Analysis of deformability modulus by linear and nonlinear elastic methods in ceramic structural masonry and mortars

There are studies analyzing the parameters of structural masonry strength, however few are performed evaluating the interference of the mortar in the deformability parameters. The objective of this study was to verify the theories of elasticity (Hooke’s linear model and nonlinear models by Ghosh, Duffing, and Martin, Roth, and Stiehler) applied to structural masonry. Ceramic blocks were pressed and fired at 890 ºC and mortars prepared with the proportion 1:1:5:0.5:2 of cement: hydrated lime: sand: PVA binder: water. The materials were tested in compression individually and in prisms with and without the use of mortars. The results obtained with the linear elastic analysis were incoherent since the deformability modulus obtained for the mortar prisms was higher than those without mortar. Performing the analysis by nonlinear theories, it was found that the results obtained were more coherent, mainly by Duffing’s theory that uses one parameter for stiffness and another for damping of the material.

Mechanical behavior of pumpkin fruits subjected to compression during maturation

During handling operations, many problems that reduce the quality of vegetables may occur. Mechanical injuries are the leading cause of postharvest losses for the pumpkin, and can take place at any point of the production chain. This study aimed at evaluating the pumpkin fruits behavior, during their ripening stages, on the values of maximum compression force for fixed deformations, and determining the proportional deformability modulus of the fruits under compression at the repose position. Fruits were harvested at 15, 30, 40, 50 and 60 days after flowering and uniaxially compressed between two parallel plates. The results allowed to conclude that both the required compression force and the proportional deformability modulus increased during the maturation course, reaching a maximum force of 1,778 N and a maximum deformation modulus of 164 MPa, after 30 days. After this period, both the maximum force and the modulus values decreased, reaching 1,514.8 N of maximum force and a modulus of 132.09 MPa, after 60 days of ripening. Over the course of a longer maturation time, the fruit firmness increased, therefore requiring an increase in the maximum load to achieve greater deformation. The ideal period for harvest and transport of 'Jacarezinho' pumpkin fruits was set from 30 to 40 days after anthesis.

Tentative hierarchization of the influence of milk properties and technological practices on rheological properties of Abondance cheese

An attempt at classifying the influence of different characteristics of milk and cheesemaking on the rheological properties of Abondance cheese is presented. Abondance is a traditional farmhouse French hard cheese with protected denomination of origin (PDO). Thirty-nine cheeses made from unpasteurized cows' milk were sampled. Spline partial least squares regression was used to relate milk properties and cheesemaking practices to rheological properties of the six-month-old cheeses. These properties were the deformability modulus and the strain and stress at fracture measured by compression. Milk properties and technological practices had overall the same degree of relationship with the rheological properties investigated: plasminogen-derived activity in milk and mineral-protein equilibrium, on the one hand, and brining and resting, on the other hand. However, acidification kinetics and 1-d pH, which result from both milk properties and technological practices, showed the strongest relationships with rheological characteristics. Factors that were most appropriate for modelling Abondance rheological properties are discussed.

Proteolysis and its role in relation to texture of Feta cheese made from ultrafiltered milk with different amounts of rennet

The relationship between proteolysis and texture in Feta-type cheese made from ultrafiltered cows' milk was studied using capillary electrophoresis, chemical analysis and uniaxial compression. For this purpose cheeses were made with almost identical gross chemical compositions, but wide variations in texture, obtained by varying the amount of rennet and the coagulation conditions. αs1-Casein (CN) 8P, αs1-CN 9P and αs1-CN 8P-I were degraded during ripening, while β-CN A1, β-CN A2 and para-κ-CN were slightly degraded at the highest rennet additions and longest storage time tested (39 weeks). αs1-CN 8P, αs1-CN 9P and αs1-CN 8P-I were degraded even in cheeses made without rennet, and this was ascribed to cathepsin D activity. αs1-CN 9P disappeared faster than αs1-CN 8P, which suggests that milk acid phosphatase was active during storage. During ripening, stress at fracture (σf), strain at fracture (εf), the deformability modulus (E) and work to fracture (Wf) all decreased. Since the gross chemical composition was essentially constant during storage, these changes could be ascribed purely to proteolysis. Although εf could be predicted fairly well from capillary electrophoresis results (correlation coefficient 0·85), there were no unique relationships between degradation of casein components and σf when both storage time and the amount of rennet used were varied. In the young cheese a high level of proteolysis could coexist with high values of σf. This suggests that high levels of rennet caused σf to increase, via an effect unrelated to general proteolysis, whereas general proteolysis caused the reverse effect.