Joël René Pierre Wallecan

Strong cationic polyelectrolyte adsorption on a water swollen cellulosic biomaterial and its relevance on microstructure and rheological properties

A multiscale approach was taken to study the swelling and viscosifying properties of a cellulose-rich biomaterial as a function of environmental conditions. First, the impact of pH and ionic strength on the surface properties of the fiber was investigated by means of potentiometry and cationic polyelectrolyte adsorption. Three adsorption regimes were identified: the first one occurred in acidic conditions and was related to the ionization of the carboxylic groups of pectin. A very sharp adsorption was then observed in the mild-acidic to neutral region which was most likely related to a conformation change in the plant cell wall architecture. The third adsorption regime happened in the alkaline region and was related to ionization effects. Based on this information, the impact of environmental conditions on the hydrated microstructure was studied in DSC by means of thermoporosimetry. It clearly demonstrated a structural collapse of the hydrated fiber when pH decreased or the amounts of ions increased. This phenomenon was in line with the surface charge measurements. Finally, the link between the wet microstructure and the macroscale behavior of the fiber was demonstrated by studying the flow properties of the reconstituted fiber, below and above its percolation threshold. In line with the surface properties and microstructure data, yield stresses increased when the pH was adjusted from acidic to alkaline conditions. Salt addition resulted in a loss of the texturizing properties.Graphical Abstract

Understanding the Effect of Processing on the Structure of Plant Cell Walls as a Mean to Design Novel Clean Label Ingredients

Plant cell walls are complex assemblies consisting of cellulose, hemicellulose, pectin, proteins, lignin... These composite materials are synthesized by the plant in order to provide strength, shape, growth, integrity and protection to the cells. Food processes on the other hand aim at disrupting these tight networks in order to extract the high-value ingredients inside the cell and cell wall: oil, starch, proteins, pectin, carrageenan, vitamins... This leads to the generation of 2 main streams: a high-value ingredient stream (e.g. pectin) and a disrupted plant cell wall side stream. Until recently, limited attention was paid to these side streams and they were often poorly valorized or even discarded without added value. However, these plant cell wall streams have gained accrued interest over the last decade for various reasons: economical, sustainability, consumer behavior, cost of raw materials...