2.2.2 Proteases
Proteases help to hydrolyze the oleosins, the lipophilic protein
surrounding lipid bodies, thereby reducing the surface activity of the
oleosin and removing the lipid (Rosenthal A, 1996). In terms of the
enzymes evaluated, protease was the only one that led to a significant
increase in protein extraction under certain circumstances, i.e. when
large particles or heat-treated flour were used (Rosenthal A, 2001,). In
another study, 0.5% (g enzyme per gram of biomass) of protease was
combined with 0.5% of cellulase simultaneously to extract protein from
soybean flakes. This combination resulted in a 75% increase in the
yield of protein from soy flakes (Lamsal, 2006, ). A response surface
methodology was used to assess the effect of protease on protein
extraction rates. The protein yield increased from 27.8% to 66.2% only
when heat-treated flour or large grains of non-heat-treated flour were
used in the extraction process (Rosenthal A, 2001,). The effect of two
commercial endoproteinases (Protex 6L and Protex 7L) on the extraction
rate of soy protein during enzyme-assisted extraction was investigated.
Protex 6L was more effective than Protex 7L in extracting free oil,
protein, and total solids. The protein extraction rate was 85% using
0.5% Protex 6L (De Moura, 2008). Protease-assisted extraction methods
have the potential to hydrolyze proteins. Without enzymatic treatment,
the molecular weight of the soy protein ranges from 99 to 7 kDa. Protex
7L and Protex 6L hydrolyze the soybean to produce extracted proteins
with molecular weights below 54.1 kDa and 30 kDa (De Moura, 2008).