Rate of fat bloom development in under-tempered dark chocolate
is dependent on the component particle size distribution and
storage time of products. During storage, measurements on texture
and surface whiteness showed initial rapid increases with consequential
reductions in gloss within the first 96 h, followed by gradual
decreasing gradients until reaching asymptotic values.
Blooming was initiated in products within 24 h in storage causing
rapid increases in hardness and surface whiteness with the gradual
disappearance of gloss until 96 h when no further changes were
observed, attributed mainly to growth of re-crystallised fat within
the structural network of the product during blooming, and thus
influencing light reflections to produce the whiteness of the surface
with the resultant changes in texture. Bloom development
influenced melting properties (Tonset, Tend, Tpeak and DHmelt) in
products causing polymorphic transformation from bIV to bV within
24 h in storage, with further transformation to bVI after 72 h.
Micrographs showed similar surface crystal network structure
and inter-particle interactions on products from different PS after
tempering. Within 24 h in storage, liquid and unstable (crystallised)
fat appeared on the surface of products with the initiation
of bloom. The unstable fat then re-crystallised during storage into
more stable polymorphs and crystal growth was promoted by Ostwald
ripening (larger crystals growing at the expense of smaller
ones), with the appearance of white crystalline structure which
spread gradually throughout the entire chocolate mass after 96 h.
Product containing the largest PS (50 lm) showed the fastest fat
bloom rate, with the smallest PS (18 lm) the least, suspected to
be attributed mainly to hydrodynamic forces by capillary action.
It was hypothesised that fat bloom development is initiated by
movement of both liquid and unstable fat onto the surface of products
by capillarity created by hydrodynamic forces within the inter-
particle pores and crevices, followed by growth of the recrystallised
fat by diffusion gradient across the entire chocolate
mass until fully bloomed. These findings provide valuable progress
in the understanding fat bloom formation and development in dark
chocolate systems, and can have potential applications for the prevention
of fat bloom in chocolates.