3.6 Foaming properties
The foaming properties of proteins are important in the production of a
variety of foods (Hettiarachchy et al. , 2012). Foaming properties
can be defined as two parts, the ability to form a two-phase system
consisting of air cells surrounded by a thin continuous liquid layer
(the lamellar phase) and the ability to stabilize the foams. All canola
protein products in this study regardless of the source of meal or
fermentation treatment showed FC of 131.1-480.0 % and moderate FS
ranging from 68.0-89.0% at pH 3, 5, and 7.
Among the controls, the defatted AE-IP CP control (306.7% at pH 3 and
243.8% at pH 7) had higher FC than the CP (224.4% pH 3 and 165% at pH
7) and the HE control (244.4% at pH 3 and 154.4% at pH 7) possibly due
to the residual oil in the CP control and a low protein content
(~60%) of both controls. As for the SE products, the CP
control had a higher foaming capacity (322.2%) than the defatted CP
(246.7%) and the HE (266.7%) control at pH 3. At pH 7, the SE defatted
CP control showed the highest FC in all products (480.0%), higher than
the SE CP (464.4%) and the HE (145.6%) control. At pH 5, only the CP
(241.1% for AE-IP and 211.1% for SE) and the defatted CP control
(131.1% for AE-IP and 222.2% for SE) showed the ability to form stable
foams for both AE-IP and SE products. However, the poor solubility at pH
5 still had an adverse impact on the foaming properties compared to the
values at pH 3 and pH 7. Besides, the high temperature and the exposure
to hexane during oil extraction may be the factors that contribute to
the loss of foaming ability of the HE control at pH 5. In addition, the
SE products showed significantly higher FC values than AE-IP. This might
be due to the higher purity of protein in the SE products
(>93%) than AE-IP (<80%) and possible
differences in protein composition (napin and cruciferin).
Among the AE-IP products, only the AE-IP CP protein products by A.
oryzae fermented meals showed the ability to form foams (228.9%) with
a low FS of 33.0% at pH 3 after SSF. At pH 7, all fermented AE-IP
products showed foaming properties of 230.7% (CP, A. niger ),
180.0% (CP, A. oryzae ) 244.2% (HE, A. niger ), and
136.7% (HE, A. oryzae ) with comparable FC compared to the
controls ranging 72.0-84.6%. The AE-IP HE samples pre-treated withA. niger even showed a significantly higher FC value (244.2%)
compared to the HE control (154.4%). As for the SE products, all
samples were able to form foams at pH 3 and 7. In detail, the FC values
of CP products from fermented meals decreased to 196.5% (A.
niger at pH 3), 175.6% (A. oryzae at pH 3), 191.1% (A.
niger at pH 7), and 153.3% (A. oryzae at pH 7) compared to the
CP control at pH 3 and 7. For the HE products, decreases were also found
for products at pH 3, at 195.6% (A. niger ) and 135.6% (A.
oryzae ), while significant increases were reported at pH 7 as 306.7%
(A. niger ) and 155.6% (A. oryzae ) compared to the HE
control (266.7% at pH 3 and 155.6% at pH 7). In addition, the FS
decreased to ~52% for all products from fermented meals
at pH 3, while they remained relatively unchanged (77.6-88.4%) at pH 7.
At pH 5, none of the products extracted from fermented meals showed the
ability to form stable foams. All proteins had poor foaming properties
at pH 3 and 5 and could only form weak foams with large bubbles that
disappeared within 5 min. This was possibly due to the extremely low
protein solubility (<10%) of proteins extracted from
fermented meals at pH 5. The SSF was found to decrease the solubility of
canola protein products to <10% at pH 5, which could have
further adverse impacts on the foaming properties. Overall, protein
products prepared from the fermented HE meals using both extraction
methods showed better FC and FS than the HE controls, while opposite
results were found for CP canola meal products.
The above results indicate the potential of SSF for improving the
foaming properties at pH 7 of protein products extracted from HE meal,
especially when using A. niger . In other words, A. nigerwas preferred to provide protein products with better foaming properties
compared to A. oryzae . The CP products had better foaming
properties demonstrated by some foam when non was observed for HE
isolates under certain conditions. Although the FC and FS values
decreased after SSF, proteins extracted from the fermented CP meal
displayed acceptable foaming properties compared to other plant proteins
like soybean, pea, and lentil (~200%) (Chabanonet al. , 2007; Stone et al. , 2015). However, they still
could not produce comparable protein products similar to the ones from
unfermented CP meals.