Mi. Beck et al., PHYSICOCHEMICAL CHARACTERIZATION OF ZEIN AS A FILM COATING POLYMER - A DIRECT COMPARISON WITH ETHYL CELLULOSE, International journal of pharmaceutics, 141(1-2), 1996, pp. 137-150
Zein, an alcohol-soluble protein contained in the endosperm tissue of
Zea mais, occurs as a by-product of corn processing. Although zein has
been empirically employed as an edible coating for foods and pharmace
uticals for decades, it has not attracted considerable attention as a
possible alternative for film-forming agents in drug formulations such
as derivatives of cellulose or polyacrylates. In this report, the the
rmal, thermomechanical, water sorption and gas barrier properties of z
ein and plasticized mixtures of zein are discussed. With the objective
of classifying these properties within the field of polymers used as
pharmaceutical film formers, zein was compared with various types of e
thyl cellulose that had a degree of substitution (DS) in the range 1.7
-2.6. In order to quantify the plasticizing efficiency of low molecula
r weight compounds when added to zein, the compatibility of the mixtur
es was investigated by means of dynamic-mechanical thermal analysis (D
MTA). The esters of tartaric acid were found to have superior properti
es with respect to miscibility, depression of the glass transition tem
perature and reduced water sorption of the respective mixtures. With r
egard to solvent-free extrusion, pressure-volume-temperature measureme
nts were performed on mixtures of zein and diethyl tartrate and evalua
ted according to the Simba-Somcynsky equation of state for multicompon
ent systems. Generally, the results give reason to believe that zein m
ight serve as an inexpensive and most effective substitute for the fas
t-disintegrating synthetic and semi-synthetic film coatings currently
used for the formulation of substrates that allow extrusion coating.