Bhaskar Sanyal

A New Electron Paramagnetic Resonance Method to Identify Irradiated Soybean

Low-dose gamma irradiation causes minimal changes in food matrix making identification of radiation-processed foods a challenging task. In the present study, soybean samples were irradiated with commercially permitted gamma radiation dose in the 0.25 to 1.0 kGy range for insect disinfestations of food. Immediately after irradiation electron paramagnetic resonance (EPR) spectrum of the skin part of soybean showed a triplet signal (g = 2.0046, hyperfine coupling constant hfcc = 3.0 mT) superimposed on naturally present singlet. These signals were characterized as cellulose and phenoxyl radicals using EPR spectrum simulation technique. Kernel part of the samples exhibited a short-lived, radiation-induced singlet of carbon-centered radical superimposed on naturally present sextet signal of Mn2+. A detailed study on relaxation and thermal behavior of induced radicals in skin part was carried out using EPR spectroscopy. These findings revealed that progressive saturation and thermal characteristics of the induced radicals may be the most suitable parameters to distinguish soybean subjected to radiation dose as low as 0.25 kGy from thermally treated and nonirradiated samples, even after a prolonged period of storage.

Tin oxide nanocrystals: controllable synthesis, characterization, optical properties and mechanistic insights into the formation process

A novel, surfactant-free, solution-phase method has been successfully developed for the synthesis of SnO2 nanocrystals using a solvothermal route. The nanocrystals having average diameters in the range 4–8 nm, have been synthesized by a non-aqueous sol–gel reaction using tin(IV) bis(acetylacetonate)dichloride, [(Sn(acac)2Cl2)] with benzyl alcohol as the reaction medium at 200 °C. The crystal structure, morphology, and sizes of the SnO2 nanocrystals have been determined by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman studies. Raman peaks at 627, 768 cm−1 characteristic of the rutile phase of bulk SnO2 are observed along with broad surface vibration modes in the range 400–600 cm−1. Optical properties of the nanocrystals have been explored by optical absorption and photoluminescence (PL). A blue shift of the optical band gap of the nanocrystals is observed due to size effects. The estimated band gap of the SnO2 nanocrystals from optical absorption data is found to be 3.81 eV. The photoluminescence spectrum showed broad UV as well as visible emission. Based on the GC-MS and carbon-13 NMR analysis of the final reaction solution, a formation mechanism encompassing the ether elimination and solvolysis of acetylacetonate ligand is proposed.

Identification of Irradiated Cashew Nut by Electron Paramagnetic Resonance Spectroscopy

Cashew nut samples were irradiated at gamma-radiation doses of 0.25, 0.5, 0.75, and 1 kGy, the permissible dose range for insect disinfestation of food commodities. A weak and short-lived triplet (g = 2.004 and hfcc = 30 G) along with an anisotropic signal (g perpendicular = 2.0069 and g parallel = 2.000) were produced immediately after irradiation. These signals were assigned to that of cellulose and CO 2 (-) radicals. However, the irradiated samples showed a dose-dependent increase of the central line (g = 2.0045 +/- 0.0002). The nature of the free radicals formed during conventional processing such as thermal treatment was investigated and showed an increase in intensity of the central line (g = 2.0045) similar to that of irradiation. Characteristics of the free radicals were studied by their relaxation and thermal behaviors. The present work explores the possibility to identify irradiated cashew nuts from nonirradiated ones by the thermal behaviors of the radicals beyond the period, when the characteristic electron paramagnetic resonance spectral lines of the cellulose free radicals have essentially disappeared. In addition, this study for the first time reports that relaxation behavior of the radicals could be a useful tool to distinguish between roasted and irradiated cashew nuts.

Application of EPR spectroscopy to identify irradiated Indian medicinal plant products.

UNLABELLED A study of gamma-irradiated Indian medicinal plant products was carried out using electron paramagnetic resonance (EPR) spectroscopy. Improved approaches like high-power measurement, microwave saturation, and thermal behavior of the radicals were explored for detection of irradiation. Aswagandha (Withania somnifera), vairi (Salacia reticulata), amla (Emblica officinalis), haldi (Curcumin longa), and guduchi (Tinospora cordifolia) exhibited a weak singlet at g = 2.005 before irradiation. Aswagandha, immediately after radiation treatment, revealed a complex EPR spectrum characterized by EPR spectrum simulation technique as superposition of 3 paramagnetic centers. One group of signal with organic origin was carbohydrate and cellulose radical and the other was isotropic signal of inorganic origin (g⟂ =2.0044 and g|| = 1.9980). However, other products did not exhibit any radiation-specific signal after irradiation. Power saturation and thermal behavior techniques were not suitable for these products. However, amongst all the 3 approaches, high-power measurement of EPR spectra emerged as a suitable technique in identification of the irradiated aswagandha. PRACTICAL APPLICATION Gamma-irradiation confirms hygienic quality and improves shelf life of food and other products. However, there is a lack of international consensus over considering this as a general application and different regulations are being enforced. EPR is one of the most promising techniques to identify irradiated foodstuffs for regulatory requirements but it has many limitations. Improved approaches based on the EPR technique explained in this study may be useful to identify irradiated products and become beneficial to food regulators and food irradiation enterprises to enhance confidence in irradiation technology.

Thermoluminescence, ESR and x-ray diffraction studies of CaSO4 : Dy phosphor subjected to post preparation high temperature thermal treatment

Thermoluminescence (TL), electron spin resonance (ESR) and x ray diffraction studies of CaSO4 : Dy phosphor subjected to post preparation high temperature treatment were carried out. Analysis of the TL glow curve indicated that the dosimetric glow peak at 240 °C reduces, whereas the low temperature satellite peak increases with the increase in the annealing temperature in the range 650–1000 °C. The influence of the annealing atmosphere on the TL glow curve structure was also observed. Reduction of the photoluminescence intensity of the annealed phosphor indicated that the environment of Dy3+ ions might have undergone some change due to high temperature treatment. Reduction in the ESR signal intensity corresponding to and radicals was observed initially with the increase in the annealing temperaure; subsequently their intensity increased with temperature. Signals due to the radical vanished, when the phosphor was annealed beyond 800 °C. A signal corresponding to SH2− radicals was also observed in the ESR spectra for samples subjected to annealing in the temperature regime 800–1000 °C. XRD of the in situ annealed phosphor showed a change in the unit cell parameters. An endothermic peak at 860 °C in the DTA spectrum was observed.

Alcoholic extraction enables EPR analysis to characterize radiation-induced cellulosic signals in spices.

Different spices such as turmeric, oregano, and cinnamon were γ-irradiated at 1 and 10 kGy. The electron paramagnetic resonance (EPR) spectra of the nonirradiated samples were characterized by a single central signal (g = 2.006), the intensity of which was significantly enhanced upon irradiation. The EPR spectra of the irradiated spice samples were characterized by an additional triplet signal at g = 2.006 with a hyperfine coupling constant of 3 mT, associated with the cellulose radical. EPR analysis on various sample pretreatments in the irradiated spice samples demonstrated that the spectral features of the cellulose radical varied on the basis of the pretreatment protocol. Alcoholic extraction pretreatment produced considerable improvements of the EPR signals of the irradiated spice samples relative to the conventional oven and freeze-drying techniques. The alcoholic extraction process is therefore proposed as the most suitable sample pretreatment for unambiguous detection of irradiated spices by EPR spectroscopy.

An Improved Approach to Identify Irradiated Spices Using Electronic Nose, FTIR, and EPR Spectroscopy

Changes in cumin and chili powder from India resulting from electron-beam irradiation were investigated using 3 analytical methods: electronic nose (E-nose), Fourier transform infrared (FTIR) spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy. The spices had been exposed to 6 to 14 kGy doses recommended for microbial decontamination. E-nose measured a clear difference in flavor patterns of the irradiated spices in comparison with the nonirradiated samples. Principal component analysis further showed a dose-dependent variation. FTIR spectra of the samples showed strong absorption bands at 3425, 3007 to 2854, and 1746 cm(-1). However, both nonirradiated and irradiated spice samples had comparable patterns without any noteworthy changes in functional groups. EPR spectroscopy of the irradiated samples showed a radiation-specific triplet signal at g = 2.006 with a hyper-fine coupling constant of 3 mT confirming the results obtained with the E-nose technique. Thus, E-nose was found to be a potential tool to identify irradiated spices.

Radiation processing: An effective quality control tool for hygienization and extending shelf life of a herbal formulation, Amritamehari churnam

Abstract Amritamehari churnam (AC) is an antidiabetic polyherbal formulation constituting of four herbal medicinal plants namely Phyllanthus emblica, Salacia reticulata, Tinospora cordifolia and Curcuma longa. The feasibility of using gamma irradiation at doses between 2.5 and 10 kGy to reduce microbial load and enhance shelf life of this formulation was investigated. The irradiated and non-irradiated products were stored at room temperature (25–32 °C and 50–85% R.H., 1.5 years). Acceptability of the irradiated product was assessed based on sensory, microbial, physical and chemical attributes as well as their antioxidant status. A dose 7.5 kGy was sufficient to maintain microbial quality within acceptable limit up to 18 months of storage. No significant differences in sensory properties were observed between the non-irradiated and irradiated sample. The applied dose did not cause any significant qualitative and quantitative changes in the chemical constituents, antioxidant activities as well as physical properties when measured by EPR spectroscopy.

Effects of sample pretreatments on EPR spectral characteristics of irradiated sea algae – an advanced approach to identify irradiation status

Different sea algae, such as sea tangle, seaweed and sea mustard, were gamma-irradiated at 1, 5 and 10 kGy. The influence of different sample pretreatments namely, freeze drying (FD), alcoholic extraction (AE), NaOH extraction (NOE) and KOH extraction (KOE) on the paramagnetic characteristics of the sea algae after irradiation was studied using electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra of the non-irradiated samples were characterized by a single central line (g = 2.006). In the case of irradiated sea tangles, two types of paramagnetic species were identified. Sugar-like radicals were observed in the samples subjected to FD and AE. A triplet signal of the cellulose radical was identified after NOE and KOE. In case of seaweed a new radiation-induced paramagnetic centre with a hyperfine coupling (hfc) of 2.3 mT was detected after NOE and KOE. However, AE was found to be an appropriate approach to detect the radiation-induced cellulose signal for irradiated sea mustard. Thus, the importance of different sample pretreatments for EPR spectroscopy to identify and characterize detection markers in irradiated sea vegetables was demonstrated.

Role of flux and co-dopants on the luminescent properties of BaSO4:Eu2+ phosphor synthesized by co-precipitation route

ABSTRACT The thermoluminescent (TL) and photoluminescent (PL) sensitivities of BaSO4:Eu2+ synthesized by co-precipitation technique in aqueous medium were found to enhance drastically with Na2SO4/BaCl2 molar ratio. The above result reported for the first time is explained on the basis of stabilization of defects and Eu impurity by the synergistic effect of combined flux incorporated during co-precipitation and subsequent sintering at high temperatures in reduced atmosphere. The PL sensitivity of BaSO4:Eu2+ made with Na2SO4/BaCl2 ratio of 3 was 40% of the commercial phosphor CaMgSi2O6:Eu2+. In the absence of flux, Eu could not be incorporated into BaSO4 host lattice. The increased conversion efficiency of EuCl3 to Eu2(SO4)3 with increased Na2SO4 content could also be a part of the above stabilization process. Such a synergistic action giving rise to a white colored phosphor powder with high luminescence efficiency could not be achieved by solid-state diffusion reactions involving physical mixtures of BaSO4 and Eu2O3 along with different flux materials. XRD data revealed that the precipitate phase obtained is always BaSO4 irrespective of the Na2SO4/BaCl2 molar ratio. This shows that point defects created during co-precipitation of impurities provided by the flux materials rather than the crystal structure itself influence the luminescence properties of BaSO4:Eu2+. Incorporation of Na+ at Ba2+ sites or the incorporation of interstitial ions would create anion vacancies which could act as electron traps. Oxygen or chlorine interstitial ions could act as hole traps. Increased TL with Na2SO4/BaCl2 molar ratio could occur due to increased number of such electron and hole traps. Though conductivity measurements indicate that precipitation reaction is complete at a molar ratio of Na2SO4/BaCl2 = 1, weight measurements showed for the first time that the quantity of BaSO4 precipitated is less than the expected value at molar ratios <1 and more than the expected value at molar ratios >1. This could be attributed to the instability of xBaSO4·yBaCl2 mixed crystal formed in aqueous medium at low molar ratios and incorporation Na2SO4 into the BaSO4 host forming a stable 0.84BaSO4·0.16Na2SO4 mixed crystal at the molar ratio of 3. BaSO4:Eu2+ exhibits a major TL peak at 235°C with shoulder peaks at 195°C and 290°C. The hole traps corresponding to these peaks were tentatively assigned to 2-hole interstitial traps (either or ) associated, respectively, with or Ba2+ ions and to Cl− associated with Na+ ions. The TL response of 195°C peak increased linearly with gamma dose in the high-dose region while other two peaks increased sublinearly. As a result, the integrated glow curve area increased sublinearly before saturating around 3 kGy.