FLUIDIZED BED ROASTING MODIFYING THE MICROSTRUCTURE OF COCOA NIBS AND
IMPROVING COCOA BUTTER QUALITY
Abstract
The extraction of butter from cocoa seeds involves various processing
steps that weak the lipid-storing cell walls of cocoa cotyledons.
Roasting is particularly critical, making cocoa nibs porous and brittle.
In this study, the degree of disruption of the microstructure of cocoa
nibs, and the quality and aroma profile of cocoa butter, were evaluated
using two roasting techniques, forced convective oven, and fluidized
bed. Fluidized bed roasting, recognized for its energy efficiency and
low-footprint synthesis, was more than 10 times faster than oven
roasting. This technique allowed a fast release of steam when parenchyma
cell walls were still in a glassy state, while oven roasting caused
gradual physical modification allowing the cell wall to become more
elastic. Consequently, when using fluidizing bed technique, small pores
of unroasted cocoa nibs swelled and coalesced to produce more
large-sized ones. 3-D microscopic image analysis showed a total porosity
in unroasted cocoa beans of 8.5 ± 2.0% (v/v): this value doubled upon
oven roasting and triplicated upon fluidized bed roasting. The higher
porosity in fast-roasted nibs was reflected in the lowest densities and
highest cocoa butter yield. Cocoa butter obtained from fluidized-bed
roasted cocoa showed a higher presence of pyrazines and 3-methylbutanal,
and a lower concentration of hydroperoxides, thus enhancing the
chocolate flavor and quality. In this paper, we showed that
pore-structure of cocoa nibs is a key quality descriptor of roasting
processing, and we concluded by energetic and quality considerations
that fluidized bed roasting of cocoa nibs should be preferred over
conventional roasting.