A systematic approach for the chromatographic fractionation and purification of major steroid saponins in commercial extracts of Yucca schidigera Roezl.

Yucca schidigera Roezl. (yucca) is one of the major industrial sources of steroid saponins used as animal and human food additives. This work describes a new, systematic and reproducible three-step method by medium and high-pressure liquid chromatography (under RP, NP and RP conditions), for the isolation and purification of three groups of saponins, which were further purified in six sub-fractions, and finally into twelve individual steroid saponins previously reported in Y. schidigera. In accordance to the increasing applications of yucca extracts, further analytical, biological and physicochemical studies are still required. The presented method is applicable to the preparation of steroids saponins previously reported in commercial extracts of Y. schidigera, both as highly purified mixtures of defined composition, including twelve pure components.

MALDI-TOF mass spectrometry and reversed-phase HPLC-ELSD chromatography for structural and quantitative studies of major steroid saponins in commercial extracts of Yucca schidigera Roezl.

This paper describes a new, improved systematic qualitative analysis of yucca saponins in commercial products by combined use of high-pressure liquid chromatography (HPLC) coupled to an evaporative light scattering detector (ELSD) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS). Three groups with four saponins in each were completely resolved by HPLC-ELSD under C18 reversed-phase conditions using a linear gradient composed of methanol and water. The selectivity of the described HPLC-ELSD method is given by the sapogenin differences at C12 (carbonyl group) and at C2 (hydroxyl group), followed by the presence or absence of an exomethylene group at C25, and the composition and length of the oligosaccharidic chain at C3 in the sapogenins. The saponins were identified by chemical and spectroscopic methods including MALDI-TOF MS(1) and MS(2), high resolution MS, and one and bi-dimensional nuclear magnetic resonance (NMR) experiments. Among the twelve saponins identified, eleven were previously reported, and one is reported for the first time in Yucca schidigera. An identification flowchart procedure based on the analysis of the sodium adducts of intact saponins [M+Na](+) and the oligosaccharidic chain ions obtained in the MALDI-TOF MS(1) and the MS(2) spectrums, was developed for the analysis of Y. schidigera saponins. Two intact isomeric saponins were differentiated by this method, which could also be applied to the structural assignment of other steroid and triterpenic saponins. Using the four-major saponins as reference standards, a C18 reversed-phase HPLC-ELSD method was validated for their specific analysis in commercial extracts of Y. schidigera. Finally, the applicability of the HPLC-ELSD method for the relative quantification of yucca saponins is discussed.

Physical properties of emulsion-based hydroxypropyl methylcellulose films: effect of their microstructure.

The initial characteristics of emulsions and the rearrangement of the oil droplets in the film matrix during film drying, which defines its microstructure, has an important role in the physical properties of the emulsion-based films. The objective of this work was to study the effect of the microstructure (two droplet size distributions) and stability (with or without surfactant) of HPMC oil-in-water emulsions over physical properties of HPMC emulsion-based edible films. HPMC was used to prepare sunflower oil-in-water emulsions containing 0.3 or 1.0% (w/w) of oil with or without SDS, as surfactant, using an ultrasonic homogenizer. Microstructure, rheological properties and stability of emulsions (creaming) were measured. In addition, microstructure, coalescence of oil droplets, surface free energy, optical and mechanical properties and water vapor transfer of HPMC films were evaluated. Image analysis did not show differences among droplet size distributions of emulsions prepared at different oil contents; however, by using SDS the droplet size distributions were shifted to lower values. Volume mean diameters were 3.79 and 3.77 µm for emulsions containing 0.3 and 1.0% without surfactant, respectively, and 2.72 and 2.71 µm for emulsions with SDS. Emulsions formulated with 1.0% of oil presented higher stability, with almost no change during 5 and 3 days of storage, for emulsions with and without SDS, respectively. Internal and surface microstructure of emulsion-based films was influenced by the degree of coalescence and creaming of the oil droplets. No effect of microstructure over the surface free energy of films was found. The incorporation of oil impaired the optical properties of films due to light scattering of light. Addition of oil and SDS decreased the stress at break of the emulsion-based films. The replace of HPMC by oil and SDS produce a lower "amount" of network structure in the films, leading to a weakening of their structure. The oil content and SDS addition had an effect over the microstructure and physical properties of HPMC-based emulsions which lead to different microstructures during film formation. The way that oil droplets were structured into the film had an enormous influence over the physical properties of HPMC films.

Modeling texture kinetics during thermal processing of potato products.

A kinetic model based on 2 irreversible serial chemical reactions has been proposed to fit experimental data of texture changes during thermal processing of potato products. The model links dimensionless maximum force F*(MAX) with processing time. Experimental texture changes were obtained during frying of French fries and potato chips at different temperatures, while literature data for blanching/cooking of potato cubes have been considered. A satisfactory agreement between experimental and predicted values was observed, with root mean square values (RMSs) in the range of 4.7% to 16.4% for French fries and 16.7% to 29.3% for potato chips. In the case of blanching/cooking, the proposed model gave RMSs in the range of 1.2% to 17.6%, much better than the 6.2% to 44.0% obtained with the traditional 1st-order kinetics. The model is able to predict likewise the transition from softening to hardening of the tissue during frying.