OJ: High-pressure processing from Australia

Interest in the use of high pressure processing to combat microbes in food products has grown since Japan, more than 10 years ago, first made the method commercially available.

Dr. Michelle Bull, a research food microbiologist at Food Science Australia​, Australia's largest food research organisation and a joint venture between CSIRO​ and the Australian Food Industry Science Centre (Afisc) has been working on a new technology to help food manufacturers beat the microbes in processed orange juice. In an interview with Dr. Bull, FoodProductionDaily.com got up to date with this new food science.

What are the results of your work on using 'high pressure processing'​ to kill microbes?​

In 2001, Food Science Australia​ initiated a study of the safety, quality, storage and cost issues associated with utilising high pressure processing to produce Australian Navel and Valencia orange juice products.

As part of this project we examined the microbiological safety and quality of high pressure processed juice, as well as the physical and chemical characteristics and other quality indicators like nutrient content (Vitamin C and beta -carotene), and conducted descriptive sensory analysis and consumer acceptability testing.

The microbiology results revealed that we were able to extend the shelf life of orange juice using a pressure treatment of 600 MPa (approximately 87000 pounds per square inch) for 60 seconds. This treatment killed the bacteria and most of the yeasts and moulds which normally cause fresh juice to spoil very quickly.

Acid foods such as fruit juices have historically been considered safe products, but acid tolerant pathogens such as Salmonella​ and Escherichia coli​ O157:H7 have been shown to be able to survive in refrigerated juices. We were interested in looking at the level of reduction of Salmonella​ we could obtain by pressure treating the orange juice.

By inoculating the orange juice with differing amounts of Salmonella​, we were able to show that the same pressure treatment which gave orange juice a 3 month refrigerated shelf life would also kill very high levels of Salmonella​ in the juice. After the pressure treatment, we also held the juice at 4°C for 4 days and found no pressure-injured Salmonella​ were been able to recover in the juice during refrigerated storage.

We developed a mathematical model to predict inactivation of Salmonella​ in orange juice in terms of the pressure magnitude and hold time required to obtain a specified log reduction of Salmonella​ in orange juice. With the Salmonella​ inactivation model we can determine the magnitude of pressure and hold times required when processing orange juice to achieve a Salmonella​ a reduction that will meet potential future Australian regulation requirements.

How long have you been researching this process?​

Food Science Australia has had a strategic research alliance with Avure Technologies​ (a subsidiary of Flow International Corporation) since 2000. Since the installation of a 2 L batch processing unit at our Sydney laboratory in 2000 we have been looking at the pressure effects on a range of food products for Australian companies. We have also been examining the effects of high pressure processing on food spoilage microorganisms and on foodborne pathogens, such as Listeria monocytogenes​.

For how much longer can the juice retain its fresh taste?​

Orange juice that was pressure treated remained unspoiled and retained its fresh taste for at least 3 months when stored at 4°C, compared with untreated orange juice which spoiled, and therefore was not consumable, within 2 weeks. The 'fresh taste'​ was judged by a trained sensory panel and consumer acceptability testing.

What are the clearest benefits of 'high pressure processing' for both the food manufacturer and the consumer?​

For the food manufacturer, high pressure processing can be used to make value-added premium foods that have high consumer appeal. The longer shelf life obtained with high pressure processing might also offer access to distant markets - an important consideration for Australian food manufacturers.

For the consumer, pressure treatment of food leaves the nutrient and flavour compounds of the food are intact, resulting in a product that often has a superior taste and quality as compared to thermally processed counterparts. High pressure processing of foods gives a safe and stable product with no chemical additives.

Did your work concentrate solely on orange juice or have you carried out research on other food products?​

This project concentrated on orange juice products, but we have also done some research on apple juice, and peach, nectarine and mango fruit pieces. We are also investigating applications for high pressure processing of dairy, processed meat and seafood.

What other potential applications exist for this process?​

High pressure processing may also be used to modify the functionality of food proteins to produce gels or emulsions with novel textures or tastes.

Were you working in partnership with any food manufacturers?​

For the high pressure processing of orange juice project we were not working with a specific manufacturer. The research was initiated by Food Science Australia as a public domain project to generate data about the effects of high pressure processing on orange juice for the whole Australian juice industry. We have held a series of workshops in Australia to inform the fruit juice and horticultural industry about the research results.

As Food Science Australia had the first high pressure unit in Australia, we have worked with many food companies to help them evaluate the potential for this technology for their products.

Have you had any interest from Australian food manufacturers?​

Food Science Australia has both confidential and public domain projects on the application of HPP in the horticulture, dairy, seafood, and meat areas. More than twenty companies have run product trials in our pilot scale equipment. One company has proceeded to purchase HPP equipment, initially for applications in the seafood area.

Because the cost of evaluating novel technologies like High Pressure Processing exceeds the budget of individual food processors, especially small companies, Food Science Australia together with Avure Technologies and Horticulture Australia Ltd developed a funding scheme to enable horticultural companies to invest in HPP.

The approach used in the HP 3 Funding Scheme shares, and hence minimises, costs and risks to SME's, making their investment in R&D vastly more commercially attractive. Currently, two companies have taken advantage of this scheme.