Cyclodextrin production from rice starch

Abstract

The present study aims at the development of efficient cyclodextrin production from rice starch. The result demonstrated that pretreatment of rice starch with the enzyme a-amylase was necessary for high cyclodextrin yield. Appropriate conditions were 10 g % of rice starch treated with 0.1% α-amylase at 50 °c for 15 minutes. The pretreated starch was subsequently used for cyclodextrin production by the action of the enzyme cyclodextrin glycosyltransferase (CGTase) from Bacillus sp. A 11. with the use of complexing agent, cyclohexane, which was selected as the solvent of choice, the production yield of cyclodextrins was twice of that without complexing agent. The optimum conditions were pretreated starch incubated with CGTase (25 Units/g starch) and cyclohexane (5 %, v/v) for 18 hours. Furthermore, preference production of certain cyclodextrin could be achieved by varying the concentration of rice starch or CGTase used. Less than 5 g % starch and more than 200 Units CGTase/g starch mainly yielded α-CD, while 10-30 g % starch and less than 200 Units CGTase/g starch resulted in β-CD as the major product. Besides cyclodextrins, some non-cyclic (linear) oligosaccharides were also detected in the reaction products, as analyzed by HPLC. Those overlapped with CD peaks were maltotetraose (G4), maltopentaose (G5) , maltohexaose (G6) . Amyloglucosidase and p-amylase were used in the attempt to differentiate the linear from the cyclic oligosaccharides. It was found that β-amylase (20 Units, 1 hr, 25°C) completely digested linear oligosaccharides (G4-G5) without destroying the cyclodextrin products. By using cyclohexane in the production of cyclodextrins, the crude β-CD obtained was 42 g %, which constituted for most of the CDs (total CDs was 44 g %). If purer β-CD is preferred, β-amylase treatment which yielded 34 g % β-CD (80 % recovery) and crystallization at 4°c were performed. By the 1st crystallization, the β-CD crystals obtained was about 12 g % (28 % recovery, 95 % purity).