License heat transfer and microbial lethality model for aseptic systems.

Innovative segmented-flow aseptic processing technology makes it possible for foods containing particulates to be processed without many of the problems inherent in traditional pipe-flow aseptic processing systems. Moreover, this can be done while still maintaining the ability to rapidly heat and cool the product.

A patented, recently developed segmented system is able to control the residence time of each food particle by emulating a series of retort-like cans. Modeling heat transfer in the system yields data that can be useful in determining process parameters for effectively achieving commercially sterile products while at the same time retaining quality.

The objective of researchers at Pennsylvania State University was to develop a model that accurately predicts the microbial lethality of a food particle processed in a segmented-flow system. Synthetic food comprised of xanthan solution and chickpeas was processed in the system. Investigators used the collected particle and temperature data to determine heat transfer coefficients as a function of viscosity, chain speed and particle concentration. From this model, a particle's center temperature can be determined and used to calculate the cumulative microbial lethality for given system conditions.

The segmented flow technique has improved the quality of food. The lethality model is complete except for the heat transfer coefficients, and these data are being collected. It is expected that these data will show that increasing viscosity, increasing particle concentration and decreasing chain speed all lead to decreasing heat transfer in the system, both at the heat exchanger wall-to-liquid boundary and at the liquid-to-particle boundary.

Because residence time is intrinsically controlled in segmented-flow processing systems, the heat transfer model can be used to determine microbial lethality. This would make the system practical for processing foods that contain particulates. Simultaneously, it can improve the quality of food, compared to either canning or conventional aseptic processing techniques.

The technology is available for licensing. Researchers are continuing to optimize the system and have chosen mushrooms as a test product. Preliminary testing has been performed on tomatoes and beans, so adjustments are needed to accommodate mushrooms. Investigators are determining the operating conditions required--time, temperature, feed rate--to achieve both commercial sterility and optimal mushroom quality. The segmented flow technology should improve mushroom appearance, taste, texture and yield (drained weight/raw weight) compared to the canned product, we're told.

Patent. 6,457,513--Segmented flow device. Issued Oct. 1, 2002. Inventor: Paul Walker. Assigned to the Penn State Research Foundation. A segmented flow device performs the functions of a reactor, heat exchanger or holding tube. The device controls the residence time of all of liquid and solid particles which make up a flow in the device. By controlling the residence time, the prediction of residence time becomes less of an issue during processing. The segmented flow device reduces the difference in residence time between the fastest and slowest moving particles of the flow.

Further information. Paul Walker, Department of Agricultural and Biological Engineering, Pennsylvania State University, 223 Agricultural Engineering Building, University Park, PA 16802; phone: [phone]; fax: [phone]; email: [e-mail].