Steve Smith, Purdue University, Department of Food Science

PROCESS EXPO | Expert in Residence
High Pressure Pasteurization (HPP)
Steve Smith | Purdue University

High Pressure and its effects on microorganisms has been studied for over 100 years. In 1884, Pascal tested the effects of pressure on microorganisms. Later that decade, preservation of various food products was tested at the West Virginia Agriculture station.

However, it wasn't really until the turn of the twenty-first century that it has caught on commercially. Now there are a number of food products that utilize pressure to help preserve their fresh nature. Products such as juices, nectars, meat and seafood. Perhaps just as importantly, we are observing that consumers are willing to pay premium prices for more fresh-like products.

Some of the benefits of HPP are:

  • Increased shelf life- as much as 2-3 times longer
    • This is accomplished by a reduction in the vegetative microbial count in the food.
  • Improved product freshness- sensory/nutritional
    • Even though HPP is effective against vegetative microorganisms, it has very little effect on low molecular weight properties in foods such as flavors, vitamins and colorants.
  • Elimination of post processing and packaging contamination
    • The food is pasteurized in the container
  • No need for chemical preservatives

The use of this technology certainly has a lot of potential benefits to high acid and acidified food products. However, there is a very definite concern regarding low acid foods. That is, HPP is not effective against spore forming microorganisms, specifically Clostridium botulinum. In 2006, there was an outbreak of botulism poisoning resulting from pasteurized carrot juice. Although the juice should have been refrigerated, it may have been held at elevated temperatures during distribution.

As a result, the FDA is looking more closely at low acid extended shelf life beverages. HACCP rules were written for high acid products not low acid products. FDA will require low acid processors to do a microbial validation to prove the efficacy of the HPP process against the most pressure stable pathogen, Clostridium botulinum. As this microorganism is dangerous to test, a suitable surrogate organism must be found.