Results and discussion
Moisture content
Moisture content is an important powder property,
which is related to the drying efficiency. Furthermore,
lower moisture content limits the ability of water to act
as a plasticiser and to reduce the glass transition
temperature. Moisture content of blackberry powders
varied from 1.74% to 3.32% (Table 2), close to the
values reported by Tonon et al. (2009a,b), Quek et al.
(2007) and Sae´nz et al. (2009), working with spray dried
ac¸ aı´, watermelon and cactus pear powder, respectively.
Blackberry powder produced with 7% maltodextrin
showed significant lower moisture content (P £ 0.05) in
comparison to other samples, meaning that the combination
of maltodextrin and gum arabic did not affect
this response. In a similar study, Kurozawa et al. (2009)
did not observe a significant effect of maltodextrin or
gum arabic on the moisture content of spray dried
chicken meat protein hydrolysate. Righetto & Netto
(2005) verified that maltodextrin was more effective in
the reduction of moisture content of acerola powder
produced by spray drying. This behaviour was probably
due to the differences between the chemical structure of
both carrier agents, because gum arabic is a complex
heteropolysaccharide with a highly ramified structure,
containing shorter chains and more hydrophilic groups.
Anthocyanin content and antioxidant activity
Total anthocyanin content of spray dried blackberry
powder varied between 628 and 642 mg⁄ 100 g dried
juice (Table 2). These values are higher than those
obtained for purple sweet potato flour (from 520 to 570 mg⁄ 100 g dry matter) and bayberry powder
(around 570 mg⁄ 100 g dry matter), both produced by
spray drying process using maltodextrin as the carrier
agent (Ahmed et al., 2010; Fang & Bhandari, 2011).
Antioxidant activity of blackberry powders ranged from
213 to 266 lmol TE g)1 dried juice. In a similar work,
Tonon et al. (2010) reported that anthocyanin content
and antioxidant activity of spray dried ac¸ ai powder was
about fivefold higher (approximately 3400 mg⁄ 100 g
dried juice and 1100 lmol TE g)1 dried juice, respectively),
because ac¸ai has higher antioxidant capacity
than other anthocyanin-rich fruits, such as blackberry,
blueberry and others.
Powders produced with maltodextrin or a blend of
maltodextrin and gum arabic showed higher pigment
retention (around 85%), whereas the use of gum arabic
resulted in lower anthocyanin retention (around 78%).
The same trend was verified for antioxidant activity of
spray dried powder, suggesting that anthocyanins found
in blackberry are mainly correlated to its antioxidant
capacity. Studying the microencapsulation of guava
juice by spray drying, Osorio et al. (2011) concluded
that maltodextrin better preserved fruit vitamin C
content. Guava powder encapsulated with maltodextrin
showed higher vitamin C content (about 50%) in
comparison to the results obtained for samples produced
using a mixture of gum arabic and maltodextrin
(1:5 w⁄ w). Tonon et al. (2010) evaluated the use of
maltodextrin, gum arabic and tapioca starch as carrier
agents during the spray drying process of ac¸ai pulp. No
significant differences were observed between the maltodextrin
and gum arabic with regard to anthocyanin
content and antioxidant activity. However, ac¸ai powder
produced with tapioca starch showed the lowest anthocyanin
retention and antioxidant capacity. According to
the authors, highly insoluble materials, such as tapioca
starch, did not provide high microencapsulation
efficiency, and consequently, lower anthocyanin retention
and antioxidant activity were verified in this case.
Colour parameters
According to the results, the colour parameters of
blackberry powders were located in the first quadrant of
CIELAB colour diagram (+a* and +b*), corresponding
to the region of red and yellow.
Lightness values were significantly lower (P £ 0.05)
for the samples produced using 7% maltodextrin or
both carrier agents, indicating that these powders were
slightly darker. Parameter b* did not show statistical
differences, regardless of carrier agent. The use of
maltodextrin significantly increased parameter a* and
chroma C* values, decreasing hue angle H* and leading
to the formation of more red powders. This behaviour
can be related to anthocyanin content and antioxidant
activity results, because powders produced with maltodextrin showed better pigment retention and
higher antioxidant activity (Table 2).
Bulk density, absolute density and porosity
Table 3 shows the results of bulk density, absolute
density, porosity, wettability and mean diameter of
powders produced using different carrier agents.
Blackberry powder produced with the blend of both
carrier agents exhibited the highest bulk density,
whereas the use of maltodextrin resulted in significantly
lower bulk density values. Tonon et al. (2010) observed
higher bulk density values for spray dried ac¸ ai powder,
when tapioca starch was employed as carrier agent. The
authors attributed this behaviour to the highest molecular
weight of tapioca starch in comparison to maltodextrin
and gum arabic. The heavier the material, more
easily it accommodates into the spaces between the
particles, occupying less space and resulting in higher
bulk density values. Furthermore, the polymer interactions
between the carrier agents and powder product
also affect bulk density, meaning that the combination
of maltodextrin and gum arabic used in the present
work contributed to the increase in powder bulk density.
Similar results were also pointed out by Osorio et al.
(2011), working with guava powder produced by spray
drying. Powder encapsulated with maltodextrin exhibited
a minor bulk density than that obtained with a
blend of maltodextrin and gum arabic. Chegini &
Ghobadian (2005) reported that spray dried powders
with higher moisture content tend to have a higher
bulking weight, because of the presence of water, which
is considerably denser than the dry solid. This behaviour
can be associated with the results observed in our study,
because blackberry powders produced with gum arabic
or both carrier agents showed higher moisture content
and higher bulk density.
With respect to absolute density, all the samples
showed similar values, not significantly differing between each other. The knowledge of food density is
important for processing, packaging, storage and shipping.
Absolute density corresponds to the real solid
density and does not consider the spaces between the
particles, in contrast to the bulk density, which takes
into account all these spaces. The lower the bulk density,
the more occluded air within the powders and therefore,
a greater possibility for product oxidation and reduced
storage stability. Lower bulk density also implies in
greater volume for packaging (Lewis, 1987).
Porosity is also related to the bulk density, because
this property measures the fraction of the total volume
which is occupied by the air. Blackberry powder
produced with maltodextrin showed higher porosity
values (Table 3), which indicates the presence of a larger
number of spaces between the particles, containing
oxygen available for degradations reactions. Nevertheless,
as the differences between the porosity values were
quite small (ranging from 70.50% to 72.47%), this
property did not have a significant effect on the
anthocyanin retention and antioxidant activity (Table 2)
of spray dried blackberry powder. Tonon et al. (2010)
reported that spray dried ac¸ai powder produced with
tapioca starch presented lower porosity values (around
68%), in comparison to the samples encapsulated with
maltodextrin or gum arabic (around 75%). Despite the
small number of interparticle spaces observed for ac¸ ai
powder produced with tapioca starch, maltodextrin was
the carrier agent that showed the best pigment protection
and the highest antioxidant activity.
Wettability and particle size
Wettability can be defined as the ability of a powder
bulk to be penetrated by a liquid because of the capillary
forces (Hogekamp & Schubert, 2003). As observed in
Table 3, blackberry powder produced with 7% maltodextrin
showed the lowest wettability values and the
highest mean diameter. Wettability is inversed related to
the particle size, because larger particles show more
spaces between them, being more easily penetrated by
water. On the other hand, smaller particles are less
porous, making more difficult the liquid penetration into
the food matrix, which results in poor reconstitution
properties.
According to Gong et al. (2007), spray-dried powders
often have a small particle size (<50 lm), with poor
handling and reconstitution properties. To improve
these properties, bayberry powder produced by spray
drying was subjected to the agglomeration process,
using a fluidised bed granulator and dryer. Wettability
markedly increased from the wetting time of 120 s to a
satisfactory value of 15 s after agglomeration, whereas
particle size increased from 74 lm to about 200 lm. In a
similar work, Quek et al. (2007) reported that
the agglomeration decreases the powder exposure to oxygen, protecting lycopene and beta-carotene present
in spray dried watermelon powder from oxidation.
Rodrı´guez-Herna´ndez et al. (2005) verified that the
increase in the particle surface area because of decreased
particle size accelerated the degradation of vitamin C
content in cactus pear juice produced by spray drying.
Therefore, it is possible that the higher mean diameter
obtained for spray dried blackberry powder produced
with maltodextrin or both carrier agents (around 49 and
28 lm, respectively) may have contributed to the greater
anthocyanin retention and higher antioxidant activity
observed in these conditions (Table 2).
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