α-Cyclodextrin (α-CD) is now industrially produced and widely used in various application fields. The turbidity of α-CD aqueous solution has been sometimes observed in spite of much higher water solubility of α-CD (14% at 25℃) than that of β-CD (2% at 25℃). The cause of the turbidity has long been uncertain. Here we report on our finding that small amounts of fatty acids coming from the raw material, corn starch are a potential source of the turbidity.
|●||CAVAMAX® W6 FOOD (Wacker Chemie) was used as an industrially produced α-CD. The oil fraction in α-CD was extracted by an organic solvent, and the fatty acid component was determined by an official method of food analysis using GC-MS.|
|●||The turbidity of saturated α-CD solution was evaluated by visual observation and visible adsorption at 660 nm. The effects of the fatty acid component in α-CD on the turbidity of the solution were investigated.|
Evaluation method of turbidity of saturated α-CD solutions by visual observation
|●||Evaluation method of turbidity of saturated α-CD solution|
Fatty acid component of oil fraction in α-CD
|●||Fatty acid component of oil fraction extracted from α-CD|
Visual evaluation of saturated α-CD solutions
|●||Turbidity of saturated α-CD solutions evaluated by visual observation|
Turbidity of saturated α-CD solutions evaluated by UV-Vis spectrum
|●||UV spectrum of saturated α-CD solutions|
Turbidity of saturated α-CD solutions after filtration evaluated by UV-Vis spectrum
|●||UV spectrum of saturated α-CD solutions after passing 0.8 mm filter|
Turbidity change of saturated α-CD solutionsbefore / after filtration
|●||Change of absorbance at 660 nm before / after passing 0.8 mm filter|
Relationship between oil fraction content in α-CD and turbidity of saturated α-CD solution
|●||Oil fraction content in α-CD and turbidity of saturated α-CD solution|
Comparison of water solubility of α-CD of different production lots
|●||Water solubility of saturated α-CD solution|
|●||A small amount of palmitinic acid, linoleic acid, and the oleic acid was observed in the industrially produced α-CD, and the fatty acid component was 74.0%, 17.9% and 8.0% respectively. The big differences were observed in fatty acid component between α-CD and a corn starch（10%, 59%, 26%）of the raw material.|
|●||The visible adsorption of an industrially produced α-CD at 660 nm was 1.9〜107.8 times higher than that of an assay reagent of α-CD.
Since the turbidity was decreased after passing 0.8 mm filtration, it might be originated by microparticle.
|●||A significant correlation was observed between the quantity of oil fraction in α-CD and the turbidity of saturated α-CD solution.
1) T. Yamamoto, N. Taira, Y. Akihara and Y. Matsui, 20th Cyclodextrin Symposium（2002, Chiba, Japan） pp. 124-125