Anais da IX Conferência Internacional de Proteínas e Coloides Alimentares

Rice is a highly versatile crop and has been adapted to different soil and climate conditions. This cereal is cultivated and consumed on all continents, being one of the leading plant-based proteins widely explored, presenting a high potential for application in the food industry. Knowledge about Osborne solubility is paramount to understanding the technological performance of food proteins. This method solubilizes the protein into albumin, globulin, prolamin and glutelin fractions. This work aimed to quantify the protein content of red rice (known as mulatinho and trigueiro) in the whole form (brown rice) of the species Oryza sativa L. purchased in Vitória da Conquista/BA and to determine protein fractions related to Osborne solubility and the isoelectric point. The brown rice grain was milled in a ball mill, defatted with hexane under agitation (150rpm/2 h), filtered and dried in an oven (40ºC/overnight). Protein solubilization was carried out in the proportion of defatted flour: solvent (1:6 - w:v). The solvent systems used were aqueous (albumins), 2% saline solution (globulins), alkaline – 0.02 M NaOH (glutelins) and alcoholic – 70% ethanol (prolamins). After extracting the proteins, the samples were centrifuged (1,700g/10min.), and the protein content was quantified by the Kjeldahl method (N=5.95) for rice flour and the glutelin fraction and by the biuret method for the other solubilized proteins. The isoelectric point was determined between pH 1 to 9, with the samples centrifuged (1,700g/10min.) and the soluble protein quantified by the biuret method. Analysis of variance and Tukey's test (P<0.01) evaluated data between protein fractions. The protein content of red brown rice was 10.39±0.29%. Data for the soluble protein fractions from red brown rice were 1.50±0.32% for albumin, 3.31±0.11% for globulins, 6.30±0.19% for glutelins and 10.36±1.03 % for prolamins, with all fractions differing from each other (P<0.001). According to the protein solubility curve in different pHs, verifying a greater solubility in an alkaline medium (pH 9) than the acidic medium (pH 1) was possible. The isoelectric point is defined as the pH at which the protein has the lowest solubility due to the nullity of the sum of the positive and negative charges present in the polypeptide chain. In the case of red brown rice protein, the isoelectric point was set at 5.25. Based on the results obtained, it was possible to observe that the solubility values of the protein fractions were low. According to the literature, the glutelin and prolamin fractions are rich in sulfur amino acids (methionine and cysteine), and the formation of disulfide bonds promotes the construction of a dense protein matrix, reducing the possibility of extraction. The low solubility of rice protein limits its applications in the food industry. Therefore, there is great potential for applying green technology and biotechnological processes to favor the solubilization of rice proteins, such as ultrasonication, ultraviolet, pulsed electric fields, electron beam, gamma irradiation, high hydrostatic pressure, cold plasma, microwave, sprouting, fermentation, enzymatic hydrolysis. With this, it will be possible to favor the extraction of rice proteins and allow subsequent functionalization for application in different.