Pascalization is a non-thermal processing technique used widely in food Industries to knockdown pathogenic microorganism by inactivating them. Further, it also helps in reducing the count of vegetative spoilage microbes. Other terminology for pascalization process are High Pressure Processing (HPP), High-Hydrostatic Pressure Processing (HHP) or Ultra High Pressure Processing (UHP).
Today food industries are demand driven rather than supply driven hence need for non-thermal processing was felt. Thermal processing at high temperature can develop burnt flavour, inactivate essential enzymes or can also denature the proteins, whereas processing on lesser temperature then required can be ineffective in making the product contamination free. Adverse effect of chemical preservatives used are not hidden. Consumer awareness towards healthy eating they are giving up on foods that have chemical preservatives in them that led to identification of preservation process that can be substitute the thermal processing and chemical preservatives completely or partially.
High pressure of about 400-600 M Pa is used for processing, however the pressure over product being isostatic, doesn’t degrade the characteristics of the product and keep them integrated as it is evenly distributed over packaged food. Correct selection of packaging material is also influential in increasing the efficiency of HPP processing. Importantly, packing material should be flexible type like pouches or plastic bottles which can withstand pressure rather than that of brittle or hard packages like ceramic, glass or metal which cannot with stand high pressure leading to deformation, cracks or losing of barrier properties of the material making the process futile.
High Pressure Processing: Working Principle
Le Chatelier’s principle and the Isostatic principle are the two basic principle behind HPP. Behind achieving the microbiologically safe foods criteria, intense pressure is used of about 300-800 M Pa depending upon the product to be processed. The process last from few seconds to minutes. This increased in pressure makes the condition unfavourable for microbes to thrive. Pressurized condition affects the microbial metabolism adversely which at the other hand increases the shelf life of product. USDA has also approved HPP as an intervention method for Listeria contaminated pre-packed ready to eat meat products.
Phenomena behind this is phase transition and chemical changes along with decrease in volume. Parameter’s influencing high pressure processing are temperature, pressure and exposure time of product. HPP works at ambient temperature i.e., below 40-degree C as well as in refrigerated condition. During process also, product temperature rises up to 3-degree C for every rise in pressure of 100 M Pa.
High Pressure Processing: Components
Important component of HPP process is
- Pressure vessel in which pressurized processing is done. Construction parameter for vessel is to be durable enough to with stand several pressurized process cycle without any distortion or damage in vessel.
- Transmitting Fluid, most commonly used one being water or mixture of oil or alcohol, depending on the system being used.
- Additional Accessories: Automatic deaeration valve, drain pumps, compressor, heating/cooling system, intensifier pump, water tank, low pressure pump,
NOTE: a. Hydraulic oil used for intensifier pumps should be of food grade
- Water should be free of salts and lime or else in long run they will deposit on pipelines and will clog the nozzles.
High Pressure Processing: Impact on Food
Due to non-thermal effect there are minimal changes on the sensory and nutritional values of food. HPP is compatible for both liquid and solid foods having higher moisture content. Food products like vegetables, meat products, seafood & fishes, juices & beverages, jam, jellies, purees, and other products can be processed by pascalization. This do not alter the food chemistry but do inactivate the vegetative bacteria and spores present with no evidence of toxicity. HPP has least effect on low molecular weight molecules causing no or minimal changes in the nutritional components of food like vitamins, flavour and pigments compared to thermal processing. Though some irreversible changes do take place during HPP process, like change in volume are sometime irreversible and gelatinization of carbohydrates can also be discovered during processing.
High Pressure Processing: Impact on Microorganism
The effect of HPP is variable on different microorganism. The applied pressure, time period of pressure exposure, target organism, and chemical composition of food are some of the parameters affecting the HPP efficiency. Yeast’s are comparatively more sensitive to HPP. If taking examples in bacteria Listeria monocytogenes (gram positive bacteria) shows higher resistance to pressurized condition than Salmonella (gram negative bacteria). Likewise spores of bacteria and viruses have wide range of pressure resistance to HPP. For curbing the more resistant microorganisms it is advisable to use temperature factor along with pressure processing.
Hence to attain desired efficiency and result from HPP it is imperative to select correct parameter like pressure range and holding time depending upon the targeted microorganism and type of product to be processed.
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