Effect of SPI Concentration on Physical
Properties of Batter Cake
The Bostwick number is negatively correlated with consistency.
Determination of the Bostwick number of the batter
(Table 1) showed that the Bostwick number of the batters
decreased with increasing the level of SPI. The Bostwick
number of the control batter decreased from 8.6 to 5.6 cm
as the level of the SPI increased from 0 to 30%. Similar
results were reported for the gluten-free batters containing
10 and 20% SPI (Ronda et al. 2011). In the cake batter, pro-teins and hydrocolloids present in the flour are the main
molecules responsible for batter consistency. Addition of
SPI dramatically increases the protein content of the batter.
These proteins can form intermolecular interactions with
each other and with gluten proteins resulting in higher consistency
of the medium. The major forces that facilitate such
interactions are electrostatic and covalent disulfide bondings
(Kumar et al. 2002). In addition, SPI has higher water
absorption capacity compared with wheat proteins (Dogan
et al. 2005; Roccia et al. 2009). Therefore, the increase in the
batter consistency could also be related to the higher water
capacity of the SPI. The increase in the water-binding
capacity of ingredients reduces the amount of free water
available to assist the movement of particles in batters and
accordingly gives higher consistency. Sufficient batter consistency
is required to retain air bubbles formed during
mixing and the CO2 produced by the sodium bicarbonate
during baking. Too high or too low batter consistency may
result in low cake volume (Hoseney 1994; Gómez et al.
2010).
In general, under constant condition, batter density correlates
with the air quantity in the batter (Gómez et al.
2007; Turabi et al. 2008). Determination of the batter
density (Table 1) showed that the presence of SPI reduced
the density of the batters from 1.15 for the control to 1.00 g/
cm3 for the batter containing 30% SPI. This means that by
increasing the SPI level, batter could retain more air during
mixing. Air is probably entrapped physically because of
the increase of consistency, or chemically by stabilization
because of the interaction with proteins (Keller et al. 1997).
The decrease in the batter density is also related to the
increase in batter consistency. Similar results were reported
by Ronda et al. (2011) by addition of SPI into a gluten-free
batter. They established a positive correlation between
batter density and apparent viscosity (r = 0.66) and a negative
correlation between batter density and its consistency
index (r = -0.46).