Rheological study into the ageing process of high methoxyl pectin/sucrose aqueous gels

The ageing process of high methoxyl pectin (HMP)/sucrose gels was followed at different ageing temperatures by small amplitude oscillatory experiments. Dynamic mechanical measurements allowed the characterisation of the point at which the system undergoes the sol/gel transition. The HMP/sucrose system is extremely sensitive to temperature variation during ageing, especially in the lower temperature range. The viscoelastic behaviour through the gel point changes with the ageing temperature, probably due to variations in mobility of the pectin chains, and consequently, in the lifetime of junction zones. Weaker pectin networks are formed under thermal conditions unfavourable to the development of hydrophobic interactions. Gel time and elastic modulus have a complex dependence on temperature, which could be attributed to the different thermal behaviour of the intermolecular interactions that stabilise the nonpermanent cross links of these physical networks

Influence of temperature on the dynamic and steady-shear rheology of pectin dispersions

The influence of temperature on the dynamic and steady-shear rheology of ionic polysaccharides, high-methoxyl and low-methoxyl pectins, has been studied and compared with the behaviour of locust bean gum, a virtually neutral biopolymer. Using the time-temperature superposition principle, the rheological parameters were reduced to an arbitrary reference temperature. Activation energies were calculated and their dependence on temperature and shear rate analysed. Concerning the viscosity dependence on temperature, two approaches have been considered: one associated with the theory of absolute reaction rates leading to an Arrhenius type equation, and the other associated with the free volume theory, expressed by the Williams-Landel-Ferry equation. The difficulties encountered in the superposition of the dynamic properties of the pectin dispersions, the high activation energies, yield values and elastic plateau at low oscillatory frequency, are consistent with a macromolecular organization of these polymers dominated by important aggregation phenomena, which could be attributed to important intermolecular interactions like hydrogen bonding and hydrophobic interactions, especially in conditions of low degree of ionization of the carboxylic groups

Kinetics and thermal behaviour of the structure formation process in HMP/sucrose gelation

The concentration and temperature dependence of the gelation kinetics of high-methoxyl pectin (HMP; 60% sucrose, pH 3) was investigated using measurements of small-amplitude oscillatory shear. The rate of gelation close to the gel point can be described as a second-order rate process using the kinetic model of Ross-Murphy (Carbohydr. Polym. 1991, 14, 281) and a critical exponent close to that predicted by the percolation approach. The modulus after a long ageing time showed a power concentration dependence with an exponent around 3.1, higher than the classical square of concentration dependence, which was probably either due to the non-equilibrium state of the HMP gels even after long ageing times, or due to the proximity of the concentration range studied to the critical gelling concentration. The gelation rate of HMP/sucrose systems is strongly dependent on the temperature. An Arrhenius relationship was applied to describe this dependence. Two different processes are proposed to explain the discontinuity observed, each one having rates with different temperature dependence. The applicable kinetics at longer times are quite different, with a lower dependence on polymer concentration and ageing temperature. A non-isothermal kinetic model was used to describe the gelation process of the HMP/sucrose system during cooling

Environmental Risk Assessment Based on High-Resolution Spatial Maps of Potentially Toxic Elements Sampled on Stream Sediments of Santiago, Cape Verde

Geochemical mapping is the base knowledge to identify the regions of the planet with critical contents of potentially toxic elements from either natural or anthropogenic sources. Sediments, soils and waters are the vehicles which link the inorganic environment to life through the supply of essential macro and micro nutrients. The chemical composition of surface geological materials may cause metabolic changes which may favor the occurrence of endemic diseases in humans. In order to better understand the relationships between environmental geochemistry and public health, we present environmental risk maps of some harmful elements (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, V, and Zn) in the stream sediments of Santiago, Cape Verde, identifying the potentially harmful areas in this island. The Estimated Background Values (EBV) of Cd, Co, Cr, Ni and V were found to be above the Canadian guidelines for any type of use of stream sediments and also above the target values of the Dutch and United States guidelines. The Probably Effect Concentrations (PEC), above which harmful effects are likely in sediment dwelling organisms, were found for Cr and Ni. Some associations between the geological formations of the island and the composition of stream sediments were identified and confirmed by descriptive statistics and by Principal Component Analysis (PCA). The EBV spatial distribution of the metals and the results of PCA allowed us to establish relationships between the EBV maps and the geological formations. The first two PCA modes indicate that heavy metals in Santiago stream sediments are mainly originated from weathering of underlying bedrocks. The first metal association (Co, V, Cr, and Mn; first PCA mode) consists of elements enriched in basic rocks and compatible elements. The second association of variables (Zn and Cd as opposed to Ni; second PCA mode) appears to be strongly controlled by the composition of alkaline volcanic rocks and pyroclastic rocks. So, the second PCA mode is also considered as a natural lithogenic mode. The third association (Cu and Pb; third PCA mode) consists of elements of anthropogenic origin

Allergen sensitization associates with worse lung function parameters

To assess the association between the number of allergen sensitizations and lung function variables in individuals with airway symptoms. Methods. Retrospective study with all individuals who performed lung function and skin-prick tests at CUF-Porto (01/2011-06/2016). Six allergen groups were considered. % predicted Pre-Bronchodilator test (BD) and % change after BD were analysed for spirometry and plethysmography parameters. Results. A total of 1293 individuals were included, 54% (n = 698) adults and 69% (n = 891) with sensitization to ≥ 1 allergen group. % FEV1 was significantly higher and % change in FEV1 significantly lower in non-sensitized individuals. % sRaw was higher in polysensitized (vs non-sensitized). Conclusions. The presence of allergen sensitizations was significantly associated with worse key lung function parameters.info:eu-repo/semantics/publishedVersio

Matéria orgânica, densidade e porosidade do solo submetido à trituração de capoeira em porto velho, Rondônia.

A queimada como meio para preparar áreas para plantio é considerado um método prático, rápido e barato de limpeza. Por causa do impacto ambiental e a diminuição da fertilidade do solo, tanto a médio como a longo prazo, outros métodos vem sendo estudados para diminuir os danos ambientais acarretados pelo uso do fogo. Deste modo, o manejo da capoeira por meio de corte e trituração pode ser uma opção. Sendo assim, o objetivo deste trabalho foi avaliar o efeito da trituração de capoeira na densidade e na porosidade do solo no município de Porto Velho, Rondônia. O experimento foi realizado em três locais no município de Porto Velho, Rondônia. Foram avaliadas, logo após a trituração da capoeira, a matéria orgânica, a densidade e a porosidade do solo, em diferentes camadas de solo, em áreas com capoeira contínua e em áreas submetidas à trituração. A matéria orgânica, a densidade e a porosidade do solo não foram alteradas pela trituração da capoeira. Portanto, concluiu-se que não houve impacto negativo do uso do equipamento, para a trituração da capoeira, na matéria orgânica, densidade e porosidade do solo

Caracterização físico-química e reológicas da polpa de cupuaçu congelada (Theobroma grandiflorum Schum).

Cupuaçu, uma das principais e mais consumidas frutas da região amazônica brasileira, pertence à família Sterculiacea, cuja denominação binomial é Theobroma grandiflorum schum. É uma fruta típica da Amazônia, sendo cultivada nos estados do Pará, Maranhão e Tocantins. Esta fruta apresenta crescente utilização no Brasil para o mercado interno e externo, sendo comumente comercializada como polpa congelada. Apesar de sua importância, há poucos dados de caracterização e contaminação da polpa de cupuaçu. Amostras de polpa de cupuaçu foram avaliadas quanto à viscosidade aparente, tensão de cisalhamento, umidade, cinzas, nitrogênio total, extrato etéreo, acidez, sólidos solúveis e pH. Os resultados demonstram a necessidade de aprimorar as boas práticas agrícolas e de fabricação e implantação de sistemas de controle de qualidade para minimização dos riscos associados à contaminação por micro-organismos