Formação do pomar de tangerina 'Poncã', em função da adubação química e orgânica

Avaliou-se o efeito do esterco de curral curtido na adubação de formação do pomar de tangerineira 'Poncã' (Citrus reticulata, Blanco), comparando com a adubação química convencional. O experimento foi conduzido na Fazenda Experimental São Manuel da Faculdade de Ciências Agronômicas da UNESP, Câmpus de Botucatu-SP. Os tratamentos foram aplicados na adubação de formação do pomar durante dois anos. No primeiro ano, utilizaram-se 7,5; 15,0; 22,5 e 30,0 kg planta-1 de esterco de curral curtido e 400 g planta-1 de sulfato de amônio. Na adubação de formação do segundo ano, as doses de esterco de curral foram 15,0; 22,5; 30,0 e 37,5 kg planta-1 e 800 g planta-1 de sulfato de amônio. Nos dois anos, a adubação foi parcelada em três aplicações. Realizaram-se as avaliações aos 30; 150 e 270 dias após a última parcela de adubação do segundo ano, determinando-se: altura da planta, diâmetro do caule, volume, projeção e circunferência da copa. O delineamento experimental foi inteiramente casualizado, em parcelas subdivididas no tempo, e 3 repetições, sendo as parcelas representadas pela adubação e as subparcelas pelas épocas de avaliação. Verificou-se que, na média das avaliações, houve aumento linear das características avaliadas com o incremento das doses de esterco de curral curtido. Não houve diferença significativa entre os tratamentos com adubo orgânico e químico.

Análise química da madeira e casca de diferentes tipos de eucalipto antes e durante o cultivo de shiitake em toras

Avaliaram-se a composição química da madeira e da casca de sete espécies (E. saligna E. grandis, E. urophylla, E. camaldulensis, E. citriodora, E. paniculata e E. pellita) e três clones de eucalipto (híbridos de E. grandis x E. urophylla), antes e durante o cultivo das linhagens LE-95/01 e LE-96/18 de shiitake (Lentinula edodes), em toras. Cada linhagem de shiitake foi inoculada em nove toras de cada tipo de eucalipto com 1 m de comprimento e 9 a 14 cm de diâmetro. Assim, o delineamento experimental foi inteiramente casualizado, com 20 tratamentos e nove repetições, sendo cada repetição correspondente a uma tora. As toras foram mantidas em estufa climatizada, com temperatura de 25 ºC ± 5 e umidade relativa do ar entre 60-80%, durante 12 meses. Para a determinação da composição química da madeira, analisaram-se cunhas de discos e cascas de eucalipto recém-cortadas (sem inoculação das linhagens de L. edodes) e cunhas de discos e cascas retirados de toras já inoculadas com as linhagens de L. edodes após oito meses de incubação. Os resultados mostraram diferenças nos teores de holocelulose, lignina e extrativos totais na madeira e casca após o corte e depois de oito meses de incubação nas espécies e clones de eucalipto; o maior índice de decomposição da holocelulose na madeira, ao longo do tempo, ocorreu no E. saligna (5,5%), indicando, assim, ser o mais favorável para o desenvolvimento micelial do L. edodes. Já na casca aconteceu no clone 24 (22,2%). O E. camaldulensis apresentou o maior índice de decomposição da lignina na madeira (6,8%), ao longo do tempo. Já na casca, entre os eucaliptos testados, o E. grandis sofreu a maior decomposição de lignina (21,9%); o L. edodes degradou muito mais a holocelulose e lignina da casca que da madeira, tornando evidente a importância da casca; a casca da maioria dos tipos de eucaliptos apresentou menor teor de holocelulose, maior teor de extrativos totais e teores de lignina semelhantes ou superiores quando comparados com a madeira. O fator tipo de eucalipto (espécies e clones) teve maior efeito que o fator linhagem de L. edodes na degradação da holocelulose e lignina.

Caracterização físico-química, reológica e sensorial de iogurte obtido pela mistura dos leites bubalino e caprino

Milk from different animals can be used for dairy production. Yoghurt is a popular fermented milk product and considered to be one of the greatest importance in terms of consumer acceptance and consumption. The present research deals with the production of strawberry set-type yoghurt by mixing goat and buffalo s milk and it has the objective of taking advantage of the intrinsic characteristics of each milk to produce a final product with desirable attributes. It was conducted by analyzing five experimental groups with different proportions of goat and buffalo s milk: C 100% goat s milk; 7C3B - 70% goat s milk and 30% buffalo s milk, 5C5B - 50% goat s milk and 50% buffalo s milk, 3C7B 30% goat s milk and 70% buffalo s milk; B - 100% buffalo s milk. Each group was evaluated for total solids content and the acidification profile was monitored every 30 minutes by pH analysis. The yoghurt samples were analyzed for physical-chemical (pH, acidity, protein, fat, total and reducing sugars, ash and total solids), rheological (syneresis and viscosity) and sensory characteristics (appearance, odor, consistency and flavour). Samples with higher percentual of bubaline milk reached Vm faster, but the time necessary for pH 4.6 (Te) were similar between groups. Statistical differences (p<0.05) were observed for fat and total solids content of yoghurt, with superior values for groups higher proportions of buffalo s milk. The parameters of behavior reached by the model of Ostwald of Waale pointed yoghurt samples as non-Newtonian and pseudoplastic fluids. Yoghurt made only with goat s milk (C) had higher values (p<0.05) for syneresis, which can be explained by its fragile coagulum. Additionally, this group also had the lowest sensory scores for the attributes consistence and taste, while bubaline yoghurt (B) obtained the best acceptance indexes for all of the appraised parameters

Avaliação físico-química e funcional da algaroba prosopis juliflora proveniente da mesorregião agreste do Rio Grande do Norte

Algaroba (Prosopis juliflora) is a typical legume from arid and semi arid regions, which is composed by sugar-rich pods and high protein seeds. Phenolic compounds are secondary metabolites recognized as potent bioactive compounds, found in several vegetables.Therefore, the objective of this work is to characterize the algaroba flour in terms of its physicalchemical composition, total phenolic content, antioxidant activity by DPPH and ABTS methods, a-amylase and a-glycosidase inhibition, as well as to analyze its organic compounds by high performance liquid chromatography (HPLC). Three experimental groups were investigated (seeds, seeds and pod together and only pod), which were prepared by oven drying and posterior grinding. Water and ethanol extracts (70, 80, 100% v/v) were prepared and used for functional studies. Organic compounds were detected by using HPLC equipment coupled to mass spectrometer. Results show important physical-chemical differences among the experimental groups, seeds, seeds and pod together and only pod. The algarroba seed flour is high in protein (49.49%) and fat (3.10%), while the pod flour is especially rich in sugar (60.3% to 67.9%). Algaroba phenolics are concentrated in pod flour, mainly in water extracts (1.30 mg GAEQ/100g sample). All seed extracts showed high DPPH activity and maximum antioxidant activity was registered for ethanol 80% extracts (19.81 μM Trolox/g sample). The ABTS activity ranged from 9.73 to 12.74 μM Trolox/g sample. Nearly all the extracts were able to inhibit α-amylase activity mildly (30.50% to 48.80%), while the maximum α-glycosidase inhibition was observed for pod water extracts (81.03%). Algaroba water extracts proven to be especially rich in organic compounds, observed by the high number of chromatographic peaks. Results demonstrate that algaroba is a potential candidate for further investigations concerning its possible functional applications

Suco desidratado de caju (Anacardium occidentale L.) por atomização: caracterização físico-química, bioativa e estudo da vida de prateleira do produto

Despite the relatively organized cashew (Anacardium occidentale L.) productive chain and the number of cashew derivatives found in the market, it is estimated that over 90% of the cashew peduncle is wasted. A possible strategy for a better commercial exploitation of this agroindustrial commodity would be the production of spray dried cashew pulp. Thus, this paper approaches the yellow cashew pulp spray drying process and the final product evaluation. Based on that, the shelf life of the spray dried cashew pulp packed in different packaging was evaluated. Drying was conducted in two drying temperatures (140 °C to 150 °C) and two concentrations of Arabic gum (AG, 15% and 25%), which summed four experimental groups. The drying performance was evaluated as well as the physicochemical characteristics (moisture, water activity, total soluble solids, pH, density, solubility, particle diameter, hygroscopicity, degree of caking, color, scanning electronic microscopy and X-ray diffraction), composition (protein, ash, fat and sugars) and bioactive and functional value (total phenolic compounds, carotenoids, ascorbic acid and antioxidant activity) of the final products. Results showed spray drying efficiency higher than 65% for all experiments, mainly for the C4 group (150 °C and 25% AG) which reached efficiency of 93.4%. It was also observed high solubility (94.7% to 97.9%) and the groups with lower hygroscopicity (5.8% and 6.5%) were those with the highest proportion of drying coadjuvant. The particle diameters ranged between 14.7 μm and 30.2 μm and increased with the proportion of AG. When comparing the product before and after spray drying, the drying impact was evident. However, despite the observed losses, dried yellow cashew showed high phenolic concentration (from 235.9 to 380.4 mg GAE eq / 100 g DM), carotenoids between 0.22 and 0.49 mg/100 g DM and remarkable ascorbic acid levels (852.4 to 1346.2 mg/100 g DM), in addition to antioxidant activity ranging from 12.9 to 16.4 μmol TE/ g DM. The shelf life study revealed decreased phenolic content over time associated to a slight water activity increase. Overall, our results unveil the technological and bioactive potential of dried yellow cashew as a functional ingredient to be used in food formulations or as a ready-to-use product. The technological approach presented here can serve as an efficient strategy for a rational use of the cashew apple, avoiding its current underutilization

Fertilidade do solo e nutrição de tangerineiras Ponkan manejados com resíduos sólidos e adubação química

The objective of this research was to evaluate some soil chemical attributes and the nutritional status of 'Ponkan' mandarin managed with organic residues and chemical fertilization. The experiment was carried out at the Natural Resource Department-Soil Science Area, in the College of Agronomic Sciences -UNESP/Botucatu, SP. 'Ponkan' Mandarin seedlings were cropped and managed using the organic residues sewage sludge, cattle manure and chemical fertilization. The results allow the conclusion that there was an increase in the CEC, OM, N-total, P and K values in the soil managed with organic residues. The sewage sludge application did not harm the soil quality because the input of elements As, Cd, Cr and Hg present in its constitution were not significant. The soil management with organic residues increased significantly contents of N, P, Ca and S in 'Ponkan' leaves but did not contribute to increase significantly the elements B, Cu, Fe, Mn, Zn, As, Cd, Cr and Pb. The soil management with sewage sludge did not result in significant increase in the As, Cd, Cr and Hg content of leaves and fruits.

Extração supercrítica do óleo de linhaça: construção do extrator, estudo de parâmetros de processo, avaliação química e antioxidante do produto

The aim of the present study was to extract vegetable oil from brown linseed (Linum usitatissimum L.), determine fatty acid levels, the antioxidant capacity of the extracted oil and perform a rapid economic assessment of the SFE process in the manufacture of oil. The experiments were conducted in a test bench extractor capable of operating with carbon dioxide and co-solvents, obeying 23 factorial planning with central point in triplicate, and having process yield as response variable and pressure, temperature and percentage of cosolvent as independent variables. The yield (mass of extracted oil/mass of raw material used) ranged from 2.2% to 28.8%, with the best results obtained at 250 bar and 50ºC, using 5% (v/v) ethanol co-solvent. The influence of the variables on extraction kinetics and on the composition of the linseed oil obtained was investigated. The extraction kinetic curves obtained were based on different mathematical models available in the literature. The Martínez et al. (2003) model and the Simple Single Plate (SSP) model discussed by Gaspar et al. (2003) represented the experimental data with the lowest mean square errors (MSE). A manufacturing cost of US$17.85/kgoil was estimated for the production of linseed oil using TECANALYSIS software and the Rosa and Meireles method (2005). To establish comparisons with SFE, conventional extraction tests were conducted with a Soxhlet device using petroleum ether. These tests obtained mean yields of 35.2% for an extraction time of 5h. All the oil samples were sterilized and characterized in terms of their composition in fatty acids (FA) using gas chromatography. The main fatty acids detected were: palmitic (C16:0), stearic (C18:0), oleic (C18:1), linoleic (C18:2n-6) and α-linolenic (C18:3n-3). The FA contents obtained with Soxhlet dif ered from those obtained with SFE, with higher percentages of saturated and monounsaturated FA with the Soxhlet technique using petroleum ether. With respect to α-linolenic content (main component of linseed oil) in the samples, SFE performed better than Soxhlet extraction, obtaining percentages between 51.18% and 52.71%, whereas with Soxhlet extraction it was 47.84%. The antioxidant activity of the oil was assessed in the β-carotene/linoleic acid system. The percentages of inhibition of the oxidative process reached 22.11% for the SFE oil, but only 6.09% for commercial oil (cold pressing), suggesting that the SFE technique better preserves the phenolic compounds present in the seed, which are likely responsible for the antioxidant nature of the oil. In vitro tests with the sample displaying the best antioxidant response were conducted in rat liver homogenate to investigate the inhibition of spontaneous lipid peroxidation or autooxidation of biological tissue. Linseed oil proved to be more efficient than fish oil (used as standard) in decreasing lipid peroxidation in the liver tissue of Wistar rats, yielding similar results to those obtained with the use of BHT (synthetic antioxidant). Inhibitory capacity may be explained by the presence of phenolic compounds with antioxidant activity in the linseed oil. The results obtained indicate the need for more detailed studies, given the importance of linseed oil as one of the greatest sources of ω3 among vegetable oils

Composição química e aspectos morfológicos de mudas de Tabebuia chrysotricha (Standl.) produzidas em diferentes substratos e soluções de fertirrigação

The work aimed to study the formation of Tabebuia chrysotricha Standl. seedlings in function of four substrates, varying the covering fertilization solutions. To compose the substrate it was used fibrous and granulated coconut fiber obtaining the following treatments: 100% fibrous (100% F), 60% fibrous + 40% granulated (60% F+40% G), 40% fibrous + 60% granulated (40% F+60% G) and 100% granulated (100% G). The basis fertilization was the same for all treatments and the solutions of covering fertilization varied in order to obtain complete solutions with electric conductivities of 1.06 dS m(-1), 2.12 dS m(-1), 3.2 dS m(-1) and 4.25 dS m(-1). The propagative material was sowed directly in plastic containers (120mL) with the respective substrates. The fertilization was received through sub-irrigation once a week, respecting the treatments of fertilizations. Seedlings produced in 100%G had been taller and higher than the others. The chemical analyses of aerial part were obtained when the seedlings were ready for expedition (height of 20 cm). The seedlings production in substrate 100% F and 60% F+40% G allowed them to have higher N, S, B, Mn and Zn concentrations in the aerial part. The production of T chrysotricha seedlings is recommended in granulated coconut fiber substrate and fertilizer solutions with EC of 1.06 dS m(-1)

A tabela periódica: um recurso para a inclusão de alunos deficientes visuais nas aulas de química

Nowadays there are many reasons that aim to include people with special necessities, like those with visual deficiency, in the world of work, education, and in the society as a whole. However it is observed that when we talk about schooling inclusion, especially in High School, there is a huge gap between the theory and the practice. The lack of didactic resources, the inadequate installations, unprepared teachers, the families´ lack of information, are some of the factors that hinder the process of inclusion. Furthermore, the educators also have to deal with the roughness of the disciplinary contents and, refering to the study of Chemistry, with the use of signals related to this subject´s language. So, the objective of our research is to reflect about the apprehension of this language by the visually handicapped people, and try to contribute with their process of inclusion in the school life. On this perspective we work with the Periodic Table, which constitutes one of the indispensable tools necessary to the Chemistry learning. In order to acomplish it, the way followed by us happened in three passages. Initially, by means of a semistructured interview, we tried to get acquainted with the blind students opinion, who were participating in the research about the Periodic Table used by them throughout High School, as well as the dificulties felt when using it. After getting the answers, the Table was reelaborated to fill those students´necessities. Here, two new Tables were designed, one in Braille which shape is more compacted, and another made with high printed dots, built with sand and glue. On the third moment, the new designed Tables were tested by the students and, by means of a semi-structured interview, we tried to identify if this new resource would solve the problems concerned to the old Table. The students showed that the compacted Tables would facilitate the touch reading of the chemical elements simbols, making it clear and fast. We hope that, with the elaboration of this learning tools we can contribute with one of the elements to favor the effective participation of blind students in Chemistry classes, when studying the Periodic Table

A química no ensino médio e a contextualização: a fabricação dos sabões e detergentes como tema gerador de ensino aprendizagem

El conocimiento químico es muy importante a la comprensión de procesos físicos y químicos que nos acercan, por una opción de una vida mejor con calidad, fomentando y acompañando el desarrollo tecnológico. Sin embargo, la formación de un pensamiento químico fruto de un aprendizaje significativo es hoy, en todo el país, un reto paro los educadores de química. Estúdios señalan la contextualización de los contenidos químicos como recurso para promover una interrelación entre conocimientos escolares y hechos/situaciones presentes en el cotidaiano de los alumnos, añadiendo significado a los contenidos escolares, proporcionando a los alumnos un aprendizaje significativo. Con tal objetivo, la siguiente pesquisa se realizó con la intención de contribuir con la enseñanza de química y con el propósito general de proponer un materila didáctico que presentase una forma contextualizada de trabajar algunos conceptos y contenidos fundamentales a la química, con tema generador de la enseãnaza y aprendizaje a la fabricación de jabones y detergentes. Con objetivo de justificar la elección del planteamiento de la contextualización y la elaboración del material didáctico, se hizo una pesquisa acerca de la enseãnaza de química en al red pública de educación y la relación de ésta con los contextos pertenecentes a la realidad de los alumnos. Se observó que la enseñanza de química actual en la red pública de educación es tradicional y descontextualizada. Los resultados de esta pesquisa muestran la necesidad de cámbios la forma de como se enseñan los contenidos químicos. En la segunda parte de la pesquisa, se produjo la elaboración de la unidad didáctica de enseñanza, con el objetivo de promover el aprendizaje significativo de conocimientos químicos a partir del tema de la fabricación de jabones y detergentes. Se observó que el trabajo alcanzó los objetivos propuestos. Una evaluación cualitativa mostró que los alumnos estuvieron más participativos e interesados al estudiar química de esta forma. Relatos y decalraciones de los alumnos también indicaron que hubo un aprendizaje significativo de los contenidos trabajados y que los alumnos son capaces de transferirlos para la comprensión de situaciones reales. Y una evaluación cuantitativa del material nos reveló que 87,09% de los alumnos obtuvieron apuntes iguales o superiores a la media necesaria para la aprobación. Esperamos que hayamos contribuído para mejorar la calidad de la enseñanaza de química y que este trabajo sea solamente un comienzo de una gran jornada

A formação inicial do professor de química e o uso das novas tecnologias para o ensino: um olhar através de suas necessidades formativas

La disertación, desarrollada en el Programa de PostGraduación en Enseñanza de las Ciencias Naturales y de la Matemática de la UFRN, estudia las necesidades formativas de licenciandos en Química sobre el uso de las nuevas tecnologías de la información y de las comunicaciones (NTIC), en especial, las relacionadas con la utilización de programas computacionales para la enseñanza de la química. En la actual sociedad del conocimiento, se torna imperativo la eclosión de nuevas formas de aprender y de enseñar, que requieren de nuevas concepciones del trabajo pedagógico. En ese sentido, se exige de los profesores el desarrollo de nuevas habilidades y competencias. El presente trabajo está comprometido con la búsqueda de elementos que puedan nortear los procesos formativos de profesores de química con el objetivo de contribuir con una mejor preparación de la formación inicial, tomando en cuenta sus necesidades de formación. Fue utilizado el cuestionario como instrumento de investigación para diagnosticar y caracterizar las necesidades fomativas, buscando establecer correlaciones entre diferentes variables que cacarterizan el estudio, con el fin de establecer semenazas y discrepancias entre las habilidades docentes en estudio y las necesidades formativas. Los analises de los datos tomo elementos de la estadistica descriptivo e inferencial, con analises multivariados, lo que posibilitó identificar las necesidades formativas. Los resultados muestran ue de forma general los licenciandos evaluan como de bajo, el grado de desarrollo de las habilidades para enseñar usando las NTIC, así como manifiestan sentir necesidades formativas en todas las habilidades referentes a esa esfera del trabajo docente

Opiniões sobre estágio curricular e prática de ensino na licenciatura em química: o caso do CEFET-PB

The Brazilian legal documents are directing the reformulation of the courses that prepare students to be teachers. Through out the country many institutions look for to fit themselves in such documents. On the other hand, other IES (Superior Education Institutions), when they are setting up such courses they looked for to be adequate to the new public politics. Based on the National Curricular Norms to form teachers for Basic Education, in tertiary level, in 2004 it was created at the CEFET-PB,the Chemistry Course (Licenciatura) to prepare people to be teachers, whose organization. This work presents the results of a research of phenomenological nature that aimed to comprehend the teachers opinions, in the range of discussions about the current politics of formation, particularly related to the CNE/CP 1 and CNE/CP 2/2002 resolutions. This work based on the curricular proposal for the Chemistry Course (Licenciatura), presents the relationship between the probationary period and the teaching practice at the CEFET-PB, in order to contribute for a reflection about these categories to clarify the teachers of the course. It started from the consideration of all changes operated in contemporary society implies changes on teacher's pedagogical practices. It was used tow instruments for the data collection: a questionnaire with open and closed questions and recordable interviews. Nine teachers form the CEFET-PB took apart and four licensed teachers. It was based in a theoretic frame as a support for discussions about the different models of teachers formation. We concluded that the representations of teachers about probationary period the practice on the activity for the teachers formation was strongly anchored in characteristic elements of the formative tendency of a institution that historically acted on a technician formation, and the results pointed to strong signs of attitudes based on a model of the technical rationality

Abordando as relações ctsa no ensino da química a partir das crenças e atitudes de licenciandos: uma experiência ormativa no Sertão Nordestino

Este estudio investigó las actitudes y creencias de los estudiantes universitarios en Ciencias Químicas por la Universidad de Río Grande do Norte (UERN) como un paso hacia la elaboración de una propuesta de material didáctico para el estudio de las relaciones CTSA en la licenciatura en química. Para el conocimiento de las actitudes y creencias fue utilizado dos instrumentos (Escala Likert y un cuestionario), que proporcionó un análisis dentro del nuevo paradigma de investigación (cuantitativa y cualitativa) en la Enseñanza de la Ciencia y Matemáticas. Los resultados mostraron que los estudiantes de licenciatura en química tienen creencias positivistas y que suelen son considerados por algunos como ingenuas, como la creencia en el modelo de decisión tecnocrática, la linealidad del desarrollo científico y tecnológico que lleva a el bienestar social y neutralidad de los conocimientos científicotecnológico. Basándose en estos datos y la literatura sobre el tema se elaboraron tres módulos de aprendizaje: a) Cuestionando la hegemonía del conocimiento técnico y científico, b) Las relaciones entre ciencia, tecnología, sociedad y medio ambiente - las relaciones CTSA c) Propuesta de temática para la enseñanza de la química en una perspectiva de CTSA: El Río Mossoró. Por último, el material producido se utilizó en dos cursos ocurridos en el Campus Central en el Centro de Educación Superior en São Miguel, ambos de UERN. Los participantes expresaron su aprobación al enfoque trajo de el experimento propuesto y de el caso de simulación contenidos en la propuesta de

A estratégia didática de resolução de problemas na formação de professores de química

In this work it is presented a research developed in the initial training of teachers of the chemistry graduation course at the Universidade Federal do Rio Grande do Norte (UFRN). The intervention was realized in two classes in the context of a discipline in the curricular structure with nineteen undergraduate students of chemistry. The study utilizes characteristics of the qualitative approach and uses observation, questionnaires, interviews and examination papers. The experiment involved a sequence of activities fundamented on the Problem Solving (PS) teaching strategy to approach chemical concepts. The proposal was planned and organized according to the theoretical presupposition of the work developed by the authors of the Science Education in PS, of teaching experience and from the initial hypotheses of the research. The goal was that the future teachers could experience the strategy and advance to the new meanings. The themes addressed in the activities were the difference between exercises and problems, exercises turning into problems, the steps of problem solving and some implications of the teaching strategy for the work of the teacher. The results showed evidence that through a process of collective reflection, and from the difficulties experienced in the strategy practice, the undergraduates are introduced to new perspectives of reflection and action of teaching practice, and understanding some benefits of innovative proposals for the teaching of chemistry. It also showed that, although this theme is approached, in some moments of the graduation, the future teachers don‟t know when or how to realize activities in this perspective. From the aspects that rose in research we highlighted the difficulties in the problem solving steps, the use of the strategy in school and the knowledge and skills of the teacher for planning activities in Problem Solving

Análise das provas objetivas de química dos vestibulares da UFRN de 1997 a 2010: uma caracterização a partir das mudanças

Las pruebas de vestibular, en los últimos años en el Brasil, han sido objeto de diversas investigaciones, considerando que ese proceso selectivo es una de las vias para ingresar en las universidades públicas y termina por influenciar la enseñanza en las escuelas. De esa forma, algunos vestibulares han pasado por cambios, de un simple proceso selectivo clasificatorio a un proceso fundamentado en reflexiones sociológica, pedagógica y crítica, lo que ha promovido cuestionamientos respecto del aprendizaje y de su papel en la escuela. Delante de esa realidad, la Universidad Federal de Rio Grande del Norte (UFRN) ha implementado cambios en sus vestibulares procurando una aproximación a las Orientaciones Curriculares Nacionales, como los PCNEM, los PCN+ y las OCEM. Siendo así, el objetivo de este estudio fue caracterizar el avance cualitativo en las pruebas de preguntas objetivas a partir de los cambios ocurridos en el vestibular de la UFRN en el periodo de 1997 a 2010, definiéndose las siguientes cuestiones de estudio: ¿Cuáles son los tipos de preguntas que caracterizan las pruebas objetivas de Química del vestibular? ¿Cuáles cuestiones presentan las mayores dificultades para los candidatos? ¿Cuáles son los contenidos conceptuales privilegiados? ¿En qué tipo de preguntas los candidatos presentan mayores índices de éxitos? ¿Qué diferencias pueden ser establecidas entre las preguntas antes y después del periodo que establece los cambios en el vestibular de la UFRN? Las discusiones teóricas del estudio están fundamentadas en las siguientes referencias: PCNEM (BRASIL, 1999), PCN+ (BRASIL, 2001), OCEM (BRASIL, 2006), Zabala (1999), Jiménez Aleixandre et al. (2003), Pozo (1999), Álvarez de Zayas (1992), Núñez (2009), Relatorios Comperve/UFRN (1997 a 2010), e en relación a las evaluaciones: Pasquali et al. (2003), Silva y Núñez (2008), Marín y Benarrouch (2009). Para el estudio fueran construidas las siguientes categorías que permitieran el análisis de las cuestiones: contextualización de la cuestión, temas conceptuales, problema, representación semiótica, cálculo matemático, pertinencia de la cuestión e índice de acierto. Los resultados muestran un avance cualitativo de las preguntas de Química, en los cuales se observa un modelo de prueba que prioriza el uso de verdaderos problemas, de situaciones contextualizadas, de pocos cálculos, dándose prioridad al razonamiento que implica la comprensión, la aplicación y la interpretación de los conocimientos conceptuales, todo lo que puede estimular una enseñanza más adecuada en relación a las exigencias actuales de la Educación en Química