New wideband electromagnatic on-line system for microalgae production monitoring

Hyaluronic acid (HA) is present in almost all biological fluids and tissues. The chemical HA structure is described as a linear polysaccharide with a high molecular mass (about one MDa) formed from disaccharide units containing Nacetyl-d-glucosamine and glucuronic acid. This chemical structure ensures an excellent biocompatibility. In addition its viscoelastic properties are singularly appreciated in cosmetic products like moisturizing preparations, anti-wrinkle effect cream (for the elasticity restoration) [1], and skin protection against ultraviolet irradiation [2]. HA is usually produced from non-sustainable resource, or from genetically modified (GMO) bacteria, or from animal waste [3]. A novel method production of this high value product (more than 100 k€/kg [4]) had recently emerged based on microalgae production process [5]. In order to be competitive, users of this new manufacturing method need to assess in-line the quality of the product and if it possible use this information for product quality optimization. Electromagnetic sensors are well known in the food industry for reliability and quick quality assessment of hydrocarbon based food like wheat [6]. This paper reports some preliminary results on microalgae by product of an electromagnetic wideband radiofrequency sensor. This sensor consists of an open coaxial line cell filled with a liquid solution and impedance measurement of the cell is carried by an network analyzer at a temperature of 25°C. The microalgae studied where separated in two phases, a liquid one extracted directly from the reactor (MC) and a foam like extracted by an in-reactor skimmer (ME). In order to assess the sensibility of the measurement and simulate different production yield, extracted fraction MC and ME where diluted. These dilutions were carried with respectively microalgae nutriment solution (NS) and pure water in order to keep a constant ionic strength to achieve the low frequency conductivity constant and to avoid a measurement bias. The preliminary results show a good sensitivity of impedance vs HA microalgae concentration in the 1 MHz to 10 MHz range.