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).