In the preliminary experiment, crude RBP was prepared
from DRB by alkaline extraction procedures followed
by isoelectric precipitation according to Adebiyi et al
(2007). Protein solution (5% w/v) was used for the
investigation. Three treatments of the protein solution
were examined: First, protein solutions at various pH
(6.0–11.0) were prepared using distilled water and
glycerol was added at a concentration of 2.0% (w/v),
with constant stirring for 30 min. Secondly, protein
solution at pH 8.0 was prepared using distilled water
and glycerol at different concentrations (1.5–3.0% w/v)
was added in the solution, with constant stirring for
30 min. Thirdly, protein solution at pH 8.0 was
prepared using distilled water at glycerol concentration
of 2% (w/v); the solution was placed in a water bath at
various temperatures (50–90 C) and kept for 30 min
with constant stirring. The pH of the treatments were
appropriately adjusted with 1 m NaOH or 1 m HCl.
Films were made from the three treatments by casting
the protein solution on plates, dried in the oven and
stored as described in the main experiment, before the
evaluation of thickness and puncture strength (PS).
Main experiment
Preparation of refined rice bran proteins for film formation
A schematic diagram for the refined RBP by alkaline
extraction followed by isoelectric precipitation method has
been presented in Fig. 1. DRB was dispersed in 0.02 m
NaOH,pHadjusted to9.5andhomogenised at 20 500 r.p.m.
for 30 min using an Ultra-Turrax homogeniser (Janke and
Kunkel IKA-Labortechnik, Staufen, Germany). The lyophilised
RBP was stored at 4 C until use.
Film formation
Protein solutions (5% w/v) and glycerol (2%, 3%, and
4% w/v) were mixed thoroughly in distilled water and the
pH of the solution was appropriately adjusted with 1 m
NaOH or 1 m HCl. Subsequently, the protein solutions
were heated in a water bath at 80 C for 30 min. The
heated and unheated protein solutions were cast on a
levelled Nafron sheet (Nich