Towards a better understanding on agglomeration mechanisms and thermodynamic properties of TiO2 nanoparticles interacting with natural organic matter

Interaction between engineered nanoparticles and natural organic matter is investigated by measuring the exchanged heat during binding process with isothermal titration calorimetry. TiO2 anatase nanoparticles and alginate are used as engineered nanoparticles and natural organic matter to get an insight into the thermodynamic association properties and mechanisms of adsorption and agglomeration. Changes of enthalpy, entropy and total free energy, reaction stoichiometry and affinity binding constant are determined or calculated at a pH value where the TiO2 nanoparticles surface charge is positive and the alginate exhibits a negative structural charge. Our results indicate that strong TiO2-alginate interactions are essentially entropy driven and enthalpically favorable with exothermic binding reactions. The reaction stoichiometry and entropy gain are also found dependent on the mixing order. Finally correlation is established between the binding enthalpy, the reaction stoichiometry and the zeta potential values determined by electrophoretic mobility measurements. From these results two types of agglomeration mechanisms are proposed depending on the mixing order. Addition of alginate in TiO2 dispersions is found to form agglomerates due to polymer bridging whereas addition of TiO2 in alginate promotes a more individually coating of the nanoparticles.Comment: 30 pages, 6 figures, 11 figures in S

Isothermal titration calorimetry as a powerful tool to quantify and better understand agglomeration mechanisms during interaction processes between TiO₂ nanoparticles and humic acids

The association processes between engineered TiO2 nanoparticles and Suwannee River humic acids are investigated by isothermal titration calorimetry and by measuring the exchanged heat during the binding process, allowing the determination of thermodynamic (change in enthalpy, Gibbs free energy and entropy) and reaction (binding affinity constant, reaction stoichiometry) parameters. Our results indicate that strong TiO2–Suwannee River humic acid interactions are entropically and enthalpically favorable with exothermic binding reactions and that the mixing order is also an important parameter. High humic acid concentrations induce homoagglomeration (“self”-assembly) and are shown to favor an enthalpically driven association process. Light scattering techniques are also considered to investigate the influence of TiO2 surface charge modifications and agglomeration mechanisms. Patch and bridging mechanisms are found to result in the formation of large agglomerates once charge inversion of TiO2–humic acid complexes is achieved. Moreover, van der Waals interactions are also found to play a significant role during interaction processes due to the amphiphilic character of humic acids

Influência da atmosfera modificada por filmes plásticos sobre a qualidade do mamão armazenado sob refrigeração Influence of a modified atmosphere by plastic film on the quality of papaya fruit stored in a refrigerator

A utilização de embalagens constitui uma ferramenta importante no armazenamento de frutas. Neste trabalho foi avaliado o efeito dos filmes plásticos, Xtend® e PEBD, sobre a conservação do mamão. Frutos de mamoeiro "Golden", apresentando de 10 a 15% de coloração amarela na casca, após passarem por tratamentos térmicos e químicos, foram embalados individualmente e armazenados por 32 dias a 10 &deg;C (90-95% UR). Frutos sem embalagem serviram de controle. Durante o período de armazenamento foram avaliadas as características de perda de massa, firmeza, sólidos solúveis totais, acidez titulável, pH, a razão SST/AT e a quantidade relativa de CO2 no interior das embalagens. Os resultados mostraram que os frutos embalados com o filme Xtend® apresentaram menor acúmulo de CO2 do que os frutos embalados com PEBD. Entretanto, a perda de massa foi minimizada pelo filme de PEBD, evitando o enrugamento da superfície durante os 32 dias de estocagem a 10 &deg;C. Os dois tipos de filmes suprimiram o aumento de SST nos frutos ao final da estocagem, minimizando também a concentração de ácidos orgânicos. Os frutos embalados com o filme Xtend® apresentaram os maiores valores da razão SST/AT devido ao menor conteúdo final de acidez e de sólidos solúveis totais.<br>The use of plastic packaging is an important tool for storing fruit. The aim of this work is to evaluate the effect of plastic film, Xtend® and PEBD on preserving papaya. Papaya fruit cv "Golden", showing 10 to 15% of yellowish peel and also having had chemical and thermal treatments, were wrapped individually in film and stored for 32 days at 10 &deg;C (90-95% UR). Fruit without packaging served as a control. Throughout the storage period, the characteristics of mass loss, firmness, total soluble solids, titratable acidity, pH, SST/AT ratio and the relative amount of CO2 inside the packaging were evaluated. Results showed that fruit wrapped in Xtend® film presented lower CO2 accumulation than those stored in PEBD film. However, the mass loss was minimized by using PEBD film, also avoiding wrinkles on the surface of the fruit up to 32 days of storage at 10 &deg;C. Both types of film suppressed the SST and organic acid accumulation in the fruit at the end of storage. The papaya wrapped in Xtend® film presented a higher SST/AT ratio due to the final lower acidity and SST concentration

Influência dos estádios de maturação na qualidade do suco do maracujá-amarelo Influence of the ripening stages on quality of the yellow passion fruit juice

Neste trabalho, foi avaliada a influência dos estádios de maturação sobre as características químicas do suco de maracujá-amarelo (Passiflora edulis f. flavicarpa Degener), durante o período que antecedeu a mudança de cor da casca até o período de abscisão dos frutos, quando apresentavam coloração da casca totalmente amarelada. Durante o amadurecimento dos frutos, foi observado aumento progressivo dos parâmetros de Hunter L e b, sendo que a região inferior do fruto apresentou aumento de luminosidade e do amarelecimento mais rapidamente do que a superior. O conteúdo de Sólidos Solúveis Totais (SST) aumentou progressivamente, desde a condição de frutos imaturos, com 52 Dias Após Antese (DAA), até os 76 DAA, quando apresentaram cerca de 65% de cor amarela, permanecendo constante após este período. As medidas de acidez titulável e de pH indicaram pequeno acúmulo de ácidos orgânicos até os 60 DAA e, posteriormente, durante o amadurecimento dos frutos de maracujazeiro, ocorreu um consumo parcial desses ácidos, confirmados pela redução da acidez titulável e aumento de pH. Observou-se também, neste período, que a relação SST/AT aumentou progressivamente.<br>This work evaluated the influence of the ripening stages on the chemical characteristics of the yellow passion fruit juice (Passiflora edulis f. flavicarpa Degener.), during the period that precedes the peel color change until the period of fruits abscission, when they show the peel totally yellowish. During the ripening of the fruits was observed a progressive increase in the Hunter L and b parameter, in a way that the lower area of the fruit presented higher brightness and yellowing indexes than the upper area. The content of SST showed a progressive increase from an immature condition of the fruits (52 DAA) until a ripening stage with 65% of yellowish peel, in 76 DAA, staying constant after this period. The measures of total acidity and pH indicated a small accumulation of organic acids in the immature fruits (60 DAA) and, later, it occurred a partial consumption of these acids, as showed by the decreasing of titrable acidity and the increasing of pH during the ripening of the yellow passion fruit. The TSS/TA ratio also increased progressively in this period

Determinação da escala de coloração da casca e do rendimento em suco do maracujá-amarelo em diferentes épocas de colheita Determination of the peel color scale and juice yield of yellow passion fruits in different harvest seasons

Este trabalho teve como objetivo determinar uma escala de coloração da casca para identificar o estádio de maturação do maracujá-amarelo e avaliar o rendimento em suco, em diferentes épocas de colheita. Os experimentos foram constituídos de 2 épocas de colheita, contemplando a estação de menor temperatura e menor precipitação de chuvas (EP1-Maio/Setembro), a estação de maior temperatura e precipitação de chuvas (EP2-Outubro/Dezembro) e 7 estádios de maturação, com 10 repetições. Os resultados foram avaliados pelo teste de Tukey, a 5% de significância. O parâmetro b de Hunter foi utilizado como o indexador da mudança da coloração amarela. Verificou-se que a mudança de coloração ocorreu no sentido da base para o pedúnculo do fruto. Os frutos da época EP2 apresentaram a maior espessura de casca e o menor rendimento em suco, nos estádios iniciais de amadurecimento. Nos frutos com mais de 65,9% da casca amarelada, a época de colheita não influenciou na espessura da casca e no rendimento em suco, apresentando níveis máximos de suco. Frutos da época EP1 apresentaram o máximo rendimento a partir do estádio com 21,3% de cor amarela.<br>This work had the aim to determinate the peel color scale intended to identify the ripening stage of the yellow passion fruit and evaluate its juice yield in different harvest seasons. The experiments were constituted of 2 harvest seasons and they were accomplished during the period of low temperatures and less precipitation (EP1 - May/September) and high temperatures and more precipitation (EP2 - October/December), and seven ripening stages using ten replications. The results were compared by applying the Tukey test at the level of 5% of probability. Hunter b parameter was used as the yellowing index. It was verified that the yellow color progressed from the base to the fruit peduncle. Fruits from the EP2 season presented the lowest juice yield and the highest peel thickness in the early ripening stages. In fruits with at least 65% of yellow color peel, the harvest season did not influence in the peel thickness and in the juice yield, showing the highest level of juice. Fruits from the EP1 season showed the higher juice yield after 21,3% yellow color