Extração e caracterização de amido de Adlay (coix lacryma Jobi L.)

AUTOR(ES)
DATA DE PUBLICAÇÃO

1987

RESUMO

The objective of this research was to study the conditions for starch extraction from the cereal Adlay (Coix lacryma joblL.) as well as to carry out physico-chemical characterization of this probable starch source. Like other cereals, the Adlay grain showed high levels of carbohydrate (69.51%) but accompanied by relatively high levels of protein (16.82%). Processing and milling studies of the grain showed that it was possible to produce flour using a rice processor and subsequent Killing in the Brabender Quadrumat Senior mill. Using toluene: water mixture in the proportion 1:8, starch yields of approximately 44.9% were obtained from Adlay flour with protein and lipid levels of approximately 0.5% and 0.89% respectively. The level of damaged starch was 1.2 Farrand units. Under the optical microscope, the Adlay starch grain was shown to be small (1.2-3.5 u), spherical and, flattened, with a central depression. Under polarized light, the granules presented a central malta cross. The loss of birefringence started at approximately 68ºC, being practically complete at 75ºC. The absolute density was 1,4793 g/ml and the Intrinsic viscosity 1.3257 dl/g. The absorption capacity in cold water was 119.2% and the solubility index 0.09%. The swelling power and solubility index at 95ºC were 48.35 g/g and 20.81% respectively. A dark brown colour was produced with iodine similar to that obtained with waxy corn starch, but different from the blue colour obtained with the starch from normal corn. The Blue Value indicated a 2,32% content of amylose,, which justifies the colour obtained in the lodine reaction and the fact that there was no precipitation of amilse during the fractionation of the starch. The diffractograms obtained in the determination of cristallinity by X-rays were of the type A pattern, typical of cereal starches. In a study of the properties of Adlay starch paste, it was shown that the temperature for the inicial paste formation was high as compared to other cereal starches , but that the gelatinization range was narrow, showing that the forces maintaining the structure of the grain were homogeneous. Once maximum viscosity was attained there was a rapid loss, up to 50% of the maximum viscosity. The viscosity increase during the cooling cycle was small, amounting to aproximately 10% of the minimum viscosity at the constant temperature of 95ºC. Retrogradation tests showed no exudation of water from the starch after 15 days of storage at -2ºC. The optical transmittance values at 95ºC and/as with subsequent coolling, were higher than those obtained with normal corn starch, treatment of the starch at different pH values (3-8) showed no significant changes In the properties of the starch paste and nor did the addittions of sucrose (10-60%) , glucose (2-30) or sodium chloride (2-6%).

ASSUNTO(S)

coix amido graminae

ACESSO AO ARTIGO

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