3.3 Water holding capacity
The ability of a protein to absorb and retain water is critical in
stabilizing the structure, improving flavour retention and mouth feel,
and reducing moisture loss of food products (Khattab & Arntfield,
2009). As shown in Table 3(a), the AE-IP CP control protein product
showed higher WHC (2.1 g/g) than the products of the HE control (1.8
g/g), which may be due to the thermal and chemical changes of HE
proteins that occurred during the solvent extraction processing, leading
to an increase in the protein-protein aggregations and limiting the
protein-water or protein-oil interactions. However, the value of the
defatted CP control (2.7 g/g) was higher than that of non-defatted ones
(2.1 g/g), which was mainly due to the presence of residual oil that
impacted the hydrophilic ability. Similar results were found in the SE
controls of which the defatted CP control (2.1 g/g) had a higher WHC
value than the HE (1.3 g/g) and non-defatted CP controls (1.1 g/g) as
shown in Table 3(b).
After a period of 72-h fermentation of the source meal, a significant
increase (p <0.05) in the WHC of AE-IP products was
found. The WHC increased from 2.1 g/g (CP control) and 2.7 g/g
(non-defatted CP control) to 3.1 g/g (A. niger fermented) and 3.0
g/g (A. oryzae fermented). No significant difference
(p >0.05) was found between the strains for AE-IP CP
products. In addition, A. oryzae showed a higher increase in WHC
of AE-IP HE products (3.2 g/g) than A. niger. (2.9 g/g). Similar
results were found for SE HE products as SSF increased the WHC values
from 1.3 g/g to 2.3 g/g (A. niger ) and 2.7 g/g (A.
oryzae ). The partial protein hydrolysis during the fermentation process
may change the compact protein structure and expose more hydrophilic and
hydrophobic sites (additional binding sites available for water), which
made it easier for the protein to adsorb and hold water (Kinsella,
1982). In contrast, the WHC values of the SE CP products remained stable
(p >0.05) after SSF using A. niger (1.3 g/g)
and A. oryzae (1.4 g/g) compared to the non-defatted CP control
(1.1 g/g) and decreased when compared to the defatted CP control (2.1
g/g). For the type of strains, A. oryzae was preferred to improve
the WHC of both AE-IP and SE HE products. In addition, all HE products
showed higher increases in WHC than the CP products.
Overall, the defatted CP controls showed higher WHC values than the
non-defatted CP controls and the HE controls. As for the difference
between the AE-IP and SE products, the AE-IP protein products showed a
slightly higher WHC value than the SE ones. This was possibly due to the
lower protein level in AE-IP products, which led to a larger sample
amount of AE-IP products used for testing than the SE products
(corrected by protein content). The non-protein compounds in AE-IP
products such as the soluble fibre and polysaccharides may contribute to
the ability of water to absorb and bind. Thus, it is important to take
the possibly contained fibre and polysaccharides into consideration. The
presence of these compounds can enhance the overall water holding
capacity of canola products (Aider & Barbana, 2011).