Abstract
A novel tubular industrial apparatus for the surface pasteurization of particles has been studied. Particles are conveyed through a helical pipe by vibrations created by off-balance motors. The residence time of barley grains was characterized. The behaviour of the system was a function of motor angle and motor speed. The residence time could vary up to 21% during one experiment of 2 h (20°, 740 rpm). However, ranges of processing conditions were identified that produce stable operation and thus effective pasteurization of product. In some cases, residence time increased by up to 7% of the initial value over consecutive experiments (40°, 710 rpm). Some reasons for this phenomenon have been proposed and tested. The formation of a powder layer inside the pipe has been proven to affect the residence time of barley grains. A simple model for pasteurization of particles has been developed to characterise the impact of variation in residence time on microbial inactivation.
Highlights
Thermal processing is a major part of the food industry; it is carried out for a range of reasons, both to improve product quality and to enhance the microbiological safety of products
At motor angles of 20 and 30, the motor speed affected the dynamics of the system rather than the magnitude of the residence time; motor speed at 40 influenced both the mean and standard deviation to a much greater extent
The residence time was characterized in both single experiments and over the period of multiple experiments
Summary
Thermal processing is a major part of the food industry; it is carried out for a range of reasons, both to improve product quality and to enhance the microbiological safety of products. It is essential to ensure that the thermal process does not damage the product. Careful selection of the correct temperature-time combination of the thermal process is critical in determining the success of the overall product. Foodborne pathogen infections associated with the consumption of low water activity products such as almonds, peanut butter, or powdered infant formula have received increased attention (Beuchat et al, 2013). Even though a low water activity generally inhibits microbial growth, cells can remain viable at these conditions (Penaloza Izurieta and Komitopoulou, 2012; Mattick et al, 2000). Microorganisms can be more resistant to heat in matrices with reduced water activity (Barrile and Cone, 1970; Penaloza Izurieta and Komitopoulou, 2012; Podolak et al, 2010; Villa-Rojas et al, 2013)
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