Summary
The objective of this study was to evaluate the influence of pH on rheological and viscoelastic properties of solutions based on blends of type A (GeA) or type B (GeB) gelatin and chitosan (CH). Solutions of GeA, GeB, CH, GeA:CH, and GeB:CH were prepared in several pH (3.5–6.0) and analyzed for determination of zeta‐potential. Rheological analyses (stationary and dynamic essays) were carried out with blends allowing to study the effect of pH on shear stress, apparent viscosity, loss (G”) and storage (G’) moduli, and angle phase (Tanδ). Zeta potential of all biopolymers decreased linearly as a function of pH. CH presented higher values, and GeB, the lowest one, being the only having negative values at pH > 5. Overall, the pH influenced the rheological and viscoelastic properties of the colloidal solutions: shear stress and apparent viscosity increased as a function of pH. Other assays were carried out at 3% and 5% strain, for GeA:CH and GeB:CH, respectively. In the sol domain, G’ and G” (1 Hz) increased linearly for GeA:CH. But for GeB:CH, they increased in two linear different regions: one function between pH 3.5 and 5.0 and another one between 5.0 and 6.0, being a more important effect was visible in this last domain probably due to the negative net charge of gelatin, above it pI. An effect in two domains was also visible for Tanδ, explained in the same manner as previously. The GeB:CH blends behaved like diluted solutions, and transition temperatures increased as a function of pH.
AGRADECIMENTOSÀ Deus, pela rica oportunidade de fazer um Mestrado, ampliar a minha capacidade de raciocínio, direcionar as minhas escolhas e colocar as pessoas certas no meu caminho. Aos meus amados pais, Nelson e Cristina.Ao meu orientador, Prof. Dr. Paulo José do Amaral Sobral, pela imensa paciência, compreensão e disponibilidade. Faltariam linhas para descrever as qualidades do senhor, contudo expresso aqui a minha admiração e gratidão pelo crescimento pessoal e profissional que o senhor fez surgir em mim. Vou seguir os seus passos. À Profª. Dra. Izabel Cristina Freitas Moraes, pelo carinho, paciência, conhecimento, disponibilidade, amizade e bom humor. A senhora é luz por onde passa.Aos meus colegas do Laboratório de Tecnologia de Alimentos (LTA), por toda ajuda e troca de experiências. Em especial à Andresa Gomes Brunassi e ao David Willian Bertan, pela ajuda profissional e espiritual.À minha amiga, Lía Ethel Velásquez Castillo, por nunca medir esforços em me ajudar e sempre estar disponível. Nunca poderei agradecer o suficiente por todas as palavras e atitudes de apoio. Você terá minha eterna gratidão. Eu amo você.À especialista em laboratório, Ana Mônica Barbosa Quinta Bittante, pela ajuda e conhecimento compartilhado.Aos especialistas em laboratório, Rodrigo Vinícius Lourenço e Marcelo Thomazini. À Profª. Dra. Samantha Cristina de Pinho, por disponibilizar seu laboratório para análises de potencial zeta.
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