Protein Processing in Food and Bioproduct Manufacturing and Techniques for Analysis - Food and Industrial Bioproducts and Bioprocessing - page 91

SE on the other hand increases with increasing G/F as it enhances the amount of protein
molecules transferred from the liquid to the foam phase. At high gas to feed flow rate ratios,
however, there is greater likelihood of bubble burst. Additionally, Hossain and Fenton
(1998) reported higher enrichment and protein recoveries with continuous processing
compared to semi-batch mode.
Wang and co-workers (2009) successfully used foam fractionation to separate lysozyme
from chicken eggs and reported that separation efficiency was significantly influenced by pH
and sodium chloride concentration. Activity recovery and protein recoveries were highest
(40% and 60%, respectively) at pH 7 and 0.3 M NaCl concentration. Addition of sodium
dodecyl sulfate (SDS), cetyltrimethylammonium bromide, Triton-X and Tween 80, resulted
in protein recoveries of 93%, 88%, 68% and 72% and activity recoveries of 30%, 20%, 55%
and 58%, respectively.
Gas flow requirements to produce stable foams were found to be lower for bovine serum
albumin and beta-lactoglobulin, which had greater surface activity compared to beta-casein
and alpha-lactalbumin, and the enrichment factor and percentage volume loss in foam were
also higher for the former proteins (Hossain and Fenton, 1998).
Matouq (2008) compared the separation of proteins from yogurt whey and cheese whey.
Less foam formation occurred with cheese whey compared to yogurt whey and higher
enrichment values were obtained with yogurt whey, although the cheese whey contained
higher protein content. As higher concentrations of fat tend to decrease foam formation, the
author concluded that the higher fat content of the cheese whey may explain the decreased
foam formation and stability.
Various workers have explored ways to enhance the SE of the foam fractionation by
using adsorptive ligands, such as Cibacron blue of a triazine dye bound with a polyethylene
glycol, kaolin, iron oxide, graphite and SDS (Keiichi et al ., 1998 ; Yoshihiro and Toshiro,
2000 ; Suzuki et al ., 2002 ).
Yoichiro (1986) proposed continuous countercurrent foam separation equipment in
which samples are introduced into the middle portion of a gas-liquid dual countercurrent
flow system. Material having an affinity to the foam is carried with the foam stream whereas
other materials are carried with the liquid stream.
As conditions used during foam fractionation can change the molecular structure of
target proteins and, consequently, protein function, it is important that these conditions be
selected carefully. Changes can occur due to the direct effects of ligands used, unfolding
of proteins at the gas-liquid interface, high shear stress rates and chemical damage due to
oxidation (Maruyama et al ., 2007 ).
Extraction using reverse micelles
Proteins can be extracted from solution using liquid-liquid separation techniques, also
known as reverse micellization. The technique involves the use of a biphasic liquid system
comprising an aqueous solution of the protein and an organic micellar solution containing
monodisperse aggregates of surface-active molecules, usually ranging in diameter from 1 to
10 nm (Asenjo and Chaudhuri, 1996). Shaking of the two solutions results in partitioning of
proteins from the aqueous into the micellar phase (Figure 3.5). Synthetic protein chaperones
can be added to protect proteins from extensive denaturation and to aid in renaturation
especially for pharmaceutical type applications.
A solid state extraction version of the method involves suspension of protein powder in
the micellar phase followed by gentle stirring to allow the selective separation of the target
proteins into the organic micellar solution.