Caracterização de variedades de arroz e avaliação da influência do tempo de prateleira nas suas propriedades físicas

Abstract

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.

Date of Award	29 Sept 2022
Original language	Portuguese
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Diogo Barbosa Amorim de Lemos (Supervisor) & José António Couto (Co-Supervisor)