Browsing by Author "Buonocore, Giovanna"
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- Determination of rhodamine and tetramethylrhodamine-5-maleimide by ultra high performance liquid chromatographyPublication . Silva, Ana Sanches; Vilarinho, Fernanda; Buonocore, GiovannaNanoscale materials present unquestionable advantages, however there is a need to understand how the nanoscale influences the toxicological properties of materials, as well as the possibility of exposure. Nowadays, we are still facing the lack of tools and methodologies available to easily track the movement and position of engineered nanomaterials (ENMs) from nanocomposites. Elemental analysis via atomic absorption spectrometry or inductively coupled plasma mass spectroscopy are the most commonly used techniques for tracking and detecting nanoclays. However, these methods lack the ability to track single or clustered nanoclay particles and their positions, which is an important feature. Recently fluorescent labeling has been proposed as a simple method to track particle at nanoscale. In this method fluorescent compound (tag) bonds covalently to the nanoclay allowing to track them. The main objective of this study was to develop an analytical method by Ultra High Performance Liquid Chromatographic (UHPLC) to determine simultaneously rhodamine and tetramethylrhodamine-5-maleimide, two potential labels of MMT. Due to the lack of information regarding the analytical behaviour of the selected fluorescent tags, there was the need of carrying out numerous tests to develop an UHPLC method that allowed determining the selected fluorescent tags. Different conditions of the methods were tested including chromatographic column, column temperature, mobile phase composition, mobile phase gradient and detectors conditions were tested. UHPLC was used because it allows reducing the time of analysis and to obtain well defined peaks and low quantification limits. Fluorescence detector and diode array detector (DAD) were compared as well as different solvents. The results of the calibration curves of rhodamine and tetramethylrhodamine-5-maleimide, prepared in ethanol and methanol, presented excellent determination coefficients in all cases, indicating suitability for quantification. Better response was obtained with fluorescence detector, allowing working at lower concentrations.
- Fluorescein 5-maleimide: label of food contact nanocompositesPublication . Silva, Ana Sanches; Vilarinho, Fernanda; Buonocore, GiovannaEngineered nanomaterials (ENMs) are increasingly being used due to their physical and chemical properties that allow improving a wide range of consumer products. Although they present a vast number of benefits, they also present risks to human health and the environment. Therefore, there is the need of evaluating the risks of nanotechnologies in foods. To fulfill this require new techniques are being developed. Fluorescent labeling is a simple approach for particle tracking that presents low detection limits. A fluorescent organic dye can be directly incorporated into layered silicates like montmorillonite (MMT) by ionic exchange but this can be dislodged from the substrate during the extrusion process. However the covalent bond of the fluorescent tag to the nanoclay can be a good alternative because it provides stability between the fluorescent tag and the clay. The main objective of this study was to develop an analytical method by Ultra High Performance Liquid Chromatographic (UHPLC) to determine fluorescein 5-maleimide, a fluorescent compound, as potential label of MMT. Conditions like chromatographic column, column temperature, mobile phase composition, mobile phase gradient as well as detector conditions were tested. Fluorescence detector and diode array detector (DAD) were compared. In general good linearity was found, excellent determination coefficients were achieved in all cases. Regarding the response of both detectors, as expected, better response was also obtained with fluorescence detector, allowing obtaining lower limits of quantification. The quantification limits of fluorescein 5-maleimide with the fluorescence detector were, at least, 10 times lower than with the DAD detector. Different behaviour was found in the two solvents tested. Ethanolic solutions allowed obtaining lower detection limits (LOD) than methanolic solutions (LOD ethanol = 0.03 µg/mL; LOD methanol =0.06 µg/mL, using fluorescence detector).
- Lipid oxidation of a meat product packaged with poly (lactic acid)/clay nanocompositesPublication . Vilarinho, Fernanda; Buonocore, Giovanna; Vaz, M.; Sanches-Silva, A.Introduction: Polylactic acid or polylactide (PLA, Poly) is a biodegradable thermoplastic aliphatic polyester derived from renewable resources, such as corn starch, tapioca roots, chips or starch, or sugarcane. Biopolymer nanocomposites are of great interest to the packaging industry as they can overcome the limitations of biopolymers compared to synthetic polymers. In the last two decades, the nanocomposites have been studied intensively, once the addition of fillers such as organoclays, in particular, montmorillonite (MMT), can improve rheological, thermal and mechanical properties of the biopolymers (Jollands M. et al. 2010). The presence of MMT can lead to materials which generally exhibit great property enhancements, mainly due to its intercalation or exfoliation into the polymer chains. In this work, PLA was incorporated with 5% (w/w) Cloisite Na+ prepared through a two-step process: first extrusion of pellets and secondly melted matter was pressed. The nanocomposite was used to pack a model food (salami) in order to evaluate of the ability of the new packaging to inhibit lipid oxidation. Thiobarbituric Acid Reactive Substances (TBARS) assay was used to evaluate the lipid oxidation stage. This assay allows to measure malondialdehyde (MDA) content, which is formed in the lipid oxidation of polyunsaturated fatty acids. Material and Methods: Packaged salami was homogenized with trichloroacetic acid (10 %) in 0.02 M of orthophosphoric acid and the solution was filtered. The filtered solution was homogenized with thiobarbituric acid aqueous solution (0.02 M) and heated at 100 °C for 40 min. Solutions were cooled down and absorbance was measured at 530 nm. Results were expressed as mg MDA per kg of salami. Results and Discussion: Salami slices were packaged with a control film and with the nanocomposite and analysed at initial time and after 15, 30, 60 and 90 days of contact. Results showed that salami packaged with the nanocomposite presented lower amount of MDA after all contact periods, except after 60 days, where there were no differences between control and nanofilm. Conclusion: Although the results showed that the new nanocomposite tends to reduce the production of MDA, further studies should be carried out to confirm the inhibition of lipid oxidation, such as the peroxide index, p-anisidine value, or the monitorization of a lipid oxidation indicator like hexanal.
- Monitorization of hexanal as lipid oxidation indicator in a processed meat product packaged with poly(lactic acid)/clay nanocomposite filmsPublication . Vilarinho, Fernanda; Buonocore, Giovanna; Stanzione, M.A.; Vaz, M.; Sanches-Silva, A.One of the most detrimental processes in fatty foodstuffs is lipid oxidation, which occurs during production and storage, and influences food composition and safety. Through the analysis of volatile lipid oxidation products we can have an insight into the oxidation, and some volatiles, such as hexanal, which can be markers of undergoing oxidation processes. Hexanal is formed when fatty acids are oxidized and is one of many well-documented aromatic components that contributes to flavour and aroma in common food products containing fatty acids. During the last decade, the interest in polymer layered silicate (PLS) nanocomposites has rapidly increased due to their potential for enhancing physical, chemical, and mechanical properties of conventional materials. Polymer nanocomposites are represented by a polymeric matrix reinforced with nanoscale fillers, among them the most common silicate clays are represented by montmorillonite (MMT), which is naturally occurring and readily available in large quantities. The presence of MMT can lead to materials which generally exhibit great property enhancements, mainly due to its intercalation or exfoliation into the polymer chains. In this work natural MMT Cloisite Na+ was incorporated in PLA. The PLA/Cloisite® Na+ films were prepared through a two-step process. In the first step, PLA pellets were fed into a corotating laboratory twin-screw extruder at 170 °C and 50 rpm for 2 min. Subsequently, Cloisite® Na+ powder (5%, w/w) were added and mixed. After extrusion, the melted matter was then pressed with a P300P hot press at 170 °C and 100 bar to obtain the PLA/Cloisite® Na+ films. Salami slices were packaged with PLA-OMMT film and with a control film (PLA). After different storage times (0, 15, 30, 60 and 90 days), salami slices were analysed regarding their hexanal content. The hexanal derivatization was performed in a solution of 2,4-dinitrophenylhydrazine in sulfuric acid during 4 h in the dark, and the hexanal extraction was performed with n-hexane and evaporation till dryness. The residue was dissolved in methanol, filtered and analysed. The quantification of hexanal was performed by Ultra High Performance Liquid Chromatography coupled with Diode Array Detector at 365 nm, with a Pre-column AcquityTM UPLC® BEH C18 (2.1 x 5 mm, 1.7 μm particle size) and a column AcquityTM UPLC® BEH C18 (2.1 × 50 mm, 1.7 μm particle size), the mobile-phase was acetonitrile-water (75:25, v/v). The amount of hexanal in packaged salami decreased in the first 60 days of storage. In this period of time the hexanal content of the salami packaged with the PLA/Cloisite® Na+ films was lower than the salami packaged with control film, except after 15 days of storage, where there was no difference between two films. After 90 days of storage, the amount of hexanal in the samples increased, although it was higher in the samples packaged with control film (94.7 ± 6.02 μg/100g salami) than salami packaged with PLA/Cloisite® Na+ films (65.1 ± 6.12 μg/100g salami). The presence of MMT in the polymer film can reduce the lipid oxidation of processed meat products, extending their shelf life. Further studies to evaluate differences between PLA and the nanocomposite (PLA-5%Cloisite®Na+) in what regards to the mechanical and barrier properties are in progress.