Enzyme and Microbial Technology 40 (2007) 1035–1044 Polyhydroxybutyrate production from a novel feedstock derived from a wheat-based biorefinery Apostolis A. Koutinas ∗ , Yunji Xu, Ruohang Wang,Colin Webb The University of Manchester, School of Chemical Engineering and Analytical Science, Satake Centre for Grain Process Engineering, Sackville Street, PO Box 88, Manchester M60 1QD, United Kingdom Received 23 May 2006; received in revised form 31 July 2006; accepted 4 August 2006 Abstract A wheat-based biorefining strategy was evaluated for polyhydroxybutyrate (PHB) production by Cupriavidus necator (formerly classified as Ralstonia eutropha but currently designated Wautersia eutropha). Wheat was bioconverted into two feedstock streams, wheat hydrolysate (WH) and fungal extract (FE) that were rich in glucose and nitrogen, respectively. WH and FE were mixed in appropriate proportions to provide media with varying glucose (5–26 g l -1 ) and free amino nitrogen (FAN) (0.1–1.2 g l -1 ) concentrations for batch shake flask fermentations. Increasing FAN concentration resulted in higher microbial growth and less PHB accumulation. The consumption of various carbon sources (carbohydrates, amino acids, peptides) resulted in high growth yields (up to 1.07 g cells (g glucose) -1 ) as related to glucose. Specific growth rates up to 0.16 h -1 were observed. Three WH with similar glucose (200–220 g l -1 ) and varying FAN (0.3–1.48 g l -1 ) concentrations were evaluated in fed-batch shake flask fermentations for C. necator growth and PHB accumulation. The medium with the highest nitrogen concentration (WH3) gave the highest microbial biomass concentration (29.9 g l -1 ), growth yield (0.28 g residual microbial biomass (g glucose) -1 ) and PHB yield (0.43 g (g glucose) -1 ). WH2 gave the highest PHB concentration (51.1 g l -1 ) and content (0.7 g g -1 ). © 2006 Elsevier Inc. All rights reserved. Keywords: Cereal-based biorefinery; Sustainable bioprocessing; Wheat hydrolysates; Fungal extracts; Polyhydroxybutyrate 1. Introduction It is widely accepted that the viability of microbial large-scale production of polyhydroxyalkanoates (PHAs) is dependent on the development of a low cost process that produces biodegrad- able plastics with properties similar or superior to petrochemical plastics [1]. Recently, some researchers and industrialists have expressed their concerns regarding large-scale microbial production of PHAs and poly-(3-hydroxybutyrate) (PHB) in par- ticular, due to economic and technological barriers [2,3]. Those concerns were based, however, on traditional fermentation practices. In recent years, there is growing interest on the development of biomass-based biorefineries for the production of biofuels, chemicals and biodegradable plastics [4]. This work demon- strates the potential of a novel feedstock derived from wheat for viable PHB production by Cupriavidus necator. This feedstock ∗ Corresponding author. Tel.: +44 161 306 4418. E-mail address: apostolis.koutinas@manchester.ac.uk (A.A. Koutinas). was produced from a novel wheat-based biorefinery (Fig. 1) that has been developed at the Satake Centre for Grain Process Engi- neering. As shown in Fig. 1, the outer layers of wheat kernel are ini- tially removed by a novel pearling technology. Pearlings could be used separately to produce various added-value co-products that improve overall process economics [5–10]. A fungal fer- mentation is used to produce the enzymes required to hydrolyse pearled wheat flour suspensions into a medium (WH) rich in glucose. Gluten could be extracted from pearled wheat flour pro- viding another added-value co-product that could be processed for new or traditional markets [11,12]. The remaining solids from the fungal fermentation that contain fungal mycelia and undigested wheat components are used to produce nutrient-rich supplements (FE) for bacterial bioconversions through fungal autolysis [13]. The autolysate or fungal extract has similar com- position to yeast extract. The high cost of yeast extract hinders their industrial utilisation. WH and FE can be mixed in order to formulate media capable to sustain bacterial growth and PHB accumulation. Detailed description of this process can be found in other publications [8,14,15]. 0141-0229/$ – see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.enzmictec.2006.08.002