The preparation of gels by charge interaction methods has been extensively studied, but it is not yet clear how these methods influence gel characteristics. The objective of this work was to study differences in morphology and surface charge of hydrogels prepared by ionotropic gelation, polyelectrolyte complexation, and a combination of both methods. Thus, the anionic charge was provided by carboxymethylcellulose (CMC), carboxymethylated starch (CMS), and alginic acid (AA); calcium chloride (CaCl₂) and chitosan (CS) were used for the ionotropic gelation and polyelectrolyte complexation, respectively. Those materials are commercially available, have low toxicity, and are widely used in the area. These compounds interact through physical crosslinks, which are affected by physical changes of the medium. Our results showed that these two methods produced changes in the morphology of the hydrogels. CMC gels exhibited larger pores in the presence of CaCl₂. In polyelectrolyte complexation, CMS produced an increased agglomeration of particles, while the addition of CaCl₂to AA generated dispersed particles of size in the order of millimeters. Mixing both ionotropic gelation and polyelectrolyte complexation methods yielded gels of varied charge (568 mV for CMC, 502 mV for CMS, and 1713 mV for AA). FTIR spectra of the hydrogels showed interactions between the different polymeric compounds, being the greatest changes between 1250 and 1600 cm⁻¹, due possibly to the replacement of Na by Ca at crosslinking points. Therefore, the method of gel preparation employed had a major influence on the size and pore distribution, parameters which in turn influence encapsulation and drug delivery in these systems.

Cyclodextrin glycosyltransferase (CGTase) is an enzyme that produces cyclodextrins (CDs) from starch and related carbohydrates, producing a mixture of α-, β-, and γ-CDs in different amounts. CGTase production, mainly by Bacillus sp., depends on fermentation conditions such as pH, temperature, concentration of nutrients, carbon and nitrogen sources, among others. Bacillus megaterium CGTase produces those three types of CDs, however, β-CD should prevail. Although waxy corn starch (CS) is used industrially to obtain CGTase and CDs because of its high amylopectin content, alternative sources such as amaranth starch (AS) could be used to accomplish those purposes. AS has high susceptibility to the amylolytic activity of CGTase because of its 80% amylopectin content. Therefore, the aim of this work was evaluate the AS as carbon source for CGTase production by B. megaterium in a submerged fermentation. Afterwards, the CGTase was purified partially and its activity to synthesize α-, β- and γ-CDs was evaluated using 1% AS as substrate. B. megaterium produced a 66 kDa CGTase (Topt=50°C; pHopt=8.0), from the early exponential growth phase which lasted 36 h. The maximum CGTase specific activity (106.62±8.33 U/mg protein) was obtained after 36 h of culture. CGTase obtained with a Km=0.152 mM and a Vmax=13.4 µM/min yielded 40.47% total CDs using AS which was roughly twice as much as that of corn starch (CS; 24.48%). High costs to produce CDs in the pharmaceutical and food industries might be reduced by using AS because of its higher α-, β- and γ-CDs production (12.81%, 17.94% and 9.92%, respectively) in a shorter time than that needed for CS.