ABSTRACT. We evaluated various sieving methods to estimate particle size (PS) and geometric standard deviation (GSD) of ground corn. The corn had been previously divided in six fractions and each one ground in a hammermill (1-, 2-, 3-, 4-, 5- or 12-mm sieves). The stacked sieving method, with prior drying at 105ºC without agitators was the reference. We evaluated eight sieving methods, distributed in a factorial design (2 x 2 x 2 x 6), consisting of the following treatments: i) with and without agitators (two 25-mm rubber spheres), ii) with and without previous drying, iii) with a nest of test sieves set in a stacked or reverse, and iv) employing six ground corn degrees, totaling 48 treatments (four replicates). There was a linear increase in PS estimation for methods without drying and stacking and quadratic increases for the others. Reverse, drying, and agitator methodologies gave better sieving of corn, and consequently gave the lowest PS and highest GSD. The results were more pronounced for high-intensity grinding (hammermill sieve with small apertures) in which the differences between the reference method with the drying and reverse methods were up to 210 µm. Reverse sieving combined with agitators allowed the greatest passage of corn particles through the test sieves and promoted better characterization of ground corn.

RESUMO Foi conduzido um estudo para avaliar diferentes graus de hidratação e adição de fubá de milho (FMI) para a ensilagem do farelo de arroz integral (FAR) para conservação do produto. Foram utilizadas relações FAR: FMI 10:0; 9:1; 8:2; 7:3 e 6:4 e níveis de hidratação da mistura 10, 20, 30, 40 e 50% do peso inicial, perfazendo um esquema fatorial de 5×5 com quatro repetições. Paralelamente, foram fabricados quatro silos de características semelhantes aos demais com FAR sem a hidratação, denominados silos referência, e avaliada a peroxidação lipídica. Após a abertura (120 dias de ensilagem) foram avaliados o pH, acidez titulável (AT), índice de acidez (IA), índice de fungos (IF) e atividade de água (Aw). A temperatura (análise para verificar a estabilidade aeróbica) e o pH, pós abertura, foram determinados em 24, 48 e 120 horas após a abertura. Houve interações entre as variáveis para: pH na abertura, AT, IA e IF. Para a variável Aw não houve interação. A inclusão de 40% de FMI e 42,3% de água melhorou o pH da silagem na abertura, e a inclusão de 43,6% de água melhorou o pH 24 horas pós abertura. Após 48 horas de abertura as silagens estavam inapropriadas para o consumo, e a inclusão do milho acelerou a deterioração da massa ensilada após este período. Somente nos silos controles foi observado peroxidação lipídica. O uso do método de ensilagem para preservar a qualidade do FAR foi promissor como ferramenta para diminuir a peroxidação, independentemente do nível de hidratação. Para a confecção de silagem de farelo de arroz recomenda-se a inclusão de FMI de 40% e hidratação de 42,3% sobre o peso para otimizar o pH na abertura.

SUMMARY A study was carried out to evaluate the addition of cornmeal (FMI) at different hydration degrees to rice bran, as a strategy for its conservation by silage (FAR). Five relations of FAR and FMI were used: 10:0; 9:1; 8:2; 7:3 and 6:4, combined with five hydration levels: 10, 20, 30, 40 and 50% over initial weight, performing a 5×5 factorial design with four replications. In parallel, were prepared four similar silos only with FAR, without hydration (control silos). After 120 days of storage, the pH, titratable acidity, acidity index, fungi index, and water activity (Aw) were evaluated. The temperature (regarding to verify the aerobic stability) and the pH were determined at 24, 48 and 120 hour after opening. Interactions were observed for pH at opening time, titratable acidity, acid index and fungi index. No interactions were observed with Aw. The inclusion of 40% of cornmeal and 42.3% water improved the silage pH at opening and 43,6% improve the silage pH at 24 hours after opening. However, after 48 h of opening, all silages were inappropriate for consumption, the addition of cornmeal accelerated the deterioration of silage. Only on the control silos, the peroxidation process was observed. Then, the use of silage method for preserving the quality of rice bran was promising as a tool to reduce peroxidation independent of hydration level. We recommended for silage rice bran the inclusion of FMI 40% and 42.3% of water to optimize the pH in the opening.

RESUMO Este trabalho foi realizado para avaliar as características fermentativas e a estabilidade aeróbica das silagens de grãos úmidos de milho: convencional, doce e reidratado. Foi utilizado um delineamento em esquema fatorial 3x3 com três tipos de milho (Fortuna, doce e reidratado) e três tratamentos de inoculação (sem inoculação; com inoculação bacteriana; inoculação bacteriana mais enzimas). Foram avaliados a estabilidade aeróbica (diferença entre temperatura do bulbo seco e temperatura das silagens) e os valores de pH com: 0, 24, 48, 72, 96, 168, 192, 216, 240 e 296 horas de exposição aeróbica. Adicionalmente, foram testados diferentes modelos matemáticos para estimar os valores médios de pH pós abertura. Houve interação (P < 0,05) entre os tratamentos de inoculação e tipos de milho para a estabilidade aeróbica e para pH nas horas 72, 168 e 192 após a abertura dos silos. As silagens de milho doce inoculadas apresentaram melhor estabilidade aeróbica quando comparadas com as demais silagens. Para o pH às 48 horas a silagem de milho doce apresentou os menores valores de pH. O tratamento inoculação mais enzimas para a silagem de milho reidratado reduziu o pH 168. A equação de Richard (1959) foi a que melhor estimou os valores de pH para os tipos de inoculação e para o milho reidratado. Para as silagens de milho fortuna e doce o modelo proposto por Morgan et al. (1975) foi o que melhor ajustou os dados.

SUMMARY This work was carried out to evaluate the fermentation characteristics and aerobic stability, regarding the conventional high moisture corn grain silage (Fortuna variety), the high moisture sweet corn grain silage and the high moisture rehydrated corn silage. Data were statistically analyzed as a 3x3 factorial arrangement in a completely randomized design, and the factors were three types of corn (Fortuna, sweet and rehydrated) and three inoculation treatments (without inoculum, bacterial inoculum and bacterial inoculum plus enzymes). The aerobic stability values were assessed, collecting the temperatures from the room dry bulb and from the silage thermometers, and the pH values, at 0, 24, 48, 72, 96, 168, 192, 216, 240 and 296 hours after aerobic exposition. Additionally, different mathematical models to estimate the mean pH values after opening were tested. Interactions were observed (P<0.05) between types of corns and inoculants for aerobic stability and pH at 72, 168 and 192 hours after opening. Inoculated sweet corn silages presented better aerobic stability after aerobic exposition compared to the other silages. The sweet corn silage presented lowest pH values at 48 hours after opening. The pH values at 168 hours of rehydrated corn silage treated with bacterial inoculum plus enzymes was more acid. Richard’s Equation (1959) was the best tool for the pH estimation when either types of inoculants or rehydrated corn silage were considered. On the other hand, the model proposed by Morgan et al. (1975) was the best equation model to fit the data regarding either Fortuna or sweet corn silages.