Centre for Biotechnology and Fine Chemistry

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Ultrasound sonication prior to electrospinning tailors silk fibroin/PEO membranes for periodontal regeneration

Publication . Serôdio, Ricardo; Schickert, Sónia L.; Costa-Pinto, Ana R.; Dias, Juliana R.; Granja, Pedro L.; Yang, Fang; Oliveira, Ana L.

In this study, silk fibroin (SF)/poly(ethylene oxide) (PEO) membranes were designed and fabricated by combining ultrasound sonication prior to electrospinning (0 to 20 min) as a strategy to physically control the rheological properties of solutions (10 to 30% w/v PEO) and to improve the spinnability of the system. PEO has proved to be essential as a co-spinning agent to assure good membrane reproducibility and enough flexibility for clinical manipulation. The rheological tests indicated that sonication greatly increased the viscosity of SF/PEO solutions and further enhanced the quality of the produced electrospun fibers with consequent improved mechanical properties in dry and wet conditions. By tuning the viscosity of the solutions using a simple sonication step prior to electrospinning, it was possible to induce water stability in the as-electrospun matrix, as demonstrated by infra-red spectroscopy. This reduced complexity in the process since it was not necessary to concentrate silk prior to electrospinning while avoiding the use of toxic solvents to perform a post-processing stabilization treatment which usually causes dimensional changes to the SF materials. Sonication pre-treatment allowed for minimizing the amount of synthetic polymer used to achieve the desirable mechanical properties (with the modulus ranging between 90 and 170 MPa), while avoiding a further water stabilization treatment. It also had a positive impact in the in vitro cell behavior of human primary periodontal ligament cells (hPDLs), resulting in a marked increase in cell proliferation. The present developed work constitutes a step forward towards simplicity and a better fabrication control of viable electrospun SFbased membranes for periodontal regeneration.

2019Journal article

Open access

Quality changes of carrots under different frozen storage conditions: A kinetic study

Publication . Gonçalves, Elsa M.; Abreu, Marta; Pinheiro, Joaquina; Brandão, Teresa R. S.; Silva, Cristina L.M.

In order to improve the overall quality of frozen carrots (Daucus carota L.), the degradation kinetics of several attributes were quantified during frozen storage under isothermal and nonisothermal conditions. The experimental results showed that the analyzed quality parameters were significantly affected by both tested frozen regimes. For both storage conditions, the degradation of color parameters and drip loss followed zero-order kinetics, and the texture was successfully described by a fractional kinetic model. A first-order kinetic model was adequate in describing total vitamin C decay under isothermal storage conditions. The storage temperature effect was adequately modeled by the Arrhenius law. The carrots shelf life under isothermal storage conditions of −18°C, using a threshold of 50% vitamin C content, will be of 118 days. Practical applications: The objective of this work was to evaluate the degradation kinetics of several quality attributes of carrots when subjected to various frozen storage temperature conditions that may occur along the distribution chain. The quality attributes degradation mechanisms are governed by chemical and/or physical changes that need to be systematically evaluated for further incorporation into product and process designs. The achieved results will be an insight to help manufacturers to predict and optimize products quality and determine its shelf life.

2020Journal article

Restricted access

Mathematical Models for Prediction of Temperature Effects on Kinetic Parameters of Microorganisms’ Inactivation: Tools for Model Comparison and Adequacy in Data Fitting

Publication . Gil, Maria M; Miller, Fátima A.; Brandão, Teresa R. S.; Silva, Cristina L. M.

Microbial inactivation often follows a sigmoidal kinetic behaviour, with an initial lag phase, followed by a maximum inactivation rate period and tending to a final as ymptotic value. Mathematically, such tendencies may be de scribed by using primary kinetic models (Gompertz based model is one example) that describe microbial survival throughout processing time when stressing conditions are ap plied. The parameters of kinetic models are directly affected by temperature. Despite the number of mathematical equa tions used to describe the dependence of the kinetic parame ters on temperature (so-called secondary models), there is a lack of studies regarding model comparison and adequacy in data fitting. This work provides a review of mathematical models that describe the temperature dependence of kinetic parameters related to microbial thermal inactivation. Regression analysis schemes and tests seeking model compar ison are presented. A case study is included to provide guid ance for the assessment of secondary model adequacy and regression analyses procedures. When modelling temperature effects on sigmoidal inactivation kinetics of microorganisms, one should be aware about the regression methodology ap plied. The most adequate models according to the two-step regression methodology may not be the best selection if a global fit is applied.

2017-09-18Journal article

Open access