Elena Rivo López

Extracellular polysaccharides production by Arthrobacter viscosus

Abstract In this study the production of extracellular polysaccharides by the non-pathogenic soil bacteria Arthrobacter viscosus has been investigated. Different variables affecting extracellular polysaccharide production such as the carbon source (glucose or xylose), the agitation speed and the pH have been analysed. In a first stage, experiments in shaken conical flasks (250 ml), containing 50 ml of culture medium, were carried out. Using xylose (25 g/l) as the carbon source at an initial pH 8 improved the extracellular polysaccharides levels obtained. In a second stage, the experiments were scaling in bioreactors. Cultivation was carried out in discontinuous mode and with/without pH control. Polysaccharide production reached a maximum of 10 g of crude product per litre of growth medium after 14 days and the relationship between product formation and cell growth of A. viscosus is 2.7 g polysaccharide per gram biomass. This production was obtained at the optimal conditions determined with pH control at pH 7, xylose as carbon source (25 g/l) and an agitation rate of 800 rpm.

Strategies for utilisation of food-processing wastes to produce lipases in solid-state cultures of Rhizopus oryzae

The aim of the present study was to investigate the feasibility of several food-processing wastes as support substrate for lipolytic enzymes production by the fungus Rhizopus oryzae under solid-state conditions. Different experiments were conducted to select the variables that allow obtaining high levels of lipolytic enzyme activity. In particular, the use of inert and non-inert solid materials and lipidic and surfactant compounds was evaluated. It was observed that the addition of Triton X-100 together with barley bran involved lipolytic production values tenfold higher than the cultures exclusively grown on an inert support. In addition, from preliminary thermoinactivation kinetics studies, it was concluded that the strategy proposed in this investigation entails another benefit in terms of resistance of the produced enzymes against thermoinactivation.