, made impossible.
On the other hand, HPP is not effective against all microbial forms. Spore-forming microorganisms are highly resistant to HPP when in spore form. Thus, a combination of pressure and heat, or other antibacterial treatment is required to achieve a significant reduction of bacterial spores in foods.
Compared to vegetative cells, endospores tend to be extremely resistant to high pressure processing. They require a combination of high-pressure treatment at pressure exceeding 1000 MPa and heat treatment with temperatures above 80°C.
Yeasts and molds are relatively sensitive to HPP. Most vegetative species are inactivated within a few minutes by 300-400 MPa at room temperature. However, yeast and mold ascospores may require treatment at higher pressures. Viruses show a wide range of sensitivity in response to high pressure.
Clostridium botulinum spores are of particular concern because they can germinate, grow, and produce the highly potent paralytic neurological toxin in low acid foods. Two of the factors influencing the effectiveness of the HPP treatment against microorganisms are: the chemical composition of the food products and the type of microorganisms. Some may be able to grow or survive in the product, becoming the dominant microflora, thus a careful evaluation of HPP should be made when applying the treatment on a specific food product.
Regulatory agencies have specified "critical processing parameters" for HPP treatment of foods. They include target pressure, the interval of time to achieve target pressure, decompression time, initial temperature of the product, initial temperature of the pressurization fluid, pH of the product, the water activity of the product. Currently, several HPP products are commercially available such as vegetable and fruits - juices, salsas des, me ready-to-eat meats and poultry, seafood, shellfish and fish products.
Effect of High pressure processing on chemical composition
It is important to note that some temperature increases do naturally occur during a typical HPP treatment due to adiabatic heating. They depended on the target pressure and the chemical composition of food. The temperature increase of water is approximately 3°C per 100 MPa, but it can be significantly higher for more compressible food ingredients such as fats. Thus, the temperature increase is higher during HPP for foods with a higher fat content.
The effect of HPP on molecules with a low molecular weight is minimal. Therefore, vitamins, flavor compounds, and pigments survive HPP processing relatively undamaged compared to thermal processing. In this way the nutritional value and quality of the food is preserved.
On the other hand, some compounds are irreversibly changed during HPP. Gelatinization of carbohydrates can be achieved through pressure increases rather than through temperature increases, and proteins can be denatured at high increasing the temperature.
The egg shown in figure is visually similar to a thermally processed hardboiled egg. The taste of the pressure- treated egg is, however, closer to that of raw egg, as temperature-induced flavor changes (chemical reactions) did not occur during HPP. This opens new product development possibilities.
To achieve the best pressure transmission, the ideal food for HPP has no gas inclusions, no empty spaces in the package, and a high content of moisture. Additionally, the packaging material has to be appropriate: it has to be flexible enough to transmit the pressure with no structural damage. The food is compressed during pressurization, and the package has to permit a reversible deformation.
The most common packaging materials used for HPP of food are polypropylene (PP), polyester tubes, polyethylene (PE) pouches, and nylon cast polypropylene pouches. Plastic packaging materials are best suited for HPP because of their reversible response to compression, their flexibility and resiliency.
Rigid materials such as metal and glass are not recommended, as they will not be able to undergo HPP treatment. Vacuum packed products in flexible packages appear ideal for HPP, particularly if the packaging could be compressed by about 15% with no structural damage and if it were able to return to its original shape upon pressure release. Currently, flexible packs, jars, trays and bottles are used as HPP packaging.
Application of High-Pressure Processing.
Juice and Beverage Preservation: HPP is commonly used in the production of fresh juices and beverages to extend their shelf life while preserving their taste, nutrients, and color.
Guacamole and Salsa: HPP can be applied to guacamole and salsa products to inhibit microbial growth and maintain freshness, allowing for longer shelf life without the use of preservatives.
Deli Meats and Ready-to-Eat Meals: HPP is used to extend the shelf life of deli meats, cooked poultry, and ready-to-eat meals by reducing spoilage bacteria, yeasts, and molds while retaining their flavor and texture.
Seafood and Shellfish: HPP is applied to seafood products, such as raw fish, shrimp, and oysters, to eliminate harmful pathogens like Vibrio and extend their shelf life without the need for high-temperature processing.
Dairy Products: HPP can be used in dairy products like yogurt and cheese to inhibit spoilage bacteria, improve safety, and maintain the sensory properties of the products.
Baby Food: High-pressure processing is utilized in the production of baby food to ensure the elimination of harmful bacteria and maintain the nutritional value of the food without the use of heat or chemical preservatives.
Sliced Fruits and Vegetables: HPP is applied to sliced fruits and vegetables to extend their shelf life and maintain their color, texture, and nutritional content by reducing microbial contamination.
Dips and Spreads: HPP is commonly used in the production of dips and spreads like hummus, pesto, and bean dips to ensure safety and quality while extending their shelf life.
Soups and Broths: HPP can be applied to soups and broths to eliminate harmful bacteria, improve safety, and preserve the flavor and nutritional value of the products.
Meat Tenderization: High-pressure processing can be used to tenderize meat by breaking down connective tissues, resulting in more tender and flavorful meat products.
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