Q&A with Research Team Studying Ability of HPP and Thermosonication to Inactivate AAT Spores in Orange Juice

The June 2015 edition of Food Control Journal looked at the ability of HPP to serve as an effective pre-treatment when trying to inactivate the spores of Alicyclobacillus acidoterrestris. A representative from the research team, which involved researchers in both New Zealand and Indonesia, answered a few questions. Their research study can be purchased here.

Q: Describe your research, namely your published article “High pressure processing pretreatment enhanced the thermosonication inactivation of Alicyclobacillus acidoterrestris.”

A: Alicyclobacillus acidoterrestris (AAT) is a long name for a big problem to juice manufacturers. This gram-positive, spore-forming bacterium is very durable and hard to detect. It can grow at a wide pH level (between 2 and 7) and broad temperature (25–60°C) range. Its spores are known to survive thermal pasteurization, and in comparison to major spoilage microbes found in high-acid shelf-stable foods, it exhibits very high heat resistance, requiring novel treatment approaches. Because limited information exists on the inactivation of AAT by power ultrasound, especially on spores, our research team analyzed the effect of thermosonication (a process that simultaneously employs ultrasound and heat shock) on store-bought orange juice that was deliberately inoculated with AAT. We also ​experimented with pre-treatment of the juice with High Pressure Processing before thermosonication. Interestingly, we concluded that the samples that had undergone HPP treatment prior to thermosonication clearly provided the best recipe for spore inactivation of all our samples.

Q: What effects on spore presence did you observe in the orange juice samples?

A: The thermosonication of orange juice pre-treated with HPP at a pressure of 600 MPa for 15 min was the best technique to inactivate A. acidoterrestris spores in our study. However, a higher thermosonication temperature might improve the pasteurization efficiency.

Q: What visual and sensory effects did you observe in your juice samples when they were subjected to HPP? Did you evaluate the impact on shelf-life?

A: Thermosonication required at least 8°C lower temperatures than conventional thermal pasteurization to achieve the same spore inactivation. Theoretically, this lower temperature could enhance juice quality in addition to saving energy. However, while our study demonstrated the advantage of high pressure-assisted thermosonication for the inactivation of AAT spores in orange juice, we did not specifically analyze juice sensory/quality attributes or shelf-life preservation. Further research would be needed to investigate those qualities.

Q: Do you think HPP-aided thermosonication is commercially viable? Could it ultimately result in less beverages being wasted?

A: It might be viable but in order to be implemented efficiently and to facilitate quick inactivation of AAT spores, the ultrasound unit would need to allow for working at a higher temperature. For example, we found that a process of 15 min only reduced AAT by 1 log. By increasing the temperature or acoustic power, this inactivation rate could also be higher.

The other limitation of ultrasound is that it requires new machines designed to produce at a commercial scale. To my knowledge, it is currently only employed in academic laboratories for research.

Q: What do you think is/are the most important next step(s) to facilitate more adoption of HPP as a food processing and preservation method?

A: HPP is a ready-to-use commercial technology, but improving the price of large-scale units would enhance commercial adoption.

More attempts could also certainly be done with the combination of HPP pre-treatment and thermal processing. Achieving at least 6 log reductions for microorganisms such as A. acidoterrestris is very difficult, so any success from other combinations of pressure, ultrasound and heat technologies that can lead to quick inactivation of AAT will be market-desirable.