2.3.1 Advantages of the ultrafiltration membrane method
Compared to traditional soybean processing methods, the ultrafiltration
membrane method offers significant advantages as relatively new
technology. The main advantages of ultrafiltration are the mild
operating conditions and the high selectivity. The use of a gentle
process produces less denatured protein than traditional disappointing
precipitation. Intact soy proteins offer many special features such as
water binding, adhesion, fat absorption, solubility, texture,
emulsification, foaming, and flavor formation that are required by the
processing of food products. Protein is recovered directly from the soy
extract using an ultrafiltration membrane, thus avoiding the whey
produced by traditional isoelectric precipitation methods. This process
not only increases the yield of the isolate (as whey protein is
recovered from the isolate) but also produces a product with enhanced
functionality and nitrogen solubility (Lawhon et al., 1981).
Treatment of soybean meal with commercial pectinase followed by
ultrafiltration resulted in a soybean concentrate with a protein content
of 78.5%, which had a very low concentration of phytic acid. Based on
the calculated yield of the membrane separation technology, the protein
recovery was 17% to 26% higher than the commercial process currently
used for soy protein separation (Shallo et al., 2001). Membrane
processing enables proteins to be maintained in their native state and
therefore membrane-treated soy concentrates and soy powders are
functionally similar. Although solubility and emulsion stability
decreased with heating, hydration and emulsification activity were
favorably correlated with denaturation. The essential amino acid profile
of the membrane-treated soy concentrate was similar to that of the
commercial isolate (Rao et al., 2002).
Ultrafiltration membrane extraction is a more environmentally friendly
method, consuming less energy than other concentration techniques such
as freeze-drying or evaporation. The lower energy consumption is because
there is no change in the state of the solvent during the
ultrafiltration process. Another advantage of ultrafiltration is that it
can operate at low and ambient temperatures as well as high
temperatures. Because the separation process does not use heat treatment
or chemical reagents, ultrafiltration products offer better performance
than conventionally produced SPI (Cheryan, 1983).