Water solubility. Water solubility is one of the most
important characteristics of proteins, as it influences other
properties, including emulsion, foaming, and gel forming
ability. Water soluble proteins induce homogeneous
dispersibility of the molecules in colloidal systems, and
improve the interfacial properties [Villanueva et al.,
1999]. Fig. 4 shows the protein solubility profiles of
enzymatically and/or heat-induced modified RBPI. The
solubility curves of RBPI and modified RBPI evidenced
a typical ‘V’ pattern and the lowest solubilities at pH 4.0,
the isoelectric point of rice bran protein. The solubility
pattern was consistent with the reports of Gnanasambandam
and Hettiarachchy [1995] and Tang et al. [2003]. At
extremely acidic and alkaline pHs, proteins carry net
positive and negative charges, respectively, and thus,
electrostatic repulsion and ionic hydration promoted the
solubilization of the protein [El Nasri and El Tinay,
2007]. Autoclaving drastically increased the solubility of
RBPI at alkaline pHs [autoclaved rice bran protein isolate
(H-RBPI)]. Enzymatic hydrolysis profoundly increased
the solubility of RBPI at all pH ranges [proteasehydrolyzed
rice bran protein isolate (E-RBPI)]. The
highest improvements in RBPI solubility were detected in
the autoclaved rice bran protein isolate after proteasehydrolysis
(EH-RBPI), the RBPI autoclaved after
enzymatic hydrolysis, which reached a level of up to
97.4% at pH 10. The enzymatically modified RBPIs, E