Optimize thermodynamics of flavor adsorption

Emerging Food R&D Report, August, 2007

The physical and chemical adsorption of flavor compounds onto food matrices is key in controlling flavor retention, balanced release and flavor quality. Previous research at Rutgers University involving flavor adsorption on soy protein and zein--proteins with different hydrophobic characters--has shown that the thermodynamics of flavor adsorption on protein matrices depends not only on flavor chemistry but also on the functional groups on the proteins.

The objective of current Rutgers research was to investigate what effect individual amino acids, with distinct hydrophobic and hydrophilic behaviors, would have on the thermodynamics of flavor adsorption. Scientists also examined the effect of matrix particle size on the thermodynamics.

The researchers used three amino acids--proline and leucine with hydrophobic character, and serine with hydrophilic character--with specific particle sizes as the individual stationary matrix materials. Hexanal, hexanol and limonene were used as the flavor compounds. The thermodynamic parameters, including enthalpies and free energies of adsorption, were measured using inverse gas chromatography (IGC) under dry conditions.

It appears from the research that the hydrophobic nature of an amino acid or a flavor compound is not the only factor controlling the strength and spontaneity of adsorption as measured by free energy and heat of adsorption. The chemical complexity of the specific amino acid and the steric hindrance of the flavor molecules that influence the binding sites also are important determinant factors.

As the particle size of the matrix material decreases, the adsorption thermodynamics become more favorable, and the energy of interaction increases, especially when there are more available binding sites on the flavor molecule. Such a quantitative understanding of flavor-food matrix interactions will enable the development of products with desired flavor retention and release properties.

Further information. Jozef Kokini, Food Science Department, Rutgers University, 65 Dudley Rd., Cook College, New Brunswick, NJ 08901; phone: 732-932-9611; fax: 732-932-6776; email: kokini@aesop.rutgers.edu.

Adsorption is a process that occurs when a gas or liquid solute accumulates on the surface of a solid or, more rarely, a liquid--the adsorbent--forming a molecular or atomic film (the adsorbate).