Uso de aminoácidos como agentes limitantes da reação de Maillard no processo de parboilização de arroz e seus efeitos sobre a qualidade de três genótipos

Abstract

Rice is the main source of energy for more than half of the world's population and it is estimated that 25% of rice consumption occurs in the form of parboiled rice. Parboiling is a hydrothermal process that consists of three additional steps to the conventional process: (a) soaking, (b) pressure steaming, and (c) drying before hulling. With parboiling, rice achieve greater nutritional value when compared to polished rice, as well as harder and looser grains after cooking. Also, parboiled rice exhibits longer shelf life and lower percentage of broken grains than non-parboiled rice. However, the color of rice changes from white to amber in this process, mainly due to non-enzymatic Maillard-type reactions, affecting acceptability by consumers. Therefore, mechanisms to control and delay these reactions have been the subject of studies in recent years. Thus, the aim of this study was to evaluate the efficiency of the amino acids glycine, methionine, glutamine, sodium glutamate, and aspartate, during the soaking step in the rice parboiling process, at different concentrations (1.5% and 3.0%), as limiting agents of the Maillard reaction. Furthermore, the effects of amino acids on physicochemical and technological attributes were evaluated in two conventional genotypes (Irga 424 RI and Guri Inta CL) and a hybrid (Titan CL), which varied in protein and amylose content. First, the effects of the five amino acids on the Irga 424 RI genotype were evaluated through the parameters of color, whole and broken grain percentage and cooking time, and the two most effective amino acids in the control of browning were selected for application in the other genotypes and, in addition to the previous analyses, the free hydroxymethylfurfural (HMF) content, cooking yield, X-ray diffraction and relative crystallinity, pasting properties, and amino acid hydration isotherms were also evaluated. Glycine and sodium glutamate were able to provide a whiter color to parboiled rice, but only sodium glutamate, depending on its concentration and genotype, reduced HMF levels. Broken grain percentage and cooking time were dependent on genotype, structure, and amino acid concentration. The percentage of broken ones only increased in the Irga 424 RI and Titan CL genotypes, but the cooking time decreased in these genotypes and increased in the Guri Inta CL genotype. Amino acids interfered with the absorption of the soaking solution by the grains, reflecting on the degree of gelatinization of these samples. Thus, the treatments with the best technological properties for the three genotypes were: 1) Irga 424 RI – 1.5% of both amino acids; 2) Guri Inta CL – GLI 1.5% and both amino acids at 3%; and 3) Titan CL – 3% of both amino acids. Sodium glutamate showed potential for industrial application, since it delayed the browning of grains and improved technological properties; however, the sensory evaluation of the grains must be considered in future studies.