RESUMO
The inhibitory effect of glucose on the activity of αamylase used for starch hydrolysis was explored in this study. Four gelatinized corn starch dispersions (5â¯g/100â¯mL) containing different glucose concentrations (0.5, 1.0, 2.0 and 4.0â¯g/100â¯mL) and a control without added glucose were subjected to enzymatic hydrolysis with αamylase (0.33â¯IU/mL) for 2â¯h. The hydrolysis kinetics showed that the limiting hydrolysis advance was reduced as glucose concentration increased. A Michaelis-Menten scheme was used for developing a mathematical model of the hydrolysis kinetics. The mathematical model predicted that the maximum hydrolysis value was consequence of the inhibition of the enzyme activity by the initial glucose load added to the gelatinized starch dispersions and by the glucose produced by amylolytic action. FTIR analysis of the Amide I band showed that glucose disrupted the secondary structure of the αamylase, an effect that could be related to the inhibition of the enzymatic activity.
Assuntos
Inibidores Enzimáticos/farmacologia , Glucose/farmacologia , Modelos Biológicos , Amido/química , alfa-Amilases/antagonistas & inibidores , Relação Dose-Resposta a Droga , Inibidores Enzimáticos/análise , Géis , Glucose/análise , Hidrólise , Cinética , Estrutura Secundária de Proteína , alfa-Amilases/químicaRESUMO
Aqueous dispersions of normal and waxy corn starch (3% w/w) were mixed with Tween 80 (0, 7.5, 15, 22.5 and 30â¯g/100â¯g of starch), and gelatinized (90⯰C, 20â¯min). Optical microscopy of the gelatinized starch dispersions (GSDx; xâ¯=â¯Tween 80 concentration) revealed that the microstructure was characterized by a continuous phase of leached amylose and amylopectin entangled chains, and a dispersed phase of insoluble remnants, called ghosts, on whose surface small granules were observed, imputed to Tween 80. The apparent viscosity of the GSDx decreased as the concentration of Tween 80 increased (up to about 70-90%). FTIR analysis of dried GSDx indicated that Tween 80 addition decreased short-range ordering. The content of rapidly digestible starch (RDS) and resistant starch (RS) fractions tended to increase significantly, at the expense of a significant decrease of slowly digestible starch (SDS) fraction, an effect that may be attributed to the increase of amorphous structures and starch chain-surfactant complexes. The RDS and RS increase was more pronounced for normal than for waxy corn starch, and the significance of the increase was dependent on Tween 80 concentration. Overall, the results showed that surfactant can affect largely the digestibility of starch chains.
Assuntos
Amilopectina/química , Amilose/química , Glucana 1,4-alfa-Glucosidase/química , Pancreatina/química , Polissorbatos/química , Zea mays/química , Animais , SuínosRESUMO
This work considered gelatinized wheat flour fraction with properties similar to hydrocolloid to enhance the strength of dough network by improving water retention and rheological characteristics. The gelatinized (90 °C) fraction of the wheat flour was incorporated in the dough formulation at different levels (5, 10, and 20% w/w). The effects of the gelatinized flour (GF) fraction on the dough rheology and thermal properties were studied. The incorporation of GF induced a moderate increase of dough viscoelasticity and reduced the freezing and melting enthalpies. On the other hand, the changes in bread textural properties brought by incorporation of GF were insignificant, indicating that the gelatinized fraction acted as a binder that enhanced water trapping in the structure. SEM images showed a more heterogeneous crumb microstructure (e.g., gas cells, porous, etc.) bread prepared using GF. Drying kinetics obtained from TGA indicated that the water diffusivity decreased with the incorporation of GF, which suggested that the bread had a compact microstructure.
RESUMO
Using calcium salts instead of lime allows for an ecological nixtamalization of maize grains, where the negative contamination impact of the traditional lime nixtamalization is reduced. This work assessed the effects of calcium carbonate (0.0-2.0%w/w CaCO3) on the morphology, crystallinity, rheology and hydrolysis of gelatinized maize starch dispersions (GMSD). Microscopy analysis showed that CaCO3 changed the morphology of insoluble remnants (ghosts) and decreased the degree of syneresis. Analysis of particle size distribution showed a slight shift to smaller sizes as the CaCO3 was increased. Also, X-ray patterns indicated that crystallinity achieved a minimum value at CaCO3 concentration in the range of 1%w/w. GMSD with higher CaCO3 concentrations exhibited higher thixotropy area and complex viscoelastic behavior that was frequency dependent. A possible mechanism involved in the starch chain modification by CaCO3 is that starch may act as a weak acid ion exchanger capable of exchanging alcoholic group protons for cations (Ca(+2)).