Hernani Yee-Madeira

Physicochemical and Digestibility Properties of Double-Modified Banana (Musa paradisiaca L.) Starches

Banana starch was chemically modified using single (esterification or cross-linking) and dual modification (esterification-cross-linking and cross-linking-esterification), with the objective to increase the slowly digestible starch (SDS) and resistant starch (RS) concentrations. Physicochemical properties and in vitro digestibility were analyzed. The degree of substitution of the esterified samples ranged from 0.006 to 0.020. The X-ray diffraction pattern of the modified samples did not show change; however, an increase in crystallinity level was determined (from 23.79 to 32.76%). The ungelatinized samples had low rapidly digestible starch (RDS) (4.23-9.19%), whereas the modified starches showed an increase in SDS (from 10.79 to 16.79%) and had high RS content (74.07-85.07%). In the cooked samples, the esterified starch increased the SDS content (21.32%), followed by cross-linked starch (15.13%). Dual modified starch (cross-linked-esterified) had the lowest SDS content, but the highest RS amount. The esterified and cross-linked-esterified samples had higher peak viscosity than cross-linked and esterified-cross-linked. This characteristic is due to the fact that in dual modification, the groups introduced in the first modification are replaced by the functional group of the second modification. Temperature and enthalpy of gelatinization decreased in modified starches (from 75.37 to 74.02 °C and from 10.42 to 8.68 J/g, respectively), compared with their unmodified starch (76.15 °C and 11.05 J/g). Cross-linked-esterified starch showed the lowest enthalpy of gelatinization (8.68 J/g). Retrogradation temperature decreased in modified starches compared with unmodified (59.04-57.47 °C), but no significant differences were found among the modified samples.

Nanocomposites of rice and banana flours blend with montmorillonite: partial characterization.

Rice and banana flours are inexpensive starchy materials that can form films with more improved properties than those made with their starch because flour and starch present different hydrophobicity. Montmorillonite (MMT) can be used to further improve the properties of starch-based films, which has not received much research attention for starchy flours. The aim of this work was to evaluate the mechanical and barrier properties of nanocomposite films of banana and rice flours as matrix material with addition of MMT as a nanofiller. MMT was modified using citric acid to produce intercalated structures, as verified by the X-ray diffraction pattern. The intercalated MMT was blended with flour slurries, and films were prepared by casting. Nanocomposite films of banana and rice flours presented an increase in the tensile at break and elongation percentage, respectively, more than their respective control films without MMT. This study showed that banana and rice flours could be alternative raw materials to use in making nanocomposite films.

Physicochemical, Rheological and Structural Characteristics of Starch in Maize Tortillas

Fresh and stored maize (white and blue) tortillas were evaluated for physicochemical, rheological and structural characteristics assessed by calorimetry, x-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, dynamic viscoelastic tests, and high-performance size-exclusion chromatography. Two endotherms were found in studies of fresh and stored tortillas. The low temperature endotherm (50–56xa0°C) was due to reorganized (retrograded) amylopectin, while the high temperature endotherm (105–123xa0°C) was attributed to retrograded amylose. The enthalpy value for the lower temperature transition was minor than that of the high temperature transition. Fresh tortillas showed an amorphous starch arrangement by x-ray diffraction study. Stored samples showed the presence of peaks at 2θ = 17º and 23º, indicating re-crystallization of starch components. FTIR results confirmed the development of higher levels of starch crystals during storage. Differences in the viscoelastic parameters were also observed between fresh and stored samples. At the longest storage times, white tortillas were more rigid than blue tortillas. Molar mass values for starch increased for both white and blue tortillas as storage time progressed, though relatively higher values were obtained for white tortillas. More starch reorganization occurred in white tortillas, in accordance to calorimetric, x-ray diffraction, FTIR and rheological results. These results corroborate that changes occurring in tortillas during storage are related to reorganization of starch components, and the maize variety more than the color plays an important role.

Physico-chemical, nutritional and infrared spectroscopy evaluation of an optimized soybean/corn flour extrudate

A central composite design using RMS (Response Surface Methodology) successfully described the effect of independent variables (feed moisture, die temperature and soybean proportion) on the specific parameters of product quality as expansion index (EI), water absorption index (WAI), water solubility index (WSI) and total color difference (ΔE) studied. The regression model indicated that EI, WAI, WSI and ΔE were significant (pu2009<u20090.05) with coefficients of determination (R2) of 0.7371, 0.7588, 0.7622, 0.8150, respectively. The optimized processing conditions were obtained with 25.8xa0% feed moisture, 160xa0°C die temperature and 58xa0%/42xa0% soybean/corn proportion. It was not found statistically changes in amino acid profile due to extrusion process. The electrophoretic profile of extruded soybean/corn mix presented low intensity molecular weight bands, compared to the unprocessed sample. The generation of low molecular weight polypeptides was associated to an increased in In vitro protein digestibility (IVPD) of the extrudate. The FTIR spectra of the soybean/corn mix before and after extrusion showed that the α-helix structure remained unchanged after extrusion. However, the band associated with β-sheet structure showed to be split into two bands at 1624 and 1640xa0cm−1 . The changes in the β-sheet structures may be also associated to the increased in IVPD in the extruded sample.

The temperature-dependence of the energy band gap of CSVT-grown CdTe films determined by photoluminescence

Semiconducting films of CdTe grown by close-spaced vapour transport (CSVT) were studied by photoluminescence. One luminescence band located around 1.588 eV and labelled as /BE was observed at a temperature of T=10 K. Such a band was studied over a wide range of temperatures (10-300 K), and the mechanisms involved in it were identified. Both band-to-band (B-B) and excitonic (BE) recombination mechanisms are important at high temperatures (T>or=150 K), whereas at low temperatures the BE mechanism is the most important.

Calculation of the relaxation times for an inhomogeneous ESR line

A method for separately determining the longitudinal, T1, and transverse, T2, relaxation times from the saturation curve of an inhomogeneously broadened slow-passage ESR absorption line is presented. It imposes no restriction on the relative values of the spin packet (Lorentzian) and Gaussian widths conforming with the overall inhomogeneous width. It gives a simple way of calculating T2=2/(spin-packet width) through the deconvolution of a non-saturated experimental spectrum and then, in a direct and elegant way, the T1 is calculated once the amplitude of the microwave magnetic field, H1, for which the saturation curve of the absorption line reaches its maximum, is known. In addition, algebraic relations for T1 and T2 are given for the case of inhomogeneous broadening which, in the limit of Gaussian distribution width to 0, reduce to the homogeneous case. These algebraic relations give the spectroscopist the possibility of a direct calculation of T1 once a saturation curve up to its maximum has been obtained.

A Mössbauer study of hemoglobin in paroxysmal nocturnal hemoglobinuria

The57Fe Mössbauer spectra of concentrated hemoglobin (Hb) of normal subjects and six patients with Paraxysmal Nocturnal Hemoglobinuria (PNH) were studied at 300°K and 77 K. PNH is a very rare autoimmune hematological disease. The possibility of structural alterations of Hb induced by, or as part of the altered PNH-red cell membrane was the objective of this study. The Mössbauer parameters of the Hb of the normal subjects, both at 300 K and at 77 K, are identical to values previously reported. The PNH-Hb spectra show clear differences. They are wider and more asymmetric. At 77 K an extra doublet grows in with an isomer shift of 0.425 mm/sec. and a quadrupolar splitting, of 1.951 mm/sec. The other two doublets have δ′s and ΔQs slightly, but significantly, different from the corresponding values for normal Hb. These results are rationalized in terms of a population of Hb molecules with structures varying very slightly in a narrow range. The spread in structures manifests itself in a wider and more asymmetric Mössbauer spectrum.

Program for the analysis of pulse height spectra and the background from a proportional detector

A PC-Fortran program is presented for fitting of lineshapes and the analysis of pulse height spectra obtainable with proportional detectors. The common fitting and analysis of pulse height spectra by means of mixed Gaussian lineshapes is readily improved by using Voigt lineshapes. In addition, the background can be evaluated during the fitting process without the need of extra measurements.As an application of the program, a pulse height transmission spectrum accumulated with a static57Co source and detected with an argon-metane proportional detector, was least squares fitted to an elaborated complex trial lineshape function containing two Voigt lines plus a straight line. The fitting straight line parametersa andb characterize quantitatively the background. The very good PC-fitting obtained shows that the fitting of experimental spectra with the more realistic Voigt lineshapes is no longer a formidable task and that it is possible to evaluate and subtract the background inherent to the experiment during the fitting process.