Research Items (8)
The objective is to determine the biochemical characteristics to propose adapted processing In Burkina Faso, processed mango volumes rose from 12 000 tons in 2008 to 36 635 tons in 2017 . Despite this growing volume, only 20% of annual mango production is processed. It relies mainly on dried mango and mango juices using the varieties Amelie, Brooks, Kent, Keitt, Lippens and Springfrield. The dried mango from Burkina Faso is labeled "organic" and "fair trade" and represents between 10% and 20% of the total European dried mango market . However biochemical characteristics of the varieties are not well known and the products derived from mango are not sufficiently diversified.
- Oct 2015
Proteins in white wines may aggregate and form hazes at room temperature. This was previously shown to be related to pH-induced conformational changes and to occur for pH lower than 3.5. The aim of the present work was to study the impact of wine polysaccharides on pH-induced haze formation by proteins but also the consequences of their interactions with these proteins on the colloidal stability of white wines. To this end, model systems and purified global pools of wine proteins and polysaccharides were used first. Kinetics of aggregation, proteins involved and turbidities related to final hazes were monitored. To further identify the impact of each polysaccharide, fractions purified to homogeneity were used in a second phase. These were: 2 neutral (mannoprotein and arabinogalactan polysaccharides) and 2 negatively charged (rhamnogalacturonan II dimer (RG-II) and arabinogalactan polysaccharides). We highlighted that the impact of major wine polysaccharides on wine protein aggregation at room temperature was clearly less marked than those of the pH and the ionic strength. Polysaccharides modulated the aggregation kinetics and final haziness, indicating that they interfere with the aggregation process, but could not prevent it.
- Jul 2014
Filtrodynamic behavior of trans-filter time-dependent pressure signals ΔP(t) is determined for membrane and frit filters using latex spheres of varying diameter D. Membrane data are best interpreted via a time-dependent, accreting filtration bed, based on Darcy's law. A single parameter, permeability k, describes each membrane/particle pair. For small particles, k increases with increasing D, then becomes D-independent for large ones. Predictable behavior for polydisperse mixtures of small spheres is obtained. The mechanism and behavior of filtration for non-membrane metallic frits is dramatically different, and better described by a previous “characteristic loading” model. Use of frit and membrane filters in series allowed monitoring each filter's separate response to particle accumulation.
- Jul 2013
Our studies focused on the determination of aggregation mechanisms of proteins occurring in wine at room temperature. Even if wine pH range is narrow (2.8 to 3.7), some proteins are affected by this parameter. At low pH, the formation of aggregates and the development of a haze due to proteins sometimes occur. The objective of this work was to determine if the pH impacted on the conformational stability of wine proteins. Different techniques were used: circular dichroism and fluorescence spectroscopy to investigate the modification of their secondary and tertiary structure, but also the SAXS to determine their global shape. Four pure proteins were used, two considered as stable (invertase and thaumatin-like proteins) and two as unstable (two chitinase isoforms). Two pHs were tested to emphasize their behavior (pH 2.5 and 4.0). The present work highlighted that the conformational stability of some wine proteins (chitinases) was impacted by partial modifications, related to the exposure of some hydrophobic sites. These modifications were enough to destabilize the native state of the protein. These modifications were not observed on wine proteins determined as stable (invertase and thaumatin-like proteins).
- Feb 2013
The use of ion-exchange chromatography and 31P nuclear magnetic resonance (31P NMR) to analyse the composition and the chain length of phosphate emulsifying salts were studied, as well as the impact of these salts in dairy products. Ion chromatography was more appropriate than 31P NMR to study polyphosphate composition in complex environments, whereas interactions between phosphate species and dairy components were elucidated by 31P NMR. Phosphate species interacting with calcium, as well as the percentage of chelated calcium, were identified using 31P NMR. Thus, ion chromatography and solid-sate 31P NMR could be used as complementary methods to study compositions of polyphosphate blends and their interactions with dairy matrices.
- Feb 2012
Protein haze development in white wines is an unacceptable visual defect attributed to slow protein unfolding and aggregation. It is favored by wine exposure to excessive temperatures but can also develop in properly stored wines. In this study, the combined impact of pH (2.5-4.0), ionic strength (0.02-0.15 M), and temperature (25, 40, and 70 °C) on wine protein stability was investigated. The results showed three classes of proteins with low conformational stability involved in aggregation at room temperature: β-glucanases, chitinases, and some thaumatin-like protein isoforms (22-24 kDa). Unexpectedly, at 25 °C, maximum instability was observed at the lower pH, far from the protein isoelectric point. Increasing temperatures led to a shift of the maximum haze at higher pH. These different behaviors could be explained by the opposite impact of pH on intramolecular (conformational stability) and intermolecular (colloidal stability) electrostatic interactions. The present results highlight that wine pH and ionic strength play a determinant part in aggregation mechanisms, aggregate characteristics, and final haze.
- Sep 2010
High temperatures (typically 80 °C) are widely used to assess wine stability with regard to protein haze or to study mechanisms involved in their formation. Dynamic light scattering experiments were performed to follow aggregation kinetics and aggregate characteristics in white wines at different temperatures (30-70 °C). Aggregation was followed during heating and cooling to 25 °C. Results were coupled with the study of the time-temperature dependence of heat-induced protein aggregation. At low temperature (40 °C), aggregation developed during heating. Colloidal equilibria were such that attractive interactions between species led to the rapid formation of micrometer-sized aggregates. At higher temperatures (60 and 70 °C), enhanced protein precipitation was expected and observed. However, high temperatures prevented aggregation, which mainly developed during cooling. Depending on the wine, cooling induced the formation of sub-micronic metastable aggregates stabilized by electrostatic repulsions, or the rapid formation of micrometer-sized aggregates, prone to sedimentation.
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