Kenneth R. Swartzel

Process engineers are facing the challenges of today and engineering the future to meet the increased demand for an ever-safer, higher quality, lower-cost, and more-abundant food supply.

The world today for the process engineer is focused on thermal systems. Process designs, evaluations, and regulatory process filings focus on a system’s minimum F0 value, using a conservative z value for the most-heat-resistant pathogen. It is further assumed that the F0 is determined at the point in the product receiving the least thermal treatment. With the advent of commercial use of continuous-flow sterilization processes, including those for products containing particulates, new techniques have had to be developed to identify the coldest spot in the food and assure a safe product. Additionally, several investigators have reported that resistance of organisms is influenced by the method of heat treatment, even when such treatments provide equivalent total heat, implying that physical factors may be involved. And emerging pathogens continue to demonstrate that traditional conservative values could be in question for many of our regulated food processes.

Today, a variety of methods exist for thermal processing of biomaterials. Beyond the traditional canning and conventional continuous flow processing, there exist ohmic, microwave, infrared radiation, and radiofrequency methods. In these systems, conventional evaluation techniques are applicable, so long as appropriate times and temperatures can be measured. Claims of additional destruction due to the method of delivery beyond the thermal energy delivered would have to be documented, and the destruction kinetics of the most-resistant pathogen would need to be determined to support these claims.

Nonthermal processing techniques have long had the interest of industry and university researchers. These techniques include radiation, high pressure, filtration, chemical, and, more recently, electric pulse and oscillating magnetic waves. Traditional evaluation methods do not apply. Now instead of integrating a time–temperature curve in pursuit of an F0 value, one must examine radiation dose levels, pressure levels, degree and depth of filtration bed, chemical concentration, and electric power levels and pulse durations—all as a factor of time. The most-resistant pathogen for the treatment must be identified, and the appropriate kinetics for the full extent of the process operating range must be known. Then, and only then, can appropriate design models be developed and used with reliability. In all cases, correlations to a traditional innoculated study must be carried out.

Packaging issues are adding additional process challenges for the engineer. Aseptic package sterilization validation has been limited to biovalidation techniques. No general method for determining an F0 value–like parameter exists. For many aseptic packaging units, a variety of process steps exist—ambient temperature chemical sterilization, followed by hot chemical sterilization, followed by dry heat sterilization. Lacking this information, packaging manufacturers are left with mathematical models and final biovalidation as the only system checks. Biovalidation provides a needed final assurance, but it does not provide detailed system-to-system and stage-to-stage sterilization comparisons, nor does it provide definitive information useful to aid design models.

In the future, systems will be available to track every particle in the multiphase streams. Each particle will have a thermal or other treatment profile. Treatment distributions will be controllable, and system constituent changes will be designable. Initial raw component monitoring, along with the treatment log, will allow for precise shelf-life projections under controlled distribution conditions.

Beyond these achievements, where will technology take us? Cell-generation techniques offer the greatest potential ever in ridding the world of its endless dependency on the land and water for its nourishment. Today we are growing cells in our labs. Most animal cell generation experiments are medical in scope, e.g., skin tissue for burn victims. The knowledge and the technology we are developing may, however, be the source for the greatest change in the ways we produce, process, and distribute our food. Imagine a tissue being grown in a completely controlled atmosphere (sterile), with no toxins, a highly controlled nutrient delivery system, little or no waste, and accelerated growth, anytime, anywhere. No more planting seeds, no more animal rights issues. The product may be so pure that it may not even need processing (at least not traditionally). 

Tissue grown in a sterile reactor—such as potato or turkey breast—continuously growing, continuously being harvested, processed, and packaged, all at the same location represents a bright new era for food processing.

by Kenneth R. Swartzel is William Neal Reynolds Professor and Head, Dept. of Food Science, North Carolina State University, Raleigh, and Managing Director, Center for Advanced Processing and Packaging Studies