Optimisation of granola breakfast cereal manufacturing process by wet granulation and pneumatic conveying
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Date
2010-07
Authors
Pathare, Pankaj B.
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Publisher
University College Cork
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Abstract
This study has considered the optimisation of granola breakfast cereal manufacturing
processes by wet granulation and pneumatic conveying. Granola is an aggregated
food product used as a breakfast cereal and in cereal bars. Processing of granola
involves mixing the dry ingredients (typically oats, nuts, etc.) followed by the
addition of a binder which can contain honey, water and/or oil.
In this work, the design and operation of two parallel wet granulation processes to
produce aggregate granola products were incorporated:
a) a high shear mixing granulation process followed by drying/toasting in an
oven.
b) a continuous fluidised bed followed by drying/toasting in an oven.
In high shear granulation the influence of process parameters on key granule
aggregate quality attributes such as granule size distribution and textural properties
of granola were investigated. The experimental results show that the impeller
rotational speed is the single most important process parameter which influences
granola physical and textural properties. After that binder addition rate and wet
massing time also show significant impacts on granule properties. Increasing the
impeller speed and wet massing time increases the median granule size while also
presenting a positive correlation with density. The combination of high impeller
speed and low binder addition rate resulted in granules with the highest levels of
hardness and crispness.
In the fluidised bed granulation process the effect of nozzle air pressure and binder
spray rate on key aggregate quality attributes were studied. The experimental results show that a decrease in nozzle air pressure leads to larger in mean granule size. The
combination of lowest nozzle air pressure and lowest binder spray rate results in
granules with the highest levels of hardness and crispness. Overall, the high shear
granulation process led to larger, denser, less porous and stronger (less likely to
break) aggregates than the fluidised bed process.
The study also examined the particle breakage of granola during pneumatic
conveying produced by both the high shear granulation and the fluidised bed
granulation process. Products were pneumatically conveyed in a purpose built
conveying rig designed to mimic product conveying and packaging. Three different
conveying rig configurations were employed; a straight pipe, a rig consisting two 45°
bends and one with 90° bend. Particle breakage increases with applied pressure drop,
and a 90° bend pipe results in more attrition for all conveying velocities relative to
other pipe geometry. Additionally for the granules produced in the high shear
granulator; those produced at the highest impeller speed, while being the largest also
have the lowest levels of proportional breakage while smaller granules produced at
the lowest impeller speed have the highest levels of breakage. This effect clearly
shows the importance of shear history (during granule production) on breakage
during subsequent processing. In terms of the fluidised bed granulation, there was no
single operating parameter that was deemed to have a significant effect on breakage
during subsequent conveying.
Finally, a simple power law breakage model based on process input parameters was
developed for both manufacturing processes. It was found suitable for predicting the
breakage of granola breakfast cereal at various applied air velocities using a number
of pipe configurations, taking into account shear histories.
Description
Keywords
Granola breakfast cereal , High shear granulation , Fluidised bed granulation , Texture properties , Pneumatic conveying
Citation
Pathare, P.B., 2010. Optimisation of granola breakfast cereal manufacturing process by wet granulation and pneumatic conveying. PhD Thesis, University College Cork.