Polyhydroxyalkanoates (PHAs), biocompatible and biodegradable plastics, can be microbially produced using agricultural wastes (e.g., rice straws) as carbon sources. Agricultural wastes are often subject to pretreatments that produce mainly sugars, and sugars can produce P(3HB), the most abundant kind of PHAs. The limited applications of P(3HB) due to its crystalinity triggered studies on developing methods for producing copolymers such as P(3HB-co-3HV) that have improved mechanical properties. Therefore, this study is set out to develop a two-phase pretreatment method that can synthesize P(3HB-co-3HV) from rice straws. Specifically, this study investigates the effect of the second phase heating peroid on P(3HB-co-3HV) accumulation in Cupriavidus necator. The two-phase treatment consists of the 1st phase where rice straws are treated in 2% (w/v) H2SO4 (S/L ratio 1:10) at 121oC for 60 min and the 2nd phase where the hydrolysates from the 1st phase are heated at 121oC for different periods (20, 40, and 60 min) after separating out the solid phase. C.necator was then fed with the neutralized hydrolysate (20% v/v) and incubated at 30 oC and 200 rpm for 96 h. Changes in dry cell weights (DCW), PHAs concentrations, and hydrolysates constituents with time were determined. When the hydrolysates obtained from the 1st phase was fed as carbon sources, 52.7% PHAs were obtained with 8.8% 3HV. With the 2nd phase heating, the overall PHAs accumulation decreased to approximately 40%, but the 3HV fraction increased. The 3HV fraction increased from 15% to 23% with increasing heating period from 20 min to 60 min. The decrease in the overall PHAs acummulation could be attributed to either a decreased amount of sugars after 2nd phase heating or a relatively higher amount of intermediate products such as furfural and 5-Hydroxymethylfurfural. Also, increasing heating time increases the amount of levulinic acid produced and this, in turn, increase the 3HV fraction. This study will be meaningful as it will expand the types of PHAs that can be produced using rice straws hydrolysates without adding any other external carbon sources.

Effect of two-phase pretreatment of rice straw on polyhydroxyalkanoates (PHAs) synthesis by Cupriavidus necator

249th National Meeting (2015)

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