Sérgio Sousa

Impact of enzyme- and ultrasound-assisted extraction methods on biological properties of red, brown, and green seaweeds from the central west coast of Portugal.

Seaweeds are an excellent source of bioactive compounds, and therefore the use of sustainable and food compatible extraction methods such as enzyme-assisted (EAE) and ultrasound-assisted extraction were applied on Sargassum muticum, Osmundea pinnatifida, and Codium tomentosum. Extracts were evaluated for proximate characterization and biological properties. Higher extraction yields were observed for C. tomentosum EAE (48-62%; p < 0.05 for Cellulase and Viscozyme), followed by O. pinnatifida (49-55%; p < 0.05 except Alcalase) and S. muticum (26-31%; p < 0.05). S. muticum extracts presented the highest nitrogen (25 ± 2 mg/glyoph extract) and total phenolics (261 ± 37 μgcatechol equiv/glyoph extract) contents, whereas higher sugars (78 ± 14 mgglucose equiv/glyoph extract) including sulfated polysaccharide (44 ± 8 mgNa2SO4 acid/glyoph extract) contents characterized O. pinnatifida extracts. A higher effect on hydroxyl-radical scavenging activity (35-50%) was observed for all extracts, whereas S. muticum Alcalase and C. tomentosum Cellulase extracts exhibited higher prebiotic activity than fructooligosaccharides. O. pinnatifida and C. tomentosum EAE showed inhibitory potential against α-glucosidase (38-49%).

Encapsulation of probiotic strains in plain or cysteine‐supplemented alginate improves viability at storage below freezing temperatures

Four probiotic bacteria (Lactobacillus paracasei L26, L. casei‐01, L. acidophilus Ki, and Bifidobacterium animalis BB‐12®) were encapsulated in plain alginate or alginate supplemented with L‐cysteine·HCl, and resulting microcapsules were stored at different temperatures, namely 21, 4, −20, or −80°C for a period of up to 6 months. The results showed that the encapsulation in calcium alginate microcapsules was only effective in promoting protection at freezing temperatures, independently of the sensitivity of the strain. Storage of calcium alginate microcapsules at −80°C indicated a protective effect upon viability of all four probiotic strains and the presence of L‐cysteine·HCl in the alginate matrix improved protection upon cell viability of B. animalis BB‐12®. An increase in storage temperature of encapsulated bacteria caused an increase in rate of loss in their viability that was strain dependent. This study suggests that microencapsulation of probiotic cells in calcium alginate can be suitable for sustaining the viability of probiotics in food products that require storage below freezing temperatures, even in the absence of cryoprotectors, contributing to an increased shelf life.

Evaluation of chitoligosaccharides effect upon probiotic bacteria.

The main objective of the present study was to evaluate the antibacterial effect - through the determination of minimum inhibitory (and lethal) concentrations, as well as the possible prebiotic potential of chitooligosaccharides (COS) - through the determination of growth curves, on Bifidobacterium animalis Bb12, Bifidobacterium animalis Bo and Lactobacillus acidophilus Ki. Atomic force microscopy was further used to obtain high resolution images of COS effects upon the cell morphology. Our results demonstrate that COS do not stimulate the growth of those strains, neither the strains are capable of using COS as a primary source of carbon. Analysis of morphology when exposed to inhibitory/bactericidal concentrations, suggested that COS do not exert any direct damage upon the bacteria structure, instead the bacteria are apparently covered by COS, which likely prevent nutrient uptake.

Implementation of a low cost data acquisition board for photovoltaic arrays analysis and diagnostic

Testing PV modules are one of the important procedures to ensure the conformity with the standards and quality of this equipments. To implement some of the PV modules tests a data acquisition system is required. This paper presents the design and implementation of a data acquisition system for photovoltaic systems. The developed system is characterized by a low cost board based on a microcontroller. The description of the hardware as well an application to test its performance is presented. The developed system can be used for reading, storing and analyzing information from several photovoltaic systems. Experimental tests are presented to confirm the characteristics of the developed data acquisition board.

Implementation of a new structure for a closed-loop Class D amplifier

In this paper is proposed the implementation of a novel structure for a Class D amplifier based on a robust closed loop control. The proposed control it is based on a multi level sliding mode controller. This allows of being able to converge to a stable status in spite of unknown or nonlinear elements present in the amplifier. The methods and systems proposed are also described. Several simulation results are presented. The obtained results confirm the potential of this configuration, as it is shown in the last part of this paper.