Amparo López-Rubio

A novel approach for calculating starch crystallinity and its correlation with double helix content: a combined XRD and NMR study.

A peak fitting procedure has been implemented for calculating crystallinity in granular starches. This methodology, widely used for synthetic polymers, is proposed to better reflect the crystalline content of starches than the method normally used, in which it is assumed that relatively perfect crystalline domains are interspersed with amorphous regions. The new approach takes into account irregularities in crystals that are expected to exist in semicrystalline materials. Therefore, instead of assuming that the amorphous background extends up to the base of diffraction peaks, the whole X‐ray diffraction (XRD) profile is fitted to an amorphous halo and several discrete crystalline diffraction peaks. The crystallinity values obtained from the XRD patterns of a wide range of native starches using this fitting technique are very similar to the double helix contents as measured by 13C solid state NMR, suggesting that double helices in granular starches are present within irregular crystals. This contrasts with previous descriptions of crystalline and noncrystalline double helices that were based on the analysis of XRD profiles as perfect crystals interspersed in a noncrystalline background. Furthermore, with this fitting methodology it is possible to calculate the contribution from the different crystal polymorphs of starch to the total crystallinity.

Overview of Active Polymer-Based Packaging Technologies for Food Applications

Abstract There has been a growing interest and effort over the last few years in the development of novel food packaging concepts, which can play a proactive role regarding product preservation, shelf-life extension, and even improvement. Several strategies have been devised to exert a positive action over the packaged foodstuff, including retention of desirable molecules (i.e., aldehydes, oxygen) and release of substances (i.e., carbon dioxide, aromas). These new developments have been generally termed active packaging technologies. However, many of these emerging active packaging technologies are finding in the versatility and special properties of plastic materials an efficient vehicle to exploit and enhance their commercial interest. This overview examines the most recent developments and technologies designed to include the active principle within the plastic packaging materials and generally termed active plastics technologies. Due to the novelty of most of these active packaging developments, the s...

Molecular rearrangement of starch during in vitro digestion: Toward a better understanding of enzyme resistant starch formation in processed starches

Resistant starch (RS) is defined as the fraction of starch that escapes digestion in the small intestine, serving as a fermentation substrate for beneficial colonic bacteria. Several studies have been focused on the description of the RS fractions from different starch varieties, but little attention has been paid to the digestion process itself that, from the present work, seems to play a key role in the generation of enzyme-RS (ERS), as determined in vitro. High-amylose starch samples, extruded at two different processing conditions, have been characterized at different stages of in vitro digestion using scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), infrared spectroscopy (FT-IR), solid state (13)C NMR spectroscopy, and X-ray diffraction (XRD). Control samples kept for 18 h in the digestion solution without starch hydrolyzing enzymes (alpha-amylase and amyloglucosidase) were used for comparison purposes. An increase in molecular order was favored by the hydrolytic action of the enzymes, reflected in an increase in double helical order observed by NMR, higher crystallinity measured by XRD, and corresponding changes in FT-IR spectra. An increase in the intensity of the scattering objects was also observed by SAXS as a function of digestion. SAXS from the dry ERS fractions reveals the 001 reflection of crystallites formed during the digestion process, corresponding to a characteristic dimension of the resistant crystalline fraction of approximately 5 nm. The changes found suggest that enzyme resistant starch does not refer to a specific structure present in predigested starches, but may in fact be formed during the digestion process through the rearrangement of amylose chains into enzyme-resistant structures of higher crystallinity. Therefore, the resistance to enzyme digestion of a specific processed starch is the result of a competition between the kinetics of enzyme hydrolysis and the kinetics of amylose retrogradation.

Encapsulation of Living Bifidobacteria in Ultrathin PVOH Electrospun Fibers

This study shows the application of the electrospinning technique as a viable method for the encapsulation and stabilization of bifidobacterial strains. Poly(vinyl alcohol) (PVOH) was used as the encapsulating material because it is generally recognized as safe (GRAS), has a high oxygen barrier when dry, and is water soluble, hence allowing easy recovery of the bacteria for viability testing. A coaxial setup was used for encapsulation, and the so-obtained electrospun fibers had a mean diameter of ca. 150 nm. Incorporation of B. animalis Bb12 led to a decrease in melting point and crystallinity of the PVOH fibers and to an increase in the polymer glass transition temperature. The viability tests, carried out at three different temperatures (room temperature and 4 and -20 degrees C) showed that B. animalis Bb12 encapsulated within the electrospun PVOH fibers remained viable for 40 days at room temperature and for 130 days at refrigeration temperature, whereas a significant viability decrease was observed in both cases when bacteria were not encapsulated (p = 0.015 and p = 0.002, respectively).

Encapsulation of folic acid in food hydrocolloids through nanospray drying and electrospraying for nutraceutical applications

In this work, two different technologies (electrospraying and nanospray drying) were evaluated for the encapsulation of folic acid using both a whey protein concentrate (WPC) matrix and a commercial resistant starch. The morphology of the capsules, molecular organization of the matrices upon encapsulation, encapsulation efficiency, and stability of the folic acid within the capsules under different storage conditions and upon thermal exposure were studied. Results showed that spherical nano-, submicro- and microcapsules were obtained through both techniques, although electrospraying led to smaller capsule sizes and to an enhanced control over their size distribution. Greater encapsulation efficiency was observed using WPC as encapsulating matrix, probably related to interactions between the protein and folic acid which favoured the incorporation of the bioactive. The best results in terms of bioactive stabilization in the different conditions assayed were also obtained for the WPC capsules, although both materials and encapsulation techniques led to improved folic acid stability, especially under dry conditions.

Characterization of polyhydroxyalkanoates synthesized from microbial mixed cultures and of their nanobiocomposites with bacterial cellulose nanowhiskers.

The present work reports on the production and characterization of polyhydroxyalkanoates (PHAs) with different valerate contents, which were synthesized from microbial mixed cultures, and the subsequent development of nanocomposites incorporating bacterial cellulose nanowhiskers (BCNW) via solution casting processing. The characterization of the pure biopolyesters showed that the properties of PHAs may be strongly modified by varying the valerate ratio in the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) copolymer, as expected. Increasing the valerate content was seen to greatly decrease the melting temperature and enthalpy of the material, as well as its rigidity and stiffness, resulting in a more ductile behaviour. Additionally, the higher valerate PHA displayed higher permeability to water and oxygen and higher moisture sensitivity. Subsequently, BCNW were incorporated into both PHA grades, achieving a high level of dispersion for a 1 wt.-% loading, whereas some agglomeration took place for 3 wt.-% BCNW. As evidenced by DSC analyses, BCNW presented a nucleating effect on the PHA matrices. BCNW also increased the thermal stability of the polymeric matrices when properly dispersed due to strong matrix-filler interactions. Barrier properties were seen to depend on relative humidity and improved at low nanofiller loadings and low relative humidity.

Surfactant-aided electrospraying of low molecular weight carbohydrate polymers from aqueous solutions.

In this work it is demonstrated, for the first time, that it is feasible to develop, using the electrospraying technique, low molecular weight carbohydrate-based capsule morphologies from aqueous solutions through the rational use of surfactants. Two different low molecular weight carbohydrate polymers were used, a maltodextrin and a commercial resistant starch. The solution properties and subsequent high voltage sprayability was evaluated upon addition of non-ionic (Tween20, and Span20) and zwitterionic (lecithin) surfactants. The morphology and molecular organization of the structures obtained was characterized and related to the solution properties. Results showed that, while unstable jetting and dropping occurred from the pure carbohydrate solutions without surfactant, the addition of some surface active molecules above their critical micelle concentration facilitated capsule formation. Higher surfactant concentrations led to smaller and more homogeneous capsule morphologies, related to lower surface tension and higher conductivity of the solutions.

Protein-based emulsion electrosprayed micro- and submicroparticles for the encapsulation and stabilization of thermosensitive hydrophobic bioactives

This work shows the potential of emulsion electrospraying of proteins using food-grade emulsions for the microencapsulation and enhanced protection of a model thermosensitive hydrophobic bioactive. Specifically, gelatin, a whey protein concentrate (WPC) and a soy protein isolate (SPI) were compared as emulsion stabilizers and wall matrices for encapsulation of α-linolenic acid. In a preliminary stage, soy bean oil was used as the hydrophobic component for the implementation of the emulsion electrospraying process, investigating the effect of protein type and emulsion protocol used (i.e. with or without ultrasound treatment) on colloidal stability. This oil was then substituted by the ω-3 fatty acid and the emulsions were processed by electrospraying and spray-drying, comparing both techniques. While the latter resulted in massive bioactive degradation, electrospraying proved to be a suitable alternative, achieving microencapsulation efficiencies (MEE) of up to ∼70%. Although gelatin yielded low MEEs due to the need of employing acetic acid for its processing by electrospraying, SPI and WPC achieved MEEs over 60% for the non-sonicated emulsions. Moreover, the degradation of α-linolenic acid at 80°C was significantly delayed when encapsulated within both matrices. Whilst less than an 8% of its alkene groups were detected after 27h of thermal treatment for free α-linolenic acid, up to 43% and 67% still remained intact within the electrosprayed SPI and WPC capsules, respectively.

Development and Optimization of Novel Encapsulation Structures of Interest in Functional Foods Through Electrospraying

The aim of this work was to establish strategies for the development of electrosprayed encapsulation structures, of interest in food applications, based on aqueous hydrocolloid dispersions. Specifically, various polysaccharides and two different proteins were evaluated for capsule formation. To this aim, the hydrocolloid dispersion properties were analysed and compared with the solution properties of two polymers readily spinnable in water (polyvinyl alcohol (PVOH) and polyethylene oxide (PEO)). Increasing the hydrocolloid concentration to promote chain entanglements resulted in a valid strategy only for a few matrices (related to their greater Mw). As alternative strategies to improve the physical properties and, thus, the sprayability of the dispersions, addition of gums and surfactants to modify their viscosity and surface tension, respectively, was evaluated. Moreover, denaturation of proteins was also carried out in order to investigate the effect of this treatment on the electrospraying process and on capsule formation. Results showed that the incorporation of some of these molecules, as well as protein denaturation, significantly changed the physical properties, allowing the development of encapsulation structures from all the hydrocolloids assayed. The morphology of the structures obtained was characterized, and the molecular organization of some of the capsules was studied and related to the electrosprayability and capsules morphology.

Resistant starch in vitro and in vivo : factors determining yield, structure and physiological relevance

Knowledge of the food processing methods and conditions as well as the underlying mechanism that leads to the formation of resistant starch (RS) in foods is of great importance for nutritionists as well as food industries, since it offers the possibility of increasing the RS content in processed foods. RS is normally defined as that portion of dietary starch that escapes digestion in the small intestine of a healthy human. The amount of RS in a given food is determined by many different factors. Food form and structure, botanical source of the starch and its amylose content, other dietary constituents, notably protein and fat, the presence of a-amylase inhibitors and other antinutrients, the methods used to manufacture and store foods, and culinary practices all directly influence starch digestibility in the gut. Although most of the attention that RS has attracted from health professionals relates to its positive effects on bowel health, there is theoretical and mounting experimental evidence that RS has beneficial physiological properties, which extend beyond the gastrointestinal tract. Food scientists have attempted to enhance the level of enzyme-resistant retrograded starch in the diet. Numerous studies are carried out to characterize the molecular and microstructural organization of RS fractions, aiming at unraveling the mechanisms of amylolysis resistance.