Freezing Conditions Research Articles

Thalamic nucleus reuniens coordinates prefrontal-hippocampal synchrony to suppress extinguished fear

Traumatic events result in vivid and enduring fear memories. Suppressing the retrieval of these memories is central to behavioral therapies for pathological fear. The medial prefrontal cortex (mPFC) and hippocampus (HPC) have been implicated in retrieval suppression, but how mPFC-HPC activity is coordinated during extinction retrieval is unclear. Here we show that after extinction training, coherent theta oscillations (6–9 Hz) in the HPC and mPFC are correlated with the suppression of conditioned freezing in male and female rats. Inactivation of the nucleus reuniens (RE), a thalamic hub interconnecting the mPFC and HPC, reduces extinction-related Fos expression in both the mPFC and HPC, dampens mPFC-HPC theta coherence, and impairs extinction retrieval. Conversely, theta-paced optogenetic stimulation of RE augments fear suppression and reduces relapse of extinguished fear. Collectively, these results demonstrate a role for RE in coordinating mPFC-HPC interactions to suppress fear memories after extinction.

Preparation of various Co/Cu and Co/Fe molar ratios and gel-modified nanomaterials as anodes for Li-ion batteries

Co-based binary metal oxides with higher theoretical capacity have attracted increasing attention as anodes for lithium-ion batteries (LIBs). In this study, Co-based bimetallic oxides were prepared by optimizing different molar ratios of Cu/Co and Fe/Co using an electroconversion method. The purity and microstructure of the synthesized powders were investigated, and their lithium storage properties were studied by assembling half-cells. Cu/Co oxide exhibited three different microstructures, while Fe/Co oxide showed a nanoparticle morphology. The electrochemical performance results revealed that the optimal molar ratio of Co: Cu was 2:1, and the optimal molar ratio of Fe: Cu was 5:1. Particularly, Fe: Cu = 5:1 exhibited the best electrochemical stability and higher specific capacitance. Therefore, Fe3O4/Co3O4 (Fe: Cu = 5:1) was used as the raw material for modification, and a hydrogel method was employed with sodium alginate (SA) serving as the fixing agent and carbon source to prepare microspheres. Taking advantage of the natural freezing conditions in the winter of Northeast China, the dried microspheres were subjected to calcination to obtain Fe3O4/Co3O4/SA with enhanced conductivity. Even at a current density of 2 A/g, Fe3O4/Co3O4/SA still maintained a discharge capacity of around 280 mAh/g, demonstrating excellent cycling stability and rate capability.

Thermal properties of treatment wetlands operated under freezing conditions.

The use of treatment wetlands (TWs) presents particular challenges in regions with sub-zero winter temperatures, due to reduced biological activity and risk of pipe breakage or clogging due to freezing. We studied the vertical temperature distribution in four pilot-scale TWs exposed to winter temperatures in order to determine the impact of operational system parameters and the role of insulation on heat conservation inside the filtering bed. The overall temperature pattern was similar in all wetlands, with a trend of increasing temperature from the surface toward the bottom during the cold season. No freezing was detected in the wetlands despite average daily temperatures as low as -20 °C. Influent water temperature and hydraulic loading had a stronger influence on TW temperatures in winter than air temperature. The vertical distribution of temperatures in TWs is more sensitive to hydraulic loading variation in the percolating operating condition than in the saturated flow with forced aeration configuration. Our results suggest that TW systems can remain operational under cold winter conditions provided the surface is properly insulated by vegetation, mulch and/or snow.

Analysis of soil behavior under freezing and thawing conditions

Understanding of the thermal, hydraulic and mechanical behavior of soils under freezing and thawing is important in solving problems of permafrost engineering and artificial ground freezing. Accurate mathematical descriptions of heat and moisture transport and the associated mechanical deformations is critical for developing such understanding. Phase change and transition during freezing and thawing are characterized by a strong non-linearity due to the rapid variations of thermo-physical properties of the material and the release of the latent heat of solidification. Such processes cannot be easily and accurately modelled via the use of local (differential) formulations [1,2]. A non-local formulation, developed within the framework of peridynamics [3–5] is proposed here for ground freezing and thawing. It expands the domain of applicability of the first work on non-local modelling of heat transfer with water flow in saturated porous media [6] into modelling the thermo-hydro-mechanical behavior of unsaturated soils.
 The mathematical description of unsaturated soil behavior is based on three governing equations of conservations of water mass, energy and linear momentum, which are complemented by constitutive relationships that represent the change of soil properties.
 Using the local mathematical model of unsaturated soils [7,8], a peridynamics mathematical framework is formulated. Following [6], the bond-based peridynamics considers a soil body as a collection of particles, see Fig. 1 for the 1D case. The term `bond' refers to the interactions between two points, located at depths and . The point interacts with all other points within a certain finite region , called the horizon of z.
 The peridynamic form of the water mass conservation is:
 where is the water pressure head; is time; is the volumetric content of a soil component; is the density of a soil component; and is the vertical coordinate. The micro-diffusivity function can be defined following [9]. Here, the subscripts i, l, a and s refer to ice, liquid water, air and soil particles respectively.
 The peridynamic form of the energy conservation is:
 where is temperature; is the latent heat of water solidification; is the average thermal conductivity of soil; is the vector of water flux; is the average heat capacity of unsaturated soils and is the specific heat capacity of liquid water. Here, is a micro-conductivity function and is a micro-velocity function, for more details see [6,10].
 The peridynamic form of the linear momentum conservation is:
 where is the acceleration of the peridynamics particle ; is a pairwise force density vector between particles and that depends on its initial and deformed positions Z and Z’; is the horizon volume associated with the particle ; is the body force on the particle . The elastic stress-strain relation for unsaturated soils can be stated as:
 where is the stress increment tensor; is soil compressive modulus for unsaturated conditions, and is the strain increment tensor due to the elastic deformation of the soil matrix, that can be find from the relation for the total strain increment tensor of unsaturated soils . Here is the strain increment tensor corresponding to the change of soil volume due to the frost heave; and is the strain increment tensor corresponding to the plastic deformations of soils.
 The numerical implementation of the peridynamic formulation is verified by comparing the results of simulations with analytical solutions and the formulation is validated by comparing these results with experimental data under the condition of one-dimensional heat and water transfer obtained by laboratory experiments. In the experiments, soil cylinders were cooled from one surface by a source of negative temperature. As a result, the freezing front propagated along the cylinder. The temperature profile in the column was changing, and water migration was observed. The developed model is shown to predict the results of these experiments well.
 The proposed peridynamic model is the first to combine the flow of liquid water with heat transfer and mechanical deformations in the presence of a change of the water phase state in unsaturated soils. It is demonstrated that for the soils with relatively high initial water content, the developed approach describes effectively the change of liquid water content and predict soil deformation. The set of integral-differential equations are solved by a simple numerical scheme.

The freeze-thaw stability of flavor high internal phase emulsion and its application to flavor preservation and 3D printing.

Volatilization of flavor substances may reduce consumers' perception of flavor, and the research on preservation of flavor substances by high internal phase emulsions (HIPEs) under freeze-thaw conditions is still blank. Herein, flavor HIPEs prepared by adding more than 15% litsea cubeba oil in the oil phase could be used as food-grade 3D printing inks, and showed better stability after 5 freeze-thaw cycles, which could be interpreted as the reduced ice crystal formation, more stable interface layer, and more flexible gel-like network structure resulting from the protein binding to flavor substances. The constructed HIPEs system in this study could preserve the encapsulated flavor substances perfectly after 5 freeze-thaw cycles. Overall, this study contributes a food-grade 3D printing ink, and provides a new method for the preservation of flavor substances under freezing conditions and expands the application range of flavor HIPEs in food industry.

Practical Advice on Scientific Design of Freeze-Drying Process: 2023 Update

ObjectiveThe purpose of this paper is to re-visit the design of three steps in the freeze-drying process, namely freezing, primary drying, and secondary drying steps. Specifically, up-to-date recommendations for selecting freeze-drying conditions are provided based on the physical–chemical properties of formulations and engineering considerations.Methods and ResultsThis paper discusses the fundamental factors to consider when selecting freezing, primary drying, and secondary drying conditions, and offers mathematical models for predicting the duration of each segment and product temperature during primary drying. Three simple heat/mass transfer primary drying (PD) models were tested, and their ability to predict product temperature and sublimation time showed good agreement. The PD models were validated based on the experimental data and utilized to tabulate the primary drying conditions for common pharmaceutical formulations, including amorphous and partially crystalline products. Examples of calculated drying cycles, including all steps, for typical amorphous and crystalline formulations are provided.ConclusionsThe authors revisited advice from a seminal paper by Tang and Pikal (Pharm Res. 21(2):191-200, 2004) on selecting freeze-drying process conditions and found that the majority of recommendations are still applicable today. There have been a number of advancements, including methods to promote ice nucleation and computer modeling for all steps of freeze-drying process. The authors created a database for primary drying and provided examples of complete freeze-drying cycles design. The paper may supplement the knowledge of scientists and formulators and serve as a user-friendly tool for quickly estimating the design space.

Analysis of test methods for frost resistance of concrete

Introduction. Frost resistance of concrete is one of the most challenging problems in concrete studies. Particularly important is the issue of methods of testing concrete for frost resistance. The existing standard methods require more detailed regulation of the test process in order to improve the reliability of the results.Aim. To analyze the regulatory procedures of testing concrete for frost resistance with a view to make suggestions for improving standards.Materials and methods. The analysis involved Russian and foreign standards and publications on methods of testing concrete for frost resistance.Results. The authors analyzed the methods of testing concrete for frost resistance, included in Russian and some foreign standards. The quality of determining the frost resistance of concrete can be improved by controlling the temperature while freezing and thawing, in particular, by assessing the temperature in the concrete of the test samples. Controlling the air temperature in the freezer should be recognized as insufficient. The criteria for the state of concrete samples during and after cyclic freezing and thawing should be further verified. It is necessary to continue full-scale testing of concrete under severe climatic conditions, taking into account the real conditions of freezing and thawing of concrete in structures, and comparing the results of laboratory and full-scale tests, including satellite samples.Conclusion. The analysis revealed the necessity to continue the research on clarifying the test methodology and criteria for assessing the state of concrete samples after freezing and thawing cycles. It is advisable to recreate devices for determining the dynamic modulus of elasticity of samples in freeze-thaw testing, to resume long-term full-scale tests of concrete under severe climatic conditions, and to develop a manual for creating frost-resistant concrete, taking into account the current level of concrete technology. Elimination of the existing drawbacks of the methodology will improve the reliability of test results.

Quantitative evidence for Arctic continental freezing in a high-CO 2 world: Junggar Basin, NW China

Abstract We show that the Late Triassic–Early Jurassic continental Arctic experienced wintertime freezing conditions, despite the exceptionally high atmospheric CO 2 levels, by quantifying common lake ice-rafted debris (L-IRD) identified in the Junggar Basin of Xinjian, NW China. This L-IRD consists of outsized (0.1–12 mm) lithic clasts ‘floating’ in otherwise fine-grained, profundal lake sediment matrix. Laser-diffraction grain-size analysis demonstrates that the grain-size distribution for lacustrine strata of Junggar Basin is very similar to modern sediments from the seasonally ice-covered Sea of Okhotsk, reflecting a similar depositional mechanism. Three-dimensional computed tomography and two-dimensional thin sections demonstrate that the outsized clasts are dispersed, rather than confined to sand lenses or layers. These results are inconsistent with alternative methods of bimodal sediment deposition such as mud flows, algae rafting or root rafting. The discovery of Triassic–Jurassic continental freezing provides new context for understanding global climate during periods with high-CO 2 conditions and climate and biotic changes in the Mesozoic Era.

Lattice Shrinkage of 2D-COFs under Electron Beam Irradiation

Over the past two decades, covalent organic frameworks (COFs) have become the most widely studied porous crystalline materials. Their specific physical and chemical properties are determined by the arrangement of atoms (crystal structure). Therefore, the determination of their structure is arguably the most important characterization step for COFs. Although single-crystal X-ray diffraction is the most widely used method for structure determination, confirmation of the structure of COFs is limited to lattice fringes in transmission electron microscopy (TEM) because of their small crystal size (nanocrystals) or poor crystal quality. At present, many two-dimensional COFs (2D-COFs) have clear powder X-ray diffraction (PXRD) patterns, but specific lattice fringes are not available for all 2D-COFs. This severely hinders the development of the COF field. Here, we discovered the lattice shrinkage behavior of COFs under electron beam irradiation by comparing the lattice fringes of 2D-COFs under different conditions. By comparing the lattice fringes of a 1,3,5-tris-(4-aminophenyl)triazine-1,3,5-tris-(4-formylphenyl)triazine covalent organic framework (TAPT-TFPT COF) at room temperature and under liquid nitrogen freezing conditions, we found that the lattice fringes are in good agreement with the PXRD and the theoretical values of the COF (2.213 nm) under freezing conditions. However, the lattice fringe spacing is only 1.656 nm at room temperature. The discovery not only provides new insights into the TEM characterization of COFs, but also further expands the range of crystalline COF materials.

Effects of different plant proteins on the quality and characteristics of heat induced egg white protein gel under freezing conditions

Eggs white is rich in protein, whose gel property is one of the most important functional characteristics during processing. The purpose of this study was to reveal the effect of different plant proteins (2% (w/w), 2.5% (w/w), 3% (w/w)) on the quality of heat induced egg white protein (EWP) gel after freezing. Gels were prepared by adding 2.5% soy protein isolates (SPI) or pea protein isolates (PPI), and then were frozen for 14 days. Compared with the control group (EWP without adding any plant proteins), the hardness, chewiness and gumminess of SPI-EWP gel were increased by 58.23%, 71.11% and 66.35%, respectively, which was better than PPI-EWP. The thawing loss rate of SPI-EWP and PPI-EWP gel decreased by 16.8% and 13.0%, respectively, and the centrifugal loss rate decreased by 13.2% and 11.8%, respectively. The addition of plant proteins resulted in a decrease in the proton signal intensity of the T23 peak. Hydrogen proton imaging and rheology results showed that water content of gels added with plant proteins after freezing was higher than control group and showed better viscoelasticity (SPI was better than PPI). The results of intermolecular forces indicated that with the increase of plant protein, the ionic bonds decreased, the contribution of disulfide bonds significantly increased (p < 0.05). Fourier Transform Infrared Spectroscopy (FTIR) indicated that the α-helix content decreased, β-sheet increased. In brief, this study provides valuable reference for the development and application of plant protein to improve the quality of egg white protein in food industry.

Mode of formation of cryogenic cave carbonates: Experimental evidence from an Alpine ice cave

Coarsely crystalline carbonates that formed cryogenically in caves (CCCcoarse for short) are important paleoenvironmental archives that provide evidence of former perennial ice deposits in currently ice-free caves and allow the timing of the past freezing conditions close to 0 °C in the subsurface to be determined. Despite their significance, the mode of formation of these deposits has never been observed in statu nascendi.We conducted a series of freezing experiments in an Alpine ice cave to test the conceptual model of CCCcoarse formation in freezing pools of water in perennial ice deposits. Our results document a number of features associated with the freezing of such confined water bodies, including ice bulging, cracking and episodic expulsion of water. These observations help explain the degassing of carbon dioxide required to maintain carbonate precipitation in these semi-closed pockets of slowly freezing water. Our experiments yielded a range of morphological types of cryogenic calcite crystals and aggregates comparable to those reported from CCCcoarse from currently ice-free caves elsewhere. The experimentally grown crystals also exhibit the same depleted O isotope composition characteristic of natural carbonates interpreted as being formed subaqueously in a semi-closed pools subject to freezing. The main difference to naturally formed CCCcoarse is their smaller crystal size, reflecting the comparably short freezing time of our experiments of less than two weeks.This study confirms the conceptual model explaining the formation of CCCcoarse in localized pools in ice and calls for a revision of the currently existing classification scheme for cryogenic cave carbonates.

Experimental and Theoretical Study of the Influence of Saline Soils on Frozen Wall Formation

This paper examines the impact of salinity on the thermophysical properties of soils during artificial freezing. It focuses on analyzing heat and mass transfer in saline soils for constructing a frozen wall around a mineshaft at a potash salt deposit. The presence of salts in the groundwater near the contact point with water-protective strata is common in these deposits. Experimental studies were conducted on clay, chalk, and sand to understand the effect of salinity on the freezing temperature, unfrozen water content, specific heat capacity, and thermal conductivity of wet soil. These findings were used to simulate heat and mass transfer in saline soils using a one-dimensional model. The technique of circumferential averaging was introduced to account for the thermal impact of freeze pipes. The results indicate that higher soil salinity leads to a faster decrease in soil temperature under freezing conditions, although this dependence is weak for clay. This study also revealed that an increase in initial salinity results in a reduction in the thickness of the frozen wall. It was found that, for chalk and sand, there exists a range of initial salinity during which the frozen wall’s thickness is almost independent of the initial salinity.

Investigation of freezing temperature and time to improve resistant starch content and quality of pure mung bean starch vermicelli

Mung bean vermicelli is one of the commonly consumed styles of noodles because of its convenience in Asian countries as well as being a good source of resistant starch (RS). It was hypothesized that suitable freezing conditions could produce mung bean vermicelli with a greater RS content and good cooking quality compared to the commercially available product. Therefore, this study investigated the optimum freezing conditions to increase the RS content in mung bean vermicelli. After extrusion, boiling, and cooling, the drained vermicelli was incubated at 4 C for 1 h 30 min before using different freezing conditions by varying the processing temperature (-5, -10, -15, or -20 C) and time (6, 12, 18, or 20 h for each temperature).The highest RS content was observed in dried mung bean vermicelli (12.83% at -10 C for 18 h; V1018), whereas the commercial vermicelli had the lowest RS content (9.73%). The cooking time, water absorption, volume increase, and resistant starch content of cooked V1018 were higher with values of 12.69 min, 502.97%, 19.13% and 7.32%, respectively, than those of the commercial vermicelli (8.56 min, 347.34%, 15.19% and 5.58%, respectively). Furthermore, the cooking loss, tensile strength, and elasticity of V1018 were 1.08%, 0.0101 N, and 11.96 mm, respectively, which were lower than for the commercial vermicelli (1.96%, 1.16-folds, and 2.16-folds, respectively). The color of dried V1018 vermicelli had more lightness, redness, and yellowness, while the cooked V1018 vermicelli had more lightness, greenness, and blueness than the respective commercial products. Hence, incubating at 4 C for 1 h 30 min, followed by freezing at -10 C for 18 h was recommended to produce pure mung bean starch vermicelli with a high resistant starch content and good quality

Burr formation mechanism and morphological transformation in grinding of nickel-based superalloy honeycomb cores under ice freezing and MQL conditions

Nickel-based superalloy honeycomb core (NBSHC) is extensively used in aerospace field due to the light weight, high specific strength and high temperature resistance. The burrs of NBSHC are extremely prone to be formed during machining and the insufficient welding strength or false welding between NBSHC and skin is generated because of the large or unreasonable burr morphology, resulting in premature failure of the parts. In this work, a novel method of ice freezing combining with minimum quantity lubrication (MQL) was proposed to grind NBSHC to improve the burr morphology and size. The burr formation mechanisms of NBSHC under ice freezing and MQL conditions were revealed by single abrasive particle grinding cell wall and verified by grinding experiments. The grinding force, burr morphology transformation mechanisms and size were investigated in-detail by experiments combining with FEM results. The results indicated that MQL and ice freezing decreased the plastic flow property of material by reducing the temperature and friction of NBSHC, thereby promoting the transformation of burr size from large into micro, and the burr shape from long strip into block. Decreasing grinding depth can also improve the burr morphology by decreasing the volume of plastic flow material. The improving effects of full of ice freezing were better than MQL for NBSHC grinding. The machining efficiency under full of ice combining with MQL was 3 times of that under quasi-dry grinding. These findings are significant for improving the machining quality and exploring the burr morphology transformation of NBSHC.

Effect of Different Chloride Salts on the Transport of Water, Heat, and Solutes in Sandy Soil under Freezing Conditions

Effect of Different Chloride Salts on the Transport of Water, Heat, and Solutes in Sandy Soil under Freezing Conditions

Observation on the ice crystal formation process of large yellow croaker (Pseudosciaena crocea) and the effect of multiple cryoprotectants pre-soaking treatments on frozen quality

By observing the formation behavior of ice crystals, the quality of food products under different freezing conditions can be intuitively judged. In this paper, large yellow croaker was taken as the research object, and a novel cryomicroscopic system was developed to directly observe the structure of ice crystals during the freezing process. The cryoprotective effects of 4% sucrose +4% sorbitol (SU + SO), 4% xylo-oligosaccharide (XO), 4% xylo-oligosaccharide + 0.3% tetrasodium pyrophosphate (XO + TSPP) and 0.2% antifreeze protein (AFP) at different freezing temperatures were investigated. And the evaluation indicators, such as cell deformation degree, equivalent diameters, roundness, elongation and fractal dimension were introduced to quantify the damage of ice crystals to muscle tissues and fibers. The results indicate that reducing the freezing temperature and adding cryoprotectants can improve the quality of large yellow croaker. AFP has the best cryoprotective effect, with a reduction in cell deformation degree of 54.78% and 67.83% compared to the Control group at −5 °C and −20 °C, respectively. SU + SO and XO have the equivalent antifreeze effect, which is slightly inferior to XO + TSPP. In addition, physical parameters of large yellow croaker samples were measured to verify the influence of ice crystal structure on product quality. Therefore, direct observation of the ice crystal formation process and evaluation of ice crystal structure can accurately reflect the quality of frozen products, which is of great significance for the development of refrigeration and preservation technology.

Slope stability analysis model for the frost-susceptible soil based on thermal-hydro-mechanical coupling

Slope stability analysis has been performed through various analysis methods ranging from general limit equilibrium methods, such as those proposed by Janbu, Bishop, and Fellenius, to finite element methods. Using these methods, analyzing the slope stability considering the change in soil stiffness due to the freezing or thawing conditions resulting from temperature changes is infeasible. Therefore, considering this shortcoming, a thermal-hydro-mechanical slope stability analysis model (THM-SSA model) is proposed for slope stability analysis. The main feature considered in the THM-SSA model was the slope of the critical state line based on the load angle. Additionally, this model could calculate the local factor of safety (LFS) for the slope based on the isotropic tensile strength of the unfrozen soil and the changes in it after being subjected to repeated freeze–thaw cycles. To verify the proposed THM-SSA model, the stress–strain results were compared with those of the experimental triaxial compression tests that were conducted under different temperatures of the frozen soil with a corresponding number of freeze–thaw cycles. Based on this, a simulation of slope stability analysis was performed as demonstration, and using the verified THM-SSA model, the LFS was calculated according to the freeze–thaw cycles of the slope.

Development of an instrument-free and low-cost ELISA dot-blot test to detect antibodies against SARS-CoV-2.

Most laboratory tests to detect the presence of anti-SARS-CoV-2 antibodies use enzyme-linked immunosorbent assays (ELISA) or chemiluminescence immunoassays (CLIA); however, equipment for these immunoassays is unavailable in many areas of low- and middle-income countries. Rapid lateral flow immunoassay (LFIA) tests are an equipment-free option, but their high price may make them less suitable for conducting seroprevalence surveys. Here, we describe a simple dual antigen ELISA dot-blot test to detect anti-SARS-CoV-2 IgG antibodies with high sensitivity (94-98%) and specificity (92-100%), compared to commercially available ELISA and CLIA options. Additionally, this ELISA dot-blot test can be completed in one hour using minimal laboratory equipment. Importantly, this immunoassay is significantly more affordable than most LFIA tests available on the global market. The dot-blot strips may be stored for up to 7 days under freezing conditions. This ELISA dot-blot test is a cost-effective option for conducting seroprevalence screenings in areas lacking ELISA or CLIA facilities, compared to LFIA tests.

Grey relativity correlations between the pore structures and compressive strength of aeolian sand concrete undergoing carbonation and freeze-thaw cycles

In this study, the compressive strength of aeolian sand concrete (ASC) was predicted using pore structure parameters and pore structure types under the conditions of a complex environment. The relationships between the pore structures and the compressive strength of the ASC undergoing carbonation and freeze-thaw coupling actions were examined. Full ASC with a 100% replacement rate of aeolian sand (AS) was used in this study’s experiments. The microstructure characteristics of the ASC were analyzed using nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). At the same time, the correlation degrees of the pore structures and compressive strength were examined using a grey relativity analysis method. A GM (1, 3) prediction model of the ASC compressive strength under different carbonization times was established. The model showed that the effects of the carbonization and freeze-thaw cycles (FTCs) on the pore structures and the compressive strength of the ASC were different. According to the grey relativity analysis results, the bound fluid saturation and harmless pore ratios had the greatest impacts on the compressive strength of the ASC. The model established based on those factors had the ability to accurately predict the compressive strength of the ASC under the conditions of a carbonation-salt freezing and thawing environment.

Stability of pesticide residues in citrus fruits during storage

Introduction. Storage of selected samples before transportation to the laboratory and immediately before analysis is an important component in the process of product quality control and evaluation.&#x0D; Purpose of the work was to evaluate the degradation of pesticide active substances in real samples of citrus fruit left for long periods of storage in deep freezing conditions.&#x0D; Materials and methods. High-performance liquid chromatography with triple quadrupole mass detector (HPLC-MS/MS) was used to identify and quantify pesticide active substances. According to the method of analysis MUK 4.1.3657–20, cryogenic grinding of samples was carried out in a cutter using dry ice. Sample preparation was carried out using the QuEChERS technology. To extract analytes from a homogenized sample acetonitrile was used in the presence of salts containing citrate buffer, followed by purification of the extract by SPE.&#x0D; Results. In the studied samples of citrus, the analytes showed stability. Thirty months after storage of samples in deep freezing conditions (temperature not higher than –20 °C), the identified levels of active ingredients of the pesticides imazalil, pyrimethanil and prochloraz did not change by more than 20% compared to the previously detected concentrations. Insignificant amounts of imidacloprid, thiabendazole and pyriproxyfen, as well as traces of azoxystrobin and trifloxystrobin, detected in the study of samples, were also found in samples after long-term storage. &#x0D; Limitation. The study is limited to the study of the stability of individual active substances found in real samples of citrus fruits intended for sale to the consumer.&#x0D; Conclusion. Proper storage of samples should ensure the preservation of the levels of active substances in the samples and exclude their change due to various processes (volatilization, enzymatic and hydrolytic decomposition, etc.), which requires the performance of preliminary experimental studies to assess their stability. The work showed the stability of residual quantities of imazalil, pyrimethanil, prochloraz, imidacloprid, thiabendazole, and pyriproxyfen in citrus fruit matrices under storage conditions in a freezer at not more than –20 °C for 30 months.