Abstract
Considering the importance of cassava starch for Brazilian industries, the current work aimed at evaluating the effects of extrusion parameters on the physical characteristics, mainly viscosity properties of extruded cassava starch. A factorial central composite design (2³) with three independent variables and the response surface methodology were used to evaluate the results of expansion index, specific volume, water absorption index, water solubility index, color and paste properties, according to the variations in the moisture content, barrel temperature and screw speed. Results indicated that barrel temperature influenced the expansion index, specific volume, water absorption index, all the color parameters, the initial viscosity, peak and final viscosity. Feed moisture influenced the specific volume, color parameters, final viscosity and retrogradation. The screw speed had effects on water absorption index, color components as well as on the final viscosity and retrogradation of extruded starch. High moisture, low screw speed and intermediate temperature provided lower starch degradation, which is desirable for pre-cooked starch.
Highlights
Cassava is the second most important source of starch in Brazil, constituting an industrial input into strategic sectors of the economy
The ‘central composite rotational’ design for three factors was adopted, according to Cochran & Cox (1957), including a total of 15 treatments, as follows: eight treatments corresponded to a 23 factorial, where the three factors were S = screw speed; T = barrel temperature; M = feed moisture (%); each one at two levels coded as –1 and +1; six treatments included the minimum and maximum levels of each factor coded as –α and + α, respectively, where α = 23/4 = 1.682 ; one central treatment was repeated six times, in which all factors were at an average level coded as zero (Table 1)
The centesimal composition of the cassava starch indicated: 12.2% of moisture, 88.43% of starch, 0.15% of fiber, 0.14% of total sugar, 0.26% of lipids, 0.07% of protein and 0.1% of ash, showing that the product is in agreement with the legislation demands ( BRASIL, 1978)
Summary
Cassava is the second most important source of starch in Brazil, constituting an industrial input into strategic sectors of the economy. In 2005, the country produced 26.8 million tons of cassava roots within an area of 1.9 million ha, and the main producers were the states of Pará, Bahia, Paraná, Maranhão and Rio Grande do Sul. In the same year, the production of cassava starch yielded 546.5 thousand tons, and the Paraná State was the greatest producer (IBGE, 2007). Modified starch is mainly used in Brazil by the paper industry, and smaller amounts are destined to the food and textile sectors. Native starch is not the most appropriate form for specific processing. It is modified in order to obtain starchy products that have the properties needed for specific uses (Franco et al, 2001)
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