Advancements in Oil and Oilseed Processing - Food and Industrial Bioproducts and Bioprocessing - page 122

structure. Single enzyme or mixtures of several enzymes have been tested for their efficacy
to release oil from oilseeds. In rapeseed oil extraction, pectinase was more effective than
cellulase,

-glucanase and xylanase, but was less effective than the mixture of these four
enzymes (Zhang et al ., 2007). A similar trend was observed when protease, pectinase and
mixtures of cell wall-degrading enzymes were used for oil extraction from canola seeds.
The use of protease for soybean oil extraction resulted in higher yields than those obtained
by using cellulase (Lamsal et al ., 2006 ). However, in corn germ oil extraction protease
resulted in lower oil yield than that obtained by cellulase, indicating the importance of
choosing the right enzyme for different oilseeds (Moreau et al ., 2004). Not only do the types
of enzymes, but also sources of the same type of enzyme may have different impacts on oil
extraction yield. For example, protease isolated from fungus was superior to protease from
papaya (papain) (Hanmoungjai et al ., 2002). Similarly, cellulase secreted by Trichoderma
reesei showed higher efficacy in extracting oil than those produced by Trichoderma viride
and Aspergillus niger (Moreau et al ., 2004 ).
Smaller particle size of feed material is an indication of efficient grinding, which
mechanically breaks apart the cell structure of materials (Rosenthal et al ., 1996 ). In addition,
smaller particle size results in larger surface area, which allows better contact between oil-
bearing material and solvent and reduces resistance to the diffusion of oil, as well as other
components, from the solid matrix to the aqueous medium. The rate of enzyme diffusion
into the solid substrate is also improved with smaller particle size. Although the importance
of smaller particle size has been well recognized, only a few studies have been carried out
to investigate its effect on oil extraction yield. A study on enzymatic soybean oil extraction
showed that the oil extraction yield increased with decreasing particle size from 1200 μm to
less than 200 μm (Rosenthal et al ., 2001 ).
The enzyme to be used for the process dictates the pH and temperature of the extraction
medium. Optimum temperature and pH for enzyme activity are usually the conditions used
for extraction process. The pH of the medium could actually change the solubility of some
cell components, especially that of proteins. In enzymatic extraction, protein solubility is
closely associated with oil extraction yield. In general, a high oil extraction yield is obtained
when the solubility of protein is high (Rosenthal et al ., 1996 , 1998 ; Hanmoungjai et al .,
2002). High protein solubility is achieved when pH is away from the isoelectric point of the
protein (pI) (Rosenthal et al ., 1996 , 1998 ; Hanmoungjai et al ., 2002 ). The amount of solvent
used for recovery of target substances is an important parameter that must be optimized to
achieve high extraction yields and minimize solvent use, which leads to lower energy
consumption for residual meal drying and waste processing. It has been shown that during
the enzymatic extraction of soybeans oil yield increased as the liquid to solid ratio increased
from 5:1 to 10:1 (de Moura and Johnson, 2009). Unfortunately, an optimization study was
not conducted to minimize water use.
The concentration of enzyme in the extraction medium greatly affects the enzymatic
reaction rate and the oil extraction yield. It has been demonstrated that an increase in enzyme
concentration from 0.2 to 2.5% (v/w) resulted in significant improvement in oil recovery,
but further increase to 5% did not bring additional enhancement in rapeseed oil extraction
yield (Zhang et al ., 2007). The amount of enzyme needed to achieve acceptable oil yields
needs to be determined to optimize yield and the cost of enzyme for economic feasibility.
Action of enzyme on oilseeds and mass transfer between the aqueous medium and the seed
material are time dependent processes. In most cases an increase in extraction time results
in an improvement in the oil extraction yield, but the improvement slows down and
eventually stops as time prolongs (Sharma et al ., 2002). Hence, extraction time is a variable

β