Anais da IX Conferência Internacional de Proteínas e Coloides Alimentares

Rice stands out for being a good source of protein and carbohydrates. In addition, it has unique characteristics because it is hypoallergenic due to the absence of gluten-forming proteins and can be used as an alternative source for people with gluten-related disorders. In addition, rice proteins can be divided into four different fractions, such as prolamin, glutelin, globulin and albumin, where each fraction has differences in terms of solubility. However, this solubility can be varied depending on the presence of other components, such as rice husk. This work aimed to determine the protein and ash content of red rice with the husk of the species Oryza sativa L. (mulatinho or trigueiro) purchased at the local market in Vitória da Conquista/BA city and to determine the isoelectric point of the protein, as well as the fractions proteins related to Osborne solubility. The unhusked rice grain was crushed in a ball mill, and the flour was defatted with hexane under agitation (150rpm/2h), filtered and dried in an oven (40ºC/overnight). Protein solubilization was carried out in the proportion defatted flour: solvent (1:6-p:v): 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 others. The isoelectric point was determined between pH 1 to 9, with the samples centrifuged (1,700g/10min.) and the soluble protein measured by the biuret method. Analysis of variance and Tukey's test (P<0.01) evaluated data between protein fractions. Red rice's protein and ash content was 8.79±1.53% and 1.21±0.12%, respectively. The results obtained showed differences in the soluble protein fractions, with values of 3.79±0.33% for albumin (soluble in water), 2.56±0.48% for globulin (soluble in saline solution), 6 .32±0.08% for glutelin (soluble in diluted alkaline solution) and 7.89±1.89% for prolamin (soluble in 70% alcoholic solution), with all fractions differing from each other (P<0.001). The solubility curve from the proteins extracted from red rice flour with husk it was verified that the isoelectric point was 4.5. However, at a pH above the isoelectric point (pH 9), the protein solubility was 6.07 times higher than in an acid medium (pH 1), indicating the formation of chelates with the minerals present in the medium, thus reducing protein solubility. Red husked rice has a mineral content 37.22% lower than rice with husk (data not shown). Based on the data obtained, it was possible to observe that the protein contents are below those listed in the literature, and this can be justified by the presence of the rice husk, which was ground together with the grain, thus providing a greater supply of dietary fiber and minerals solubilized in the extraction in alkaline medium. Innovative and environmentally friendly technologies can be applied as an alternative to increase protein solubilization and not compromise the bioavailability of nitrogen compounds and minerals (especially multivalent minerals) for the human diet.