Orion versa star

Freshly cut peels of Opuntia ficus-indica fruits were collected from local food restaurants, washed with distilled water at room temperature, and cut into small pieces. OFI fruit peels presented a pH of 5.44 ± 0.02 and soluble solids content of 9.7 ± 0.02 ° Brix, which were determined using a digital pH meter (ORION™ Versa Star™, Thermo Scientific Inc., Waltham, MA, USA) and a digital handheld refractometer (Boeco model 32395, Hamburg, Germany), respectively.

The mixing ratio varied between 0.3–0.6 (mole fraction ratio = MO_x/Na₂O + MO_x, M = Ti, Si, and W) to determine the eutectic melting point of the mixture (pulverized feedstock and Na₂CO₃). The alkali fusion time was fixed at 20 min for all mixed samples. Process flows, which is a sequence with pulverization, alkali fusion, and water leaching, of this study is shown in Fig. 1. Simultaneous thermogravimetric analysis (TGA) and differential thermal analysis (DTA) for the various mixtures were carried out using a DTG-60H (Shimadzu, Japan) analyzer from ambient to 1100 °C in air. The heating rate was 10 °C min⁻¹. In order to investigate the leaching efficiency of vanadium, tungsten and titanium in each fused feedstock, water leaching was conducted under the following conditions: Temp., ambient temperature; S/L (V/W) ratio, 0.2; time, 2 h; particle size distribution, ≥70 mesh (<210 μm).
Phase characterization of the fused samples and residues was carried out using an X-ray diffractometer (XRD, X’pert MPD, Phillips, USA). pH measurement was done using Orion Versa Star (Thermo Scientific, USA).

Physicochemical determinations were evaluated as follows: protein (AOAC 981.10), fat (AOAC 2007.04), ashes (AOAC 920.153) and moisture (AOAC 2007.04) [58 ]. The pH was determined with a potentiometer (Orion Versa Star, Thermo Scientific^®, Singapore) [59 (link)]. Colour was evaluated in terms of CIELAB parameters, L* (whiteness or brightness), a* (redness or greenness) and b* (yellows or blueness), with a spectrophotometer (Chroma meter, Konica Minolta, CR-410, Japan), and the differences in colour (ΔΕ*) were calculated according to the following formula [60 ]: $$∆E=\sqrt{{\left(L^{*}-L_{ref}^{*}\right)}^2+{\left(a^{*}-a_{ref}^{*}\right)}^2+{\left(b^{*}-b_{ref}^{*}\right)}^2}$$
where, L*_ref, a*_ref and b*_ref = control parameters and L*, a* and b* = parameters for the different treatments.