Production of PHB from Chicory Roots – Comparison of Three Cupriavidus necator Strains

Renewable resources constitute a ‘limited infinity’, meaning that a limited amount is being produced, but for an infinite time.1 One of the most promising approaches to reduce the resource intensity is to use the existing biomass more efficiently: the biorefinery concept. It aims to use the complete biomass and all by-products emitted by the processes. Particularly the by-products of established processes have been disregarded in the past and are receiving more attention now.2 Chicory (Cichorium intybus) is a very versatile plant as its varieties are either grown for salad, inulin or coffee-substitute production.3 The leafy salad (also called Belgian endive, chicon or witloof) is grown predominantly in Belgium, the Netherlands, France and Spain.4 In Spain, the major growing region is Navarra, where 13,000 tons of chicory are produced by hydroponic cultivation per year.5 The production is not seasonal as the salad is consumed throughout the year. Alongside the chicory production, 10000 tons of roots accumulate, which are presently used as animal feed or are composted. However, the nutritional value of the roots after hydroponic cultivation is limited because inulin, a fructose polymer that is the main carbonand energy-storage of the plant, is not metabolised during the intrinsic mammalian digestion process. It is only metabolised by the colon microflora to gases and organic acids.6,7 Hydroponic cultivation, growing plants using aqueous mineral nutrient solutions instead of soil, is carried out in complete darkness. In order to provide the energy required for the salad (chicon) formation, the polymeric inulin, stored in the roots, is depolymerised into monoand oligosaccharides. This renders the classical inulin extraction and utilization pathways not economically feasible.8 An integrated process in which the inulin is extracted/ hydrolysed and the hydrolysate is directly used for fermentations is economically more viable.9 However, there have been no investigations into such a process until now. Production of PHB from Chicory Roots – Comparison of Three Cupriavidus necator Strains