AbstractA Spanish university has developed a new system to inactivate microorganisms in food combining supercritical fluids and ultrasounds technologies. The system works under low temperatures and pressures allowing reduction of costs and time, and preservation of the overall sensory and nutritional properties of the food. The technology has been tested with real foods. Researchers are looking for companies to licensing the technology or to carrying out further developments.
DetailsA researcher team of a Spanish university has developed a new system to inactivate microorganisms in food which allows its preservation, additionally improving its quality. Up to now the system has been successfully tested on fruit juices, in particular, apple and orange juices, although it could also be used, among others for dairy products, jams or beer.
To date, the most commonly used technique for the microbial inactivation is thermal treatment. This technology has the drawback that, due to heat, several components can be affected, decreasing the overall sensory (flavor, color, texture,…) and nutritional (vitamin, amino acid,…) quality of the food. To skip these inconveniences new non-thermal technologies such as electrical and light pulses, irradiation or supercritical fluids have been studied. The system created and patented by the Spanish group combines the use of ultrasound and supercritical fluids, reducing the product loss of quality.
The procedure works under low temperatures (35ºC), which results in a higher sensory and nutritional value, and low pressure, which significantly reduces the cost and process time. It consists in the immersion of the food in a carbon dioxide (CO2) supercritical fluid atmosphere. Under these conditions and through a piezoelectric transducer, the food is subjected to a high intensity ultrasonic field to inactivate microorganisms.
Laboratory plant for the microbial inactivation using supercritical fluids
The supercritical fluids inactivation system consists in a vessel where the sample is introduced. At present the system is discontinuous and must be loaded and downloaded for each treatment, however with some set-up adjustments it could work under a continuous flow of liquid.
In the case of liquids, through the bottom of the vessel samples can be extracted at different process times allowing the determination of the inactivation kinetics. The mentioned vessel is located inside a tank which allows keeping the temperature of the treatment constant. The CO2 is pumped to the treatment vessel through a two pistons pump. To improve and accelerate the charge of the supercritical CO2 a reservoir vessel pressurized with nitrogen is set out. The system also has the necessary valves, temperature and pressure gauges as well as the security systems that allow its correct work.
The high intensity ultrasonic system consists in two commercial ceramics of 35 mm diameter, 12.5 mm internal diameter, 5 mm thickness and 30 kHz resonant frequency. These ceramics are located in a sandwich transducer connected to a sonotrode. The sonotrode allows concentrating the acoustic energy which will enhance the inactivation process. The sonotrode is fed by an ultrasound generator working at 30 kHz frequency.
Regarding the ultrasonic set-up, it is important to highlight the isolating system, which allows working in a highly conductive environment without short circuits.
A lot of research has been conducted to develop new preservation technologies that allow the preservation of the sensory and nutritional properties of food. In this regard, the use of high pressure; electrical pulses; membrane filtration; microwaves and radiofrequency or supercritical fluids has been considered. In particular, at present different products treated by high hydrostatic pressure can be found in the market. The main inconvenience of this technique is the high cost of the equipment.
As a new technology, the use of supercritical fluids for the inactivation of enzymes and microorganisms is of great interest. Numerous research works have demonstrated the microbial inactivation capacity of supercritical-CO2 at low temperatures, avoiding the deterioration of the food nutritional and sensory properties. In the food industry to have cost-effective processes it is necessary to work at high product outputs. In this regard the main inconvenience of supercritical-CO2 is the long process times needed. The supercritical-CO2 inactivation is mainly due to the penetration of carbon dioxide in the cells and the extraction of vital components. Therefore, a way to improve this technology is enhancing the supercritical-CO2 penetration into the cells, accelerating the inactivation mechanisms. High power ultrasonics can be used to improve mass and heat transfer processes as well as, in combination with heat, the inactivation of microorganisms.
Compared to other preservation technologies, the advantages of Supercritical-CO2 combined with ultrasounds are:
• Heat treatments: Use of low temperatures (35ºC in our experiments) which involves a higher nutritional and sensory quality of food.
• High pressure: The use of lower pressures (100-350bar) which significantly reduces the cost of the operations and the possible texture changes. The high pressure treatments work at 3000-6000 bars.
• With respect to the inactivation using supercritical fluids only: The process time is drastically reduced.