Basic issues remain regarding high-pressure research.

Nonthermal food processing techniques are regarded with keen interest by the food industry. Among nonthermal techniques--pulse-electric field pasteurization, high-intensity pulsed lights, high-intensity pulsed-magnetic fields and ozone treatment--high-pressure processing (HPP) is gaining in popularity with processors, not only because of its food preservation capability but also because of its potential to have a functional impact on products.

HPP inactivates pathogenic microorganisms while giving a minimal heat treatment, and retaining nutritional and sensory characteristics without sacrificing a product's shelf life. Other advantages of HPP over traditional thermal processing include: reduced process times; minimal heat damage; an ability to retain a product's freshness, flavor, texture and color; no vitamin C loss; and minimal undesirable functionality alterations.

However, spore inactivation remains a major challenge for HPP. HPP methods for completely inactivating spores are yet to be optimized. Among other concerns, there's a need to develop and standardize HPP process parameters with respect to microbial inactivation. This is essential before commercialization of this technology can take place.

The need for an alternative to thermal processing as the primary means of eliminating pathogenic and spoilage microorganisms is significant. HPP holds promise since food materials treated by this method retain their natural flavor, color and texture without loss of vitamin or nutrient content. Furthermore, predictable changes in functional characteristics of proteins and complex carbohydrates, which have not been explored extensively, mean that there are some avenues of work in HPP that remain to be completed.

Although a significant amount of research has been conducted in HPP, much remains to be done in terms of understanding the critical limits of the process and the extent to which this might ensure appropriate treatment of food materials. There is a limited chance of extensively implementing this technology unless specific processing parameters are established for each food material treated by HPP. The possibility of commercialization of HPP also depends on its economic viability. Therefore, the scientific community needs to undertake a detailed economic analysis of HPP by comparing the process costs with the present costs of processing by conventional means, and at the same time factoring in the added value of the improved sensory characteristics of HPP-treated foods.

Issues needing clarification include: the variability of pressure resistance between different strains of the same microbial species; the protection of organisms by food constituents, making it important to study microbial inactivation in foods; the possible recovery of environmentally stressed microbial cells during chilled or ambient storage; the effects of high pressure and sub-zero temperature processing; and the impact of pressure-cycling on reducing microbial viability.

Further information. D.S. Jayas, University of Manitoba, Department of Biosystems Engineering, 438 Engineering Building, Winnipeg, MB R3T 5V6, Canada; phone: [phone]; fax: [phone]; email: [e-mail].