Effects of extrusion cooking and low-temperature storage on the physicochemical changes and resistant starch (RS) content in cornstarch were evaluated. The cornstarch was conditioned at 20%–40% moisture contents and extruded in the range 90–130 °C and at screw speeds in the range 200–360 rpm. The extrudates were stored at 4 °C for 120 h and then at room temperature. The water absorption, solubility index, RS content, viscoelastic, thermal, and microstructural properties of the extrudates were evaluated before and after storage. The extrusion temperature and moisture content significantly affected the physicochemical properties of the extrudates before and after storage. The RS content increased with increasing moisture content and extrusion temperature, and the viscoelastic and thermal properties showed related behaviors. Microscopic analysis showed that extrusion cooking damaged the native starch structure, producing gelatinization and retrogradation and forming RS. The starch containing 35% moisture and extruded at 120 °C and 320 rpm produced the most RS (1.13 g/100 g) after to storage at low temperature. Although the RS formation was low, the results suggest that extrusion cooking could be advantageous for RS production and application in the food industry since it is a pollution less, continuous process requiring only a short residence time.

The effect of extrusion cooking on bioactive compounds in third-generation snacks (TGSE) and microwave-expanded snacks (MWSE) prepared using black bean, blue maize, and chard (FBCS) was evaluated. FBCS was extruded at different moisture contents (MC; 22.2–35.7%), extrusion temperatures (ET; 102–142 °C), and screw speeds (SP; 96–171 rpm). Total anthocyanin content (TAC), contents of individual anthocyanins, viz., cyanidin-3-glucoside, malvidin-3-glucoside, pelargonidin-3-glucoside, pelargonidin-3-5-diglucoside, and delphinidin-3-glucoside chloride, total phenolic content (TPC), antioxidant activity (AA), and color parameters were determined. TAC and individual anthocyanin levels increased with the reduction in ET. ET and MC affected the chemical and color properties; increase in ET caused a significant reduction in TPC and AA. Microwave expansion reduced anthocyanin content and AA, and increased TPC. Extrusion under optimal conditions (29% MC, 111 rpm, and 120 °C) generated products with a high retention of functional compounds, with high TAC (41.81%) and TPC (28.23%). Experimental validation of optimized process parameters yielded an average error of 13.73% from the predicted contents of individual anthocyanins. Results suggest that the TGSE of FBCS obtained by combining extrusion and microwave expansion achieved significant retention of bioactive compounds having potential physiological benefits for humans.

Although the dry ice method used to synthesize turbostratic carbon/graphene is little known and used, it has significant advantages over others, such as the following: it is low cost, simple, and a large quantity of material can be obtained using some inorganic and highly available acids (which can be reused). Despite the above advantages, the main reason for its incipient development is the resulting presence of magnesium oxide in the final product. In the present work, three different treatments were tested to remove this remnant using some acid chemical leaching processes, including hydrochloric acid, aqua regia, and piranha solution. Based on the experimental evidence, it was determined that using aqua regia and combining the leaching process with mechanical milling was the most efficient way of removing such a remnant, the residue being only 0.9 wt.%. This value is low compared to that obtained with the other acid leaching solutions and purification processes (2.8–29.6 wt.%). A mandatory high-energy mechanical milling stage was necessary during this treatment to expose and dissolve the highly insoluble oxide without secondary chemical reactions on the turbostratic carbon. High-energy mechanical milling is an effective route to exfoliate graphite, which allows the magnesium oxide to be more susceptible to acid treatment. A yield of turbostratic carbon/graphene of 1 wt.% was obtained from the metallic Mg. The obtained surface area was 504.8 m²g⁻¹; this high value resulting from the intense exfoliation can potentiate the use of this material for a wide variety of applications.

In this work, the use of chicken manure as the raw material for obtaining metal-free biocarbons as electrocatalysts was studied. This abundant biomass waste was subjected to several treatments (pyrolysis, chemical activation using KOH and H₃PO₄ and solvothermal treatment with hydrazine) to modify its properties until nitrogen and phosphorous co-doped biocarbons were obtained. The effect of each treatment on the physicochemical characteristics and catalytic activity of the obtained catalysts for the oxygen reduction reaction (ORR) in alkaline media was studied by several techniques such as XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy), Raman spectroscopy, nitrogen adsorption analysis, scanning electron microscopy (SEM) and rotating-ring disc electrode analysis. The most active electrocatalyst was that labeled B_K, activated with KOH (an onset potential of 0.86 V vs. RHE and a current density of −4.52 mA cm⁻²); however, its electron transfer number was n = 3.6 probably due to a combined 4 and 2e⁻ transfer pathway. Nevertheless, the catalytic activity of B_K for the ORR increased after accelerated degradation tests (3000 cycles). Even more, the electrocatalysts activated with H₃PO₄ in an air atmosphere and subjected to a solvothermal process (labeled as B_H-ST) also showed good catalytic activity (an onset potential of 0.85 V vs. RHE and a current density of −3.26 mA cm⁻²) and a 4e⁻ transfer pathway. We found that co-doping with nitrogen and phosphorous has a positive effect by improving the kinetics of these electrocatalysts. Additionally, the effect of other treatments on their catalytic activity is also discussed in this study.