(106c) Vibrating Electrical Elevator and Reactor: Universal Continuous Reactor for Thermal Processing

Food thermal processing is widely used for pasteurization as an eco-friendly alternative to chemical treatments. Moreover, the constant evolution of costumer tastes and needs give an additional interest of thermal processing for value-added food (e.g. cereal roasting). Several technologies have been developed for different kind of application using hot air, steam, hot water, hot oil or microwaves [1]. This paper presents a simple and universal food processing technology, based on a direct contact with a hot tube.

REVTECH has developed and supplied industrial solutions for heat treatment of bulk solids for more than 15 years throughout the world. The main technology is the Vibrating Electrical Elevator and Reactor (REVE) which is based on three simple principles:

·         The product is transported and mixed in a stainless steel spiral tube by vibrations induced by two off balanced motors.

·         This stainless steel spiral pipe is connected to a power transformer and heated by electricity flowing in the wall of the pipe (impedance tube). The product is then heated up by contact with the hot tube.

·         During transport in the confined spiral tube, the atmosphere is controlled: steam or specific gases can be injected on one side of the reactor and air/moisture/gases can be extracted on the other side.

This technology has been validated on several products such nuts, seeds, herbs, spices, flour or cereals. Figure 1 is an example of a REVE unit for food processing.

Figure 1: Example of food processing unit

Using the pilot unit of the Research and Development department, solid hydrodynamic characterizations were carried out, as well as food application measurements. Plug flow behavior of the REVE has been validated by temperature sensors moving inside the reactor and runs with colored wheat flour. It has been shown that the value of D/uL is ranging 10^-3 to 10^-5, depending on product velocity, which assimilates the REVE to a plug flow reactor [2]. This characteristic ensures a homogeneous products treatment inside the REVE.

Pasteurization application has been validated on in-shell pistachios inoculated with Enterococcus faecium NRRL B-2354 as a surrogate organism for Salmonella [3]. Tests were conducted with a pistachios flowrate of 100 kg/h with tube temperature ranging 110-120°C, steam flow ranging 5-10% and residence time ranging 5 to 11 minutes. With the increase of all those three parameters, there is an increase of the CFU log reduction up to more than 5.41, which is higher than the Almond Board of California (4-log) and even the FDA (5-log) recommendations [4].

Malt roasting tests, as an example of value-added food processing, were also conducted in the same pilot unit. Without steam injection in this case, 200 kg/h of malt have been processed at 240°C, 243°C, 245°C and 250°C with a residence time up to 80 minutes. For every temperature, there is an increase of EBC coloration with residence time until a critical value from which the EBC is decreasing drastically. During these tests, critical residence times were approximately 40 min, 35 min, 25 min and 20 min for respectively 240°C, 243°C, 245°C and 250°C. A dark malt (1700°EBC) was obtained after 40 min at 240°C, which is quicker than typical malt roasting processes (120 minutes) [5].

Thanks to the pilot unit, several food thermal processing can be tested and validated, revealing the versatility of the REVE in food industry. From trial results, continuous industrial units are designed and installed up to 5 ton/h. For future works, new applications/products have to be tested with for instance the use of specific gases.

[1] Fellows, P. (2000). Food processing technology, Principles and Practice. Woodhead Publishing Limited. 229-384.

[2] Levenspiel, O. (1972). Chemical reaction engineering. Wiley.

[3] Almond Board of California (2007). Guidelines for Process Validation Using Enterococcus faecium NRRL B-2354.

[4] Almond Board of California (2007). Outgoing Quality Control Rule. Federal Register, 72 (61): 15021-15036.

[5] Samaras, T., Camburn P., Chandra, S., Gordon, M., and Ames, J. (2005). Antioxidant Properties of Kilned and Roasted Malts. J. Agric. Food Chem, 53: 8068-8074.