199
Biotechnology Department, applying nontoxic benzyl alcohol as appropriate betacyclodextrin precipitant. This new beta-cyclodextrin conversion process using benzyl alcohol as complexant was developed in 1986–1988 period. Briefly, partially
hydrolyzed corn starch was converted to cyclodextrins with in-house-manufactured
industrial cyclodextrin glucosyltransferase in presence of benzyl alcohol precipitant. The non-cyclic oligosaccharide content of final conversion mixture was
degraded to dextrose with glucoamylase, and the resulting mixture filtered at room
temperature. After suspending filtered material in water, the precipitant content was
eliminated via atmospheric pressure steam distillation. Continued with carbon
decolorization and subsequent evaporation, the pure beta-cyclodextrin product was
crystallized from the resulting concentrate.
Benzyl alcohol is, however, not stable under conversion-reaction circumstances.
In the late conversion, benzyl aldehyde and benzoic acid oxidation products were
formed in the reaction mixture. Therefore, many efforts were made to optimize
conversion and steam distillation parameters to eliminate the cyclodextrinbenzaldehyde complexes. Additional experiments were focused on replacement of
the original corn starch to its fiber-free corn starch grease form. Later corn starch
was replaced with cheap wheat corn grinder, but because of its relatively high protein content, it was not proved an appropriate substrate. Due to change of regime,
these technology variations were not realized in the process-scale manufacturing.
4.2.3 Production of Alpha-Cyclodextrin
and Gamma-Cyclodextrin
The other two cyclodextrins, i.e., alpha-cyclodextrin and gamma-cyclodextrin, can
be isolated from the conversion mixture by subsequent and combined application of
bromobenzene and trichloroethylene according to method of French et al. (1949).
The resulting products are of low purity materials, often contaminated by a toxic
residual solvent (Armbruster and Jacaway 1969). Starch conversion was conducted
in the presence of any aliphatic compounds having >8 carbon chain length, e.g.,
n-decanal resulted in mainly alpha- and beta-cyclodextrin-containing potato starch
conversion mixture. Bromobenzene was applied by Bender (1984) for the special
purpose to obtain a gamma-cyclodextrin-enriched conversion mixture. After removing bromobenzene by distillation, the linear dextrin fraction was precipitated by
methanol, beta-cyclodextrin was removed by crystallization, and the residual solution was treated again with bromobenzene to obtain a product with 90% gammacyclodextrin and 10% beta-cyclodextrin composition. The final purification step
was a crystallization in pyridine-methanol solvent mixture to get a gammacyclodextrin product of 98–99% purity.
Another method for separation of alpha-cyclodextrin, beta-cyclodextrin, and
gamma-cyclodextrin from the conversion mixture was based on chromatography
using ion-exchange columns (Okada et al. 1980). The main advantage of this
4 History of Cyclodextrin Production in Hungary
Biotechnology Department, applying nontoxic benzyl alcohol as appropriate betacyclodextrin precipitant. This new beta-cyclodextrin conversion process using benzyl alcohol as complexant was developed in 1986–1988 period. Briefly, partially
hydrolyzed corn starch was converted to cyclodextrins with in-house-manufactured
industrial cyclodextrin glucosyltransferase in presence of benzyl alcohol precipitant. The non-cyclic oligosaccharide content of final conversion mixture was
degraded to dextrose with glucoamylase, and the resulting mixture filtered at room
temperature. After suspending filtered material in water, the precipitant content was
eliminated via atmospheric pressure steam distillation. Continued with carbon
decolorization and subsequent evaporation, the pure beta-cyclodextrin product was
crystallized from the resulting concentrate.
Benzyl alcohol is, however, not stable under conversion-reaction circumstances.
In the late conversion, benzyl aldehyde and benzoic acid oxidation products were
formed in the reaction mixture. Therefore, many efforts were made to optimize
conversion and steam distillation parameters to eliminate the cyclodextrinbenzaldehyde complexes. Additional experiments were focused on replacement of
the original corn starch to its fiber-free corn starch grease form. Later corn starch
was replaced with cheap wheat corn grinder, but because of its relatively high protein content, it was not proved an appropriate substrate. Due to change of regime,
these technology variations were not realized in the process-scale manufacturing.
4.2.3 Production of Alpha-Cyclodextrin
and Gamma-Cyclodextrin
The other two cyclodextrins, i.e., alpha-cyclodextrin and gamma-cyclodextrin, can
be isolated from the conversion mixture by subsequent and combined application of
bromobenzene and trichloroethylene according to method of French et al. (1949).
The resulting products are of low purity materials, often contaminated by a toxic
residual solvent (Armbruster and Jacaway 1969). Starch conversion was conducted
in the presence of any aliphatic compounds having >8 carbon chain length, e.g.,
n-decanal resulted in mainly alpha- and beta-cyclodextrin-containing potato starch
conversion mixture. Bromobenzene was applied by Bender (1984) for the special
purpose to obtain a gamma-cyclodextrin-enriched conversion mixture. After removing bromobenzene by distillation, the linear dextrin fraction was precipitated by
methanol, beta-cyclodextrin was removed by crystallization, and the residual solution was treated again with bromobenzene to obtain a product with 90% gammacyclodextrin and 10% beta-cyclodextrin composition. The final purification step
was a crystallization in pyridine-methanol solvent mixture to get a gammacyclodextrin product of 98–99% purity.
Another method for separation of alpha-cyclodextrin, beta-cyclodextrin, and
gamma-cyclodextrin from the conversion mixture was based on chromatography
using ion-exchange columns (Okada et al. 1980). The main advantage of this
4 History of Cyclodextrin Production in Hungary