Margarida Moldão-Martins

Supercritical CO2 extraction of Thymus zygis L. subsp. sylvestris aroma

The supercritical fluid extraction (SFE) of aroma compounds from Thyme (Thymus zygis L. subsp. sylvestris) was studied. Extraction was conducted at different temperatures (300–323 K) and pressures (8–20 MPa). The extraction time was varied between 40 and 100 min. The study was carried out according to the response surface methodology (RSM). The extracts were analyzed by gas chromatography (GC) and gas chromatography–mass spectrometry (GC-MS). The yield and the composition of the extracts obtained by supercritical CO2 were compared with those obtained by steam distillation (SD). SFE produced higher extraction yields than SD. This may be explained by simultaneous extraction of both aroma and non aroma compounds of higher molecular weight. Higher yields were produced for the higher values of pressure (20 MPa) and extraction time (120 min). With respect to extract composition, the content of hydrocarbon monoterpenes was shown to be mainly related to the extraction temperature, higher values being produced between 308 and 310 K. Phenols, including thymol, the major component of T. zygis aroma, were also extracted at the higher tested levels of the parameters. The production of the terpenic alcohols (TA) was found to be mainly dependent on the extraction time. This study allows the conclusion that pressure is the most important extraction parameter.

Seasonal variation in yield and composition of Thymus zygis L. subsp. sylvestris essential oil

The seasonal variation in the yield and composition of the essential oil from collective samples of Thymus zygis L. collected in North Portugal is reported. Essential oil was obtained by steam distillation and by distillation in a modified Clevenger apparatus. Analysis was performed by GC and GC–MS. The yield in essential oil showed a maximum at the flowering stage (0.9–1.4%) and a minimum during the dormancy period (about 0.15%). The composition also showed different patterns at different phases of the vegetative cycle. At the flowering period the essential oil is rich in thymol and geraniol. p-Cymene showed a variation presenting a maximum at the minimum of thymol (post-flowering period). Aiming the use of the essential oil as a food ingredient, the most interesting stage is the post-flowering period, the essential oil at this time being rich in thymol (about 21%), geranyl acetate (about 17%) and geraniol (about 13%), with p-cymene presenting lower levels. Copyright

Characterization of multilayered and composite edible films from chitosan and beeswax

Chitosan-based edible films were prepared and subjected to cross-linking reactions using sodium tripolyphosphate and/or to beeswax coating on both films interfaces. In addition, chitosan–beeswax emulsion-based films were produced. The goal of these modifications of the chitosan films was the improvement of their barrier to water vapor and to decrease their affinity to liquid water maintaining or improving the mechanical and optical properties of the original chitosan films. The cross-linking with tripolyphosphate decreased both the water vapor permeability and the water absorption capacity to about 55% and 50% of that of the original chitosan films, respectively. However, there was an increase in the films stiffness, revealed by the increased Young modulus from 42 kPa up to 336 kPa. The multilayered wax–chitosan–wax films exhibited a similar improvement of the barrier properties to water vapor, with the advantage of maintaining the mechanical properties of the original chitosan films. However, these wax-coated films showed a higher water absorption capacity, which is believed to be a consequence of water entry into small pores between the film and the wax layers. Regarding the film samples subjected to cross-linking and further coating with beeswax, a similar behavior as the uncoated cross-linked films was observed. The emulsion-based composite films were characterized by a substantial decrease of the water vapor permeability (40%), along with a decrease in their stiffness. Regarding the optical properties, all films presented a yellowish color with similar values of lightness, chroma, and hue.

Optimisation of gellan gum edible coating for ready-to-eat mango (Mangifera indica L.) bars

The optimisation of an edible coating based on low acyl (L)/high acyl (H) gellan gum for ready-to-eat mango bars was performed through a central composite rotatable design (CCRD). The independent variables were the concentration of gellan (L/H90/10) and the concentration of Ca(2+) in the coating solution, as well as the storage time after coating application. The response variables studied were the coating thickness, mango bars firmness, syneresis, and colour alterations. Gellan concentration was the independent variable that most influenced the thickness of the coating. Syneresis was quite low for the conditions tested (<1.64%). Similarly, the colour alterations were low during the entire storage time (ΔE<5). Considering the model predictions, 1.0%wt L/H90/10 with addition of 6 mM Ca(2+) could represent the optimal coating formulation for the mango bars. The release of eight volatile compounds from the uncoated and coated mango bars with the selected formulation was analysed by Headspace - Solid Phase Micro Extraction-Gas Chromatography during 9 days of refrigerated storage. This work showed that the coating can improve mango bars sensory characteristics (appearance and firmness) and stability in terms of syneresis, colour and volatiles content during storage increasing the commercial value of the final product.

Using a bacterial fucose-rich polysaccharide as encapsulation material of bioactive compounds

The potential of a bacterial exopolysaccharide named FucoPol, produced by the bacterium Enterobacter A47, as encapsulation matrix was explored. Spherical capsules with a smooth surface were produced by spray drying. The obtained microcapsules had average diameters ranging from 0.5 to 26.7μm and presented thin walls (thickness from 222 to 1094nm). The capsules were loaded with two bioactive compounds: gallic acid (GA) and oregano essential oil (OEO). Both bioactive materials were encapsulated in FucoPol particles, retaining their antioxidant activity after the drying process. Release studies showed that GA release in simulated gastric and intestinal fluids was faster than that of OEO, envisaging that the latter had established stronger interactions with the polymer matrix. These results suggest that FucoPol has a good potential for use as encapsulating material of bioactive compounds for application in several areas, including food, cosmetic or pharmaceutical products.

Influence of extraction procedure on the aroma composition of Thymus zygis L. and Mentha pulegium L

Abstract The present work compares the results of two extraction procedures (Clevenger distillation and compressed CO 2 extraction) on the yield and composition of the aromatic extracts. A RSM was applied in order to determine the best extraction conditions by compressed CO 2 . The matrix was established for the following ranges: time 60–180 min, temperature 40–50°C and pressure 9–20 MPa. All the extracts were analysed by GC and GC-MS. The results showed that the yields are generally higher for compressed CO 2 : 2.1% for Mentha pulegium and about 3% for Thymus, compared to a value of 0.9% and 1% by distillation. The main compound found in M. pulegium is pulegeone. In T. zygis the main compounds are thymol, geraniol and geranyl acetate.

Supercritical Fluid Extraction of Aroma Compounds from Aromatic Herbs (Thymus zygis and Coriandrum sativum)

Supercritical fluid (SCF) extraction was compared to steam and Clevenger distillation, in terms of yield and composition of extracts, when applied to thyme and coriander leaves. In thyme extracts, higher production yields were always obtained by the Clevenger extraction method. Using SCF extraction high yields were also obtained but the extracts included other kinds of compounds. In respect of chemical composition of steam and Clevenger distillation extracts show similar profiles. Supercritical extracts present, besides the same components as that of steam distillation, non aromatic compounds. All the extraction methods tested produced very low yields of extracts when applied to coriander leaves, nevertheless the patterns of the chromatograms are quite different among those methods.

Effect of processing conditions on volatile composition of apple jellies and jams

Abstract When producing fruit jellies and jams it is intended to preserve as far as possible the presence of the aromatic characteristics of the fresh fruit. In the present work, the influences of sugar content −6 to 55°Brix—and type of pectin—low methoxyl and medium methoxyl pectin—on the volatile composition of apple jellies and jams is studied. Volatile compounds were extracted by Clevenger distillation for 180 min and collected in n -hexane. All extracts were analysed by Gas Chromatography (GC) and Gas Chromatography-Mass Spectrometry (GC-MS). The influence of jelly structure on flavor release was evaluated by measurement of objective texture. It was observed that the studied parameters quantitatively affected the chromatographic profile, keeping the composition similar. Main compounds identified were 3-methylbutanol, 2-methylbutanol, 1-hexanal, 2-hexanal, hexyl propionate and estragole. The decrease observed in volatile release from jellies and jams seemed to be related to the retention of volatiles in the gel matrix and to sugar bonding.

Aroma of Thymus zygis. Chemical and Sensorial Analysis

Thymus zygis is a botanical species commonly found in aromatic herbs. The aim of this paper is to study the composition of extracts obtained by steam and Clevenger distillation, N2 flow and the sensorial analysis of the same extracts. Chemical components were evaluated by capillary GC and GC-MS. Sensorial analysis was done by an untrained test panel of twenty judges. The minimum detection level, the preferred concentration and the preferred extract were evaluated in a vegetable oil having different added extracts and compared to the same oil having fresh herb added. Results show that the minimum detection level for 75% of the judges is about 0.01% for Clevenger and steam distillation extracts and 0.04% for N2 flow extract. The preferred extract was the one produced by steam distillation at 0.03% concentration. The disliking of the extracts seem to be related to the presence of p-cymene and γ-terpinene.