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Short communication: Application of time-of-flight near infrared spectroscopy to fruits ...

The permeability of a pulsed laser beam into Satsuma mandarin, White grapefruit and Fuji apple was compared by time-of-flight near infrared (ToF-NIR) spectroscopy. In this study, a compact measurement system including a dye-doped plastic laser cavity with a wavelength of 800 nm and an avalanche photodiode were employed. The NIR radiation attenuance (i.e. optical density) in apple was higher than in the citrus fruit. The peak maxima of transmitted radiation of intact Satsuma mandarin increased 130 times more than that of intact grapefruit. Differences in diameter related directly to attenuance. The peak maxima of transmitted radiation of peeled grapefruit increased 250 times more than that of intact grapefruit; however, these increases were not found for Satsuma mandarin or apple. NIR radiation attenuance of the grapefruit peel was greater than for the peel of the other fruits. The incident pulsed laser beam was uniformly scattered in the citrus sample, whereas the scattering condition of the pulsed laser beam in apple might not be uniform because of the presence of core tissue. Thus, while the pulsed laser beam could be transmitted through citrus fruit and apple, the effect of fruit size and peel on the NIR radiation attenuance characteristically varied.

Quality control of agrochemical formulations by diffuse reflectance near infrared spectrometry

A near infrared (NIR)-based methodology has been developed for the determination of 11 pesticides in commercially available formulations. This solvent free, fast and environmentally friendly method was based on the direct measurement of the diffuse reflectance spectra of solid samples, a hierarchical cluster classification and the use of multivariate calibration models to determine each considered active principle in agrochemicals. The proposed partial least squares (PLS) models used for quantification of each compound were built from specific calibration sets composed of nine spectra corresponding to triplicate measurements of a single well characterised commercial sample and two additional doped (under- and over- dosed) samples. Different formulations and commercial samples were employed as validation sets. Data obtained by PLS/NIR were comparable with results found by reference liquid chromatography procedures. For bensulfuron, buprofezin and metalaxyl determination, the information in the spectral range between 1000 nm and 2640 nm of the zero order reflectance spectra was used. For chlorsulfuron, cyromazine, daminozide, diuron, fenoxycarb, iprodione, procymidone and tricyclazole determination, the information of the first order derivative spectra in the range between 1000 nm and 2640 nm was used. In both cases, a linear removed correction was applied as data pre-treatment. The developed PLS/NIR method can be applied directly to solid samples without using any solvent or sample pre-treatment and thus any contact between the operator and toxic reagents is avoided providing a safe and environmentally acceptable analytical methodology.

Estimation of hexenuronic acids and kappa number in kraft pulps of Eucalyptus globulus by ...

Fourier transformed near infrared (FT-NIR) spectroscopy was evaluated as an analytical tool for monitoring residual lignin, kappa number and hexenuronic acids (HexA) content in kraft pulps of Eucalyptus globulus. Sets of pulp samples were prepared under different cooking conditions to obtain a wide range of compound concentrations that were characterised by conventional wet chemistry analytical methods. The sample group was also analysed using FT-NIR spectroscopy in order to establish prediction models for the pulp characteristics. Several models were applied to correlate chemical composition in samples with the NIR spectral data by means of PCR or PLS algorithms. Calibration curves were built by using all the spectral data or selected regions. Best calibration models for the quantification of lignin, kappa and HexA were proposed presenting R² values of 0.99. Calibration models were used to predict pulp titers of 20 external samples in a validation set. The lignin concentration and kappa number in the range of 1.4–18% and 8–62, respectively, were predicted fairly accurately (standard error of prediction, SEP 1.1% for lignin and 2.9 for kappa). The HexA concentration (range of 5–71 mmol kg^–1 pulp) was more difficult to predict and the SEP was 7.0 mmol kg^–1 pulp in a model of HexA quantified by an ultraviolet (UV) technique and 6.1 mmol kg^–1 pulp in a model of HexA quantified by anion-exchange chromatography (AEC). Even in wet chemical procedures used for HexA determination, there is no good agreement between methods as demonstrated by the UV and AEC methods described in the present work. NIR spectroscopy did provide a rapid estimate of HexA content in kraft pulps prepared in routine cooking experiments.

Detection of factors affecting the acquisition of visible-near infrared fibre-optic probe ...

Near infrared (NIR) spectroscopic analysis of sliced and packaged dry fermented sausages was standardised in order to identify the main sources of error during the spectrum acquisition process. The aim of the study was to ascertain how many of the apparent critical factors (ACFs) were really significant key factors for spectrum acquisition. Using a 2_III^7–4, Plackett–Burman experimental design, and enhancing resolution via a fold-over such as 2_IV^7–3, seven ACFs were investigated to determine their effect on root mean square (RMS) values obtained using 15 combinations of spectral range and mathematical pre-treatment. The results showed that for the on-line control of products of this type, the spectrum acquisition process was not affected by the ACFs studied when using the whole spectral range of the instrument (400–2500 nm), with the first derivative and either of the scatter corrections examined here, since in these conditions control of factor variability proved unnecessary.

Prediction of chemical composition of sugar beet pulp by near infrared reflectance spectroscopy

The feasibility of near infrared (NIR) reflectance spectroscopy to estimate the chemical composition of dehydrated sugar beet pulp was examined in the present study. Seventy three samples from different processing plants were analysed for dry matter (DM), crude protein (CP), neutral detergent fibre (NDF) and soluble (NDSF) fibre, according to the conventional chemical methods. The parameters predicted by NIR spectroscopy with the highest accuracy were DM (R² = 0.97; SE_CV = 5.69 g kg^–1 FM) and CP (R² = 0.90; SE_CV = 3.81 g kg^–1 DM) content. Furthermore, it was demonstrated that NIR technology can be used to discriminate samples of sugar beet pulp manufactured by different chemical procedures.

Quantification of rosmarinic acid levels by near infrared spectroscopy in laboratory culture ...

A method for the rapid quantification of rosmarinic acid (RA) in tissues of spearmint using near infrared (NIR) spectroscopy was developed by correlating with the results of methanol extracts analysed on an HPLC photo-diode array (PDA) system. NIR and HPLC analyses performed on over 500 samples were used to develop an NIR analytical algorithm. Applying this algorithm resulted in very good calibration statistics for the prediction of RA concentrations in dried powdered samples prepared from the cultured mints (r² = 0.90, SEP = 3.1 RPD = 2.6). NIR can be used to rapidly and accurately quantitate the levels of this secondary metabolite in plant samples. High positive correlations occur between CO₂ levels and spearmint plantlet growth (fresh weight), morphogenetic responses (leaves, roots and shoots) and production of the secondary metabolite rosmarinic acid.

Prediction of total soluble solid content in intact and cut melons and watermelons using near ...

There is currently a growing tendency for fruit to be classified and marketed in accordance with quality criteria. One parameter used to evaluate quality in melons and watermelons is total soluble solid content, measured by invasive analytical methods which are incompatible with current quality-assurance requirements for individual pieces of fruit. Use of near infrared (NIR) reflectance spectroscopy as a non- destructive technique for measuring total soluble solid content could therefore be of considerable interest to the fruit and vegetable sector. The present study assesses the use of a NIR diode array spectrometer for estimating total soluble solid content (°Brix) in intact and cut melons and watermelons. NIR calibration models were developed using two sets for each fruit, a 2006 set (N = 158) and a 2007 set (N = 415) for melon samples and a 2006 set (N = 77) and 2007 set (N = 183) for watermelon samples, grown in El Ejido (Almeria, Spain). The predictive ability of the calibrations developed were greater for cut fruit (SECV = 0.60 °Brix, ^r₂ = 0.88, RPD = 2.94 in melons and SECV = 0.49 °Brix, ^r₂ = 0.85, RPD = 2.50 in watermelons) than for intact fruit (SECV = 0.98 �Brix, ^r₂ = 0.76; RPD = 2.05 in melons and SECV = 0.93 °Brix, ^r₂ = 0.65, RPD = 1.69 in watermelons). This study demonstrates the value of NIR spectroscopy for grading cut �melons and water�melons, intact melons and �possibly intact watermelon fruits into categories of high, medium and low levels of �sweetness.

An evaluating technique for variety compatibility of fruit applied to a near infrared Brix ...

In a practical near infrared (NIR) sweetness sorting facility, there is a high possibility that the variety of incoming fruit will be different from the one(s) used to develop a calibration model. In this kind of situation, significant bias could occur and result in a high price difference. In this work, a method to identify whether the pre-installed calibration models could be used to predict Brix values of the unknown samples or not was established. Two kinds of calibration model for Brix determination of nectarines were examined, one developed from spectra of the single nectarine variety called Big Bang Maillar� (BB), the other developed from spectra of two nectarine varieties, BB and Nectaross (NT). Another variety called Sweet Red (SR) was used to demonstrate the situation of an unknown sample or a different variety. For the general biases evaluation, significant biases occurred in the SR samples whether the prediction was done using the BB calibration (bias = –6.74°Brix) or the BB+NT calibration (bias = –3.09°Brix). A survey using score plots of principle component analysis (PCA) indicated that the characteristics of the BB and the SR samples were quite different from each other, while the NT samples were located in between. Even though the trend of differences between the PCA scores of the three varieties could be observed, a clear classification result could not be obtained. Another classification attempt was made using soft independent model for classification analogy (SIMCA). For each calibration (BB and BB+NT), a SIMCA model was developed using the samples used to develop the calibration model. A calculation was performed to evaluate whether the unknown samples (BB, NT and SR) were in the same class as the calibration sample or not. It was found that, in the case of the single variety calibration where the SIMCA model was also developed from the single variety (BB), clear identification of unfitted samples could be obtained with classification accuracy more than 95% (false negative 0%). However, in the case of the two varieties calibration, the use of a SIMCA box developed from two varieties would make the in-class distance become too wide and this reduced the classification accuracy of unfitted samples (false negatives = 74%). The solution was to develop two SIMCA boxes, one for BB and one for NT, then examine the compatibility of unknown samples twice. Using this technique, satisfactory classification results with false negatives of 10% could be obtained.

Near infrared spectroscopy of the smithsonite minerals

The importance of NIR spectroscopy has been successfully demonstrated in the present study of smithsonite minerals. The fundamental observations in the NIR spectra, in addition to the anions of OH^– and CO₃^2–, are Fe and Cu in terms of cation content. These ions exhibit broad absorption bands ranging from 13000 cm^–1 to 7000 cm^–1 (770 nm to 1430 nm). One broad diagnostic absorption feature centred at 9000 cm^–1 (1110 nm ) is the result of ferrous ion spin allowed transition, (⁵T_2g → ⁵E_g). The splitting of this band (> 1200 cm^–1) is a common feature in all the spectra of the studied samples. The light green coloured sample from Namibia show two Cu(II) bands in NIR at 8050 cm^–1 and 10,310 cm^–1 (1240 nm and 970 nm ) assigned to ²B_1g → ²A_1g and ²B_1g → ²B_1g transitions. The effects of structural cation substitution (Ca²⁺, Fe²⁺, Cu²⁺, Cd²⁺ and Zn²⁺) on band shifts in the electronic spectra1 region of 11,000 cm^–1 to 7500 cm^–1 (910 nm to 1330 nm) and vibrational modes of OH^– and CO₃^2– anions in the 7300 cm^–1 to 4000 cm^–1 (1370 nm to 2500 nm ) region were used to distinguish between the smithsonites.