Amelia Farrés

Bio: Amelia Farrés is an academic researcher from National Autonomous University of Mexico. The author has contributed to research in topics: Aspergillus nidulans & Esterase. The author has an hindex of 16, co-authored 41 publications receiving 940 citations.

Yogurt production from reconstituted skim milk powders using different polymer and non-polymer forming starter cultures

Abstract: Using polymer producing (ropy) strains of lactic acid bacteria it was possible to reduce considerably the syneresis of yogurt, even with 12% total milk solids. The viscosities obtained with these strains were also similar to those obtained using normal strains and milk with 17% total solids content. The concentration of milk and the polymer produced by ropy starters had a synergic effect in increasing viscosity. Polymer production was not affected in most cases by milk concentration. One type of ropy culture (Wiesby) seemed to produce a different kind of polymer as it could not be determined by alcohol precipitation, in spite of being able to reduce syneresis and increase viscosity in yogurt. A limited number of yogurts were evaluated organoleptically, one prepared with a ropy starter strain (NCFB at 12, 14·5 and 17% total solids) and one prepared with a non-ropy strain (LL-I at 17% total solids). The results suggest that the ropy strain yogurts had different mouthfeel from the non-ropy strain yogurts; the most acceptable product overall was the ropy strain made with 12% total solids.

Effect of alkaline deamidation on the structure, surface hydrophobicity, and emulsifying properties of the Z19 α-zein.

Abstract: Different deamidation conditions for the Z19 alpha-zein were studied in order to find the best conditions for the development of the emulsifying properties. Alkaline deamidation was chosen, and the effects on the peptide bond cleavage, secondary structure, emulsifying properties, and surface hydrophobicity were studied. The Z19 alpha-zein was deamidated by using 0.5 N NaOH containing 70% ethanol at 70 degrees C for 12 h. A deamidation degree (DD) of 60.6 +/- 0.5%, and a degree of hydrolysis (DH) of 5 +/- 0.5% were achieved. Analysis by far-UV circular dichroism showed that the denaturation was mainly promoted by the high temperature used during the incubation. The adequate balance between the DD and the DH results in an effective emulsifying property improvement for the Z19 alpha-zein. Thus, after the deamidation treatment, the surface hydrophobicity decreased from 9.5 x 104 +/- 6.8 x 103 to 46 x 104 +/- 2.1 x 103, and the emulsion stability increased from 18 +/- 0.7% to 80 +/- 4.7% since the oil globules stabilized by the modified protein were smaller (57.7 +/- 5.73 nm) and more resistant to coalescence than those present in the native protein emulsions (1488 +/- 3.92 nm).

Characterization of a 19 kDa α-Zein of High Purity

Abstract: A highly pure alpha-zein was extracted from corn flour using ethanol (95%). Subsequently, ion-exchange chromatography was performed, using SP-Sepharose that yielded a highly homogeneous protein. This protein migrated as a single band in 20% SDS-PAGE and in pH gradient gels, showing an isoelectric point of 6.8. Mass spectrometry (MALDI-TOF-MS) showed a single peak with a molecular mass of 24 535 Da. It was identified as Z19, when comparing the sequence obtained in an automatic Edman sequencer with the Swissprot database using BLAST. The molar extinction coefficient, determined by dry weight in 70% methanol, was 12 415.49 M(-1) cm(-1) at 280 nm. Light scattering showed its presence in a monodispersed state of 44-66 kDa aggregates in methanol (70%). Circular dichroism spectra allowed the estimation of an alpha-helix content that was lower than the one found for a mixture of two alpha-zeins but with a higher content of beta sheets.

Heteropolysaccharides from lactic acid bacteria.

Abstract: Microbial exopolysaccharides are biothickeners that can be added to a wide variety of food products, where they serve as viscosifying, stabilizing, emulsifying or gelling agents. Numerous exopolysaccharides with different composition, size and structure are synthesized by lactic acid bacteria. The heteropolysaccharides from both mesophilic and thermophilic lactic acid bacteria have received renewed interest recently. Structural analysis combined with rheological studies revealed that there is considerable variation among the different exopolysaccharides; some of them exhibit remarkable thickening and shear-thinning properties and display high intrinsic viscosities. Hence, several slime-producing lactic acid bacterium strains and their biopolymers have interesting functional and technological properties, which may be exploited towards different products, in particular, natural fermented milks. However, information on the biosynthesis, molecular organization and fermentation conditions is rather scarce, and the kinetics of exopolysaccharide formation are poorly described. Moreover, the production of exopolysaccharides is low and often unstable, and their downstream processing is difficult. This review particularly deals with microbiological, biochemical and technological aspects of heteropolysaccharides from, and their production by, lactic acid bacteria. The chemical composition and structure, the biosynthesis, genetics and molecular organization, the nutritional and physiological aspects, the process technology, and both food additive and in situ applications (in particular in yogurt) of heterotype exopolysaccharides from lactic acid bacteria are described. Where appropriate, suggestions are made for strain improvement, enhanced productivities and advanced modification and production processes (involving enzyme and/or fermentation technology) that may contribute to the economic soundness of applications with this promising group of biomolecules.

Formation and physical properties of yogurt.

Abstract: Yogurt gels are a type of soft solid, and these networks are relatively dynamic systems that are prone to structural rearrangements. The physical properties of yogurt gels can be qualitatively explained using a model for casein interactions that emphasizes a balance between attractive (e.g., hydrophobic attractions, casein cross-links contributed by calcium phosphate nanoclusters and covalent disulfide cross-links between caseins and denatured whey proteins) and repulsive (e.g., electrostatic or charge repulsions, mostly negative at the start of fermentation) forces. Various methods are discussed to investigate the physical and structural attributes of yogurts. Various processing variables are discussed which influence the textural properties of yogurts, such as total solids content, heat treatment, and incubation temperatures. A better understanding of factors contributing to the physical and structural attributes may allow manufacturers to improve the quality of yogurt.

The sourdough microflora: biodiversity and metabolic interactions

Abstract: The production of sourdough bread can be traced back to ancient times. Sourdough is a mixture of flour and water that is fermented with lactic acid bacteria (LAB). Sourdough is an intermediate product and contains metabolically active yeast and LAB strains. The LAB that develop in the dough may originate from selected natural contaminants in the flour or from a starter culture containing one or more known species of LAB. Sourdough can be produced in bakeries or obtained from commercial suppliers. The microbial ecology of the sourdough fermentation is determined by ecological factors. Microbiological studies have revealed that more than 50 species of LAB, mostly species of the genus Lactobacillus, and more than 20 species of yeasts, especially species of the genera Saccharomyces and Candida, occur in this ecological niche. The sourdough microflora is composed of stable associations of lactobacilli and yeasts, in particular due to metabolic interactions. As shown for certain industrial sourdough processes, such microbial associations may endure for years, although the fermentation process runs under non-aseptic conditions. A reproducible and controlled composition and activity of the sourdough microflora is indispensable to achieve a constant quality of sourdough bread.