High pressure processing pushes to the fore
technologies food producers are using to extend the relatively
short shelf life for their chilled products, reports Ahmed
ElAmin.
A growing number of chilled food products are now being made using high pressure processing, fuelled by growing consumer demand for new foods and concerns about safety.
To exploit the demand for minimally processed foods without synthetic chemical preservatives, manufacturers are also exploring other preservation methods such as ohmic heating, pulsed electric field, irradiation, bright light and aseptic processing.
Extending the shelf life of chilled products also opens new opportunities for processors by allowing them to consolidate operations and extend their distribution chain.
Although high pressure processing was first developed about a century ago, it is only now that the method's full benefits are being exploited by companies, according to a report by Campden &Chorleywood Food Research Association.
Due to the high pressure resistance of some pathogens, the use of high pressure processing has so far been limited to chilled products.
The technical challenges that need to be addressed by high pressure sterilisation are slowly being addressed, potentially widening use of the method to produce high quality and safe low-acid foods,Campden & Chorleywood report writer Craig Leadley stated.
"Unfortunately, bacterial spores are very resistant to commercially achievable pressures," he stated. "As a result, products that are currently on the market tend to bechilled and many are high-acid or contain additional preservation hurdles such as the presence of antimicrobial compounds."
The costs of the process can vary widely and depend on the fill ratio of the product volume to the processing unit's volume, the process holding time and the amount of pressure applied. Espuna inSpain says high pressure processing for its ham costs about eight euro cents per kilogram.
In addition to the technical challenges that need to be worked out, the costs of processing are a major obstacle for wider commercial uptake, Leadley stated.
"This is particularly true of the UK where profit margins for food items are generally low," he stated. "For the foreseeable future, the process could only be used for veryhigh value products where a premium price could be charged."
High pressure processing is a non-thermal pasteurisation process in which a food is subjected to pressures four to seven thousand times higher than normal atmospheric levels. The pressure is heldfor a time, generally under 10 minutes.
The extremely high pressures inactivate vegetative microorganisms. Food processors can maintain the sensory and nutritional quality of their food products by not using additional heating to killthe microsorganisms, Leadley stated.
Research in Japan led to the launch of the world's first high-pressure pasteurised food in 1990, a jam manufactured by Meidi-ya Food Factory. Other products such as juices and dairy dessertsfollowed. Since then use of the process has spread to other countries.
In 2004, about 40 food companies around the world were using a total of 69 high pressure units. Half of the units were located in the US. About one-third of the units are used for juice andbeverage production, the rest for fruit and vegetables, meat and shellfish.
In Europe, Espuna in Spain makes vacuum packed sliced ham and tapas using the method. Pampryl in France, Orchard House in the UK, and Frubaca in Portugal also use the method for their products. Inthe US at least three companies use high-pressuring processing for preserving oysters.
Among the suppliers of the units are Hyperbaric in Spain, Engineered Pressure Systems in Belgium and Stork Food & Dairy Systems in the Netherlands.
