Study on the mechanism of Na2CO3-roasting decomposition for water leach residue.

In the process of treating cerium fluorocarbon-cerium lanthanide mixed rare earth concentrates by sulfuric acid roasting method, a large amount of waste leach residue containing iron, rare earths and phosphorus produced by flood neutralization needs to be solved urgently. In this paper, sodium carbonate roasting decomposition was used to treat the water leach residue, in which iron and rare earths were transformed into oxides, and the phosphorus was transformed into sodium phosphate. The main reactions and thermodynamic mechanisms of the roasting decomposition process were investigated by thermogravimetric analysis, phase analysis and chemical analysis. When the mass ratio of sodium carbonate to water leach residue is 1.5:1, the roasting temperature is 700 °C, and the roasting time is 1.5 h, the leaching rate of phosphorus with the roasted product reaches more than 98%. Meanwhile, the phase of the roasted product after washing mainly consists of iron oxide and rare earth oxides. The combination of sodium carbonate roasting decomposition and water leaching is effective for the treatment of water leach residue, which provides an experimental and theoretical basis for solving the problem of environmental and resource waste caused by the accumulation of a large amount of water leach residue. In addition, because sodium carbonate can achieve the separation of iron and phosphorus, this method also has certain reference value for the recovery and utilization of iron phosphate in lithium iron phosphate battery waste.

Extraction of rare earth Eu from waste blue phosphor strengthened by microwave alkali roasting.

Spent phosphor is an important secondary resource for extracting rare earth elements. Microwave absorption properties and enhanced extraction of Eu from blue phosphor by microwave alkali roasting were studied. Dielectric properties of alkali roasting system were measured by resonator perturbation method. Dielectric constant increases linearly from 250 °C until it reaches a peak at 400 °C. The dielectric loss reaches a higher value at 400-550 °C, due to the strong microwave absorption properties of molten alkali and roasted products. Effects of roasting temperature, roasting time and alkali addition amount on Eu leaching were investigated. The phosphor was completely decomposed into Eu2O3, BaCO3 and MgO at 400 °C. The alkaline decomposition process of phosphor is more consistent with diffusion control model with Eα being 28.9 kJ/mol. Effects of the main leaching conditions on Eu leaching were investigated. The leaching kinetic of Eu was in line with diffusion control model with Eα being 5.74 kJ/mol. The leaching rules of rare earths in the mixed phosphor were studied. The results showed that the presence of red and green phosphor affected the recovery of blue phosphor. The optimum process parameters of rare earth recovery in single blue phosphor and mixed phosphor were obtained, and the recovery of Eu were 97.81% and 94.80%, respectively. Microwave alkali roasting promoted the dissociation of phosphor and leaching of rare earths. The results can provide reference for the efficient and selective recovery of rare earths in phosphors.

Recovery of Li from waste Li-containing Al electrolytes with high F and Na contents by using a CaO roasting-water leaching process.

With the increasing demand for Li, the recovery of Li from solid waste, such as Li-containing Al electrolytes, is receiving growing attention. However, Li-containing Al electrolytes often contain large amounts of F, leading to environmental pollution. Herein, a new method for preparing water-soluble Li salt from waste Li-containing Al electrolytes with high F and Na contents is proposed based on CaO roasting and water leaching. The effects of different roasting and leaching conditions on the Li leaching efficiency and reaction pathway were systematically investigated. Under the optimum processing conditions, the Li leaching efficiency reached 98%, while those of Na and F were 98.41% and 0.24%, respectively. Phase evolution analysis showed that the addition of CaO promoted the conversion of LiF and Na2LiAlF6 to Li2O, whereas F entered the slag phase as CaF2, which could be reused as a raw material for steel refinement. Overall, this study proposes an efficient and environmentally friendly method for the treatment and resource utilization of waste Al electrolytes with high F and Na contents.

Selective preparation of lithium carbonate from overhaul slag by high temperature sulfuric acid roasting - Water leaching.

An efficient recycling process is developed to recover valuable materials from overhaul slag and reduce its harm to the ecological environment. The high temperature sulfuric acid roasting - water leaching technology is innovatively proposed to prepare Li2CO3 from overhaul slag. Under roasting conditions, fluorine volatilizes into the flue gas with HF, lithium is transformed into NaLi(SO4), aluminum is firstly transformed into NaAl(SO4)2, and then decomposed into Al2O3, so as to selective extraction of lithium. Under the optimal roasting - leaching conditions, the leaching rate of lithium and aluminum are 95.6% and 0.9%, respectively. Then the processes of impurity removal, and settling lithium are carried out. The Li2CO3 with recovery rate of 72.6% and purity of 98.6% could be obtained under the best settling lithium conditions. Compared with the traditional process, this work has short flow, high controllability, remarkable technical, economic, and environmental benefits. This comprehensive recycling technology is suitable for overhaul slag, and has great practical application potential for the disposal of other hazardous wastes in electrolytic aluminum industry.

Innovative methodology for comprehensive utilization of arsenic-bearing neutralization sludge.

Arsenic-bearing neutralization (ABN) sludge is a classical hazardous waste commonly found in nonferrous metallurgy. However, the current storage of these hazardous wastes not only has to pay costly hazardous waste taxes but also poses significant risks to both the environment and human health. To address these issues and achieve the comprehensive utilization and minimization of ABN sludge, this study proposes a new combined process. The process involves selective reduction roasting, leaching, and carbonation, through which, the arsenate and gypsum in the ABN sludge were recovered in the form of As(s), high-purity CaCO3, and H2S. The selective reduction behaviors of arsenate and gypsum were investigated through thermodynamic analysis and roasting experiments. The results indicated that the 95.35 % arsenate and 96.55 % gypsum in the sludge were selectively reduced to As4(g) and CaS at 950 °C by carbothermic reduction. The As4(g) was condensed to As(s) and enriched in the dust (As, 96.78 wt %). In the leaching process, H2S gas was adopted to promote the leaching of CaS, and resulted in 97.41 % of CaS in the roasted product was selectively leached in the form of Ca(HS)2, leading to a 74.11 % reduction in the weight of the ABN sludge. Then, the Ca(HS)2 was subjected to capture CO2 for the separation of Ca2+ and S2-. The result depicted that 99.69 % of Ca2+ and 99.12 % of S2- were separated as high-purity (99.12 wt %) CaCO3 and H2S (24.89 vol %) by controlling the terminal carbonation pH to below 6.55. The generated H2S can be economically converted to sulfur by the Clause process. The whole process realized the comprehensive resource recovery and the minimization of the sludge, which provides an alternative solution for the clean treatment of hazardous ABN waste.

Cleaner separation and recovery of valuable metals from spent ternary cathode via carbon dioxide synergetic thermite reduction strategy.

The low-carbon recycling of spent lithium-ion batteries has become crucial due to the increasing need to address resource shortages and environmental concerns. Herein, a low-carbon, facile, and efficient method was developed to separate and recover Li, Al, and transition metals from spent ternary cathodes. Initially, the cathode materials post-discharge and disassembly do not require pre-sorting. Instead of using carbonaceous materials, the Al foil in the cathode serves as the reducing agent during reduction roasting. The impact of different roasting atmospheres (air, N2, CO2) on phase transitions and the extraction of valuable metals was examined. The findings revealed that after synergistic thermite reduction in a carbon dioxide atmosphere, the cathode material is completely dissociated. Li is selectively converted to Li2CO3 rather than LiAlO2, and the reduced reactivity of the Al foil encourages the formation of lower-valence oxides of Ni and Co, rather than their metallic forms. Under optimal roasting conditions at 650 °C for 1.0 h, 91.4% of Li can be preferentially and selectively extracted through carbonation water leaching, with less than 0.1% of Al and transition metals dissolving. Subsequently, ∼98% of Al and ∼99% of Ni, Co, and Mn can be leached using alkaline and acidic solutions, respectively. Compared to the traditional carbon thermal reduction process, this process offers several advantages including the elimination of pre-sorting and additional reducing agents, lower carbon emissions, and higher recovery rates of valuable metals. Thus, this process makes the recovery of metals from spent lithium-ion batteries more environmentally sustainable, simple, cost-effective, and adaptable.

Deep resource utilization of hazardous arsenic-alkali slag: Thermodynamic analysis, mechanism investigation and process optimization.

The best solution to address environmental pollution caused by arsenic-containing hazardous waste is to prepare high-purity elemental arsenic from such waste. The key to this approach lies in the efficient separation of arsenic from various impurities. This paper presents a viable solution for producing high-purity elemental arsenic from arsenic-alkali slag, and the keylies in utilizing the selective precipitation of magnesium ammonium arsenate (MgNH4AsO4) to achieve efficient separation of arsenic from alkali, antimony, and other impurities. Thermodynamic analysis and hydrometallurgical condition experiments indicate that in complex alkaline arsenic-containing solutions, over 90% of arsenic components can selectively precipitate in the form of MgNH4AsO4. The content of arsenic in the resulting precipitate reaches approximately 30%, while the content of antimony is below 0.1%. This achieves efficient enrichment of arsenic and preliminary separation of impurities in complex arsenic-alkali slag. Thermodynamic analysis and pyrometallurgical condition experiments demonstrate that the precipitate of MgNH4AsO4 can be reduced to elemental arsenic with an arsenic content reaching 99.85%, and an antimony content as low as 0.05%. This achieves a profound separation of arsenic from impurities. Based on the research presented in this paper, a production line was established that enables the deep resource utilization of arsenic-alkali slag.

Production of Resistant Starch by Roasting Retrograded Starch with Glucose.

Starch is a natural plant raw material applicable in many areas of industry. In practice, it is most often used in a modified form, i.e., after various treatments aimed at modifying its properties. Modifications of native starch enable producing resistant starch, which, as a prebiotic with confirmed health-promoting properties, has been increasingly used as a food additive. The present study aimed to determine the effect of roasting retrograded starch with the addition of anhydrous glucose at different temperatures (110, 130 or 150 °C) and different times (5 or 24 h) on the modified starch's properties. The results of high-performance size-exclusion chromatography coupled with refractive index detector (HPSEC/RI) analysis and the changes observed in the solubility of starch roasted with glucose in DMSO, as well as in its other properties, confirm the changes in its molecular structure, including thermolytic degradation and the ongoing polymerization of starch with added glucose.

Activation Mechanism of Ammonium Fluoride in Facile Synthesis of Hydrated Silica Derived from Ferronickel Slag-Leaching Residue.

A novel process for the synthesis of hydrated silica derived from ferronickel slag (FNS)-leaching residue was proposed in this study. The products of the purification of hydrated silica with 99.68% grade and 95.11% recovery can be obtained through ammonium fluoride (NH4F) roasting, followed by the process of water leaching, ammonia precipitating, and acid cleaning under the optimized conditions. The effects of NH4F mass ratio, roasting temperature, and roasting time on the water-leaching efficiency were investigated in detail. The thermodynamic and X-ray diffraction analyses indicated that the amorphous silica in FNS-leaching residue was converted to water-soluble fluoride salts ((NH4)2SiF6) during the roasting process, which are also supported by the scanning electron microscopy and thermogravimetry analyses. The Si-O bonds in amorphous silica could be effectively broken through the ammonium fluoride activation during a low-temperature roasting process. This work provides a meaningful reference for further studies on the facile synthesis of hydrated silica with similar mineral compositions.

The Potential of NIR Spectroscopy and Chemometrics to Discriminate Roast Degrees and Predict Volatiles in Coffee.

This study aimed to establish a rapid and practical method for monitoring and predicting volatile compounds during coffee roasting using near-infrared (NIR) spectroscopy coupled with chemometrics. Washed Arabica coffee beans from Ethiopia and Congo were roasted to industry-validated light, medium, and dark degrees. Concurrent analysis of the samples was performed using gas chromatography-mass spectrometry (GC-MS) and NIR spectroscopy, generating datasets for partial least squares (PLS) regression analysis. The results showed that NIR spectroscopy successfully differentiated the differently roasted samples, similar to the discrimination achieved by GC-MS. This finding highlights the potential of NIR spectroscopy as a rapid tool for monitoring and standardizing the degree of coffee roasting in the industry. A PLS regression model was developed using Ethiopian samples to explore the feasibility of NIR spectroscopy to indirectly measure the volatiles that are important in classifying the roast degree. For PLSR, the data underwent autoscaling as a preprocessing step, and the optimal number of latent variables (LVs) was determined through cross-validation, utilizing the root mean squared error (RMSE). The model was further validated using Congo samples and successfully predicted (with R2 values > 0.75 and low error) over 20 volatile compounds, including furans, ketones, phenols, and pyridines. Overall, this study demonstrates the potential of NIR spectroscopy as a practical and rapid method to complement current techniques for monitoring and predicting volatile compounds during the coffee roasting process.

Profiling flavor characteristics of cold brew coffee with GC-MS, electronic nose and tongue: effect of roasting degrees and freeze-drying.

BACKGROUND: Roasting is an important process in the formation of coffee flavor characteristics, which determines the quality of coffee and consumer acceptance. However, the influence of roasting degree on the flavor characteristics of cold brew coffee has not been fully described. RESULTS: In the present study, the flavor characteristics of cold brew coffee with different roasting degrees were compared in detail by using chromatographic and electronic sensory approaches, and the flavor changes induced by freeze-drying were investigated. Pyrazine and heterocyclic compounds were the main aroma compounds in coffee, and gradually dominated with the increase of roasting. Pyridine was consistently present in cold brew coffees of different roasting degrees and showed significant gradient of quantity accumulation. Aroma compounds such as pyrazine, linalool and furfuryl acetate were the main contributors to coffee roasting, floral and fruity flavor. Freeze-drying preserved the fruity and floral aromas of medium-roasted cold brew coffee, whereas reducing the bitterness, astringency and acidity properties that are off-putting to consumers. CONCLUSION: The higher consumer acceptance and enjoyment in medium roast cold brew coffee may be related to its stronger floral and fruity aroma. The aroma profile qualities of freeze-drying processed medium roasted cold brewed coffee were more dominant and more suitable for freeze-drying processing than medium dark roasting. Application of freeze-drying for cold brew coffee will promote the convenience of drinking. The present study provides valuable technical guidance in improving the flavor and quality of cold brew coffee, and also promotes its commercialization process. © 2024 Society of Chemical Industry.

Comprehensive two-dimensional gas chromatography-time of flight mass spectrometry as a tool for tracking roasting-induced changes in the volatilome of cold-pressed rapeseed oil.

The aim of this study was to track changes in the volatilome of cold-pressed oil and press cakes obtained from roasted seeds and to combine it with the profile of non-volatile metabolites in a single study, in order to understand pathways of volatile organic compound (VOC) formation caused by thermal processing. Comprehensive two-dimensional gas chromatography-time of flight mass spectrometry was used for the analysis of VOCs in cold-pressed oils and corresponding press cakes obtained after roasting of seeds at 140 and 180 °C prior to pressing. Contents of primary metabolites (amino acids, saccharides, fatty acids) as well as selected secondary metabolites (glucosinolates, polyphenols) were determined, as many of them serve as precursors to volatile compounds formed especially in thermal reactions. After roasting, the formation of Maillard reaction products increased, which corresponded to the reduction of free amino acids and monosaccharides. Moreover, levels of the products of thermal oxidation of fatty acids, such as aldehydes and ketones, increased with the increasing temperature of roasting, although no significant changes were noted for fatty acids. Among sulphur-containing compounds, contents of the products and intermediates of methionine Strecker degradation increased significantly with the increasing temperature of roasting. Degradation of glucosinolates to nitriles occurred after thermal treatment. The results of this study confirmed that seed roasting before cold pressing has a significant effect on the volatiles, but also indicated roasting-induced changes in non-volatile metabolites of oil and press cake. Such an approach helps to understand metabolic changes occurring during rapeseed processing in cold-pressed oil production.

Recovery of zinc and extraction of calcium and sulfur from zinc-rich gypsum residue by selective reduction roasting combined with hydrolysis.

A novel process that includes selective reduction roasting followed by hydrolysis was proposed in this work to recover zinc, and efficiently extract calcium and sulfur from hazardous zinc-rich gypsum residue (ZGR) waste for high-purity of CaCO3 and sulfur production. The selective reduction behaviors of ZGR during the reduction roasting were investigated in detail based on thermodynamic analysis and roasting experiments. The effect of roasting temperature, carbon dosage and time on the selective reduction of ZGR was comprehensively investigated, and the results indicated that ZnO and CaSO4 in the ZGR can be selectively reduced to Zn(g) and CaS, respectively. The volatile Zn(g) was oxidized to ZnO and enriched in the dust, which can be used as a secondary zinc resource. Moreover, the hydrolysis behaviors and leaching kinetic of CaS during hydrolysis were studied intensively. Results depicted that in the H2S-H2O system, the CaS in the roasted product can be selectively and efficiently dissolved into the leachate. Furthermore, the kinetic analysis revealed that the hydrolysis of CaS conformed to the internal diffusion reaction control model in the shrinking core model and the apparent activation energy Ea = -12.02 kJ/mol. The obtained hydrolysate with low impurities could be used to capture CO2 for the production of high-purity sulfur and CaCO3. Iron and other impurities in the roasted product were concentrated into the leaching slag in the form of metallic iron and akermanite. The whole process realized the recovery of zinc, and the selective and effective extraction of calcium and sulfur, which could provide an alternative process for the large-scale treatment of these hazardous wastes.

Enhanced sequestration of CO2 from simulated electrolytic aluminum flue gas by modified red mud.

The aluminum industry is facing severe economic and environmental problems due to increasing carbon emissions and growing stockpiles of red mud (RM). RM is a strongly alkaline, high-emission solid waste from the alumina industry with potential for CO2 sequestration. However, the effectiveness of RM carbon sequestration is poor, and the mechanism behind it is not well understood. In this study, the effect of microwave and tube furnace activation of RM on CO2 sequestration in alumina was first investigated at different temperatures. The result showed that the CO2 sequestration capacity of unmodified RM (URM) was only 14.35 mg/g at ambient temperature and pressure, and the CO2 sequestration capacity could be increased to 52.89 mg/g after high-temperature activation and modification. Besides, high-temperature activation and modification will effectively improve the carbon sequestration capacity of RM. The carbonized RM was characterized by FT-IR, SEM, XRD, laser particle size, TG-DSC, and pH measurements. In addition, the mechanism of RM capturing CO2 was also proposed, which shows that CO2 was finally sequestered in the RM as CaCO3. The change in particle size distribution and the mineral phase in the RM indicated that high-temperature activation modification positively affects the application of RM to the sequestration of CO2. This study can provide a promising technology for the low-carbon and green development of the aluminum industry, as well as achieving the waste treatment and utilization objective.

Starch Properties of Roasting Rice from Naturally High-Resistant Starch Rice Varieties.

This study investigates the effects of moisture content control on the characteristics, properties, and in vitro starch digestion of roasted rice powder made from natural high-resistant starch (RS) rice varieties. The results demonstrate that adjusting the moisture content before roasting significantly affects the RS content of the roasted rice powder. Among various moisture levels tested, the addition of 15% water (rice-to-water ratio of 85:15) before roasting resulted in the highest RS content, reaching 22.61%. Several key parameters of the rice samples before and after optimal moisture control were analyzed, including thermal stability, chain length distribution, volatile flavor composition, and scanning electron microscopy. Additionally, in vitro digestion properties were measured. The findings revealed that the volatile flavor compounds in the high-RS roasted rice significantly increased compared to non-roasted rice. Moreover, the thermal stability of the rice samples improved, and the chain length distribution exhibited significant changes. The water absorption and expansion properties were significantly lower in the high-RS roasted rice. Furthermore, the in vitro starch digestion of the roasted flour made from high-RS rice showed a significantly lower digestion rate compared to common rice, indicating a lower starch hydrolysis index in high-RS rice with the sbe-rs genotype. Overall, the roasting process of natural high-RS rice modifies its characteristics, increases the RS content, enhances the flavor, and results in a lower starch digestion rate compared to common rice. This study provides valuable data for the food industry to promote the application of high-RS rice varieties with mutations in the SBEIIb gene, such as Youtangdao2 (YTD2).

Effects of Roasting Conditions on Antibacterial Properties of Vietnamese Turmeric (Curcuma longa) Rhizomes.

Processing with heat treatment has been reported to alter several therapeutic effects of turmeric. In Vietnamese traditional medicine, turmeric has been long used for bacterial infections, and roasting techniques are sometimes applied with this material. However, there have been no studies investigating the effects of these thermal processes on the plant's antibacterial properties. Our study was therefore performed to examine the changes that roasting produced on this material. Slices of dried turmeric were further subjected to light-roasting (80 °C in 20 min) or dark-roasting (160 °C in 20 min) processes. Broth dilution and agar-well diffusion methods were applied to examine and compare the effects of ethanol extracts obtained from non-roasted, light-roasted and dark-roasted samples, on a set of 6 gram-positive and gram-negative bacteria. In both investigations, dark-roasted turmeric was significantly less antibacterial than non-roasted and light-roasted materials, as evident by the higher values of minimum inhibitory concentrations and the smaller diameters of induced inhibitory zones. In addition, dark-roasting was also found to clearly reduce curcumin contents, total polyphenol values and antioxidant activities of the extracts. These results suggest that non-roasting or light-roasting might be more suitable for the processing of turmeric materials that are aimed to be applied for bacterial infections.

Bioactive Compounds, Antioxidant Activity and Sensory Properties of Northern Red Oak (Quercus rubra L., syn. Q. borealis F. Michx) Seeds Affected by Roasting Conditions.

The nutritional value and health-promoting properties cause the fruits (acorns) of Quercus spp. to have great potential for use in the food industry as functional ingredients and antioxidants source. The aim of this study was to examine the bioactive compound's composition, antioxidant potential, physicochemical properties and taste characteristics of northern red oak (Quercus rubra L.) seeds subjected to roasting at different temperatures and times. The results indicate that the roasting markedly affects the composition of bioactive components of acorns. In general, the use of roasting temperatures greater than 135 °C causes a decrease in the total phenolic compound content of Q. rubra seeds. Furthermore, along with an increase in temperature and thermal processing time, a remarkable increase in melanoidins, which are the final products of the Maillard reaction, was also observed in processed Q. rubra seeds. Both unroasted and roasted acorn seeds had high DPPH radical scavenging capacity, ferric reducing antioxidant power (FRAP) and ferrous ion chelating activity. Roasting at 135 °C caused negligible changes in total phenolics content and antioxidant activity of Q. rubra seeds. Almost all samples had lower antioxidant capacity along with an increase in the roasting temperatures. Additionally, thermal processing of acorn seeds contributes to the development of the brown color and the reduction of bitterness, and the creation of a more pleasant taste of the final products. Overall, the results of this study show that both unroasted and roasted Q. rubra seeds may be an interesting source of bioactive compounds with high antioxidant activity. Therefore, they can be used as a functional ingredient of beverages or food.

Comprehensive Analyses of Advanced Glycation end Products and Heterocyclic Amines in Peanuts during the Roasting Process.

Advanced glycation end products (AGEs) and heterocyclic amines (HAs) are two kinds of important harmful products formed simultaneously during the thermal processing of proteinaceous food. In this paper, the effect of roasting conditions on the formation of AGEs and HAs, as well as active carbonyl intermediates in common peanut (C-peanut) and high-oleic acid peanut (HO-peanut) was studied simultaneously for the first time. In general, with the increase in roasting temperature (160-200 °C) and time, the contents of AGEs, HAs and active carbonyl intermediates (i.e., glyoxal (GO) and methylglyoxal (MGO)) significantly increased in peanuts. Four kinds of HAs (i.e., AαC, DMIP, Harman and Norharman) were observed in roasted peanuts, of which Harman and Norharman accounted for about 93.0% of the total HAs content after roasting for 30 min at 200 °C. Furthermore, a correlation analysis among AGEs (i.e., Nε-(1-Carboxymethyl)-L-lysine (CML) and Nε-(1-Carboxyethyl)-L-lysine (CEL)), HAs, GO and MGO was conducted. Most of these compounds showed an excellent positive linear relationship (p ≤ 0.001) with each other. The evident increase in GO and MGO contents implied an increase in not only the content of AGEs but also HAs. However, contents of AGEs and HAs showed no significant difference between roasted HO-peanut and C-peanut. This study would provide a theoretical basis for simultaneously controlling the levels of AGEs and HAs in thermal processed peanut foods.

Roasting and Cacao Origin Affect the Formation of Volatile Organic Sulfur Compounds in 100% Chocolate.

Chocolate is a highly appreciated food that develops its characteristic flavors in large part during the roasting of cacao beans. Many functional classes have been noted for their importance to chocolate flavor, including volatile organic sulfur compounds (VSCs). Despite this, the effect of roasting on the concentration of VSCs has never been thoroughly assessed. Here, we studied the effects of roasting temperature, time, and cacao origin on the formation of VSCs. Twenty-seven 100% chocolate samples made from cacao from three different origins and roasted according to an I-optimal experimental design were analyzed by comprehensive gas chromatography with sulfur-selective detection (GCxGC-SCD). For two compounds, dimethyl disulfide and dimethyl trisulfide, the effects of roasting time, roasting temperature, and cacao origin were modelled using response surface methodology and semi-quantified relative concentration. Overall, roasting increased the number of sulfur-containing volatiles present in chocolate, with a total of 28 detected, far more than previously thought. Increased roasting time and especially roasting temperature were found to significantly increase the concentration of VSCs (p < 0.05), while cacao origin effects were only seen for dimethyl disulfide (p < 0.05). The identity of most VSCs remains tentative, and more research is needed to unravel the impact of these volatiles on flavor perception in chocolate.

Assessment of the Effects of Roasting, Contact Grilling, Microwave Processing, and Steaming on the Functional Characteristics of Bell Pepper (Capsicum annuum L.).

Bell peppers (Capsicum annuum L.) in various stages of maturity are widely used in the diets of individuals and in the food industry; they are consumed both fresh and after thermal processing. However, every type of processing impacts the overall textural and bioactive characteristics of this plant-based food. In order to quantify the changes in the bioactive substances and color-structural characteristics that occur during selected heat treatments (contact grilling, roasting, roasting combined with microwaving, and steam cooking) of bell peppers at three maturity stages (green, yellow, and red), analyses of antioxidant activity, reducing sugar content, polyphenolic compound content, textural properties, and color coordinates in the L*a*b* system were carried out. Some of the processes used, such as contact grilling (15.43 mg GAE/g d.b.) and roasting combined with microwaving (15.24 mg GAE/g d.b.), proved to be beneficial as the total polyphenol content of green peppers (2.75 mg GAE/g d.b.) increased. The roasting (3.49 mg TE/g d.b.) and steaming (6.45 mg TE/g d.b.) methods decreased the antioxidant activity of yellow bell peppers (14.29 mg TE/g d.b.). Meanwhile, the roasting (0.88 mg Glc/g d.b.), contact-grilling (2.19 mg Glc/g d.b.), simultaneous microwaving and roasting (0.66 mg Glc/g d.b.), and steaming (1.30 mg Glc/g d.b.) methods significantly reduced the content of reducing sugars and reducing substances in red bell peppers (4.41 mg Glc/g d.b.). The studies proved that in order to preserve the antioxidant and bioactive properties of bell peppers, it is necessary to consider the use of appropriately selected heat treatments, depending on the different stages of maturity. The proper selection of adequate thermal treatment can not only increase digestibility, but also improve the bioavailability of bioactive substances from this raw material.