Estudo preliminar para produção de vinagre de farelo de arroz desengordurado por processo submerso

Abstract

According to estimates of the National Supply Company (CONAB), in the period March 2013/14, Brazil produced approximately 12.8 million tons of rice, an increase of 8 % compared to the period of 2012/13. The grain processing results in by-products such as rice bran, which has B vitamins, proteins, tocopherols and over 40% carbohydrates, justifying their use in fermentation processes such as vinegar production. Vinegar is composed of 80% (v/v) water and 20% of a wide variety of other compounds such as organic acids, alcohols, minerals, polyphenols, amino acids, among others. The substrates used in vinegar production must provide fermentable carbohydrates to alcoholic fermentation, which is followed by acetic fermentation. The aims of this study were to investigate the hydrolysis process of defatted rice bran by enzymatic way, assess the stage of alcoholic fermentation to optimize ethanol production, and carry out production of vinegar by submerged fermentation and characterizing the final product. METHODS: Optimization of enzymatic hydrolysis was achieved using a sequential strategy of experimental design. Firstly, a Fractional Factorial Fesign including 25-1 trials plus 3 center points (19 runs) was applied to evaluate the effects of concentration of amylolytic enzymes, action timeand the dilution rate of defatted rice bran (DRB) on response of reducing sugars (RS) released, followed by two CCRDs (Central Composite Rotatable Design); after the analysis of the effects of Fractional Design, the optimum values of enzymes concentration was reached by the two sequential CCRD. Validation of the optimal conditions for the enzymatic hydrolysis was performed in triplicate in two tests, in the vicinity of the optimized conditions. In the step of alcoholic fermentation, initially was developed a test to evaluate the effect of inoculum size and agitation for application of a CCRD 23 that evaluated the effects of inoculum concentration, pH and temperature on the response of ethanol yield (%). After the analysis the first CCRD, aiming to increase the ethanol yield, the second test was performed to evaluate the effects of protease addition and exposure of the suspension of defatted rice bran to ultrasonic bath treatment, prior to enzymatic hydrolysis with amylases, since several studies indicate that the ethanol production can be increased under these conditions, because of increased exposure of the starch granules to amylolytic enzymes in the saccharification, after the action of proteases. The results allowed to determine the sequence of the study in the second CCRD was used to evaluate the effect of inoculum concentration and temperature, with adjusted tracks to achieve the optimization of fermentation, performing the addition of protease hydrolysis previously enzyme. Once the alcoholic fermentation step was optimized, a batch of vinegar production (acetic fermentation). The characterization of vinegar was performed by determination the parameters required by Brazilian legislation (residual alcohol content, total acidity and acetic acid, pH, total and reduced dry extract, ash and total and reducing sugars). The optimization of enzymatic hydrolysis was achieved with concentration of 200 g•L-1 FAD, 30 g•L-1 α- amylase and 40 g•L-1 amyloglucosidase, with action times of 2 and 3 hours, respectively. In the first preliminary test performed on the alcoholic fermentation step, it was observed that shaking positively influenced only in the tests with 2.0 and 5.0% of inoculums, and the higher yield of ethanol obtained was 1.90 % with the use of 0.5% inoculums, under stationary conditions. with the results obtained in the first test, the tracks of the variables were defined for the first CCRD, where the maximum ethanol content was obtained 2.10%, with the temperature at 30 °C, 2.8% of inoculums and pH 5.0. By applying the second test it was found that under the conditions applied, the ultrasonic treatment had no significant effect on the response of ethanol concentration; however, with the use of protease the yield was increased to 3.6% ethanol, after 72 hours of alcoholic fermentation. A new CCRD was performed, in order to achieve the optimization of the alcoholic fermentation; in this step, the concentration of protease was fixed at 15 μLg-1, before the enzymatic hydrolysis of polysaccharides with the amylases and the ranges studied for the significant variables in the first CCRD was adjusted (temperature: 28 - 35 °C; inoculum concentration: 1 - 7%), being achieved yield of 4.00% ethanol. The acetic fermentation was completed after eight days of inoculation of acetic bacteria (strong ethanol vinegar), and the vinegar produced answered current Brazilian legislation in all parameters, except for ash, which can be adjusted by applying a filtration step. These results may generate technological innovation for the industrial sector, as the results obtained in this work demonstrate the possibility of performing the use of rice bran as raw material for the production of vinegar.