Haroon Elrasheid Tahir

Discrimination of honeys using colorimetric sensor arrays, sensory analysis and gas chromatography techniques.

Aroma profiles of six honey varieties of different botanical origins were investigated using colorimetric sensor array, gas chromatography-mass spectrometry (GC-MS) and descriptive sensory analysis. Fifty-eight aroma compounds were identified, including 2 norisoprenoids, 5 hydrocarbons, 4 terpenes, 6 phenols, 7 ketones, 9 acids, 12 aldehydes and 13 alcohols. Twenty abundant or active compounds were chosen as key compounds to characterize honey aroma. Discrimination of the honeys was subsequently implemented using multivariate analysis, including hierarchical clustering analysis (HCA) and principal component analysis (PCA). Honeys of the same botanical origin were grouped together in the PCA score plot and HCA dendrogram. SPME-GC/MS and colorimetric sensor array were able to discriminate the honeys effectively with the advantages of being rapid, simple and low-cost. Moreover, partial least squares regression (PLSR) was applied to indicate the relationship between sensory descriptors and aroma compounds.

Rapid prediction of phenolic compounds and antioxidant activity of Sudanese honey using Raman and Fourier transform infrared (FT-IR) spectroscopy

Fourier transform infrared with attenuated total reflectance (FTIR-ATR) and Raman spectroscopy combined with partial least square regression (PLSR) were applied for the prediction of phenolic compounds and antioxidant activity in honey. Standards of catechin, syringic, vanillic, and chlorogenic acids were used for the identification and quantification of the individual phenolic compounds in six honey varieties using HPLC-DAD. Total antioxidant activity (TAC) and ferrous chelating capacity were measured spectrophotometrically. For the establishment of PLSR model, Raman spectra with Savitzky-Golay smoothing in wavenumber region 1500-400cm-1 was used while for FTIR-ATR the wavenumber regions of 1800-700 and 3000-2800cm-1 with multiplicative scattering correction (MSC) and Savitzky-Golay smoothing were used. The determination coefficients (R2) were ranged from 0.9272 to 0.9992 for Raman while from 0.9461 to 0.9988 for FTIT-ART. The FTIR-ATR and Raman demonstrated to be simple, rapid and nondestructive methods to quantify phenolic compounds and antioxidant activities in honey.

Rapid Determination of Antioxidant Compounds and Antioxidant Activity of Sudanese Karkade (Hibiscus sabdariffa L.) Using Near Infrared Spectroscopy

The extraction conditions applied in destructive analysis of Hibiscus sabdariffa L. (Hs) matrices before the measurement of antioxidant compounds may reduce their activities during isolation and purification due to decomposition. Hence, near infrared spectroscopic system was applied to determine these compounds. The calibration models developed by using partial least squares regression (PLSR) with 48 Hs samples and 24 unknown samples were used to confirm the robustness of the developed model. The results of calibration models effectively allowed the determination of the concentrations of total phenol content (TPC), total flavonoid content (TFC), total antioxidant content (TAC), ferric reducing antioxidant power (FRAP), and 1,1-diphenyl-2-picrylhydrazyl (DPPH) with high correlation coefficients (0.85–0.91) and small standard error of cross-validation (RMSECV) ranged from 0.08 to 0.33. The prediction capacity (RPD) for TPC, TFC, TAC, FRAP, and DPPH ranged from 3.30 to 8.25, thus demonstrating that the near infrared spectroscopic (NIRS) equations developed were applicable to unknown samples. This study demonstrates that NIRS can be considered as a fast tool for the nondestructive determination of antioxidant compounds (phenolics and flavonoids) and antioxidant activity of the Hs.

Rapid and wide-range determination of Cd(II), Pb(II), Cu(II) and Hg(II) in fish tissues using light addressable potentiometric sensor

A rapid and wide-range method, based on light addressable potentiometric sensor (LAPS), is introduced into determination of Cd(II), Pb(II), Cu(II) and Hg(II) in fish tissues. A compact LAPS module is prepared by integrating four LAPS chips specifically sensitive to target elements. Its responses in digestions from various settings are investigated to find suitable factors. Analytical properties of this method are evaluated in consequent experiments under optimized conditions. Measurement range for each target element exceeds 0.1 to 1000mgL-1, and response time is less than 10s. Accuracy, precision and selectivity of the proposed method are also well defined in measurements. It is successively performed to detect the target elements in real fish samples from 4 species, and obtained results are consistent with certified method.

Bacteria counting method based on polyaniline/bacteria thin film

A simple and rapid bacteria counting method based on polyaniline (PANI)/bacteria thin film was proposed. Since the negative effects of immobilized bacteria on the deposition of PANI on glass carbon electrode (GCE), PANI/bacteria thin films containing decreased amount of PANI would be obtained when increasing the bacteria concentration. The prepared PANI/bacteria film was characterized with cyclic voltammetry (CV) technique to provide quantitative index for the determination of the bacteria count, and electrochemical impedance spectroscopy (EIS) was also performed to further investigate the difference in the PANI/bacteria films. Good linear relationship of the peak currents of the CVs and the log total count of bacteria (Bacillus subtilis) could be established using the equation Y=-30.413X+272.560 (R(2)=0.982) over the range of 5.3×10(4) to 5.3×10(8)CFUmL(-1), which also showed acceptable stability, reproducibility and switchable ability. The proposed method was feasible for simple and rapid counting of bacteria.

Aroma profile and sensory characteristics of a sulfur dioxide-free mulberry (Morus nigra) wine subjected to non-thermal accelerating aging techniques

The present study was undertaken to assess accelerating aging effects of high pressure, ultrasound and manosonication on the aromatic profile and sensorial attributes of aged mulberry wines (AMW). A total of 166 volatile compounds were found amongst the AMW. The outcomes of the investigation were presented by means of geometric mean (GM), cluster analysis (CA), principal component analysis (PCA), partial least squares regressions (PLSR) and principal component regression (PCR). GM highlighted 24 organoleptic attributes responsible for the sensorial profile of the AMW. Moreover, CA revealed that the volatile composition of the non-thermal accelerated aged wines differs from that of the conventional aged wines. Besides, PCA discriminated the AMW on the basis of their main sensorial characteristics. Furthermore, PLSR identified 75 aroma compounds which were mainly responsible for the olfactory notes of the AMW. Finally, the overall quality of the AMW was noted to be better predicted by PLSR than PCR.

Near-infrared spectroscopy coupled chemometric algorithms for prediction of antioxidant activity of black goji berries (Lycium ruthenicum Murr.)

In this study, near-infrared (NIR) spectroscopy coupled with partial least-squares (PLS) regression and various efficient variable selection algorithms, synergy interval-PLS (Si-PLS), backward interval PLS (Bi-PLS) and genetic algorithm-PLS (GA-PLS) were applied comparatively for the prediction of antioxidant activity in black wolfberry (BW). The eight assays were used for quantification of antioxidant content. The developed models were assessed using correlation coefficients (R2) of the calibration (Cal.) and prediction (Pre.); root mean square error of prediction, RMSEP; standard Error of Cross-Validation, RMSECV and residual predictive deviation, RPD. The performance of the built model greatly improved by the application of Si-PLS, Bi-PLS and GA-PLS compared with full spectrum PLS. The R2 values determined for calibration and prediction set ranged from 0.8479 to 0.9696 and 0.8401 to 0.9638, respectively. These findings revealed that NIR spectroscopy combined with chemometric algorithms can be used for quantification of antioxidant activity in BW samples.

Characterization of colorimetric sensor arrays by a multi-spectral technique

A new method based on a multi-spectral technique was proposed to characterize the signal of colorimetric sensor arrays for gas detection. Firstly, the characteristic wavelengths, which are most relevant to the detected substance, were extracted from the hyperspectral information of the colorimetric sensor arrays. Then, narrowband filters with the corresponding central wavelengths were selected to isolate the effective signal of the sensor arrays. In this study, ammonia (NH3) was taken as an example to test the performance of the proposed multi-spectral method. Prediction of NH3 concentration based on the hyperspectral method and normal tri-color (R/G/B) method was also performed for comparison. Compared with the tri-color method, the correlation coefficient for the testing set (Rt) based on the multi-spectral method increased from 0.902 to 0.976, root mean squared error of prediction (RMSEP) decreased from 1.213 to 0.548, and residual predictive deviation for the testing set (RPDt) increased from 2.903 to 6.151, which means that the results were notably improved both in accuracy and stability. Furthermore, the multi-spectral method possesses the advantages of low cost, easy operation and greatly reduced data size. The proposed multi-spectral method could be used to characterize the signal of colorimetric sensor arrays for gas detection.

A dual-mode sensor for colorimetric and fluorescent detection of nitrite in hams based on carbon dots-neutral red system

Nitrite residue in hams was detected by a fluorescent and colorimetric sensor based on carbon dots (C-dots) and neutral red (NR). C-dots with green fluorescence was synthesized by a microwave-assisted method. This novel sensor was fabricated by C-dots as donors and NR as acceptors. The presence of nitrite led to decrease of absorbance and increase of fluorescence. Colorimetric and fluorescent methods for nitrite detection were developed with excellent correlation coefficients (R2 = 0.995 and 0.991) and low limits of detection (196 nM and 0.518 nM). Moreover, nitrite residue in seven types of ham was detected by the colorimetric and fluorescent methods which were verified by a standard method. The results obtained by the proposed method were comparable and agree with that of the Griess-based method (relative errors<5%). C-dots-NR system as a sensor has a potential application for nitrite detection in hams to monitor its quality and safety.

Preparation of conducting polyaniline/protoporphyrin composites and their application for sensing VOCs

Polyaniline/protoporphyrin nanocomposites were prepared via a simple chemical method in the acidic suspension of protoporphyrin. The scanning electron microscope images revealed that the polyaniline/protoporphyrin composites exhibited an interesting nanosheet structure decorated with nanoparticles, which is rather different with the usual nanofiber morphology of polyaniline. The formation of the nanosheet structure is because protoporphyrin molecules may exist as a bilayer form at low pH, which is similar with the phospholipid bilayer in membranes of cells. To demonstrate the application potential of the composites, the sensing performance of the composites was tested when exposed to four volatile organic compounds, including trimethylamine, triethylamine, ethanol, and ethyl acetate. The composites exhibited highest response value (S) of 39.482 toward trimethylamine, and fast response time of 2-4 s toward trimethylamine and triethylamine. The outstanding sensing performance showed that the prepared composites had great application potential in electronic noses system in further work.