Propriedades viscoelásticas de massa de farinha de arroz e do concentrado proteico de orizenina

• Ano de defesa: 2012
• Autor(a) principal: Machado, Ana Paula Oliveira
• Orientador(a): Pirozi, Mônica Ribeiro
• Banca de defesa: Vieira, Claudia Regina , Fontes, Edimar Aparecida Filomeno
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Mestrado em Ciência e Tecnologia de Alimentos
• Departamento: Ciência de Alimentos; Tecnologia de Alimentos; Engenharia de Alimentos
• País: BR
• Palavras-chave em Português: Farinha de arroz; Orizenina; Doença celíaca; Propriedades reológicas; Propriedades térmicas
• Palavras-chave em Inglês: Rice flour; Oryzenin; Celiac disease; Rheological properties; Thermal properties
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::CIENCIA E TECNOLOGIA DE ALIMENTOS
• Link de acesso: http://locus.ufv.br/handle/123456789/2914

Rice flour is a major substitute for wheat flour in gluten-free bakery products. These products are mainly intended for patients with celiac disease, who depends solely on a gluten-free diet for their effective treatment. To enable the production of gluten-free bread, the baking technology has used many additives and adjuvants that increase considerably the total costs of the product. The oryzenin, rice glutelin, is the most abundant protein in the endosperm. The thermal properties of oryzenin can be related to the rheological properties of rice flour. An improvement of the viscoelastic properties of rice flour dough could be expected when processing it at temperatures above its glass transition temperature (Tg.) In the first Chapter of the present work, an comprehensive review is presented, focusing in the chemical characteristics of rice flour, the alternative techniques of gluten-free baking products production, the methods for oryzenin extraction, and the relevance of rheometry studies in the evaluation of the baking quality of rice flour. The objectives of the Chapter 2 were to evaluate the chemical composition of the rice flour and to determine its protein composition using size exclusion high performance liquid chromatography. Two distinct methods of oryzenin extraction were evaluated, based on their extraction yield, and the total protein content of the resulting protein concentrate. Results showed that total carbohydrates and proteins were the main components of rice flour. The protein fraction is predominantly composed by unextractable polymeric proteins, with 59%. The extraction method proposed by Zarins and Chrastil (1992) showed better protein extraction performance than the method proposed by Agboola, Darren and Mills (2005), using starch enzymatic digestion, considering that the former provided higher extraction yields and total protein content. In the Chapter 3, the aim was to investigate the rheological properties of rice flour and the protein concentrates obtained in Chapter 2, using farinography and rheometry, at 28 °C, 35 °C, and 50 °C. Water absorption and the mixing properties of the rice flour were determined in the Brabender farinograph, under the temperatures described above, using a commercial wheat flour sample as standard for the rice flour results. The rice flour and two protein concentrates were tested in a controlled stress rheometer at temperatures of 28 °C, 35 °C and 50 °C. The water absorption of rice flour increased with the increase of the mixing temperature. It was also observed that the increase in the mixing temperature imparted a decrease in both the arrival time and the dough development time of rice flour, suggesting that temperatures near the Tg may favor its mixing properties. The increase of testing temperature also increased the G 'and G'' modules of the rice flour dough, while for both oryzenin concentrates, markedly for that obtained using the method proposed by Zarins and Chrastil (1992), there was a decrease in their viscoelasticity modules. The distinct results obtained for rice flour and protein concentrates indicates an effect of the starch viscosity in the rice flour behavior. The rheological properties of protein concentrates suggest that an increase in the temperature impart an improvement in the dough viscoelasticity. According to these results, it is possible to obtain rice flour dough with adequate baking characteristics by increasing processing temperature.