A multiscale kinetics model for the analysis of starch amylolysis.

Simple exponential decaying functions are commonly used for fitting the kinetics of starch digested by amylolytic enzymes. A common assumption is that a sole exponential function can account for the kinetics of the whole digestible starch. Recent studies using logarithm-of-slope (LOS) plots showed that digestion kinetics can exhibit multi-scale behavior, an effect reflecting starch fractions with different digestion characteristics. This work proposed an extension of the widely used Goñi et al.'s model to account for two starch fractions; one fraction linked with fast digestion rate and other with slow digestion rates. The fitting of experimental data was carried out by solving numerically a nonlinear least-squares problem. The estimated parameters have a straightforward interpretation in terms of reaction rates and digestible/resistant starch fractions. Two experimental examples were used for illustrating the performance of the multi-exponential function.

Potential of taro starch spherical aggregates as wall material for spray drying microencapsulation: Functional, physical and thermal properties.

Taro starch spherical aggregates have been considered as wall material for the microencapsulation of bioactive compounds. The distribution of particle size, morphology, stability, glass transition temperature, ζ-potential, physical properties and flowability and compression indexes, and functional properties (water, oil and dye retention capacity) were measured. The average diameter was 17.5 ±â€¯0.3 µm. Aggregates formed by a relatively high number of starch granules were observed. The residual protein in the aggregates was in the periphery of the starch granules, favoring the aggregation and the stability under aqueous stirring conditions. The ζ-potential was -21.8 ±â€¯0.3 mV. The value of the glass transition temperature was in the range from 176.8 to 75.4 °C, with 5% and excess water, respectively. The Hausner ratio and Carr index were 1.06 and 14.7, respectively. The oil holding capacity was 1.2 ±â€¯0.01 g of oil·g-1 of dry solid. Overall, the functional, physical and thermal properties of the spherical aggregates of taro starch granules showed that this material offers good potential for the microencapsulation of bioactive compounds.

Isolation and partial characterization of starch from banana cultivars grown in Colombia.

Banana starch is resistant to hydrolysis by digestive enzymes due to its structure and dietary fibre content. Starch was isolated from the following three cultivars of Colombian Musaceae: Gros Michel (dessert), Dominico Harton and FHIA 20 (cooking); also, the amylose and amylopectin contents, morphology of the granules, thermal properties, pasting, molecular characteristics and digestibility were determined. The total starch content, amylose content and digestibility (gelatinized starch) were higher in cooking varieties; the purity and gelatinization temperature were similar for the three varieties, but the enthalpy was higher in the dessert variety. The three varieties showed higher viscosities in the pasting profile compared to commercial maize starch in both acid and neutral conditions. Starch granules presented with heterogeneous sizes and shapes (elongated and ovals) that had birefringence. The Dominico Hartón variety showed the lowest rapidly digestible starch (RDS) value in the gelatinized sample that is in agreement with the greater proportion of long chains.

Composition, digestibility and application in breadmaking of banana flour.

Banana flour (BF) was obtained from unripe banana (Musa paradisiacal L.) and characterized in its chemical composition. Experimental bread was formulated with BF flour and the product was studied regarding chemical composition, available starch (AS), resistant starch (RS) and rate of starch digestion in vitro. The chemical composition of BF showed that total starch (73.36%) and dietary fiber (14.52%) were the highest constituents. Of the total starch, available starch was 56.29% and resistant starch 17.50%. BF bread had higher protein and total starch content than control bread, but the first had higher lipid amount. Appreciable differences were found in available, resistant starch and indigestible fraction between the bread studied, since BF bread showed higher resistant starch and indigestible fraction content. HI-based predicted glycemic index for the BF bread was 65.08%, which was significantly lower than control bread (81.88%), suggesting a "slow carbohydrate" feature for the BF-based goods. Results revealed BF as a potential ingredient for bakery products containing slowly digestible carbohydrates.

Chemical composition and starch digestibility of tortillas prepared with non-conventional commercial nixtamalized maize flours.

Non-conventional nixtamalized maize flours elaborated by a factory in Mexico were used for tortilla preparation. Tortillas were stored at 4 degrees C for up to 72 h and the total starch, available starch, resistant starch and retrograded resistant starch were assessed. The traditional white tortilla, used as a control, showed higher protein and fat contents than blue maize tortilla, whereas a maize-bean mixed tortilla had the highest protein, ash and fat contents. Lower total starch was obtained in the maize-bean tortilla than in white and blue maize tortillas. The available starch content in all tortillas decreased with the cold-storage, although the change was more marked for blue-maize tortillas. The maize-bean mixed tortillas exhibited the lowest in vitro digestibility, which is consistent with the relatively high resistant starch levels in the bean. Differences in resistant starch content were found between the two maize tortillas, which might be related to the softer texture of blue-maize tortilla. The starch digestibility features of these new types of nixtamalized maize flours open up the possibility of producing tortillas with variable nutritional properties.

Effect of storage time on the retrogradation of banana starch extrudate.

Starch was isolated from banana starch and the retrogradation phenomenon was studied using diverse techniques, including an enzymatic measurement. Wide-angle X-ray scattering (WAXS) showed that the sample stored for 7 h presented small peaks and when the storage time increased the peaks increased in intensity. The type of diffraction pattern found in banana extrudates is typical of the A-type crystal polymorph. The crystallinity index from the diffractograms, showed a plateau after approximately 20 h of storage. The short-range order measurement with Fourier transform infrared (FTIR) spectroscopy showed that banana starch retrogradation reached a maximum value at approximately 11 h of storage, a value that agrees with the results obtained with differential scanning calorimetry (DSC), because the maximum enthalpy value (approximately 5 J/g) was calculated in the stored sample for 8 h, without changes in the stored samples for more time. Retrograded resistant starch values did not change after 12 h of storage, obtaining the maximum starch retrogradation level. FTIR, DSC, and the enzymatic technique showed the changes at the molecular level in starch during storage; in the case of WAXS, they determine the long-range order that explains the differences found in the starch retrogradation pattern measurement in banana starch.

Isolation and partial characterization of banana starches.

Two varieties of banana green fruit growing in Guerrero, Mexico, were used for starch isolation. Chemical analysis and physicochemical and functional properties were studied in these starches. The "macho" variety presented higher starch yield than "criollo". In general, chemical compositions in both starches were similar, except in ash content, where the "criollo" variety showed a lower value than "macho". The results of freeze-thaw stability suggested that banana starches cannot be used in frozen products. Both starches presented similar water retention capacity values that increased when temperature increased. Solubility profiles showed that at low temperature "criollo" had lower solubility than "macho", but at higher temperature an inverse behavior was evident; also the solubility increased when temperature increased. Behavior similar to that for solubility was obtained in the swelling test. The banana starch studies indicate the "macho" and "criollo" varieties have different starch structures as evidenced by viscosity.