High due to the destruction suffered by the
High pressure processing is a non-thermal food preservation technique that destroys the microorganisms with the intense pressure in the range 100-1000 MPa. The vegetative microbes are killed therefore, preventing the food borne illness with minimum effect on the food quality, texture and nutritional value. High pressure processing leading to minimal effect on quality does not affect the shelf-life of product and prevents the product from any microbial damage. It is applicable to both liquid and high moisture solid foods. Principle : The basic principle that determines the behaviour of food under pressure is ISOSTATIC PRINCIPLE. The principle demonstrates that food product is compressed under uniform pressure in every direction and regains it’s original shape as the pressure is released. Processing : High pressure processing is comprised of two units : a) pressure vessel b) pressure generating device. The food package is loaded onto vessel and the top of vessel is closed. The pressure medium (generally water) is allowed to pump into the vessel from the bottom. As the desired pressure is reached, pumping is stopped. The valves are closed and pressure is maintained. The pressure was applied in an isostatic manner so that all the food in the container experiences a uniform pressure throughout. Microbial inactivation by HPP :As a food preservation technology, the utility of HHP is due to the destruction suffered by the microbial population, which allows a substantial increase in shelf-life and improves food safety (Considine et al., 2008). Broadly speaking, HHP applied at ambient temperature destroys vegetative cells and inactivates certain enzymes (Simpson & Gilmour, 1997), with a minimal change in the organoleptic properties (Farkas & Hoover, 2000; San Martin et al., 2002). The behaviour of microorganisms towards high pressure processing technique is varied between different species and among different strains of same species. Microorganisms will be broadly categorised into pressure sensitive and pressure resistant organisms. Gram-positive bacteria are found to be more resistant to pressure than Gram-negative bacteria, moulds and yeasts. Most resistant to high hydrostatic pressure are bacterial spores. The sensitivity of microbial cells is determined largely by the stage of the growth cycle at which the organisms are subjected to high hydrostatic pressure treatment. Cells in the exponential phase are found to be more sensitive to pressure treatments than cells in the log or stationary phases of growth. During pressure treatment, the temperature influences the inactivation of microbial cells. Some authors have found that pressure resistance of microbial cells is maximum at temperature 15-30*C and substantially decreases at higher or lower temperatures. High pressure has a lethal effect on vegetative microorganisms and that is the result of numerous changes that take place in the membrane of a microbial cell. The membrane becomes the most probable site of disruption in a microbial cell. The functions of membrane like active and passive transport are altered by the high pressure treatment which ultimately discomposes the physiochemical balance of the cell. The possible reason for inactivating microorganisms can be inactivation of key enzymes, also for DNA replication and transcription. The genetic material fails to function which leads to death of a microorganism. Spores offer a great resistance to inactivation by high pressure treatment. The genera Bacillus and Clostridium comprise significant species as foodborne sporeforming pathogens, such as Clostridium botu- linum, Clostridium perfringens and Bacillus cereus. To aid in the calculation of process specifications, suitable surrogates of C. botulinum such as Clostridium sporogenes have been investigated (Ahn, Balasubramaniam, & Yousef, 2007). As for other species, Bacillus amyloliquefaciens forms extremely high-pressure resistant spores and it has been suggested that it could be adopted as the target organism in the development of standards for high-pressure treatments (Margosch, Ehrmann, Ganzle, & Vogel, 2004; Rajan, Ahn, Balasubramaniam, & Yousef, 2006). There are few results on the behavior of B. cereus in foods (Oh & Moon, 2003; Van Opstal, Bagamboula, Vanmuysen, Wuytack, & Michiels, 2004) but in all cases a combination of high pressure (>600 MPa) and mild temperature (>45 C) had to be used to achieve a significant loss of viability. HPP in fruit preparations : There are different type of fruit preparations that are intended for human consumption. Fruit juices, fruit concentrates, fruit nectars, fruit jams and jellies, marmalades, fruit smoothies (usually contain crushed fruit, purees). These fruit preparations are effectively treated by HPP. Some other derivatives like soups, sauces, slices, and prepared dishes can be also treated by HPP technologies. The products to be consumed should be free from hazards and sound. Therefore, safety of food products is of utmost importance. To ensure, safe and healthy food, practices like GMP and Hazard Analysis and Critical Control Point should be implemented. Microbiological criterion should be taken into account and should not exceed as per the laws and guidelines. There is a criterion related to Listeria monocytogenes. The count recommended by law is to keep the concentration of Listeria monocytogenes in food below 100 cfu/g. Inactivation of microbes : Generally, pressure processing above 200 MPa is required to inactivate vegetative bacteria, molds and yeasts. Practically, pressure above 700 MPa applied for a time from few seconds to minutes is effective in inactivating microbial cells. On contrary, spores are highly resistant to elevated pressures, showing tolerance at pressure about 1000 MPa. Sterilisation of low-acid foods, like some fruit derivatives, can be made possible through combined high pressure (500–900 MPa) and relatively mild temperature (90-120*C) processing for about five minutes.Butz et al. (1990) 43 investigated the effect of pressures between 150 and 400 MPa at temperatures of 25-40*C on bacterial spores and showed that pre-treatment at relatively low pressures (60-100 MPa) led to accelerated inactivation of spores at high pressure. Mold and yeast are considered to be less resistant than bacterial. They are inactivated at pressure range varying between 200-400 MPa. Basak et al. (2002) 46 demonstrated that S. cerevisiae was not inactivated under a pressure equal to 400 MPa in orange juice. It was shown that the resistance of these microorganisms increased when the concentration of sugar in the environment also increased 47. This can cause a problem during the treatment of the fruit-based preparations containing a strong concentration in sugars. Ohmic HeatingHeating is considered to be an important step in food processing. Heat treatment is most common process that is put into practice for preservation and microbial inactivation in food. The conventional heating is now replaced by new food processing technique that is ohmic heating.Ohmic heating, as the name suggests, take it’s name from ohm’s law. Ohmic heating of food products involves the passage of alternating electrical current through them, thus generating internal heat as the result of electrical resistance (Reznick, 1996). The ohmic technology was first introduced at Electricity Research Council, Caphenhurst, United Kingdom. Ohmic heating is based on the principle that electric current is passed through an electrically conducting product, which results in transformation of electric energy into heat.