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Publicações

Publicações por Rui Costa Martins

2010

Moderate electric fields can inactivate Escherichia coli at room temperature

Autores
Machado, LF; Pereira, RN; Martins, RC; Teixeira, JA; Vicente, AA;

Publicação
JOURNAL OF FOOD ENGINEERING

Abstract
The inactivation of Escherichia coli using moderate electric fields (MEF) below 25 degrees C, was investigated. Keeping the temperature always below 25 degrees C demonstrated that electric fields are involved in the inactivation of E call, without possible synergistic temperature effects. Electric fields above 220 V cm(-1) promoted death rates of 3 log(10) cycles of E coli in less than 6 min, and even higher rates at greater electric fields, while presumably overcoming the thermal degradation caused by conventional high temperature treatments. A non-thermal model was proposed that successfully describes the E. coli death kinetics under this treatment. SEM observations of E. coli cells after the exposure to the MEF treatment, revealed changes at the cell membrane level, indicating a possible cause for the cell death rates. These results show that this treatment holds potential for sterilization of thermolabile products (e.g. serum and other physiological fluids, food products), by itself or as a complement of the traditional heat-dependent techniques.

2006

Principal component analysis as tool of characterization of quince (Cydonia oblonga Miller) jam

Autores
Silva, BM; Andrade, PB; Martins, RC; Seabra, RM; Ferreira, MA;

Publicação
FOOD CHEMISTRY

Abstract
Fifty-one quince jams from several different brands, commercialised in three consecutive years, traditionally prepared and industrially manufactured, were studied. Principal component analysis (PCA) was performed, in order to assess the correlations between the different components of quince jam phenolics, organic acids and free amino acids. Phenolics determination was the most interesting. The differences between phenolic profiles of traditional and industrial quince jams were emphasised during PCA. Two main PC characterise the quince jam phenolic composition (54.4% of all variance): PCl (37.4%) and PC2 (17.0%). The PCl describes the differences between the contents of 3-0- and 5-0-caffeoylquinic acids and all flavonoids and the PC2 relates the contents of 4-0- and 5-0-caffeoylquinic acids against 3-0-caffeoylquinic and 3,5-dicaffeoylquinic acids. The results indicate that many industrial manufacturers usually use unpeeled fruits in the preparation of the jams. The PCA of phenolic compounds enabled clear discrimination between quince jams prepared with peeled and unpeeled fruits.

2011

The Influence of Geometrical and Operational Factors on Supercooling Capacity in Strawberries: A Simulation Study

Autores
Martins, RC; Castro, CC; Lopes, VV;

Publicação
FOOD AND BIOPROCESS TECHNOLOGY

Abstract
Supercooling is still today one of the most challenging physical phenomena to be modelled in food bioprocess engineering. In this study, we evaluate the capacity of a finite-element-cellular automata (FEM-CA) approach to model the propagation of nucleation inside supercooled strawberries with five different morphologies (higher and lower volumes of vascular tissue, pulp, and central air void) frozen inside an air blast freezer under different operational conditions: initial temperature (0 to +20 A degrees C), air temperature (-45 to -20 A degrees C), and velocity (1 to 10 m s (-aEuro parts per thousand 1)). Results show that nucleation is highly affected by the initial temperature and heat transfer rate during phase change. The stochastic nature of nucleation only allowed us to consider it a random variable inside the model temperature restriction interval, it not yet being possible to know what triggers nucleation. However, this study allowed us to conclude that: (1) the structure of liquid water in the supercooled region plays a very significant role during the supercooling effect, (2) nucleation temperatures increase in the supercooled region due to the release of latent heat, and (3) strawberry morphology and operational variables have a profound effect on the supercooling capacity. In our opinion, supercooling is still an open subject, and only a deeper understanding of the structuring of water and dynamics of nucleation at the molecular level may lead to significant advances in the quality of frozen foods and cryopreservation.

2008

Feasability of yeast and bacteria identification using UV-VIS-SWNIR difusive reflectance spectroscopy

Autores
Silva, JS; Martins, RC; Vicente, AA; Teixeira, JA;

Publicação
BIOSIGNALS 2008: PROCEEDINGS OF THE FIRST INTERNATIONAL CONFERENCE ON BIO-INSPIRED SYSTEMS AND SIGNAL PROCESSING, VOL 1

Abstract
UV-VIS spectroscopy is a powerfull qualitative and quantitative technique used in analytical chemistry, which gives information about electronic transitions of electrons in molecular orbitals. As in UV-VIS spectra there is no direct information on characteristic organic groups, vibrational spectroscopy (e.g. infrared) has been preferred for biological applications. In this research, we try to use state-of-the-art fiber optics probes to obtain UV-VIS-SWNIR diffusive reflectance measurements of yeasts and bacteria colonies on plate count agar in the region of 200-1200nm; in order to discriminate the following microorganisms: i) yeasts: Saccharomyces cerevisiae, Saccharomyces bayanus, Candida albicans, Yarrowia lipolytica; and ii) bacteria: Micrococcus luteus, Pseudomonas fluorescens, Escherichia coli, Bacillus cereus. Spectroscopy results show that UV-VIS-SWNIR has great potential for identifying microorganisms on plate count agar. Scattering artifacts of both colonies and plate count agar can be significantly removed using a robust mean scattering algorithm, allowing also better discriminations between the scores obtained by singular value decomposition. Hierarchical clustering analysis of UV-VIS and VIS-SWNIR decomposed spectral scores lead to the conclusion that the use of VIS-SWNIR light source produces higher discrimination ratios for all the studied microorganisms, presenting great potential for developing biotechnology applications.

2009

YEAST METABOLIC STATE IDENTIFICATION BY FIBER OPTICS SPECTROSCOPY

Autores
Castro, CC; Silva, JS; Lopes, VV; Martins, RC;

Publicação
BIOSIGNALS 2009: PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON BIO-INSPIRED SYSTEMS AND SIGNAL PROCESSING

Abstract
In this manuscript we explore the feasibility of using LWUV-VIS-SWNIR (340 - 1100 nm) spectroscopy to classify Saccharomyces cerevisiae colony structures in YP agar and YPD agar, under different growth conditions, such as: i) no alcohol; ii) 1% (nu/nu) Ethanol; iii) 1% (nu/nu) 1-Propanol; iv) 1% (nu/nu) 1-butanol; v) 1 % (nu/nu) Isopropanol; vi) 1% (nu/nu) (+/-)-1-Phenylethanol; vii) 1% (nu/nu) Isoamyl alcohol; viii) 1% (nu/nu) tert-Amyl alcohol (2-Methyl-2-butanol); and ix) 1% (nu/nu) Amyl alcohol. Results show that LWUV-VISSWNIR spectroscopy has the potential for yeasts metabolic state identification once the spectral signatures of colonies differs from each others, being possible to acheive 100% of classification in UV-VIS and VIS-SWNIR. The UV-VIS region present high discriminant information (350-450 nm), and different responses to UV excitation were obtained. Therefore, high precision is obtained because UV-VIS and VIS-NIR exhibit different kinds of information. In the future, high precision analytical chemistry techniques such as mass spectroscopy and molecular biology transcriptomic studies should be performed in order to understand the detailed cell metabolism and genomic phenomena that characterize the yeast colony state.

2009

IN-SITU, REAL-TIME BIOREACTOR MONITORING BY FIBER OPTICS SENSORS

Autores
Silva, RG; Silva, JS; Vicente, AA; Teixeira, JA; Martins, RC;

Publicação
BIOSIGNALS 2009: PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON BIO-INSPIRED SYSTEMS AND SIGNAL PROCESSING

Abstract
One of the most studied bioprocesses is fermentation by yeasts. Although this is true, there is still the lack of real-time instrumentation that is capable of providing detailed information on metabolic state of fermentations. In this research we explore the possibility of using UV-VIS-SWNIR spectroscopy as a high-output, non-destructive and multivariate methodology of monitoring beer fermentation. We herein report the implementation of the a fibber optics sensor and the capacity for detecting key parameters by partial least squares regression for biomass, extract, pH and total sugars. Results show that UV-VIS-SWNIR is a robust technique for monitoring beer fermentations, being able to provide detailed information spectroscopic fingerprinting of the process. Calibrations were possible to obtain for all the studied parameters with R2 of 0.85 to 0.94 in the UV-VIS region and 0.95 to 0.97 in the VIS-SWNIR region. This preliminary study allowed to conclude that further improvements in experimental methodology and signal processing may turn this technique into a valuable instrument for detailed metabolic studies in biotechnology.

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