No. 23 Analysis of Fatty Acid in α-Cyclodextrin

Summary

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.

Study purpose

• 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.

Tested α-CDs

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

Saturated α-CD solution (0.8 mm filter passed)

Turbidity of saturated α-CD solutions evaluated by UV-Vis spectrum

UV spectrum of saturated α-CD solutions

Cell size : 9 x 9 x 44 mm

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

Cell size : 9 x 9 x 44 mm

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

Conclusion

• 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.

  → It is reported that the binding constant between α-CD and a fatty acid increases by an increase of hydrophobic strength of fatty acid1). Therefore, it would be very difficult to remove palmitic acid in the industrial manufacturing of α-CD, and the turbidity of saturated α-CD was originated by the complex between α-CD and palmitic acid.

  1) T. Yamamoto, N. Taira, Y. Akihara and Y. Matsui, 20th Cyclodextrin Symposium（2002, Chiba, Japan） pp. 124-125