Microwave Irradiation Conditions Research Articles

ALKALI ALCOHOLYSIS OF 2-PHENYL-gem-DICHLOROCYCLOPROPANE UNDER MICROWAVE RADIATION CONDITIONS

By alkaline alcoholysis of 2-phenyl-gem-dichlorocyclopropane, α-phenylacrolein acetals were synthesized under microwave irradiation (MWI) conditions: [1-(diethoxymethyl)vinyl]benzene, [1-(di-propyloxymethyl)vinyl]benzene, [1-(di- iso-propyloxymethyl)vinyl]benzene, [1-(dibutoxymethyl)vinyl]benzene, [1-(di-iso-butoxymethyl)-vinyl]benzene, {1-[bis(1-methylbutoxy)methyl]vinyl}benzene, [1-(dially-loxymethyl)vinyl]benzene, 1,1-[(2-phenylprop-1-en-3,3-diyl)bis(oxymethylene)]dibenzene. It was found that microwave radiation reduces the synthesis time by 70%, while the yield is more than 80%, and the selectivity of acetal formation is more than 90%. Using the method of competitive kinetics, it was established that primary alcohols such as ethanol, propanol and butanol are similar in activity. The structures of the obtained compounds were studied using nuclear magnetic resonance (NMR) and chromatography-mass spectrometry methods. The formation of acetals is proven by the presence of signals from the quaternary carbon atom in the region δс 142.35-146.49 ppm, and a doublet signal from protons at δн 5.01–5.71 ppm. and a singlet signal of the proton of the methine group in the region at 4.89-5.50 ppm. Analysis of the mass spectra of acetals showed the presence of maximum intensity of oxonium ions, due to α-, β-break relative to the oxygen atom. For the obtained acetals, the presence in the mass spectra of [M-H]+ cations, formed as a result of the release of a hydrogen radical from a molecular radical ion, was recorded. The peaks of [M-R]+ and [M-H]+ ions were inferior in intensity to [M-RO]+ cations. Most likely, this is explained by the stability of the [M-RO]+ cations relative to [M-C6H5C2H2]+ and [M-H]+, as well as the ease of eliminating RO• from the alkoxy group. In addition, for acetals of this type, the formation of a radical cation with m/z = 132 was observed, resulting from the release of the R radical from the second alkoxy group. Also, the mass spectra of acetals were characterized by the presence of a cation m/z = 77 and an intensity of 29-80%. Borisova Yu.G., Musin A.I., Voinov A.V., Spirikhin L.V., Raskil’dina G.Z., Sultanova R.M., Zlotskii S.S. Alkali alcoholysis of 2-phenyl-gem-dichlorocyclopropane under microwave radiation conditions. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 11. P. 15-21. DOI: 10.6060/ivkkt.20246711.7046.

One‐Pot Synthesis of C‐Substituted bis‐Benzimidazoles and Benzobisimidazoles via Reductive Cyclization of o‐Nitroaniline Derivatives and Aldehydes using Sodium Metabisulfite in a Microwave Reactor

AbstractHerein, we report a simple and an economical method to synthesize C‐substituted bis‐benzimidazole and C‐substituted benzobisimidazole derivatives in moderate to excellent yields using sodium metabisulfite, under microwave irradiation conditions. The most attractive feature of the methodology is the three‐step yet one‐pot condensation of nitroarenes with various benzaldehyde derivatives to synthesize useful benzimidazoles, and an easy product isolation method by simple solvent trituration techniques. The methodology can be fine‐tuned to synthesize selectively the mono C‐substituted benzimidazoles, leaving a nitroaniline functionality intact for preparing a variety of unsymmetrical C‐substituted bis‐benzimidazoles.

Turning Waste into Wealth: Optimization of Microwave/Ultrasound-Assisted Extraction for Maximum Recovery of Quercetin and Total Flavonoids from Red Onion (Allium cepa L.) Skin Waste

This study optimized the extraction conditions to maximize the recovery yields of quercetin and total flavonoids from red onion skin waste using sequential microwave/ultrasound-assisted extraction. Five effective factors of quercetin extraction yield were investigated using response surface methodology. The method was successfully performed under optimal 60 s microwave irradiation conditions followed by 15 min sonication at 70 °C with 70% (v/v, water) ethanol with a solvent-to-solid ratio of 30 mL/g. The variance analysis of the model for both quercetin (Y1) and total flavonoid (Y2) recovery from DOS demonstrated that ultrasound temperature (X2) was the most highly significant and influential factor, with a p-value of <0.0001 for both responses. Additionally, three key interaction terms—X1X2, X2X4, and X2X5—were identified as highly significant, further underscoring the critical role of ultrasound temperature in optimizing the extraction process for both quercetin and total flavonoids. The maximum recovery yields of quercetin and total flavonoids from red onion skin were 10.32% and 12.52%, respectively. The predicted values for quercetin (10.05%) and total flavonoids (12.72%) were very close to the experimental results. The recovery yields obtained from different extraction methods under the identical experimental conditions mentioned earlier were ultrasound/microwave-assisted extraction (7.66% quercetin and 10.18% total flavonoids), ultrasound-assisted extraction (5.36% quercetin and 8.34% total flavonoids), and microwave-assisted extraction (5.03% quercetin and 7.91% total flavonoids). The ANOVA confirmed highly significant regression models (p-values < 0.0001), with an insignificant lack of fit (p = 0.0515 for quercetin, p = 0.1276 for total flavonoids), demonstrating the robustness and reliability of the optimization. This study provides valuable insights for improving the extraction of bioactive compounds, which is critical for developing effective cancer treatments and advancing medical research. Additionally, the model shows potential for scaling up food processing applications to recover valuable products from red onion skin waste.

Investigation of Micro-Scale Damage and Weakening Mechanisms in Rocks Induced by Microwave Radiation and Their Associated Strength Reduction Patterns: Employing Meta-Heuristic Optimization Algorithms and Extreme Gradient Boosting Models

Microwave-assisted mechanical rock breaking represents an innovative technology in the realm of mining excavation. The intricate and variable characteristics of geological formations necessitate a comprehensive understanding of the interplay between microwave-induced rock damage and the subsequent deterioration in rock strength. This study conducted microwave irradiation damage assessments on 78 distinct rock samples, encompassing granite, sandstone, and marble. A total of ten critical parameters were identified: Microwave Irradiation Time (MIT), Microwave Irradiation Power (MIP), Longitudinal Wave Velocity prior to Microwave Treatment (LWVB), Longitudinal Wave Velocity post-Microwave Treatment (LWVA), Percentage Decrease in Longitudinal Wave Velocity (LWVP), Porosity before Microwave Treatment (PB), Porosity after Microwave Treatment (PA), Percentage Increase in Porosity (PP), and Uniaxial Compressive Strength following Microwave Treatment (UCSA). Utilizing the Pied Kingfisher Optimizer (PKO) alongside Extreme Gradient Boosting (XGBoost), we developed a PKO-XGBoost machine learning model to elucidate the relationship between UCSA and the nine additional parameters. This model was benchmarked against other prevalent machine learning frameworks, with Shapley additive explanatory methods employed to assess each parameter’s influence on UCSA. The findings reveal that the PKO-XGBoost model provides superior accuracy in delineating relationships among rock physical properties, microwave irradiation variables, microscopic attributes of rocks, and UCSA. Notably, PA emerged as having the most significant effect on UCSA, indicating that microwave-induced microscopic damage is a primary contributor to reductions in rock strength. Additionally, MR exhibited substantial influence; under identical microwave irradiation conditions, rocks with lower density demonstrated greater susceptibility to strength degradation. Furthermore, during microwave-assisted rock breaking operations, it is imperative to establish optimal MIT and MIP values to effectively diminish UCSA while facilitating mechanical cutting processes. The insights derived from this research offer a more rapid, cost-efficient approach for accurately assessing correlations between microwave irradiation parameters and resultant rock damage—providing essential data support for enhancing mechanical rock-breaking efficiency.

Design, Synthesis and in Silico Studies of New 2-MethylQuinazolin-4(3H)- Ones Derivatives

The concept of the green chemistry consists in the development of an environmentally friendly approach for organic synthesis using ecological and efficient protocols. In order to develop a methodology that could fit into the green chemistry field, for the synthesis of new quinazolin-4(3H)-ones derivatives via benzoxazinone, the choice was made on the use of both as catalysts, known for their efficiency, and microwave irradiations for time saving.The quinazolinone core and its derivatives form an important class of compounds, as they are present in a large family of products with broad biological activities. They generally display useful therapeutic and pharmacological properties such as anti-inflammatory, anti-convulsant, antihypertensive and antimalarial activity.The derivatives of the 2-metylquinazolin-4(3H)-ones 3a-d series was synthesized from 2- methyl benzoxazin-4(3H)-one 1 and aniline in the presence of H3PW12O40 (PW12) under microwave irradiation and solvent free conditions. The compound structures were established using IR, 1H-NMR, 13C-NMR and mass spectroscopy. The toxicity of the hydrazone derivatives was studied through ADMET (Absorption, Distribution, Metabolism, Excretion, and Toxicity) simulations using ADMET Lab 2.0 server.

Degradation by photo-Fenton process using Fe-clay as heterogeneous catalyst under sunlight and microwave irradiation

This study presents a newly developed, highly efficient heterogeneous iron-based catalyst (Fe-CY), supported on treated bentonite clay (CY), designed for the degradation of methylene blue (MB) dye. The bentonite clay underwent a two-stage treatment involving physical and chemical processes to produce the designated treated clay (CY), which served as the support material for Fe-CY catalyst preparation using the wet impregnation technique. Subsequently, the performance of the resulting catalyst was assessed in a photo-Fenton reaction aimed at degrading MB dye under both solar and microwave irradiation conditions. To determine the optimal decolorization conditions, several variables, including catalyst dosage, H2O2 quantity, pH, and initial MB concentration in the reaction system, were systematically investigated. Miscellaneous characterization techniques were employed to assess the support, and prepared catalyst. X-ray diffraction (XRD) was used to determine crystallinity, scanning electron microscopy (SEM) to analyze morphological structure, Fourier-transform infrared spectroscopy (FTIR) to identify surface functional groups, energy dispersive X-ray (EDX) analysis for the purpose of elemental analysis, and Brunauer-Emmett-Teller (BET) for analyzing the textural properties. The experimental findings highlight the remarkable effectiveness of the catalyst in degrading methylene blue (MB). Upon exposure to sunlight and microwave irradiation, the catalyst achieved substantial MB color removal rates of 99.5% and 95.5% within 180 and 8 min, respectively. Moreover, the stability of the catalyst was evaluated across three consecutive cycles, revealing a sustained removal efficiency of 83.05%. Finally, a comprehensive investigation into the mechanism behind methylene blue (MB) removal was conducted, revealing insights into the unique catalytic properties of the Fe-clay catalyst.

An Efficient Propylphosphonic Anhydride (T3P®)-Mediated MW-induced Solvent-free Rapid Synthesis of Enamino Esters and Ketones including 5, 5-Dimethyl-3-aminocyclohex-2-enones

Abstract: This work presents a clean and convenient synthesis of various β-enaminones including 5,5- dimethyl-3-aminocyclohex-2-enones, in satisfactory to excellent yields from the condensation reaction of primary amines with β -dicarbonyls by employing T3P® as a catalyst and performing the reaction under microwave irradiation and solvent-free conditions. These rapid reactions launched readily and stood a diversity of organic functional groups. A mixture of 1,3-dicarbonyl compound, primary amine and T3P® (50% in AcOEt) was irradiated for an appropriate time under microwave at 80°C. After completing the reaction (TLC) and cooling to r.t., ethyl acetate and saturated aqueous NaHCO3 solution were added. The aqueous phase was extracted ethyl acetate. The combined organic layer was washed with brine, dried over Na2SO4, and filtered, and the solvent was removed under reduced pressure to afford the product, which was recrystallized from diisopropyl ether. The presented results exhibit a better catalytic activity of T3P in the synthesis of enaminones. It could be concluded that T3P is the best catalyst as it took only a few minutes for the completion of the reaction with an excellent yield of product, which indicates T3P is more efficient, compared to other catalysts. A comparison of the efficiency of the present procedure with some heterogeneous solid catalysts was evaluated as well. Clearly, a higher yield was established in this procedure compared to other catalysts. Furthermore, the reaction of amines with dimedone was investigated as well, delivering excellent yields. The reaction catalyzed by T3P under microwave irradiation supplies a comprehensive method for the synthesis of enaminones. In this work, T3P is an effective, efficient and green catalyst, which forms the procedure economic, suitable, and safe with widespread application in the synthesis of enaminones. background: This work presents a clean and convenient synthesis of various β-enaminones incuding 5,5-dimethyl-3-aminocyclohex-2-enones in good to excellent yields from the reaction of different primary amines with 1,3-dicarbonyl compounds by employing T3P® as a catalyst and performing the reaction under microwave irradiation and solvent-free conditions. This one-pot rapid reaction proceeded readily and tolerated a variety of functional groups.

Dichlorocarbenation of polar olefins in conditions of microwave irradiation

Dichlorocarbenation of polar olefins in conditions of microwave irradiation

A Test System for Microwave-Assisted Dual-Mode Mechanical Cutting of Hard Rock Under True Triaxial Compression

This paper introduces a test system for microwave-assisted dual-mode mechanical cutting of hard rock under true triaxial compression. The test system was developed by Northeastern University, China, to simulate the cutting and breaking of hard rock by a tunnel boring machine (TBM). The test system is mainly composed of a dual-mode mechanical cutting subsystem, a true triaxial loading subsystem and a high-power microwave presplitting subsystem. The system performs dual-mode cutting under true triaxial stress, applies a single sensor to monitor the three-dimensional force of the cutter head, and integrates the reduction in the vibration and resistance to torsion during the cutting process. Mechanical cutting tests of basalt under different amounts of microwave irradiation and true triaxial stress conditions were conducted in Chifeng, Inner Mongolia, China. The results showed that microwave radiation presplitting effectively improved the efficiency of mechanical rock breaking. However, after 180 s of microwave irradiation, true triaxial high stress inhibited the mechanical breaking of basalt in terms of the overall excavation depth. During the tests, each system performed stably. The test results verified the reliability of the test system.

Electronic Effects in a Green Protocol for (Hetero)Aryl-S Coupling.

Aryl and heteroaryl iodides have been efficiently converted into the corresponding thioacetates in cyclopentyl methyl ether (CPME), a green solvent, under Cu catalysis. The chemoselectivity of the reaction is mainly controlled by electronic factors, enabling the conversion of both electron-rich and electron-deficient substrates into the corresponding thioacetates in good to excellent yields. The products can be easily deprotected to the corresponding thiolates to carry out additional synthetic transformations in situ. Surprisingly, despite CPME's relatively low dielectric constant, the reaction rate significantly increased when conducted under microwave irradiation conditions. This synthetic methodology exhibits a remarkable tolerance to functional groups, mild reaction conditions, and a wide substrate scope, utilizing a safe and inexpensive CuI pre-catalyst in the green solvent CPME. A non-aqueous workup allowing for the complete recovery of both catalyst and solvent makes this approach an environmentally sustainable protocol for C(sp2) sulfur functionalization. Additionally, the reaction shows selective cross-coupling with iodides in competition with chlorides and bromides, allowing its use in multistep syntheses. To demonstrate the potential of this methodology, it was applied to the high-yield synthesis of a photochromic dithienylethene, where a selective synthesis had not been reported before.

A facile microwave‐mediated method of 1,4‐dihydropyridine carboxylates synthesis by multicomponent reaction

AbstractAn innovative green procedure has been devised to prepare derivatives of 1,4‐dihydropyridine (1,4‐DHP). This method works with a catalyst process using ethanol as solvent under microwave irradiation conditions, enabling swift reactions (<30 min) with impressive yields (90%–96%). It contributes to an environmentally friendly and easily executable process by using the energy efficiency method. Within 30 min, this method underscores ecologically conscious practices and offers simple purification, streamlining the process by omitting column chromatography. This method highlights the efficacy and eco‐friendly nature of synthesizing 1,4‐DHPs. This method combines four component reactions, utilizing EtOH as the solvent and triethylamine as the catalyst. Furthermore, the product was characterized by diverse spectroscopic analysis.

Butyl (2,2-Dibutoxybutanoyl)-ʟ-Tryptophanate

The multicomponent reaction between ʟ-tryptophan 1, 2-oxobutanoic acid 2, and 1-butanol in the presence of SiMe3Cl was studied using microwave irradiation conditions. The main product was identified as an unreported acetal-containing compound, namely, butyl (2,2-dibutoxybutanoyl)-ʟ-tryptophanate (3), yielding 89%. NMR experiments demonstrated that the adjacent methylene protons of the acetal group appeared as two signals exhibiting their behavior as diastereotopic protons. DFT/B3LYP calculations revealed an asymmetric molecular structure with specific angles, leading to an explanation of the NMR results. The calculated chemical shifts showed slight differences with the experimental values and suggested magnetic anisotropy and inductive deprotection around the methylene hydrogen atoms in the acetal location. The reaction mechanism was proposed in which SiMe3Cl plays a crucial role by promoting water removal through key steps.

Microwave-Accelerated Synthesis of Flavanones through Oxidative Cyclization of 2'-Hydroxychalcones Using Acetic Acid as a Sole Catalyst

Under microwave irradiation conditions, 2'-hydroxy chalcones 1a-c underwent AcOH-mediated cyclization in an oxa-Michael addition manner to afford flavanones 2a-c in acceptable yields (up to 82%). These reactions proceeded in a shorter reaction time (~ 30 min) through microwave activation; otherwise, the reaction would take several days and even weeks, if a conventional heating process was employed. For example, cyclization of (E)-1-(2-hydroxyphenyl)-3-phenylprop-2-en-1-one (1a) has required 4 days of stirring with AcOH (0.25 M), under conventional heating at 100 °C, to produce 2-phenylchroman-4-one (2a), in 75% yield; while under microwave conditions, the reaction has yielded 82% of compound 2a, after 30 min. Thus obtained products 2a-c were fully characterized by recording of melting point together with UV, 1H NMR, and 13C NMR spectra.

The direct electrochemical detection of Salmonella paratyphi A

A novel biosensor based on the direct electrochemistry of Salmonella paratyphi A immobilized on pretreated glassy carbon electrode (PGCE) was established. It was essential that the trans-membrane and trans-wall direct electron transfer of guanine (G) in DNA strand inside viable Salmonella paratyphi A was captured by microwave irradiation for melting double-stranded DNA（dsDNA） into single-stranded DNA (ssDNA). When the microwave irradiation condition reached 100 W for 9 s, the oxidation peak current reached maximal levels in pH 6.0 phosphate buffer solution (PBS). Meanwhile the typical surface controlled and irreversible electrode process of G was revealed by cyclic voltammetry (CV) with participation of 2 protons and 2 electrons respectively. In addition, A linear relationship for the oxidation current of G with the logarithm of Salmonella paratyphi A concentration was established with the range from 2.10 × 103 to 2.10 × 106 CFU ∙ mL−1. The rapid quantification of viable Salmonella paratyphi A was achieved based on the direct electrochemical biosensor.

A Review of the Synthesis of Oxazoline Derivatives.

Oxazolines are important heterocyclic systems due to their biological activities, such as antibacterial, antimalarial, anticancer, antiviral, anti-inflammatory, antifungal, antipyretic, and antileishmanial. They have been widely applied as chiral auxiliaries, polymers, catalysts, protecting groups, building blocks, and ligands in asymmetric synthesis. Due to their importance, many synthetic routes to prepare oxazoline moieties have been investigated and developed by researchers around the world. In this review, we summarized several synthetic methodologies published in the literature. The main substrates are nitriles, carboxylic acids, and acid derivatives, which react with a variety of reactants under conventional heating, microwave irradiation or ultrasound irradiation conditions. Syntheses via intramolecular cyclisation from amides have also been reported. Many publications have highlighted procedures based on solvent-free conditions using eco-friendly, reusable, and easy-availability catalysts.

Lactic, Malic, Tartaric, Citric and Ascorbic Acid as Natural and Green Organocatalysts for Microwave-Induced Solvent-Free Synthesis of Enaminones

The enaminone framework is a versatile building block used in organic synthesis. Herein, a series of β-enaminones were synthesized in good to excellent yields from the reaction of various aliphatic and aromatic primary amines with 1,3-dicarbonyl compounds using common natural organic acids (lactic, malic, tartaric, citric and ascorbic acid) as green, eco-friendly and efficient catalysts under microwave irradiation and solvent-free conditions.

Microwave-assisted synthesis of base-modified fluorescent 1,4-dihydropyridine nucleosides: photophysical characterization and insights.

A synthesis of a small library of fluorescent 1,4-dihydropyridine nucleoside analogues has been successfully carried out under solvent-free conditions via a one-pot three-component Hantzsch condensation reaction. The process involved a Ba(NO3)2 catalyzed solvent-free reaction between 3',5'-di-O-acetyl-5-formyl-2'-deoxyuridine, differently substituted β-keto ester and ammonium acetate under microwave irradiation. This facile methodology yielded the desired products with very high yields (86-96%) under solvent-free reaction conditions in a short reaction time, which was followed by a simple workup. Yields obtained under microwave and conventional heating were compared, with the microwave irradiation condition displaying superior results. The synthesized compounds were characterized by IR, 1H-NMR, 13C-NMR, 1H-1H COSY, 1H-13C HETCOR, 2D NOESY NMR and HRMS analysis. These nucleoside analogues exhibited significant fluorescence, with a prominent emission band around 460 nm (excitation at 235 nm). Photophysical studies revealed strong fluorescence intensity, excellent Stokes shifts (70-162 nm), and high quantum yields (0.022-0.579), outperforming other pyrimidine-based fluorescent nucleosides. Notably, 5-(diethyl 2'',6''-propyl-1'',4''-dihydropyridine-3'',5''-dicarboxylate)-4''-yl-2'-deoxyuridine demonstrated a quantum yield as high as 0.579 in DMSO during solvatochromic studies, highlighting their potential for probing local nucleic acid structure and dynamics. Additionally, we demonstrated the scalability of the synthesis protocol by producing one of the compounds on a gram scale, confirming its practical viability for large-scale production. This study underscores the potential of these fluorescent nucleoside analogues for various biochemical applications.

‘Cephalandole A’ analogues as a new class of antioxidant agents: Design, microwave-assisted synthesis, bioevaluation, SAR and in silico studies

Herein, a novel series of natural product alkaloid ‘Cephalandole A’ analogues 19a-y, and 20a-d were rapidly synthesised under microwave irradiation conditions using PTSA in catalytic amount dissolved in acetonitrile at 90 °C for 15 min. The developed one-pot protocol is operationally simple, rapid (15 min) and furnished the target analogues in up to 90 % yield. All the synthesised analogues of Cephalandole A were evaluated for their in vitro antioxidant activity using DPPH free-radical scavenging and FRAP assays. The in vitro studies of DPPH radical scavenging assay provided 19a (IC50 = 11.87 ± 0.14 µg/mL), 19f (IC50 = 16.34 ± 0.27 µg/mL), 19n (IC50 = 15.37 ± 0.11 µg/mL) and 20a (IC50 = 14.54 ± 0.31 µg/mL) respectively, as the most active compounds of the series. In addition, the analogous 19d (556.3 ± 13.1 µM) and 19v (551.9 ± 14.2 µM) showed promising activity in FRAP assay. However, the standard reference drug ascorbic acid showed an IC50 value of 4.57 µg/mL in the DPPH assay, and BHT showed C0.5FRAP = 546.0 ± 13.6 μM in the FRAP assay. In silico studies were performed to validate the wet results. To the best of our knowledge, this is the first report demonstrating ‘Cephalandole A’ analogues as a new class of antioxidant agents.

The Law and Mechanism of the Effect of Surface Roughness on Microwave-Assisted Rock Breaking

In physical engineering, a rock surface, whether naturally or artificially formed, is rough. When irradiating rocks, microwaves produce reflections and diffractions on the surface of rough rocks, which significantly affect the absorption of microwave energy by rocks, thus influencing the result of microwave irradiation. In order to explore the influence of rough rock surfaces on the effect of microwave-assisted rock breaking, microwave irradiation tests were carried out on basalt samples with different values of roughness to test the temperature and P-wave velocity of the samples before and after microwave irradiation. Numerical test methods were used to systematically study the influence of rough rock surfaces on microwave irradiation. The results show that, under the same microwave irradiation conditions, the effect of microwave irradiation on rough surface basalt is more significant than that of flat surface basalt. The surface temperature distribution range of flat surface specimens is narrow, the surface temperature range of rough surface specimens is wider and more inhomogeneous, and the maximum surface temperatures of rough surface specimens are much higher than those of flat surface specimens. After irradiation, new macroscopic cracks were generated on the surface of the samples, and the crack propagation of the rough surface samples was more obvious. The decrease in P-wave velocity before and after the irradiation of flat surface samples is small, and that of rough surface samples is larger. The main factors affecting the effect of microwave irradiation on the rough surface are the refraction and reflection of electromagnetic waves, heat conduction, and stress concentration on the surface.

Quinoa treated by an optimized method of microwave heating and their effect on antioxidant activity and phenolic compounds after in vitro gastrointestinal digestion

ABSTRACT Heating by microwave irradiation could be an alternative for cooking quinoa and improving its content of phenolic compounds, which have health-promoting properties. The goal of this study was to improve the bioaccessibility of phenolics content and antioxidant activity of quinoa using an optimized method of microwave irradiation. The best microwave irradiation conditions obtained by maximizing the responses were 100% irradiation power and 14 min of irradiation time. The predicted and experimentally validated values for total phenols, flavonoids, and antioxidant activity were as follows: 686.46 vs 749.67 ± 36.62 µg GAE/g; 743.94 vs 803.37 µg QE/g and 4.20 vs 4.61 µM TE/g, respectively. At the gastric level, heating by microwave irradiation promoted the bioaccessibility (>100%) of total phenols, flavonoids, and antioxidant activity, as well as gallic and coumaric acids, quercetin, and kaempferol greater. The heating treatment by microwave in quinoa could be useful to obtain new products with bioactivity potential at gastric and intestinal levels.