Lignin characterization by acetylation procedures

The amount of the total hydroxyl content of lignin is of great importance in the formulation of a lignin based polyurethane system since it allows the quantity of the polyisocyanate counterpart within the right stoichiometry. In this work, the reliability of an acetylation procedure, regarding the determination of total hydroxyl content of a commercial kraft lignin, was studied. Lignin was acetylated using acetic anhydride reagent in solution in pyridine and the recovered acetylated samples were analysed by FTIR using KBr pellets. The experimental variables investigated were: reaction time, reaction temperature, composition of the acetylation reagent, presence of a catalyst and drying process of the acetylated samples. Within this work, the obtained results indicate that acetylation was incomplete for all the studied conditions, resulting in an unreliable total hydroxyl determination and shows the limitation of this technique. This observation is in accordance with recent published works (see, for example, Gosselink et al., 2004) and could justify the lack of agreement among some published experimental results concerning interlaboratory analysis

Monitoring of lignin-based polyurethane synthesis by FTIR-ATR

FTIR (Fourier Transform Infrared Spectroscopy), working in ATR (Attenuated Total Reflectance) mode was applied to study the formation of lignin-based polyurethanes. Although some studies related to the use of lignins in polyurethane synthesis, are available in literature, still persist a gap for a systematic study of this kind of systems involving the measurement of kinetic data, optimization and modelling of the process. This methodology allows the test of different formulations at a scale of 3-5 grams, considering several process variables: temperature, NCO/OH ratio, type and MW of the polyol, type of isocyanate, type and weight content of lignin. This work aims to describe the methodology used to perform the FTIR experiments by presenting a case study

Monitoring of lignin-based polyurethane synthesis by FTIR-ATR

FTIR-ATR (Fourier Transform Infrared Spectroscopy working in the mode of Attenuated Total Reflectance) was applied to study the formation of lignin-based polyurethanes. Although some studies related to the use of lignin in polyurethane synthesis, are available in literature, still persist a gap for a systematic study of this kind of systems, involving the measurement of kinetic data, modelling and optimization of the polymerization process. The present methodology allows the test of different formulations at a scale of 3–5 g, considering several process variables: temperature, NCO/OH ratio, type and average molecular weight of the polyol, type of isocyanate, type and weight content of lignin. This work aims to describe the methodology used to perform the FTIR experiments by presenting a case study. The polyurethane samples have been prepared starting with 4,4′-methylene-diphenylene isocyanate (MDI), policaprolactonediol (PCL) of three different average molecular weights (1000, 750 and 400) and a commercial lignin (Indulin AT from Meadwestvaco) at different weight contents (10, 15, 20 and 25%). The results obtained in this work point out for the validation of the proposed experimental technique and confirm that lignin was incorporated in the final three-component polyurethane sample by chemical reaction with isocyanates, i.e., formation of urethane linkages

Rigid polyurethane foams from lignin based polyols

Rigid polyurethane (RPU) foams were synthesized using lignin-based polyols obtained by an oxypropylation process. Alcell, Indulin AT, Curan 27-11P and Sarkanda lignins have been oxypropylated using formulations deduced from an optimization study with Alcell. L/PO/C (ratio between lignin, PO and catalyst content) of 30/70/2 and 20/80/5 were used to obtain the desired polyols. The resulting RPU foams were characterized in terms of density, mechanical properties, conductivity and morphology. All Sarkanda lignin based polyols and the 30/70/2 Curan 27-11P polyol were found inadequate for RPU formulations. Alcell and Indulin AT based polyols and the 20/80/5 Curan 27-11P polyol resulted in RPU foams with properties very similar to those obtained from conventional commercial polyols. RPU foams produced with the 30/70/2 Alcell and the 30/70/2 Indulin AT polyols exhibited improved properties compared with those from 20/80/5 based formulations.Foundation for Science and Technology (grant SFRH/BD/18415/2004) and the French-Portuguese Scientific Cooperation Programme (action F-32/08

Lignin-based polyurethane materials

Four technical lignins (Alcell, Indulin AT, Sarkanda and Curan 27-11P) were used as macromonomers in the synthesis of polyurethane materials following two global approaches. In the first one Alcell and Indulin AT lignins were used directly as co-monomers in combination with a linear polycaprolactone (PCL) in order to produce polyurethane elastomers where lignin content varied between 10 and 25% (w/w) with respect to polyol mixture (PCL+lignin). The thermomechanical properties of the resulting materials were determined by dynamical mechanical analysis (DMA), differential scanning calorimetry (DSC) and swelling tests. In lignin-based elastomers Indulin AT showed to be more efficiently incorporated in the polyurethane network compared with Alcell lignin. Elastomers prepared with Indulin AT lignin exhibited a cross-linking density and storage modulus (rubbery plateau) higher than those of Alcell lignin-based counterpart and a lower soluble fraction. For both Alcell and Indulin AT based elastomers the glass transition temperature increased and extended over a wide temperature range with the increase of lignin content. The second approach consisted of producing rigid polyurethane foams (RPU) using ligninbased polyols obtained after chemical modification by an oxypropylation procedure. Two polyol formulations (20/80 and 30/70, in what concerns the weight ratios between lignin and propylene oxide, PO), were used in RPU formulations and their content varied from 0 to 100% (w/w with respect to a commercial polyol, used as a reference). The resulting RPU foams were characterized in terms of density, mechanical properties, conductivity and morphology. The prepared RPU foams with lignin-based polyols presented properties, very similar to those obtained from conventional commercial polyols. RPU foams prepared with 30/70 polyols exhibited improved properties comparatively to those arising from 20/80 formulations. Exceptions were however detected in RPU foams prepared with all Sarkanda lignin based polyols and Curan 27-11P 30/70 formulation, which were found to be inadequate for RPU formulation.Foundation for Science and Technology (grant SFRH/BD/18415/2004) and French-Portuguese Scientific Cooperation Programme (action F- 32/08)

The use of electronic nose as alternative non-destructive technique to discriminate flavored and unflavored olive oils

Cv. Arbequina extra virgin olive oils (EVOO) were flavored with cinnamon, garlic, and rosemary and characterized. Although flavoring significantly affected the physicochemical quality parameters, all oils fulfilled the legal thresholds for EVOO classification. Flavoring increased (20 to 40%) the total phenolic contents, whereas oxidative stability was dependent on the flavoring agent (a slight increase for rosemary and a decrease for cinnamon and garlic). Flavoring also had a significant impact on the sensory profiles. Unflavored oils, cinnamon, and garlic flavored oils had a fruity-ripe sensation while rosemary flavored oils were fruity-green oils. Fruit-related sensations, perceived in unflavored oils, disappeared with flavoring. Flavoring decreased the sweetness, enhanced the bitterness, and did not influence the pungency of the oils. According to the EU regulations, flavored oils cannot be commercialized as EVOO. Thus, to guarantee the legal labelling requirement and to meet the expectations of the market-specific consumers for differentiated olive oils, a lab-made electronic nose was applied. The device successfully discriminated unflavored from flavored oils and identified the type of flavoring agent (90 ± 10% of correct classifications for the repeated K-fold cross-validation method). Thus, the electronic nose could be used as a practical non-destructive preliminary classification tool for recognizing olive oils’ flavoring practice.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) for financial support by national funds FCT/MCTES to CIMO (UIDB/00690/2020) and to CEB (UIDB/04469/2020) units and to the Associate Laboratory SusTEC (LA/P/0007/2020), as well as to BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte 2020—Programa Operacional Regional do Norte. Nuno Rodrigues thanks to National funding by FCT—Foundation for Science and Technology, P.I., through the institutional scientific employment program-contractinfo:eu-repo/semantics/publishedVersio

Evaluation of the effect of extracted time conditions on the phenolic content of olive pastes from cv. Arbequina and discrimination using a lab-made potentiometric electronic tongue

The present study investigated the effect of malaxation times (Mt) (0, 15, 30, 45 and 60 min), during the industrial extraction of cv. Arbequina oils at 25 °C on total phenolic content of olive pastes. Additionally, the possibility of applying a lab-made potentiometric electronic tongue (E-tongue), comprising 40 lipid/polymer sensor membranes with cross sensitivity, to discriminate the olive pastes according to the Mt, was evaluated. The results pointed out that the olive pastes’ total phenolic contents significantly decreased (p-value < 0.001, one-way ANOVA) with the increase of the Mt (from 2.21 ± 0.02 to 1.99 ± 0.03 g gallic acid equivalents/kg olive paste), there being observed a linear decreasing trend (R-Pearson = −0.910). These findings may be tentatively attributed to the migration of the phenolic compounds from the olive pastes to the extracted oil and water phases, during the malaxation process. Finally, the E-tongue signals, acquired during the analysis of the olive pastes’ methanolic extracts (methanol:water, 80:20 v/v), together with a linear discriminant analysis (LDA), coupled with a simulated annealing (SA) algorithm, allowed us to establish a successful classification model. The E-tongue-LDA-SA model, based on 11 selected non-redundant sensors, allowed us to correctly discriminate all the studied olive pastes according to the Mt (sensitivities of 100% for training and leave-one-out cross-validation). The satisfactory performance of the E-tongue could be tentatively explained by the known capability of lipid/polymeric sensor membranes to interact with phenolic compounds, through electrostatic interactions and/or hydrogen bonds, which total content depended on the Mt.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) for financial support by national funds FCT/MCTES to CIMO (UIDB/00690/2020), to CEB (UIDB/04469/2020), to REQUIMTE-LAQV (UIDB/50006/2020) and to BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020—Programa Operacional Regional do Norte. Ítala Marx acknowledges the Ph.D. research grant (SFRH/BD/137283/2018) provided by FCT. Nuno Rodrigues thanks the National funding by FCT-Foundation for Science and Technology, P.I., through the institutional scientific employment program contract.info:eu-repo/semantics/publishedVersio

Olive oils qualitative evaluation using a potentiometric electronic tongue: a review of practical applications

Olive oil is a food product highly prone to fraud, including mislabeling of olive oil commercial category, geographical or olive cultivar origin. Several analytical techniques have been reported to assess olive oil quality, authenticity as well as to detect possible adulterations, namely gas-, liquid- and mass-spectrometry chromatography, DNA and spectroscopy based methods. However, in general, these techniques require expensive pre-sample treatments, are time-consuming and need cost equipments and high skilled technicians. So, fast and more cost-effective methods are still needed and their development a challenge. Among these, electrochemical sensors have been proposed within this field of research, including both voltammetric and potentiometric electronic noses and electronic tongues, individually or as a fused methodology. In this study it is intended to review some of the most recent applications described in the literature including those of the research team regarding the application of a potentiometric electronic tongue, containing cross-sensitive lipidic membranes, to discriminate single-cultivar extra-virgin olive oils by cultivar or sensory intensity, showing its range of applicability and the possibility of using this artificial taste sensor as a complementary/alternative methodology for olive oil sensory analysis.info:eu-repo/semantics/publishedVersio

An electronic nose as a non-destructive analytical tool to identify the geographical origin of portuguese olive oils from two adjacent regions

The geographical traceability of extra virgin olive oils (EVOO) is of paramount importance for oil chain actors and consumers. Oils produced in two adjacent Portuguese regions, Côa (36 oils) and Douro (31 oils), were evaluated and fulfilled the European legal thresholds for EVOO categorization. Compared to the Douro region, oils from Côa had higher total phenol contents (505 versus 279 mg GAE/kg) and greater oxidative stabilities (17.5 versus 10.6 h). The majority of Côa oils were fruity-green, bitter, and pungent oils. Conversely, Douro oils exhibited a more intense fruity-ripe and sweet sensation. Accordingly, different volatiles were detected, belonging to eight chemical families, from which aldehydes were the most abundant. Additionally, all oils were evaluated using a lab-made electronic nose, with metal oxide semiconductor sensors. The electrical fingerprints, together with principal component analysis, enabled the unsupervised recognition of the oils’ geographical origin, and their successful supervised linear discrimination (sensitivity of 98.5% and specificity of 98.4%; internal validation). The E-nose also quantified the contents of the two main volatile chemical classes (alcohols and aldehydes) and of the total volatiles content, for the studied olive oils split by geographical origin, using multivariate linear regression models (0.981 < R2 < 0.998 and 0.40 < RMSE < 2.79 mg/kg oil; internal validation). The E-nose-MOS was shown to be a fast, green, non-invasive and cost-effective tool for authenticating the geographical origin of the studied olive oils and to estimate the contents of the most abundant chemical classes of volatiles.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) for financial support by national funds FCT/MCTES (PIDDAC) to CIMO (UIDB/00690/2020 and UIDP/00690/2020), to CEB (UIDB/04469/2020) and to the Associate Laboratory SusTEC (LA/P/0007/2020). The authors are also grateful to the “Project OLIVECOA—Centenarian olive trees of Côa Valley region: rediscovering the past to valorize the future” (ref. COA/BRB/0035/2019), financed by FCT (Portugal). Nuno Rodrigues thanks the National funding by FCT- Foundation for Science and Technology, P.I., through the institutional scientific employment program-contract.info:eu-repo/semantics/publishedVersio