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A porous-nanostructured material made of short-chain eskolaite (a-Cr 2 O 3 ) nanoparticles has been synthesized from Cr 2 O 3 -loaded activated carbon. The size of the nanoparticles in the chain ranges from 2 to 100 nm. The Cr 2 O 3 -loaded activated carbon was prepared by adsorption of dichromate (Cr 2 O 2À 7 ) ions from aqueous solutions on ultrafine activated carbon (less than 12 mm in size) in a batch-glass-stirred reactor at 28 C. After a filtration step, the Cr 2 O 3 -loaded activated carbon was processed at high temperature under an oxidizing atmosphere to remove the carbon as CO 2 (g) and obtain a product high in Cr 2 O 3 . This thermal process was carried out in a tube furnace using air as the oxidant. At 1100 C, a product with 98% Cr 2 O 3 was produced. The synthesized material is highly porous and is composed by agglomerates of short chains of eskolaite nanoparticles. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and selected area (electron) diffraction (SAED) microscopy were used to determine the chemical composition, texture, crystal structure, and size of the product components.

In this research, we produced concentrates of banana juices from three different cultivars of bananas (Enano gigante and two hybrids FHIA-17 and FHIA-23) by the freezing and thawing method. To track the cryoconcentration process, different parameters were monitored in the melted fractions, such as variation of the content of soluble solids, concentration of polyphenols (Folin–Ciocalteu), reducing sugar (DNS assay), minerals (K, Mg, Ca, P, Na, Mn, Cu and B) by inductively coupled plasma-optical emission spectroscopy and the main volatile compounds by headspace-GC–MS. It was found that the solution obtained during thawing showed higher concentrations than the original solution. The concentrations of polyphenols were duplicated in FHIA-17 cultivar (758.53 mg/100 ml), and the concentrates obtained in this study proved to be good sources of K and Mg 5,054.6 mg/l and 485.4 mg/l with around 70% and 40% of the recommended daily intake (RDI), respectively. In addition, the concentrates contained a very low level of Na around 1% of the RDI. Furthermore, the cryoconcentration process of the bioactive compounds presented a sigmoid behavior, and the inflexion point in the function was proposed as stop point of the process. Finally, the main volatile compounds reported as responsible for the banana aroma were identified, and its cryoconcentration proved. These results suggest that consumption of banana juice concentrates obtained by the freezing and thawing method can provide bioactive compounds needed for health.

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