Hielscher - Ultrasound Technology

Consumers demand for minimally processed fresh-like food with high sensory and nutritional attributes. Hence gentle, but targeted non-thermal food processing and preservation gain importance.* Ultrasound is probably the most simple and most versatile method for the disruption of cells and for the production of extracts.* Ultrasound is efficient, safe and reliable.

Today, thermal treatment is the most common processing method for food extraction or microbial inactivation that leads to longer shelf-life (preservation). Because of the exposure to high temperature this method has often disadvantages for many food products. Thermal treatment can cause undesirable alterations of sensory attributes, i.e. texture, flavor, color, smell, and nutritional qualities, i.e. vitamins and proteins.

Ultrasound is an efficient non-thermal alternative. Ultrasonic cavitation creates shear forces that break cell walls mechanically and improve material transfer. This effect is being used in the extraction of liquid compounds from solid cells (solid-liquid extraction). In this case, the compound to be dissolved into a solvent is enclosed in an insoluble structure. In order to extract it, the cell membrane must be destructed. For this, ultrasound is faster and more complete than maceration or stirring. The particle size reduction by the ultrasonic cavitation increases the surface area in contact between the solid and the liquid phase, significantly. The mechanical activity of the ultrasound enhances the diffusion of the solvent into the tissue. As ultrasound breaks the cell wall mechanically by the cavitation shear forces, it facilitates the transfer from the cell into the solvent.

Examples:

• ultrasonic extraction of phenolic compounds from vacuolar structures by disrupting plant tissue
• ultrasonic extraction of Betacyanin (red pigments, e.g. from beets) and Betaxanthin (yellow pigments)
• ultrasonic extraction of lipids and proteins from plant seeds, such as soybean (e.g. flour)
• ultrasonic improvement of oil extraction from oil seeds
• cell membrane permeabilization of fruits, such as grapes, plums, mango
• ultrasonic processing of
  • fruit juices, e.g. orange, grapefruit, mango, grape, plum
  • purees
  • sauces, e.g. tomato, asparagus, bell pepper, mushroom
  • dairy products
• improve stability of dispersions, such as orange juice, i.e. reduce settling

Unlike other non-thermal processes, such as high hydrostatic pressure (HP), compressed carbon dioxide (cCO2) and supercritical carbon dioxide (ScCO2) and high electric field pulses (HELP), ultrasound can be easily tested in lab or bench-top scale - generating reproducible results for scale-up. The intensity and the cavitation characteristics can be easily adapted to the specific extraction process to target specific objectives. Amplitude and pressure can be varied in a wide range, e.g. to identify the most energy efficient extraction setup.

Microbial and enzyme inactivation (preservation) is another application of ultrasound in the food processing. In this case ultrasonication is often more effective when combined with other anti-microbial methods, such as:

• thermo-sonication, i.e. heat and ultrasound
• mano-sonication, i.e. pressure and ultrasound
• mano-thermo-sonication, i.e. pressure, heat and ultrasound
  e.g. for Bacillus subtilis, Bacillus coagulans, Bacillus cereus, Bacillus sterothermophilus, Saccharomyces cerevisiae, Aeromonas hydrophila*

Ultrasound is also used in the emulsification, dispersing and homogenizing as well as to improve chemical reactions and surface chemistry (sonochemistry) or to influence crystallization processes.

Hielscher offers a broad range of ultrasonic devices and accessories for the efficient processing of foods.

• Compact laboratory devices of up to 400 watts power
  These devices are mainly used for sample preparation or initial feasibility studies and are available for rental.
• 500 and 1,000 and 2,000 watts ultrasonic processors like the UIP1000 with flow cell and various booster horns and sonotrodes can process larger volume streams.
  Devices like this are used in the optimization of the parameters (like: amplitude, operational pressure, flow rate etc.) in bench-top or pilot plant scale.
• Ultrasonic processors of 2, 4, 8 and 16kW and larger clusters of several such units can process production volume streams at almost any level.

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Literature:

• D. Knorr, B. I. O. Ade-Omowaye and V. Heinz, 2002: Nutritional improvement of plant foods by non-thermal processing; in: Proceedings of the Nutrition Society (2002), 61, 311–318.
• Kim, S.M. und Zayas, J.F. 1989: Processing parameter of chymosin extraction by ultrasound; in J. Food Sci. 54: 700.