High pressure processing is already used commercially to enhance the microbiological quality of certain food products. A number of potential applications have also been reported in the scientific literature and there is a significant amount of ongoing research in this area. Fruit products have been most extensively studied. These products are acidic so, in terms of their microbiology, pathogens are generally not so important but spoilage microorganisms, particularly yeasts and moulds are of concern. The limiting factor for shelf life of such products is often the action of enzymes, particularly those which can cause browning, although the problem may be at least partially overcome by blanching or adding an oxygen scavenger such as ascorbic acid. Most fruit products are given a treatment of around 400 MPa for up to a few minutes. This can give a shelf life of up to several months provided the products are stored at 4C.
Pressure treatment of vegetables tends to be less successful due to their higher pH and the potential presence of spores, which can be very pressure-resistant. In addition, the quality of some vegetables deteriorates as a result of pressure processing, which can also be a limiting factor. However, it should be noted that one of the most successful commercial products available to date is HPP guacamole. Research has shown that clostridial spores cannot outgrow in this product and it can have a shelf life of around 1 month at 4C without modification of colour, texture or taste.
The use of HPP to improve the microbiological quality of meat, fish and dairy products has been investigated by a number of workers. These products tend to have a more neutral pH and provide a rich growth medium for most microorganisms, with pathogens being of particular concern. The need to ensure microbiological safety is one of the reasons why, to date, there are relatively few commercial applications of HPP meat and dairy products available. However, research has shown that pressure processing can be successful, in terms of improving microbiological safety and quality, for the treatment of pork, minced beef, duck Foie Gras (liver pate), fish, ovine milk and liquid whole egg. In many cases, the authors also comment on the ability of the pressure treatment to maintain or enhance sensory, nutritional or functional quality compared to conventional processing methods. In all cases, the optimum treatment conditions need to be carefully defined and thoroughly tested to ensure food safety is not compromised. For example, this may include extensive inoculation studies, under standardised conditions and using the most resistant strains of pathogens to ensure that the product will be microbiologically safe during its shelf life.
References:
Arroyo, G., Sanz, P.D., Prestamo, G. 1997, Effects of High Pressure on the Reduction of Microbial Populations in Vegetables, J. Appl. Microbiol.82, 735– 742.
Ananth, V., Dickson, J. S. Olson, D.G., Murano, E.A.1998, Shelf–Life Extension, Safety and Quality of Fresh Pork Loin Treated with High Hydrostatic Pressure, J. Food Prot.61, 1649–1656.
Carlez, A., Rosec, J.P., Richard, N., Cheftel, J. C. 1994, Bacterial Growth During Chilled Storage of Pressure-Treated Minced Meat.Lebensm.-Wiss. Technol.27, 48–54.
El Moueffak, A. C., Antoine, M., Cruz, C., Demazeau, G., Largeteau, A., Montury, M., Roy, B., Zuber, F. 1995, High Pressure and Pasteurisation Effect on Duck Foie Gras,Int. J. Food Sci. Technol. 30, 737–743.
Carpi, G., Buzzoni, M.M., Gola, S., Maggi, A., Rovere, P.1995, Microbial and Chemical Shelf-Life of High-Pressure Treated Salmon Cream at Refrigeration Temperatures,Ind. Conserve70, 386–397.
Gervilla, R., Felipe, X., Ferragut, V., Guamis, B.1997, Effect of High Hydrostatic Pressure on Escherichia coliand Pseudomonas fluorescens Strains in Ovine Milk, J. Dairy Sci.80, 2297–2303.
Ponce, E., Pla, R., Mor-Mur, M., Gervilla, R., Guamis, B.1998, Inactivation of Listeria innocua Inoculated in Liquid Whole Egg by High Hydrostatic Pressure, J. Food Prot.72, 119–122.
Written by
Syed Mudabbar Hussain Shah
The Author is final year student of
B.Sc (Hons.) in Food Engineering
Department of Food Engineering
University of Agriculture, Faisalabad
