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Este relatório foi elaborado no âmbito do estágio curricular realizado na empresa Novarroz – Produtos Alimentares, S.A. cuja principal atividade é a transformação e comercialização de arroz. O arroz (Oryza sativa) é uma das culturas mais produzidas e consumidas em todo o mundo. Este cereal é essencialmente composto por amido, seguindo-se nutrientes como proteínas e lípidos em menores quantidades. As características físico-químicas do grão de arroz bem como a sua composição estão dependentes das condições de cultivo, do solo e da variedade do próprio grão. Assim, e uma vez que o conhecimento destas características ajuda a perceber e a prever o comportamento do arroz durante o processo de cozedura, torna-se importante, especialmente para uma indústria arrozeira, realizar o estudo das suas variedades. Sendo o grande objetivo deste trabalho a caracterização de diversas variedades de arroz, foi necessária a determinação de vários parâmetros tais como as dimensões do grão, o grau de brancura, o tempo de cozedura e as propriedades de viscosidade. As amostras da subespécie Oryza sativa indica apresentam grãos longos e finos, pelo que a sua relação comprimento/largura é maior e o seu tempo de cozedura menor, contrariamente às amostras da subespécie Oryza sativa japonica. Os perfis de viscosidade auxiliam a interpretação das principais reações que ocorrem durante e após a cozedura do arroz, são elas a gelatinização e a retrogradação do amido. Verificou-se que estes perfis variaram consideravelmente entre as amostras, sendo que o arroz Vaporizado apresenta um comportamento diferente decorrente do tratamento hidrotérmico a que foi sujeito. Foi possível observar que as variedades pertencentes à subespécie japonica sofrem uma grande desintegração nos seus grãos de amido e uma curta reorganização, o que resulta numa textura final viscosa, sendo que nas variedades pertencentes à subespécie indica se observou o contrário, obtendo-se uma textura final mais seca. De forma a dar continuidade a um estudo levado a cabo pela empresa, foram analisadas as propriedades de viscosidade de várias amostras sujeitas a armazenamento, com o intuito de avaliar a influência do tempo e do modo de armazenamento na qualidade do arroz. Conclui-se que o armazenamento do arroz em casca ou em película fornece uma maior proteção ao grão contra o envelhecimento, sendo necessário um maior tempo de prateleira do que o arroz armazenado em branco para que se verifiquem alterações significativas. Contudo, as alterações observadas apresentam resultados favoráveis para a maioria das variedades estudadas. Constatou-se ainda que o envelhecimento do arroz resulta essencialmente no endurecimento do grão, devido ao aumento de resistência da estrutura do amido e que, o nível de endurecimento varia com o teor de amilose da variedade em questão.
This report was developed within the scope of the curricular internship carried out at the company Novarroz – Produtos Alimentares, S.A. whose main activity is the processing and commercialization of rice. Rice (Oryza sativa) is one of the most produced and consumed crops in the world. This cereal consists of starch, followed by nutrients such as proteins and lipids in smaller amounts. The physicochemical characteristics of the rice grain as well as its composition are dependent on the cultivation conditions, the soil and the variety of the grain itself. Thus, and since the knowledge of these characteristics helps to understand and predict the behaviour of rice during the cooking process, it becomes important, especially for a rice industry, to carry out the study of their varieties. Since the main purpose of this work is the characterization of rice varieties, it was necessary to determine several parameters such as grain dimensions, degree of whiteness, cooking time and viscosity properties. Samples of the Oryza sativa indica subspecies have long and fine grains, so their length-to-width ratio is greater and their cooking time is shorter, contrary to samples of the Oryza sativa japonica subspecies. Viscosity profiles help in the interpretation of the main reactions that occur during and after rice cooking, they are starch gelatinization and retrogradation. It was found that these profiles varied considerably between the samples, and the Parboiled rice presents a different behaviour due to the hydrothermal treatment to which it was subjected. It was possible to observe that the varieties belonging to the subspecies japonica suffer a great disintegration in their starch grains and a short reorganization, which results in a viscous final texture, and in the varieties belonging to the subspecies indica it was observed the opposite, obtaining a drier final texture. In order to continue a study carried out by the company, the viscosity properties of several samples subjected to storage were analysed, in order to assess the influence of time and storage mode on rice quality. It is concluded that the storage of rice in husk or in brown rice/caryopsis provides greater protection to the grain against aging, requiring a longer shelf life than rice stored in white for significant changes to occur. However, the changes observed show favourable results for most of the varieties studied. It was also found that the aging of the rice essentially results in the hardening of the grain, due to the increase in the strength of the starch structure, and that the level of hardening varies with the amylose content of the variety in question.
This report was developed within the scope of the curricular internship carried out at the company Novarroz – Produtos Alimentares, S.A. whose main activity is the processing and commercialization of rice. Rice (Oryza sativa) is one of the most produced and consumed crops in the world. This cereal consists of starch, followed by nutrients such as proteins and lipids in smaller amounts. The physicochemical characteristics of the rice grain as well as its composition are dependent on the cultivation conditions, the soil and the variety of the grain itself. Thus, and since the knowledge of these characteristics helps to understand and predict the behaviour of rice during the cooking process, it becomes important, especially for a rice industry, to carry out the study of their varieties. Since the main purpose of this work is the characterization of rice varieties, it was necessary to determine several parameters such as grain dimensions, degree of whiteness, cooking time and viscosity properties. Samples of the Oryza sativa indica subspecies have long and fine grains, so their length-to-width ratio is greater and their cooking time is shorter, contrary to samples of the Oryza sativa japonica subspecies. Viscosity profiles help in the interpretation of the main reactions that occur during and after rice cooking, they are starch gelatinization and retrogradation. It was found that these profiles varied considerably between the samples, and the Parboiled rice presents a different behaviour due to the hydrothermal treatment to which it was subjected. It was possible to observe that the varieties belonging to the subspecies japonica suffer a great disintegration in their starch grains and a short reorganization, which results in a viscous final texture, and in the varieties belonging to the subspecies indica it was observed the opposite, obtaining a drier final texture. In order to continue a study carried out by the company, the viscosity properties of several samples subjected to storage were analysed, in order to assess the influence of time and storage mode on rice quality. It is concluded that the storage of rice in husk or in brown rice/caryopsis provides greater protection to the grain against aging, requiring a longer shelf life than rice stored in white for significant changes to occur. However, the changes observed show favourable results for most of the varieties studied. It was also found that the aging of the rice essentially results in the hardening of the grain, due to the increase in the strength of the starch structure, and that the level of hardening varies with the amylose content of the variety in question.
Description
Keywords
Arroz Variedades Amido Viscosidade Tempo de prateleira Rice Varieties Starch Viscosity Shelf life