Research has shown that chitosan induces plant stress tolerance and protection, but few studies have explored chemical modifications of chitosan and their effects on plants under water stress. Chitosan and its derivatives were applied (isolated or in mixture) to maize hybrids sensitive to water deficit under greenhouse conditions through foliar spraying at the pre-flowering stage. After the application, water deficit was induced for 15 days. Analyses of leaves and biochemical gas exchange in the ear leaf were performed on the first and fifteenth days of the stress period. Production attributes were also analysed at the end of the experiment. In general, the application of the two chitosan derivatives or their mixture potentiated the activities of the antioxidant enzymes superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase and guaiacol peroxidase at the beginning of the stress period, in addition to reducing lipid peroxidation (malonaldehyde content) and increasing gas exchange and proline contents at the end of the stress period. The derivatives also increased the content of phenolic compounds and the activity of enzymes involved in their production (phenylalanine ammonia lyase and tyrosine ammonia lyase). Dehydroascorbate reductase and compounds such as total soluble sugars, total amino acids, starch, grain yield and harvest index increased for both the derivatives and chitosan. However, the mixture of derivatives was the treatment that led to the higher increase in grain yield and harvest index compared to the other treatments. The application of semisynthetic molecules derived from chitosan yielded greater leaf gas exchange and a higher incidence of the biochemical conditions that relieve plant stress.

Chitosan induces plant tolerance to various abiotic stresses, including water deficit. However, its use may be limited, due to its constitution and low solubility in water. Thus, chemical modifications were proposed in this study with the objective of potentializing its biological effects in maize plants. The derivatives were semi-synthesized (N-succinyl and N,O-dicarboxymethyl) and, together with chitosan, they were applied, via the leaf, in a drought-sensitive maize hybrid (BRS1030) under pre-flowering water deficit. The water deficit was maintained for 15 days and the analyses were performed at the beginning and end of stress, and also in rehydration. Leaf water potential, gas exchange, chlorophyll fluorescence, and content of chloroplastidic pigments were evaluated. The use of the derivatives modulated photosynthesis parameters, affecting the involved mechanisms, such as stomatal activity, water use efficiency and photosystem II activity. Chlorophyll fluorescence indicated that the antenna complex was damaged by the water deficit condition, with a decrease in the energy flux in the electron transport chain and in the photochemical phase of photosynthesis. However, the spraying of chitosan derivatives induced tolerance to water deficit, suggesting that chitosan derivatives are more bioavailable to plants. Water stress decreases pigment content, but both the application of chitosan and derivatives increased these contents. It is concluded that chitosan derivatives improved the photosynthetic parameters in maize susceptible to drought, inducing tolerance to this stress, and the possible reasons and consequences are discussed.

ABSTRACT. The objective of this work was to evaluate the quality of 6 samples of Arabica coffee (Red Catuaí/144, new Avaliação da qualidade de cafés cultivados em Campos Gerais, no Estado de Minas Gerias, BrasilRESUMO. Este trabalho teve como objetivo avaliar a qualidade de seis amostras de café arábica (Catuaí vermelho/144, Mundo novo 4/376, Mundo novo Acaiá 19/474, Catuaí amarelo/62, Mundo novo 9/375, Mundo novo 19/379), submetidos à torra comercial média, cultivadas no município de Campos Gerais, Estado de Minas Gerias. Foram utilizados frutos provenientes das safras 2012, adquiridos em uma fazenda situada na região da Capoeirinha. Para as análises físico-químicas (pH, umidade, acidez total titulável, sólidos solúveis totais, pH e cafeína) e sensoriais foram utilizadas quatro repetições de cada amostra. Os resultados obtidos para as análises físico-químicas demonstram que todas as amostras podem ser cultivadas no município, pois estavam dentro dos padrões de qualidade estabelecidos para café torrado. Conclui-se que os cafés das cultivares Mundo novo 4/376, Mundo novo Acaiá 19/474, Catuaí amarelo 62, Mundo novo 19/379 e Mundo novo 9/375 foram classificados como cafés não especiais com pontuação abaixo do grau de especial (< 80). E a cultivar Catuaí vermelho 144 obteve baixos teores de acidez total titulável e foi a que apresentou os melhores valores para o parâmetro de pH, atributos responsáveis pelo aroma e sabor do café. Consequentemente considerado um café muito bom classificado como especial (80 a 84,99 pontos).Palavras-chave: cofé arábica, análise físico-química, análise sensorial.

RESUMO O leite é um alimento altamente nutritivo, devido a essa abundância nutricional torna-se um excelente meio para desenvolvimento de vários patógenos. O objetivo deste trabalho foi avaliar alguns parâmetros de qualidade físico-química e enzimáticas do leite cru de um laticínio em Campos Gerais, MG. As amostras de leite in natura foram coletadas dentro do tanque de refrigeração do laticínio. Foi analisada uma amostra de 200mL de leite in natura com 4 repetições durante 13 dias consecutivos, para as avaliações do alizarol, acidez, crioscopia, atividade da redutase e para os testes de antibióticos. Os resultados obtidos para as análises físico-químicas e enzimáticas demonstraram que as amostras de leite in natura atendiam aos requisitos mínimos estabelecidos pelo ministério da agricultura (BRASIL, 2011). Concluiu-se que a atividade desenvolvida pelo laticínio em estudo pode ser considerada eficiente. Uma vez que a administração do mesmo se preocupa em treinar e capacitar os produtores e os funcionários, evitando assim, diversos fatores que poderiam ocasionar problemas na produção. Palavras-chave: Análises físico-químicas. Análises enzimáticas. Atividade da redutase. Leite cru. Segurança alimentar.