Browsing by Author "Pereira, H."
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- Chemical changes of heat treated pine and eucalypt wood monitored by FTIRPublication . Esteves, B.; Velez Marques, A.; Domingos, I.; Pereira, H.A hardwood, Eucalyptus globulus Labill., and a softwood Pinus pinaster Aiton., were heat treated at temperatures between 170 and 210ºC in an oven and in an autoclave. The samples were pre-extracted with dichloromethane, ethanol and water and ground prior to Fourier Transform Infrared (FTIR) spectroscopic analysis. The heat treatment caused significant changes in the chemical composition and structure of wood, in lignin and polysaccharides. Hemicelluloses were the first to degrade as proved by the initial decrease of the 1730 cm-1 peak due to the breaking of acetyl groups in xylan. Hardwood lignin changed more than softwood lignin, with a shift of maximum absorption from 1505 cm-1 to approximately 1512 cm-1 due to decrease of methoxyl groups, loss of syringyl units or breaking of aliphatic side-chains. The macromolecular structure becomes more condensed and there is a clear increase of non-conjugated (1740 cm-1) in relation to conjugated groups (1650 cm-1). However, the changes induced by the thermal treatment are difficult to monitor by FTIR spectroscopy due to the different chemical reactions occurring simultaneously.
- Evaluation of FT - Raman and FTIR – ATR spectroscopy for the quality evaluation of Lavandula spp. HoneyPublication . Anjos, O.; Guiné, Raquel; Santos, A. J. A.; Paula, V. B.; Pereira, H.; Estevinho, L. M.Mono fl oral Lavandula spp. honey is very appre - ciated by consumers due to its characteristic and pleasant aroma and fl avor. Given the economic importance of this type of honey, it is important to develop a rapid and non - expensive methodology that allows certifying its quality. In this context, this study aimed to compare the applic - ability and accuracy of FTIR - ATR and FT - Raman techni - ques for the quality evaluation of Lavandula spp. honey. Calibration models, with PLS regression models, were obtained for both methodologies concerning the following parameters: total acidity, reducing sugars, hidroximetil - furfural ( HMF ) , electrical conductivity, ash, proline con - tent, diastase activity, apparent sucrose, total fl avonoids, and total phenolic contents. The calibration models had high regression coe ffi cients, r 2 ( FTIR - ATR: 0.965 – 0.996; FT - Raman: 0.983 – 0.999 ) , high ratios of performance to deviation, RPD ( FTIR - ATR: 5.4 – 15.7; FT - Raman: 7.6 – 53.7 ) , and low root mean square errors ( RMSEs; FTIR - ATR: 0.005 – 3.0; FT - Raman: 0.004 – 1.02 ) . These results corrobo - rate the potentiality of FTIR - ATR and FT - Raman for quality evaluation and evaluation of the chemical properties of Lavandula spp. honey even though FT - Raman technique provided more accurate models.
- Pulping yield and delignification kinetics of heartwood and sapwood of maritime pinePublication . Esteves, Bruno; Gominho, J.; Rodrigues, J.C.; Miranda, I.; Pereira, H.In maritime pine (Pinus pinaster Ait.), heartwood represents a substantial part of the tree stem at final harvest age (80 years) corresponding to 42% at the base of the stem wood diameter and decreasing upward. The rate of heartwood formation was estimated at 0.35 rings/year, beginning at 18 years of age. Differences in the chemical composition between heartwood and sapwood were mainly in the extractives, 19.7% and 5.8%, respectively. The lignin content was 23.1% and 24.5% in the heartwood and sapwood, respectively. Pulping yield of the heartwood was lower than that of the sapwood (40.0% vs. 49.7%) and was negatively correlated with the extractives content. Extraction of heartwood prior to pulping increased the pulp yield and the delignification (lower residual lignin in pulps). Pulping kinetics showed lower yields for heartwood at all pulping stages, the difference occurring especially in the initial reaction phase. However, delignification rate constants were similar for heartwood and sapwood (3.1 1022 min21 and 2.7 1022 min21 for the main delignification phase for sapwood and heartwood, respectively), with a lower activation energy for sapwood (68.3 vs. 90.0kJ.mol21). The presence of heartwood decreases the raw-material quality for pulping and this should be taken into account when harvesting trees for pulping processes.