## 3 Important Factors in Efficacy of Amphiphiles
### Role of Amphiphiles Properties  
According to many studies, PEG competes with the protein of interest (enzyme) on adsorption to surfaces (e.g., biomass) [78]. Therefore, the higher the surface density and chain length of PEG, the more desirable the exclusion of protein will become. In agreement with [PERSON] _et al._[78], [PERSON] _et al._[79] pointed that polymer surface density is the major contributing feature for efficient protein adsorption resistance. The Increase in conversion rate from ethylene oxide (EO\({}_{4}\) to EO\({}_{6}\)) for an amphiphile enzyme stabilizer is in agreement with earlier findings that show longer E-O chains improve the enzymatic conversion yield up to EO\({}_{80}\). The result of a study that investigated surfactants with EO groups, confirmed that the differences in hydrogen bonding properties is not the factor that influences the reaction yield, and it is in fact the role of hydrophobic interactions that has a determinative role.  
Others have studied the role of surfactants as enzyme stabilizers in relation to their charge distributions and the associated impact on electrostatic interaction with the protein of interest. Many studies showed that non-ionic surfactants can affect the cellulase more positively compared to anionic surfactants [27,37]. Another study showed that the cationic surfactants are more effective in stabilizing cellulytic enzymes than anionic surfactants [34]. According to [PERSON] _et al._[30], even proteins such as whey and casein do not behave similarly when it comes to rheological properties of the liquid.  
A contradictory result shows that the surfactants enhance the hydrolysis of cellulose regardless of their charges [32]. It is apparent that in addition to surfactant charges, there are other variables affecting the impact of additives on enzymes. A finding demonstrated that surfactants with the same charge can still affect the enzyme in different ways. For instance the two anionic surfactants of DOC and SDS, exhibited different effects on enzyme structure [23].  
In agreement with [PERSON] _et al._, 2002 that suggested the association between the modifications of enzyme structure and the rheological properties of the solution imposed by surfactants, [PERSON] _et al._[30] studied the rheological behavior of different proteins of casein and whey and compared them with surfactants. It was found that flexible and disordered macromolecules such as casein form film on the surfaces with a very low viscoelasticity, while globular proteins such as \(\beta\)-lactoglobulin, Lysozyme, and BSA form films with higher viscoelasticity and lower rigidity [80]. It was proposed that the high viscoelasticity of globular proteins can be attributed to high packing density and strong intermolecular interactions (e.g., hydrogen bond, electrostatic and hydrophobic interactions) compared to that of proteins with loose mobile structure such as casein [81]. It is known that proteins and low molecular weight surfactants have different behavior from each other as well. The difference in packing density and interfacial interaction of whey, casein and BSA proteins suggest that different levels of improvement would be observed if casein (low viscoelasticity) is used as an enzyme stabilizer compared with BSA or whey proteins (with higher viscoelasticity).