Biosynthesis of CGTase by immobilized alkalophilic bacilli and crystallization of beta-cyclodextrin: Effective techniques to investigate cell immobilization and the production of cyclodextrins

• Immobilized cells on loofa sponge showed operational stability for CGTase production.
• Immobilized cells guided the relative formation of the β-cyclodextrin.
• Purity of 89.5% was obtained for the crystallization of the β-cyclodextrin.
• Tilden–Hudson technique was efficient for monitoring the cyclodextrin production.
• FTIR-ATR suggested the interaction between Bacillus and fiber sponge by adsorption.

Cyclodextrin glycosyltransferase (CGTase) catalyses the degradation of starch, producing α-, β-, and γ-cyclodextrins (CDs). Immobilized cells offer several advantages, such as their prolonged and repeated use, ease separation from the fermentation medium, and reduced risk of contamination. The biosynthesis of CGTase and β-CD was optimized by immobilization of Bacillus firmus strain 37 and Bacillus sphaericus strain 41 cells on a loofa sponge. Both microorganisms produced significant levels of CGTase for three consecutive cycles (94.2 U/mL on average), increased the relative formation of the β-CD, and inhibited the formation of other CDs. The crystallization of the CD produced by both bacterial strains, when corn starch was used as the substrate, resulted in a 64% recovery of β-CD. The purity of the β-CD was 89.5% when maltodextrin was used as the substrate for B. firmus strain 37. The Tilden–Hudson technique was used as a simple, inexpensive, and efficient method for monitoring the continuous production of CDs using immobilized cells. The innovative use of the Fourier Transform Infrared Spectroscopy technique by means of the Attenuated Total Reflectance method suggested that the interaction between the B. sphaericus strain 41 cells and the loofa sponge occurred by natural adsorption.

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