M.C. Núñez-Santiago

Physicochemical, digestibility and structural characteristics of starch isolated from banana cultivars

Banana starches from diverse varieties (Macho, Morado, Valery and Enano Gigante) were studied in their physicochemical, structural and digestibility features. X-ray diffraction indicated that the banana starches present a B-type crystallinity pattern, with slight difference in the crystallinity level. Macho and Enano Gigante starches showed the highest pasting temperatures (79 and 78°C, respectively), whilst Valery and Morado varieties presented a slight breakdown and higher setback than the formers. Morado starch presented the highest solubility value and Valery starch the lowest one. The swelling pattern of the banana starches was in agreement with their pasting profile. All banana starches showed a shear-thinning profile. The resistant starch (RS) fraction was the main fraction in the uncooked banana starches. Morado variety showed the highest amount of slowly digestible starch (SDS) and the lowest RS content reported until now in banana starches. Banana starch cooked samples presented an important amount of SDS and RS. Molecular weight and gyration radius of the four banana starches ranged between 2.88-3.14×10(8)g/mol and 286-302nm, respectively. The chain-length distributions of banana amylopectin showed that B1 chains (DP 13-24) is the main fraction, and an important amount of long chains (DP≥37) are present. The information generated from this study can be useful to determine banana varieties for starch isolation with specific functionality.

Preparation and characterization of octenylsuccinylated plantain starch.

Plantain starch was esterified with octenylsuccinic anhydride (OSA) at two concentrations (3 and 15% w/w) of OSA. The morphology, granule size distribution, pasting, gelatinization, swelling, and solubility of granules and structural features of the starch polymers were evaluated. Granules of the OSA-modified starches increased in size during cooking more than did the granules of the native starch, and the effect was greater at the higher OSA concentration. Pasting viscosities also increased, but gelatinization and pasting temperatures and enthalpy of gelatinization decreased in the OSA-modified starches. It was concluded that insertion of OS groups effected disorder in the granular structure. Solubility, weight average molar mass, Mw¯, and z-average radius of gyration, RGz, of the amylopectin decreased as the OSA concentration increased, indicating a decrease in molecular size.

Viscoelasticity, Conformational Transition and Ultrastructure of Kappa‐Carrageenan in the Presence of Potassium Ion around the Critical Total Ion Concentration

Rheology, microDSC, and confocal laser scanning microscopy were used to study the effect of potassium ion on the viscoelastic behavior, disorder‐order transition and the ultrastructure, respectively, of kappa‐carrageenan in aqueous medium in the vicinity of the critical total ionic concentration (C*). The rheological tests showed a “weak” gel behavior, with G′>G″ and both moduli dependent on frequency. However, during heating, microDSC showed two zones: one attributed to the presence of ordered double helices without aggregation, and another to the fusion of aggregated double helices. Microscopy showed a three‐dimensional network whose continuity depends of the concentration of added potassium ions. For a gel to be formed, a sufficient amount of potassium ion is necessary to promote complete aggregation of double helices so they can form a continuous three‐dimensional network.