Among all immobilization methods, physical adsorption has been elected by most researchers due to its ease, absence of expensive and toxic chemicals, ability to retain the activity and feasibility of regeneration. On the other hand, poor adsorption of the enzyme results in its leaching off the support surface, which favors other means of enzyme immobilization such as covalent bonding, entrapment and encapsulation. It is possible to strengthen the attachment between the water-soluble enzyme and the water-insoluble surfaces by using multifunctional agents that are bifunctional in nature and have low molecular weight, such as glutaraldehyde (Shamel et al, 2005; Shamel et al., 2007). Nevertheless, physical adsorption remains the most attractive method industrially, because of its simplicity and economical effectiveness.

It has been shown that the adsorption of lipases from M. miehei on porous polysulfone surface (Shamel et al., 2005) and on modified regenerated cellulose hollow fiber membranes (Shamel et al., 2007) can be described by the Langmuir isotherm (Eq. [6.1]), which relates the amount of adsorbed lipase activity, aads, to that present in the supernatant solution, afree, at equilibrium.

A convenient way to express the temperature-dependent parameters Kads and aadsmax takes advantage of Van’t Hoff’s relationship between the equilibrium constant and the standard enthalpy change associated with the process under consideration:

Dhads

Kads = b eXp [ f

aads, max = a (1 + єТ). [6.3]

Experimental results showed that, unlike the general behavior of physical adsorption, increasing the temperature results in an increase in the equilibrium amount of enzyme adsorbed on both surfaces. This was a result of the increase in the diffusion of lipase into the micropores due to expansion of the pores and the reduction of the solution viscosity at higher temperatures.