Effects of salts and sucrose on the rheological behavior, thermal stability, and molecular structure of the Pereskia aculeata Miller mucilage.

The rheological behavior, thermogravimetric analysis (TGA), and atomic force microscopy (AFM) of the Pereskia aculeata Miller (OPN) mucilage treated with sodium chloride (NaCl), calcium chloride (CaCl2), and sucrose were evaluated. The experimental design was divided in a fractional factorial 25-1 for the screening of factors (OPN, sucrose, NaCl, CaCl2, and pH) and then in a 5 × 3 × 3 full factorial (OPN, sucrose, and NaCl). The model solutions used for the screening of factors presented shear-thinning behavior and the OPN mucilage concentrations were the factors that had significant effect on the apparent viscosity. Sucrose addition increased the thermal stability of the OPN mucilage solutions. OPN mucilage, sucrose, and NaCl were the variables with significant effect on thermogravimetric responses. The samples presented Newtonian behavior in 0-1.25% OPN mucilage concentrations and non-Newtonian behavior adjusted by power-law in 2.50-5.00% OPN mucilage concentrations with predominance of elastic behavior, contributing to the formation of stronger gels. The presence of sucrose in the systems containing OPN mucilage changed their rheological properties and salt additions caused reduction in viscosity. The AFM results provided a better understanding of the mechanism of OPN mucilage interactions in different solutions that justify the changes in viscosities.

Avaliação do processo de impregnação a vácuo em melão, utilizando diferentes substâncias / Evaluation of the process of vacuum impregnation in melon using different substances

Cortes cilíndricos de melões (Cucumis melo var. inodorus Naudin tipo amarelo) foram submetidos à impregnação com soluções de cloreto de cálcio (0,5 g.100 mL-1 de solução), adicionadas de amido gelatinizado (0, 5 e 10 g.100 mL-1 de solução) e glicose (0, 10 e 20 g.100 mL-1 de solução), com pressão de vácuo (84,4; 50,5 e 16,6 kPa) controlada. Foram feitas medidas do teor de sólidos solúveis totais, perda ou incorporação de componentes e textura de pedaços dos melões antes e após impregnação a vácuo. As variações desses parâmetros foram calculadas em relação aos do fruto original. Alterações na viscosidade das soluções devido aos processamentos também foram quantificadas. A existência de processos sinergísticos entre os fluxos de solutos do fruto e da solução pode ser constatada e analisada através de superfícies de resposta para as diferentes pressões, em função das concentrações de amido gelatinizado e de glicose nas soluções. A mobilidade molecular dos componentes do fruto e da solução em relação à viscosidade foi discutida.

Cylindrical cuts of melon (Cucumis melo var inodorus Naudin, yellow type) were submitted to impregnation with calcium chloride solutions (0.5 g.100 mL-1 of solution) added with gelatinized starch (0. 5 and 10 g.100 mL-1 of solution) and glucose (0. 10 and 20 g.100 mL-1 of solution) with controlled vacuum pressure (84.4; 50.5 and 16.6 kPa). Measurements of the total soluble solids, incorporation or loss components (turgidity) and texture of melon slices were made before and after vacuum impregnation. Quality parameter variations were calculated in relation to the original fruit. Alterations in the viscosity of the solutions during the processing had been also quantified. The existence of synergistic processes between the solute flows from the fruit and from the solution was evident and could be analyzed using response surfaces for the different pressures as a function of the glucose and gelatinized starch concentrations in the solutions. The molecular mobility of components of the fruit and the solution related to viscosity was discussed.