1,720,990 research outputs found
Application of Near-Infrared Spectroscopy to statistical control in freeze-drying processes
Full text linkBatch freeze-drying of pharmaceutical products in vials may result in a high degree of intra-batch variability due to several reasons, e.g. non uniform heating rate in the drying chamber. Therefore, product quality in the final product has to be checked in a statistically significant number of samples, in particular in the stage of process development. Here, Fourier-Transform Near-Infrared Spectroscopy is proposed as a fast, non-destructive technique for an off-line Statistical Quality Control application. At first, results obtained in a batch where product features are satisfactory are used to identify a target quality threshold. Then, a statistical controller is developed in such a way that in a production run it is possible to quickly check if product quality exceeds the desired threshold or not. Two approaches based on multivariate analysis are presented: one employs the Hotelling T2 and Mahalanobis statistics to calculate control charts, the other is an application of Partial Least Squares for discriminant analysis (PLS-DA). Control charts and PLS-DA were trained with samples obtained in a run where sucrose solution was processed and validated in other runs where the final product was known to have the desired qualitative characteristics or not. Overall, out-of-specification samples can be predicted by control charts and PLS-DA with 99% and 98% accuracy respectively. PLS-DA was shown to be able to better identify samples correctly processed, while the control charts where more accurate to identify vials where something went wrong. Focusing on residual moisture of the final product, all samples where it was higher than the target value were always correctly identified
Model-based design of secondary drying using in-line near-infrared spectroscopy data
Full text linkThis article deals with the design and optimization of the secondary drying stage, via design space calculation, of a freeze-drying process. A simple and well known mathematical model was used to this purpose: the kinetic parameters of the water desorption step were determined, either off-line or in-line, using the measurement of the residual amount of water (C-s) in one of the processed samples through Near-Infrared spectroscopy. In the first approach, three tests, at different values of heating shelf temperature, are employed: the measurement of C-s versus time allows estimating the desorption rate and, finally, the kinetic constant at the given temperature. Arrhenius plot is used to get the parameters expressing the dependence of the kinetic constant on product temperature, thus allowing the calculation of the design space. In the second approach, the kinetic parameters are estimated in-line, focusing on the first part of the secondary drying stage, where the variation of product temperature is more relevant, hence allowing to track the evolution of the desorption rate (via C-s measurement) versus product temperature. A fitting procedure is then used, looking for the kinetic parameters that provide the best fit between calculated and measured values of C-s. By this way only one test is required to get the design space. Drying of sucrose and of sucrose - arginine mixtures were used as case studies, to point out the effectiveness of the proposed method. Examples of the design spaces that can be obtained are presented and discussed, focusing on the effect of operating parameters like the heating rate and the residual water content at the beginning of the secondary drying, as well as on the constraint about the maximum allowed temperature
Effect of vacuum freeze-drying on the antioxidant properties of eggplants (Solanum melongena L.)
Full text linkThe Vacuum Freeze Drying (VFD) process is a low temperature drying technique that can be used for food preservation. The aim of this work is to evaluate how VFD operating conditions affect the amount of some nutritional compounds of eggplants (Solanum melongena L.). The product samples were freeze-dried under different pressure and temperature conditions and had their ascorbic acid (AA) concentration, total polyphenol content (TPC) and antioxidant capacity (AC) measured before and after processing. Temperature was found to have a significative
effect on primary drying times: considering results obtained at 40 Pa, the duration moved from 8.6 ± 2.5 h when the process was carried out at 0 °C, to 20.9 ± 7.8 h at -30 °C.Chamber pressure had a less significant effect, being drying time, at 0 °C, ranging from 6.2± 2.3 h, for the test at 20 Pa, to 8.6 ±2.5 h, for test done at 40 Pa. Very low temperatures resulted in higher AC retentions, being the AC loss 68.6± 1.5% at 0 °C and 49.9±3.2% at -30 °C (at 10 Pa), while having a negative impact on the AA content, being the AA loss 12.2 ±1.7% at 0 °C and 37.9±3.4% at -30°C (at 10 Pa). Higher pressures were favorable for TPC retention in the dried product: being the TPC loss 47.7 ± 5.5% at 10 Pa and 32.5± 8.5% at 40 Pa (at 0 C). A similar trend can be observed for AC, where the AC loss was 68.8 ± 1.5%
at 10 Pa and 35.7 ± 12.1% at 40 Pa (at 0 C). Freezing stage had a non-significant effect on the targeted compound
Vacuum freeze-drying effect on bioactive compounds of eggplant (Solanum Melongena L.).
Full text linkVacuum Freeze Drying (VFD) is a low temperature drying technique that may be used for food preservation. The aim of this work is to evaluate how VFD operating conditions affect eggplants bioactive compounds loss after drying. Samples were freeze-dried under different pressure and temperature conditions, and had their ascorbic acid, total polyphenol and antioxidant capacity percent loss measured after processing. Under the tested conditions, lower temperatures resulted in lower antioxidant capacity in the final product, while lower chamber pressures resulted in lower total polyphenol content
Uso di un modello ad interfaccia diffusa per lo studio del processo di liofilizzazione sottovuoto di melanzane.
No full textDiffuse interface modeling of eggplants vacuum freeze-drying process
Full text linkVacuum freeze-drying (VFD) can be used for preserving food with small effects on nutritional qualities. VFD modelling is useful to select off-line the best operating conditions to avoid product overheating and reduce the drying time, thus saving energy. A 3D diffuse interface model was developed to simulate in-silico eggplant VFD. By comparing the experimental drying time and product temperature, heat transfer coefficient and vapor diffusivity were estimated under different operating conditions
Diffuse interface model of the freeze-drying process of individually frozen products
Full text linkVacuum freeze-drying (VFD) is a dehydration method based on the sublimation of the liquid phase contained in a certain product, previously frozen, at low pressure and temperature. Since it is a time and energy consuming process, it is crucial to select the best processing
conditions to minimize drying duration, thus reducing the energy requirement. Additionally, product temperature must be monitored since it plays an important role in preserving product quality. The aim of this study was to develop a Diffuse Interface Model (DIM) for in-silico simulation of the freeze-drying process of individually frozen products. Due to the geometrical features of the samples, and to the role of radiation in the heat transfer to the product, the usual one-dimensional approach is inappropriate. Using a DIM, each cell of the computational
domain can be described as a porous solid matrix filled by ice and vapor with a time-varying composition, thus allowing the use of a fixed computational grid and making the computation effort less demanding in comparison to moving interface-based models. Drying of eggplant cubic samples was considered as case study: model parameters were estimated by fitting the experimentally measured product temperature and drying time to the calculated ones. The model was proven to be reliable in providing an accurate estimate of both the drying time and the product temperature. Therefore, it can be used for off-line process design and optimization, minimizing the experimental effort required to design and optimize the proces
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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