Valorisation of confectionary industry wastes for the microbial production of polyxydroxyalkanoates

By-product and waste streams from the food industry could be regarded as ideal renewable feedstocks for the production of value-added products. The utilisation of food processing wastes could lead to the development of a sustainable chemical industry and a food industry that will cause less environmental concerns. This will be achieved via simultaneous substitution of fossil raw materials and reduction or even elimination of severe environmental burdens caused by the current disposal and treatment of food waste streams. This work is focused on the bioconversion of flour-rich waste streams generated from a confectionary industry for the production of the biodegradable polymer poly(3-hydroxybutyrate) (PHB). The flour-rich waste streams used in this study were taken either as waste generated from the processing line or as out-of-date products that have been returned from the market. These flour streams contained mainly starch and protein. They were converted into a fermentation feedstock (a 95 % of starch to glucose conversion was achieved) using enzyme-rich crude extracts from solid state fermentations conducted on wheat bran by the fungal strain Aspergillus awamori. When an initial concentration of 80 g/L flour-rich wastes were used, the two-stage bioprocess led to the production of hydrolysates that contained 70.8 g/L glucose concentration and 237.65 mg/L free amino nitrogen (FAN). The hydrolysate was employed for the production of PHB via microbial bioconversion in shake flasks and a 3 L bioreactor using the bacterial strain Cupriavidus necator DSM 4058. Shake flask fermentations using different glucose and free amino nitrogen concentrations led to the production of up to 5.95 g/L PHB concentration. The PHB structure and thermal properties were analysed by Fourier infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC).