An internal mixer connected to a torque rheometer was used to investigate the effect of moisture content (13.2 to 46.8 g.100g- 1), rotation speed (13.2 to 46.8 rpm) and processing temperature (53.2 to 86.8 °C), applying a factorial central composite design, on the specific mechanical energy (SME), pasting viscosity and crystallinity of cassava starch. Torque values were highly significant for the three variables, showing decrease with increasing moisture, temperature and rpm. The highest cold viscosity (CV) was obtained at 13.18 g.100g- 1 moisture, 86.87 °C and 30 rpm due to increased rupture of starch granules caused by processing at lower moisture condition. Peak viscosity (PV) values were higher than CV values which indicated that the processing was not able to destroy completely the molecular integrity of the starch granules. Smaller setback (SB) at high temperature and rpm and low moisture showed possible starch depolymerization causing loss of recrystallization capacity. Processing under low moisture content resulted in reduction of crystallinity. The results showed that the effect of moisture was more pronounced than rotation speed and processing temperature of cassava starch.

Foram estudados os efeitos da sacarose e da água de mistura no processamento de farinha de mandioca por extrusão. As variações de sacarose (0-20% p/p) e água (28-42% p/p) foram estudadas empregando-se metodologia de superfície de resposta. O processo de extrusão foi conduzido em uma extrusora de dupla rosca acoplado a um reômetro de torque. A energia mecânica específica (SME) dissipada no final da extrusora foi calculada. As amostras extrusadas foram analisadas quanto aos índices de absorção de água (WAI) e de solubilidade em água (WSI), e quanto às propriedades de pasta durante o ciclo de gelatinização/retrogradação usando-se um analisador rápido de viscosidade (viscosidade a frio (CV), pico de viscosidade (PV), breakdown e setback). SME e WSI diminuíram em função dos teores de água e açúcar. WAI e as propriedades de pasta foram influenciadas pelo teor de água. Não foi observado o efeito antiplastificante da sacarose nas propriedades de pasta, indicando que a adição de açúcar na mistura de farinha de mandioca não reduziu a capacidade da água em gelatinizar o amido durante o processo de extrusão. A natureza do ponto ótimo para o WAI, PV e BD foi uma sela, enquanto que para SME foi máximo e para CV e SB foi mínimo. Estes resultados podem ser usados na fabricação de produtos extrusados não expandidos de farinha de mandioca contendo açúcar com desejáveis propriedades funcionais para fins específicos.

The effects of sucrose and water contents on cassava flour processed by extrusion at varied concentrations of sucrose (0-20% w/w) and water (28-42% w/w) were studied by applying response surface methodology. The extrusion of the mixtures was performed in a twin screw extruder fitted to a torque rheometer. The specific mechanical energy (SME) dissipated inside a conical twin-screw extruder was measured. Water absorption index (WAI), water solubility index (WSI) and paste viscosity readings (cold viscosity (CV), peak viscosity (PV), breakdown (BD) and set back (SB)) during a gelatinization-retrogradation cycle measured in a Rapid Visco Analyzer were determined on non-directly extruded products. The results indicated that SME and WSI decreased as a function of water and sucrose contents. WAI and pasting properties were influenced by water content. A non antiplasticizing effect of the sucrose content was observed on pasting properties, suggesting that sucrose did not reduce the availability of water available for gelatinizing cassava flour during the extrusion process. The nature of the optimum point was characterized as a saddle point for WAI, WSI, PV and BD, whereas SME showed a maximum and CV and SB a minimum. The results indicated to be valuable for the production of non-expanded cassava flour extrudates with desirable functional properties for specific end users.

Chitinase is produced by a wide variety of plants as a defense against peste attacks. In this study, grape chitinases were purified 16 times by fractionation in 80% ammonium sulfate followed by dialysis and filtration. Purified chitinases exhibited enzymatic activity toward chitin azure. The yield of purified chitinase was 229 mg/L with chitinase activity of 563 U/g. Chitinases had molecular masses of 24 and 30 kDa, as evaluated by SDS-PAGE 12.5%. Two pH optima were determined 3.0 and 6.0. The optimal temperature was 42 °C. Pre hydrolysis of crystalline shrimp chitin by chitinases caused in an increase in the deacetylation ratio triggered by chitin deacetylase producing chitooligosaccharides with DA (degree acetylation) of 58.8%.

A farinha de arroz foi extrusada em presença de diferentes teores de água e sacarose. O processamento foi realizado em extrusora dupla-rosca, sob condições fornecidas por um delineamento experimental rotacional de segunda ordem. Os efeitos das variáveis independentes, teor de água (27,9 a 42,1%) e teor de sacarose (0,1 a 19,9%), sobre as propriedades físico-químicas dos extrusados, foram estudados. As variáveis dependentes avaliadas foram o índice de absorção de água (WAI), o índice de solubilidade em água (WSI), o índice de expansão volumétrica (VEI) e a densidade aparente (BD). A densidade aparente (BD) foi determinada para os extrusados antes e depois do processo de fritura. O aumento no teor de água resultou em maiores valores de WAI e VEI e menores valores de WSI e de BD (para as amostras fritas e não fritas). Os maiores teores de sacarose levaram a altos valores de WAI e VEI, e valores reduzidos de WSI e de BD (para as amostras fritas e não fritas). Ambas as variáveis independentes influenciaram, significativamente, as propriedades físico-químicas de extrusados de farinha de arroz. No entanto, o teor de sacarose foi a variável mais significativa. Os efeitos quadráticos, bem como a interação entre as duas variáveis independentes, também foram importantes para as variáveis das respostas estudadas.

Rice flour was processed by extrusion cooking in the presence of variable contents of water and sucrose. The process was carried out in a twin-screw extruder under the conditions given by a centre rotational experimental design of second order. The effects of the independent variables, water content (27.9 to 42.1%), and sucrose content (0.1 to 19.9%) on the physicochemical properties of the extrudates were investigated. The water absorption index (WAI), water solubility index (WSI), volumetric expansion index (VEI), and bulk density (BD) were determined as dependent variables. BD was determined for samples before and after frying. An increase in water contents resulted in higher WAI and VEI, and lower WSI and BD for extrudates before and after frying. Higher sucrose levels led to increased values of WAI and VEI and to reduced values of WSI and BD. Both independent variables had significant influence on the physicochemical properties of rice flour extrudates. However, the sucrose content was the most significant. The interaction between these two independent variables and their quadratic effect were also important for the responses studied.